Some recent 0.35 nozzle prints

[orcinus]

I've sent these to Laszlo in an e-mail discussion and he kindly asked me to post them here, so here goes...

Some things i've printed in the last two days, testing out a new brand of filament (colorFabb).

They're printed on an ORD Bot Hadron with an Arcol.hu 4.x (a mix and match of a few Arcol.hu 4 hotend versions) with a 0.35 mm nozzle.

Sliced with KISSlicer, printed running Repetier FW. Layer height 0.16ish.

https://dl.dropboxusercontent.com/u/1702513/_5230322.jpg

https://dl.dropboxusercontent.com/u/1702513/_5230327.jpg
https://dl.dropboxusercontent.com/u/1702513/_5230329.jpg

I've noticed i've been getting a lot of "ringing" near sharp edges recently.
I guess it's finally time to switch from MXL to GT2 belts.

https://dl.dropboxusercontent.com/u/1702513/_5230336.jpg
https://dl.dropboxusercontent.com/u/1702513/_5230337.jpg
https://dl.dropboxusercontent.com/u/1702513/_5230339.jpg
https://dl.dropboxusercontent.com/u/1702513/_5230341.jpg

You can notice a gap in the layers in the lions right side. That's filament's fault. It did that about 3-4 times now, and i've narrowed it down to either bubbles in the filament or trapped moisture. I've actually stopped a print once in the middle of a botched perimeter and dug out the remains of the filament from the nozzle. There was a bubble in there, but, like i've said, i wasn't sure if it's a manufacturing defect or a steam bubble.

Anyways, been using Arcol.hu 4 for a little over a year now and don't plan on stopping any time soon :)

[nop head]

Nice prints. Why do you think GT2 belts will have less ringing than MXL?

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[Ante Vukorepa]

Less backlash, more "braking" action to their profile. And they were made for positioning, unlike MXL.

Plus, anecdotal evidence - i've heard it confirmed twice now.

-- 

Ante Vukorepa

Sent with Sparrow

[Kyle Kenney]

I can't beleive the quality, jesus, that titan is amazing....the lion less so, nice work! this just goes to show why its great to have an arcol :)

2013/5/23 Ante Vukorepa <o.or...@gmail.com>

[Nicolas Arias]

wow, really nice prints, it would be great if you can tell more about
the slicing, temperatures, etc etc etc (i have samples from colorfabb
being delivered tomorrow).

have you fliped the belts, so the smooth part goes contacts the idler?
(not the teeth part)

[Laszlo KREKACS]

Hi,

On Thu, May 23, 2013 at 9:24 PM, orcinus <o.or...@gmail.com> wrote:
> I've sent these to Laszlo in an e-mail discussion and he kindly asked me to
> post them here, so here goes...

Thank you very much. I usually do not get any feedbacks of my hotend users,
so it is always nice to see an exception.

> I've noticed i've been getting a lot of "ringing" near sharp edges recently.
> I guess it's finally time to switch from MXL to GT2 belts.

I'm not that sure GT2 is the only cure for cancer:)
Read here more: http://wiki.arcol.hu/blog:arcol-t25

> Anyways, been using Arcol.hu 4 for a little over a year now and don't plan
> on stopping any time soon :)

That is really nice of you:)

I think it is time for a new monthly (june) competition.
I can offer a full pulley+ belt set as a first prize (for a machine).
Thats about 3meter of belt or so.

Best,
Laszlo

[Nicolas Arias]

im in for a second competition!

[Kyle Kenney]

Laszlo, did you not get my email about the prototype? Also, I'm down for comp too!

2013/5/24 Nicolas Arias <nico...@gmail.com>

[Ante Vukorepa]

The quality of the lion is pretty much the same as the mech, but it's much smaller and photographed at a much shorter distance (as evidenced by the shallow DoF), so all the flaws are easier to see. That's disregarding the forementioned layer gap due to filament bubble, of course.

-- 

Ante Vukorepa

Sent with Sparrow

[Ante Vukorepa]

Not much to tell, really.

Sliced using KISSlicer, skin thickness was 0.3-ish, i believe, layer thickness 0.1684, seam hiding at 0.5, loop speed 30 mm/s, solid infill 40 mm/s, sparse infill 45 mm/s.

Support on, at the "rough" setting, sheathe z-roof at 3 mm, temperature 210 deg C for the mech and 190 for the lion, bed at 50 deg C. And that's about it :)

colorFabb's specs claim the filament should be extruded at 210 deg C, but it seems to me it extrudes much better at 190 deg C. At least the pale gold filament does. Shining silver is maybe a tiny bit cleaner at 200-210. They ship the filament in cardboard boxes, without *any* wrapping or desiccants. Granted, cardboard *is* a desiccant, but still… I don't like their packaging one bit. The filament ends up full of cardboard fluff too. Also, they ship via DPD, which is probably one of the worst, slowest and priciest courier services here (Croatia).

Re: flipping the belt - tried that, didn't have much luck with it.

Speaking of, i've installed the GT2 belts today, plus, i've isolated the steppers, bed and extruder with double sided sticky foam tape. Did some other tweaks (rubber tape on the printer feet), all in an effort to reduce vibration and - hence - the ringing. End result - the ringing is still there. Exact same frequency too. It's a bit attenuated, though, and the whole thing is MUCH quieter now. The layers are a bit more even now too, i presume due to reduced belt backlash.

But yeah, ringing still present and accounted for. The only thing left in the equation now are the steppers, i.e. their natural mechanical oscillation around the poles. I've got no other explanation left for it.

-- 

Ante Vukorepa

Sent with Sparrow

[Ante Vukorepa]

I'm not sure what the competition rules are, but i'm game :)

Also, those pulleys look pretty nice!

-- 

Ante Vukorepa

Sent with Sparrow

On Friday, 24. May 2013. at 10:47, Laszlo KREKACS wrote:

I'm not that sure GT2 is the only cure for cancer:)

Read here more: http://wiki.arcol.hu/blog:arcol-t25

I think it is time for a new monthly (june) competition.

I can offer a full pulley+ belt set as a first prize (for a machine).

Thats about 3meter of belt or so.

Best,

Laszlo

[nop head]

Steppers act like a spring because they exert torque proportional the displacement. That with together with the mass of the carriage forms a resonant system. I think the motors are far more "springy" than a tight belt.

[Ante Vukorepa]

Yeah, i'm aware of that.

The thing is, i didn't expect its resonant frequency to be quite as low as what i'm seeing (30 mm/s / 0.95±0.5 mm = 33 to 30 Hz), considering it's a rather rigid system.

It also exhibits two interesting properties:

1) it's *highly* repeatable (if i print an object twice and line the prints up, the phase and frequency of the ringing match perfectly)

2) it very noticeably favours one side of symmetrical objects along Y

Property #1 suggests it's something that's not positionally dependent (in the sense that position on the bed, homing variations etc. do not have an influence on the phase). #2 suggests it's triggered or at least exacerbated by some gcode event (most likely loop start or layer change), not necessarily (just) a surface feature.

I'll need to play with it more. I want to check what effect the following will have:

- speed

- low current microstepping

- current (does the spring constant change with stepper current?)

- microstepping (going down to 4x and back to 16x)
- enabling jitter (varying the loop starting points across layers)

Ante Vukorepa

----

Sent from my iPad

[Matej Rozman]

Hey all,

first post in this group so hello to everyone!

About ringing, If you dare try marlin FW, the ringing will be completly gone.

Its funny, I have a delta and I also noticed ringing when I changed to repetier and couldnt found the issue, changed back to marlin and everything back to normal.

You dont have to search machanical issue anymore, becaose there isnt any (probably), its a firmware isssue. Im supprized nobody noticed this before? Well at least havent heard of it....

Hope it helps,

all best,

2013/5/25 Ante Vukorepa <o.or...@gmail.com>

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Matej Rozman

Robicomp d.o.o.
Koroska 37a
3320 Velenje

Office:  +38659022050
Fax:     +38659022051
Mobile: +38640188669
gotovi....@gmail.com
www.carbonautica.com

[Ante Vukorepa]

Wow, hm.

Now that you mention it, it *did* get worse around the time i updated to the latest Repetier.

It was there before, but not as noticeable. I've assumed it got worse due to my printer "shaking loose" lately.

Also, that would explain the perfect repeatability even after considerable hardware changes.

I'm gonna try and whip up a Marlin config quick and see what happens...

-- 

Ante Vukorepa

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[Ante Vukorepa]

Nope. The ripples are still there.

And once again, they look *exactly* the same.

I'm beginning to think that - somehow - this is a slicer issue…

Either that or stepper/gantry resonance, as mentioned before, although i'm stumped as to how that would produce consistent, repeatable results every print, regardless of firmware, belts, vibration dampening measures etc.

-- 

Ante Vukorepa

Sent with Sparrow

[nico...@gmail.com]

Non concentric pulleys?

---

From: Ante Vukorepa <o.or...@gmail.com>

Sender: arco...@googlegroups.com

Date: Sat, 25 May 2013 16:29:15 +0200

To: <arco...@googlegroups.com>

ReplyTo: arco...@googlegroups.com

Subject: Re: [arcol.hu] Some recent 0.35 nozzle prints

[Ante Vukorepa]

Nope. The phase would change with homing and centering shifts.

And the frequency is way too high for that.

I've tried changing the speed. It seems to have had an effect on the frequency of the ripples. It's slightly hard to tell, because the surface finish got worse with higher speeds. I'll need to do more testing later this evening or tomorrow...

-- 

Ante Vukorepa

Sent with Sparrow

[nico...@gmail.com]

Stepper drivers?

---

From: Ante Vukorepa <o.or...@gmail.com>

Sender: arco...@googlegroups.com

Date: Sat, 25 May 2013 17:34:16 +0200

[Ante Vukorepa]

Okay, latest batch of tests…

- Reducing the microstepping to 1/4 exacerbates the issue (but not as much as you'd expect).

- Enabling low current microstepping (ROSC tied to GND) makes the rippling worse (it gets sharper).

- Increasing the current and adding more foam padding to the idler plate (which, in my case, is a rather thin and bendy aluminium plate, under constant strain from the belt tension) helps a little. The ripple is now perhaps 1/3 reduced, but still present.

That's more or less it, i'm out of (possible fix) ideas :)

-- 

Ante Vukorepa

Sent with Sparrow

[nop head]

Perhaps printing something simpler like a cube would make it easier to diagnose. Are the ripples definitely from one axis, or are they flow rate variations in the extruder due to stepping?

I can't understand how low current micro stepping could do anything but make movement smoother. Especially as 1/4 step makes it worse.

Does increasing the current change the frequency? I would expect it to get higher and that might reduce the amplitude.

[Ante Vukorepa]

That's the thing, it doesn't show up on cubes, i.e. simple X-to-Y (or Y-to-X) cornering doesn't exhibit visible rippling. I'll have to whip up a test solid purpose-buikt for testing this... I'm thinking a cube with a dimple (small cylinder subtraction) in half of the faces and a vertical gash in the other half.

And yes, the low current microstepping effect doesn't make sense to me either. Especially because, inexplicably, it made printing noisier than it was (i'd expect less lost microsteps = less noise and less harmonics).

Increasing the current does indeed increase the frequency but also makes it more erratic (the ripples aren't "perfect" anymore, but result in phase variations every x layers), making them more noticable in some objects, as they result in a more mottled, orange-peel like surface (so it's a win some - lose some solution). Also, they make the print noisier as well. By ear, the noise always seems to increase around a particular frequency, which i assume is the resonant frequency of the machine or the axis.

Flow variations did occur to me, but the rippling mostly appears in the Y direction. Also, if it were flow variation, it wouldn't mimic surface features. 

Ante Vukorepa

----

Sent from my iPad

[nop head]

Which stepper drivers are you using and what voltage. Low current microstepping definitely reduces the harmonics for me. It makes the whine when stationary louder because ripple current is higher due to fast decay mode. That is far too high a frequency to show in the print.

Seems like it might be resonance on each motor step, rather than the impulse of starting and stopping. Perhaps there is something wrong with the microstepping. I assume you have seen my blog article and the video. Have you tried stepping very slowly and listening to the clicks to see if they are regular?

[Ante Vukorepa]

A4982, on Roy's (Panucatt's) carriers @24V. They are louder when stationary, as expected, and low current microstepping does reduce (but not eliminate) the "skip" at slow movements (i.e. the "rukka-rukka-rukka-rukka" buzz). That part is pretty much as you've described and as should be expected.

But for some reason, it behaves unexpectedly during fast moves. The harmonics i've mentioned are pretty much fixed in frequency regardless of the speed, they just become louder at certain speeds. My only theory so far is that noise i'm hearing during the print is the natural frequency of the machine and the missed microsteps somehow accidentally manage to "break up" the resonance, thus alleviating it. So when the low current microstepping is *on*, the effect disappears and i'm hearing the full effect of the resonance.

-- 

Ante Vukorepa

Sent with Sparrow

[nop head]

Have you tried 12V? It's hard to get the low current steps accurate with more than that. The chip regulates the peak current of a saw tooth ripple but the torque will be proportional to the average. That means there is an offset proportional to half the ripple current. On the low current steps it becomes significant and higher supply makes ripple worse.

When you say the harmonics are independent of speed do you mean audibly or spatially? If they are fixed spatially on the object, independent of speed than it is almost certainly a stepper motor problem. Possibly what is termed mid band resonance. Normally micro stepping mitigates that, but not if the waveform is badly distorted.

[Laszlo KREKACS]

Hi,

Without photos it is hard to give any advice. (ie. some side-by-side
comparison photo).
Feel free to start a page under
http://wiki.arcol.hu/blog:printing_reasonance or something more
meaningful title.

If you compile a test-object and you print it at different speed,
I try to print the same object for you for comparison.

But without reproducing the problem at my side, it is really hard to
advice anything.

So I'm waiting to your test object already printed by you at least 5
times with comparison photo.
Then I'm sure many others (myself for sure) will print to give you a comparison.

Best,
Laszlo

[Kyle Kenney]

I made up a 15mm cube, with a dimple, and a 1mm 10mm wide verticle strip, one of those on opposide sides, same as with the dimple...it's hollow aswell, so no need for infill issues.

I attached the file, lemmie know if you wanna do something different

2013/5/26 Laszlo KREKACS <li...@arcol.hu>

[Kyle Kenney]

I just realized after throwing the file through slic3r the dimples are right on the edges of the inside wall, so I updated it, here is the newer version, also I mean 1mm wide, and 10mm long gash *

Hope it helps!

2013/5/26 Kyle Kenney <dudl...@gmail.com>

[Ante Vukorepa]

Haven't tried with 12V, but i'm sure the results would be better, re: skipped microsteps. I doubt it'd have a noticeable impact on the ripple (print ripple, not ripple current), though.

Re: harmonics - i've meant audibly. Spatially, their frequency changes with speed as you'd expect if they were a fixed frequency in the time domain, which is why i'm pretty convinced it's mechanical resonance. The thing i don't understand is - why isolating the main components with silicone and foam padding doesn't affect the result much (even though it reduces the noise).

In any case, yesterday, while testing under higher jerk and acceleration in an attempt to exacerbate the effect on purpose, i've noticed the X stepper casing vibrate *noticeably* at what appeared to be somewhere within that 30 Hz range (no idea what the actual frequency is, of course, but i know a 50 Hz flicker when i see it and this seemed close). Considering the way the gantry stepper is mounted, it's no wonder it's doing that - it's a textbook example of a mass oscillating on a spring (4 bolts):

http://www.buildlog.net/blog/wp-content/uploads/2012/02/hadron_render_01.jpg

(left side of the gantry in the render)

Similar issue with the Y stepper and idlers. I've got a bunch of pre-cut 2x thicker replacement mounting plates that i never took the time to install, i'll see if those change anything. Also, probably will beef up the X stepper mount.

-- 

Ante Vukorepa

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[Ante Vukorepa]

Sorry about straying off topic :)

I'll move to wiki after the next message.

-- 

Ante Vukorepa

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[Ante Vukorepa]

Thanks for doing that! :)

I've made a slightly different version (attached).

This one is 20x20x20, has an X and Y shaped cut on corresponding faces and two dimples on each of the remaining faces.

The idea being that after you print it, you don't have to mark it in order to remember which face was which.

Also, half the object Z has sharp vertices, while the other half has fillets.

Should be useful for estimating how much impact the corners have on rippling.

-- 

Ante Vukorepa

Sent with Sparrow

Attachments:

- testsolid.stl

[Kyle Kenney]

I'll print that out and post my results :)

2013/5/27 Ante Vukorepa <o.or...@gmail.com>

[Laszlo KREKACS]

Hi,

On Mon, May 27, 2013 at 1:40 PM, Ante Vukorepa <o.or...@gmail.com> wrote:
> Thanks for doing that! :)

np
Can you please post your pictures also?

> Sorry about straying off topic :)
> I'll move to wiki after the next message.

It is not off-topic at all. It is printing related, feel free to discuss here.
So discussion here, summary on the wiki for future reference.

Updating the wiki page is the original conversation starter's job.
So that is you.
That is the "price" you pay in return of the others help.
(keeping the wiki up to date about your issue).
Others are also free to help in the wiki page, but it is your
responsibility in the end:)

So chit-chat here, summary on the wiki.

Best,
Laszlo

[Ante Vukorepa]

Yes, yes, i'm working on it :)

In the meantime, here are the first photos:

https://dl.dropboxusercontent.com/u/1702513/_5270345.jpg

https://dl.dropboxusercontent.com/u/1702513/_5270350.jpg

Now, remember, when photographing your own tests, the objective is to capture them in the *worst* light possible (i twisted these around for a while until i've found the lighting angle that makes the effect the most obvious, and i did it out in the sun - harsh light makes it more noticeable) :)

-- 

Ante Vukorepa

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[Ante Vukorepa]

Wiki page is up:

http://wiki.arcol.hu/blog:printing-reasonance

-- 

Ante Vukorepa

Sent with Sparrow

[Ante Vukorepa]

By the way, it would appear that all the changes i've made (which were mostly focused on the Y axis) seem to have had an effect after all, considering the photos now make it obvious the X axis is much much worse.

It used to be the other way around.

So maybe there is no magic bullet for this and it's a matter of tweaking and isolating and adjusting a lot of little things until the issue is attenuated enough.

-- 

Ante Vukorepa

Sent with Sparrow

[Kyle Kenney]

Mine is printing at this very moment, though I didn't realize you'd want such small layers (mines printing at .25) But yeah, I'll take some pictures aswell and load'em up when done.

2013/5/27 Ante Vukorepa <o.or...@gmail.com>

[Laszlo KREKACS]

Hi,

I have printed it in white, and it is almost impossible to do the photo right,
but I dont't have this issue.

However I have seen this issue on Stratasys machines besides on many
reprap printers.
Here are some pictures from haveblue.org:
http://haveblue.org/wordpress/wp-content/uploads/2012/06/bolt-hold-lugs-break.jpg
(on the left, the edge ripples)

http://haveblue.org/wordpress/wp-content/uploads/2012/06/rear-takedown-counterbore.jpg
(the hole under the drillbit ripples)

http://haveblue.org/wordpress/wp-content/uploads/2012/08/buffer-tower-gap.jpg
(bottom middle, the metal pin ripples)

http://haveblue.org/wordpress/wp-content/uploads/2012/08/extraction-failure.jpg
(bottom middle, the oval metal thingy)

Although it is almost unnoticable, if you don't know where to look.

I'm starting to believe it is first a mechanical reasonance caused
(exaggered) by the stepper motor
"stepping", causing the reasonance like peeling a stretched rubber
band (or guitar string).
Changing the microstepping or the firmware (ie. acceleration, edge
optimization),
makes the issue worse or less noticable.

That is my theory at least.

I don't want to talk you into my belt+pulleys
(http://wiki.arcol.hu/blog:arcol-t25), but
maybe it is worth a try.

Best,
Laszlo

[Kyle Kenney]

I printed mine..it seems I have a little echoing so to say, on the Y face...which means through the x-axis, while the X face has nothing...and the two faces with the dimples have no appearance of echoing/ringing at all...though, I printed in natural pla, and I'm find it difficult to take a picture of it, I'll try later tonight when the suns down if the lighting changes anything

2013/5/27 Laszlo KREKACS <li...@arcol.hu>

[Ante Vukorepa]

Your theory pretty much exactly matches mine (see the wiki page).

I believe ORD Bot's rigidity is its undoing in this case - it's *too* rigid and most of its construction elements are under relatively high tension, which makes it "ring" easily and makes dissipating the resonance a tough job.

I've got some TI DRV8825-based drivers on order (no idea when they'll arrive), so i'll test what difference (if any) 1/32 microstepping might have.

As soon as the paint dries, i'll install the beefed up stepper and idler brackets, see if that helps in any way.

And i need to figure out a different mount for the X gantry stepper (there's an alternative or two on Thingiverse) and see if that dampens down the X vibration i'm now seeing.

How much do you plan on charging for the belt+pulleys+idler bearings?

-- 

Ante Vukorepa

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[Ante Vukorepa]

Forgot to mention that before - the choice of filament has a HUGE effect on the ripples being noticeable vs. not.

Opaque silver and black tend to make it the most obvious.

It's invisible on white and natural, as well as any semi-transparent color (including semi-transparent silvers and metallics).

Printing at big layer heights can hide the effect somewhat.

Same for other issues like irregular layers - they all tend to muddle the "rippling" and make it less visible or invisible.

-- 

Ante Vukorepa

Sent with Sparrow

[Ante Vukorepa]

Sorry for the email spam…

Just remembered one more thing.

Slicer can affect the "ringing" too. Well, not affect, rather disguise or amplify.

I can vary the amount of "ringing" in KISS by changing the oversampling resolution and crowning threshold.

Both of these controls can soften the high frequency details, which - unsurprisingly - disguises the problem.

Of course, that's at a cost of surface detail and corner sharpness, but i'm just trying to make a point - you probably won't run into this problem unless you're printing very sharp (high spatial frequency) detail on your objects.

-- 

Ante Vukorepa

Sent with Sparrow

[Laszlo KREKACS]

Hi,

> I've got some TI DRV8825-based drivers on order (no idea when they'll
> arrive), so i'll test what difference (if any) 1/32 microstepping might
> have.

Or you could try for experiment a soft motor coupler, like aquarium tubing,
to see if it changes the output.
Although it is only a workaround, so it is always better to fix the
root cause of issue.

Maybe the reasonance coming the lack of rigidity of the machine too.
(ie. too weak frame). But it is only a wide guess.

> How much do you plan on charging for the belt+pulleys+idler bearings?

I will determine the price this week. But in your case I can give you
a special discount.
If it does not fix your issue, I only charge you the half price, or
you can send me back (at your cost),
and I full refund.
(just remember reselling an already cut to length belt will be rather
difficult.)

Best,
Laszlo

[nop head]

What is crowning?

[Ante Vukorepa]

http://kisslicer.com/forum/index.php?topic=84.0

-- 

Ante Vukorepa

Sent with Sparrow

[Matej Rozman]

It just occured to me, i was thinking of something completly different when I was mentioning changing from repetier to marlin,

but now seing the pictures, this is a mechanical problem, and It almost looks like you have a low cost servo drive with poor loop.

There are two possible problems/solutions for this.

1. Your hotend is not attached rigid enough to your carriage.
Consequence is that when machine changes direction suddenly it will produce shaking of the hotend tip (dont know how to put this in different words). But you see what I mean when looking at the pictures.

Solution: lower your acceleration by half, (not jerk) and the effect will be half the size.

2. Your belts are not strong enough to couterforce the stoping action of the carriage/table.
Consequence wery similar to upper problem, but in this case carriage will be going back and forth rather than stop. I hope you know what I want to say.

Solution: lower your acceleration in FW, try to lower the weight of the axis making problems, try stiffer belts (from 6 to 9mm or maybe even more)

To all, stepper always stops exactly where its supposed to. So I think you can rule out voltage, current and all other electrical issues, this is all phisics.

Please do me a favour and lower your acceleration to 1000 or lower and try to print another one. Please leave jerk as is.

Id really love to see where this goes, since I am also interested in one of these ORDs...

BR, Matej

2013/5/27 Ante Vukorepa <o.or...@gmail.com>

--

[László KREKÁCS]

On Fri, May 24, 2013 at 1:40 PM, Kyle Kenney <dudl...@gmail.com> wrote:
> Laszlo, did you not get my email about the prototype? Also, I'm down for
> comp too!

Oh, seems like I forgot to reply to you.
Of course, I have read it, and I like the positive feedback.

I have not decided yout what path will I follow.

Best,
Laszlo

[Ante Vukorepa]

Yes, all of that was covered before.

Acceleration (and jerk - because jerk in Marlin and Repetier aren't true jerk, but just a speed limit below which there is no firmware-based acceleration, only the acceleration caused by the stepper's torque and stiction) affect the rippling and reduce it.

But that proves nor solves anything :)

It's akin to me saying "my car shakes rather violently if i go above 60 km/h, any ideas on how to dampen that" and you replying with "then don't go above 60 km/h" :)

And yes, it's a mechanical issue. Cartesian bots have lots of degrees of freedom and oscillation modes. Nothing new there.

And yes, the Arcol.hu, being a mass suspended on a thin SS tube is rather prone to oscillating. But those are all symptoms and contributing factors, not causes.

Regarding belts - that's been covered before (plus, the table and the carriage are about the same weight, or the table is a bit heavier. But Y is currently exhibiting less rippling than X. Stiffer belts might help somewhat, tho, as they'd "eat up" some of the vibrations, or they might change the k spring constant and raise the rippling frequency (which is also a solution, if raised high enough).

By the way, whenever someone says they never saw this effect on their printer / prints, i tend to not believe it. Every design out there is prone to oscillations. Perhaps deltas might be slightly less sensitive to them. It's just a question of finding the right test case, printing with the right filament (with surface texture and color that shows undulations well) and looking at it under the right light. I guarantee you you'll find the same artifact on *every* printer if you look or try hard enough, at least to some degree.

If all you do is print herringbone gears and mostly print in clear or white PLA, you'll quite probably never encounter this issue.

-- 

Ante Vukorepa

Sent with Sparrow

[Ante Vukorepa]

Oh, one more thing.

Switching from Repetier back to Marlin was a good idea for other reasons.

It turns out Repetier has some issues with buffer underflows (regardless of the setting) with highly detailed surfaces. It slows down to a crawl, jitters and blobs, creating a mottled, orange-peel surface, which actually obfuscates the ripples (and looks bad).

I've noticed that bug before with it, but wasn't bothered enough to go back to Marlin. Your recommendation made me finally do it :)

-- 

Ante Vukorepa

Sent with Sparrow

On Monday, 27. May 2013. at 18:53, Matej Rozman wrote:

[Matej Rozman]

2013/5/27 Ante Vukorepa <o.or...@gmail.com>

Yes, all of that was covered before.

Acceleration (and jerk - because jerk in Marlin and Repetier aren't true jerk, but just a speed limit below which there is no firmware-based acceleration, only the acceleration caused by the stepper's torque and stiction) affect the rippling and reduce it.

But that proves nor solves anything :)

It's akin to me saying "my car shakes rather violently if i go above 60 km/h, any ideas on how to dampen that" and you replying with "then don't go above 60 km/h" :)

I know, but then again, if the quality is the issue, go slower, its sometimes faster ;)

And yes, it's a mechanical issue. Cartesian bots have lots of degrees of freedom and oscillation modes. Nothing new there.

And yes, the Arcol.hu, being a mass suspended on a thin SS tube is rather prone to oscillating. But those are all symptoms and contributing factors, not causes.

Sorry, wrote it completly wrong...I dont know how to put it in english....

Regarding belts - that's been covered before (plus, the table and the carriage are about the same weight, or the table is a bit heavier. But Y is currently exhibiting less rippling than X. Stiffer belts might help somewhat, tho, as they'd "eat up" some of the vibrations, or they might change the k spring constant and raise the rippling frequency (which is also a solution, if raised high enough).

Aha, we are getting closer, this is one way to find out whats wrong with your setup, so you probably have Y axis lighter than X, this is one possibility, the other one is still your hotend mounting. You can check this pretty easily if you have a dial indicator laying around. Just put it somwhere near your hotend tip (heater or some flat spot) and engage motors so they will hold the machine steady, then try gently to put pressure to the tip from the corresponding side-180 degrees opposite to the dial indicator. Then rotate dial to 90 degrees and try again. Try to put the as much the same pressure as possible to the tip and see how much play you have.

[Matej Rozman]

Yes, I had those problems also, when I turned oversamling in Kiss up (well down), it had problems, and I reckon they were even bigger since delta makes more calculations.

Im also a happy marlin user now.

2013/5/27 Ante Vukorepa <o.or...@gmail.com>

[nop head]

The picture makes it clear it is a resonance causing ringing when one axis stops. The low current micro stepping might make it worse because there might be less electrical damping when the driver is in fast decay mode, compared to slow decay.

What you need is an anti-resonance driver but they are expensive. The old fashioned method is to attach a fluid damper that adds dynamic friction without adding static friction (which would increase backlash).

[Ante Vukorepa]

So mid-band resonance + resonance of the mechanical structure?

Yeah, i've looked at anti-resonance drivers and have seen the prices.

Fluid dampers i've seen mentioned in CNC context, but never saw anything applicable to small-scale machines.

I wonder if some kind of flexible coupling would help and how much negative impact on precision and repeatability it'd have.

-- 

Ante Vukorepa

Sent with Sparrow

[Nicolas Arias]

maybe try another brand of steppers?

[Laszlo KREKACS]

Hi,

Would be nice to have an another machine to cross-check.
Fortunately I have an another one, just for issues like this.

Best,
Laszlo

[nop head]

>So mid-band resonance + resonance of the mechanical structure?

Mid band resonance is when the motor is moving. It speeds up and slows down such that it has a sinusoidal displacement from where it should be at any instant. If only one axis was moving then it would only be apparent in the width of the filament oscillating. When moving diagonally you would get a wavy line if the other axis was moving at constant velocity. That probably isn't the problem.

You have waves emanating from features where one axis has stopped and is ringing but the other is moving at constant velocity. The axis that is ringing is a mass spring resonance. If the spring element is the motor then an anti-resonant drive should help. If the frame is springy then probably not, or not as much.

I found a tiny fluid mass damper in an old disc drive, so small ones must exist, or have existed: http://hydraraptor.blogspot.co.uk/2009/04/unexpected-find.html

  

 

[Ante Vukorepa]

Hmmmmm…

http://www.astrosyn.com/section.php?xSec=44&xPage=1

Anyone tried anything similar (and by similar i don't mean cork or rubber gasket)?

Of course, these wouldn't fix the vibration transmitted down the belt, but it would at least kill the vibrations coming through the mount.

-- 

Ante Vukorepa

Sent with Sparrow

[Chris Gibson]

Funny you should mention those. I just got a bunch of the exact ones. I got them hoping they would make the printer quieter. I haven't tried them yet but I'm going to use them on the printer I'm building right now. When I have a test print done (probably in the next few of days) I will post pictures. Can you send me the file you are having difficulty with?

[Ante Vukorepa]

No particular file (or, rather, after debugging this, i've started seeing the rippling everywhere :)), but here's a test object:

https://dl.dropboxusercontent.com/u/1702513/Ripple_test.STL

Best noticed on black or silver PLA.

Did you order any extras by any chance?

-- 

Ante Vukorepa

Sent with Sparrow

[Chris Gibson]

I ordered 12. But I need them all for the printers I'm building right now. I could get some for you with my next order if you like. You do need to keep in mind that they move the stepper away from the plate by about 5mm so you need to make sure you have clearance and enough shaft length...

[Ante Vukorepa]

No worries, i've got in contact with Astrosyn in the meantime and they're willing to send some my way, despite Croatia not being listed on their web shop.

As a sidenote, i found two interesting things while googling in the off hours.

1) Vexta offers these: http://www.orientalmotor.com/products/accessories/clean-dampers-cmk.html They mount on double shaft steppers (on the "non-business end"). They also have an assortment of rather nice and expensive steppers. I wonder if they're worth their price...

2) Relatively (!) cheap DSP-based 12-48V stepper drive: http://www.servo2go.com/product.php?ID=105421 Manual here: http://www.applied-motion.com/sites/default/files/hardware-manuals/STR2_Hardware_Manual.pdf

Some more late-night developments from yesterday:

- i've mounted the extruder+hotend on a thick silicon pad, haven't tested the effect yet

- i've bought a bunch of appropriate sized (M4, M5) rubber washers and some M3 gaskets (couldn't find rubber washers in that size anywhere), i'll see if they help

- i've flicked a finger at the X stepper and realized that it continues to resonate when i do that, along with the X gantry - that's with it tight and completely solidly mounted; if i loosen the bolts a little, it doesn't resonate as badly, i'll see about printing a different mount for it, this one pretty much turns it into a tuning fork

- i've noticed a new artifact in the prints, which is unrelated to "regular" rippling - more about that below

So, yesterday, i did some slow 0.1mm prints to test something and noticed something new - one X side exhibits very regular banding. Then i went back to the test objects i've posted here and noticed the same thing in one of them:

https://dl.dropboxusercontent.com/u/1702513/_5270350.jpg

(top right shot)

You might discount it as corner ripple or a belt artifact, but take a better look and you'll notice some interesting things:

- it's present on the filleted half as well

- it's only present on one side (the top left shot is opposite to it)

- its highly regular

- its frequency coincides with the frequency of the regular ripples

- the belt is flipped on the idler and the frequency of the artifact is nowhere close to belt pitch (it's approx. 2.5x higher)

I believe *that* is the natural resonance frequency of the X gantry. The reason it's so even and not caused by the edge is because it's continuously fed by the vibration of the stepper and has nowhere to dissipate. The only question is - why is it not present on the opposite side.

By the way, i showed the test prints to a few people and had to twist and turn them for a minute and then explain for a few more before they've even noticed the ripples and vibration artifacts. So i might be obsessing too much about this :)

-- 

Ante Vukorepa

Sent with Sparrow

[nop head]

What makes the Hadron frame so apparently flexible / springy? Looking at pictures one would imagine AL extrusions bolted at right angles pretty rigid (in the relevant direction) compared to belts and motors.

[Ante Vukorepa]

They are indeed rigid and that's the main issue…

Being rigid, they conduct vibrations *very* well and don't dissipate the energy anywhere. Also, being rigid, their stiffness (k) is high, making the whole structure's natural frequency high, despite the relatively high mass.

But the frame isn't the problem. The main issue is the way steppers and idlers are attached to the frame - via thin plates that are fixed to the extrusions in a single point (single T-slot nut) and are in contact with the extrusion longitudinally (via the plate sides). On top of that, the X stepper is bolted onto the gantry with 4 very long bolts through 4 plastic tubes. Finally, the feet bottoms are an arc and are in contact with the table with a very very tiny surface.

All of that makes it into one big tuning fork - resonates easily, conducts vibrations easily, has nowhere to dissipate.

-- 

Ante Vukorepa

Sent with Sparrow

[László KREKÁCS]

Hi,

Many CNC machines (still) uses stepper motors, and they are fine.
My WIP machine will be about 80kg.

So I still vote for the lack of rigidity (+ lack of weight).
I'm curious what would happen if you would switch the two belts.
Or the two pulleys.

Best,
Laszlo

[Ante Vukorepa]

CNC machines are orders of magnitude heavier, as you've mentioned.

Fn is proportional to k and inversely proportional to mass. On top of that, if a mill spindle oscillates a micron or ten microns, nobody cares - you will never notice it on the stock. If the surface of a print oscillates by a micron or ten microns, however… you'll notice it.

You (plural) seem to keep thinking about vibration as oscillation around some fixed joint with 1 or more degrees of freedom.

That's not how structures like this behave. It's not a pendulum :)

Take a hammer and an aluminium beam, suspend it with minimum contact to the outside world (i.e. no friction damping), hit the beam with the hammer and take a listen. Is the beam non-rigid? Of course not, it's a beam. Is it resonating? Yes, like crazy!

Like i keep trying to say, it's not an issue of rigidity. If anything, less rigidity *helps*, because it lowers the frequency.

If the frequency is low enough, the energy will dissipate within one or two cycles and you'll get *better* results than with a rigid machine.

Same thing if the mass is high enough, which is why you won't find this issue with large machines.

-- 

Ante Vukorepa

Sent with Sparrow

[nop head]

So it looks like a flat sheet of Dibond and some plastic brackets works a lot better than Al extrusions. I think it is pretty dead to vibration along its plane.

However I print with much more viscous plastic at lower speeds so would probably never see vibrations at audio frequencies recorded like that.

[Ante Vukorepa]

I believe that Dibond is a better idea, yes, if the construction is sturdy enough (i.e. provided there is no wobble).

Plastic brackets probably do a better job of absorbing vibration at the joints than aluminium brackets too.

In any case, here are the initial results of last night's tweak-a-thon:

https://dl.dropboxusercontent.com/u/1702513/_5290383.jpg

Explanation later, i need to go out now.

As a sidenote, just to put things into perspective, re: the effect of lighting and filament choice, here's how one of the worse examples looks like when *not* trying to photo it in the worst possible light, without microcontrast adjustment and with non-reflective filament:

https://dl.dropboxusercontent.com/u/1702513/_5290408.jpg

-- 

Ante Vukorepa

Sent with Sparrow

[Ante Vukorepa]

(oh, and yes, all of these were printed at the same speed, with the same acceleration and jerk)

-- 

Ante Vukorepa

Sent with Sparrow

[Ante Vukorepa]

Okay, so here's a few explanations…

It comes down to this - with rigid machines, it's a matter of choice between no vibration and soft printed features, or vibration and sharp features. Yes, i know, not exactly rocket science, but let me explain.

Shot 1 is where i've left off the day before.

The first thing i've tried is loosening the belts. Yes, loosening, not tightening. Guess what - as long as there is no slack, a loose belt absorbs vibration. Good thing? Yes and no, because the trade-off is loss of detail - the corners and high frequency details get softer, same as vibration. It's a low-pass filter.

The result is in shot 2.

Shot 3 is the result of padding all the stepper and idler plates with foam and placing generous amounts of rubber washers throughout the machine.

Curiously, that helped with the Y a little, but worsened the X. It might've been due to me retensioning the belt again when i was taking the idler plates off.

Second revelation was tightening the V-wheels until they offer a significant resistance to rolling along the extrusion rail. The idea is similar, except the dampening is friction-based. The result is on shot 4.

Shot 5 was the result of turning off the fans. As you can see (X2) the high frequency continuous stripes are gone, so i guess that was one of the fans (i *did* feel one of them vibrates, unlike the other which is completely smooth - curiously enough, the vibrating one is on precisely the side that exhibited the striping the most).

Shot 6 is more tweaking and fans on again.

Shot 7 is fans off again and temperature slightly lower.

Conclusion - the vibration artifacts *can* be tweaked out by loosening the belts and increasing friction of both axes, but that comes at the cost of losing high frequency detail (softer features) and more wear (on V-wheels) and heat (steppers / drivers), so it's not a perfect solution by any means. Also, there is no magic bullet as i've previously said. It's not a single thing, but many things conspiring.

-- 

Ante Vukorepa

Sent with Sparrow

[Ante Vukorepa]

Today's batch of tweaks consisted of:

1. switching back to 12V

2. turning low current microstepping back on

3. switching out the X stepper standoffs for a much sturdier printed mount

4. switching out the idler plates for thicker ones that are less prone to bending and vibrating

5. mounting vibration absorbing feet

1 and 2 combined led to a much smoother stepper motion *at higher speeds*. There is still a particular speed range that vibrates rather strongly and, by ear, it's the same frequency or set of frequencies i kept hearing (or feeling) before. Curiously, the sound of the steppers at high speeds changed drastically - they now have a very high pitched hiss overlaid on top of the regular sound (like pink noise through a high-pass filter).

3 and 4 seem to have helped with detail, but resulted in vibration coming back. In fact, i think the prints are sharper than they've ever been now. I need to do more tests.

5 made things worse, i'd say. I didn't expect that.

-- 

Ante Vukorepa

Sent with Sparrow

[Ante Vukorepa]

Been quiet for a while and haven't done much tweaking due to work.

Here are the latest results (hope i'm not boring everyone to death):

https://dl.dropboxusercontent.com/u/1702513/beforeafter.jpg

The first print from the last set of photos is on the left.

The final result of tweaks is on the right.

Like i've said before, it's a matter of compromise. You can either have rigidness and repeatability, nice and even layers and sharp features, but vibration issues and rippling, OR you can have less rigidness and repeatability, uneven layers and softer surface features and no vibration nor rippling. I believe the photos show that rather clearly. The layer evenness is visibly worse, as well as corner sharpness, but the ripples have been all but eliminated.

This is what it looks like on less reflective filaments:

https://dl.dropboxusercontent.com/u/1702513/gray.jpg

There are other issues that popped up as a result of all the dampening as well. The slack in the belts (has nothing to do with tightness - this is caused by the deformation of belts as the carriage travels along them, due to idlers being wider than pulleys) changes across the travel range, causing gaps between infill and perimeters. The top and bottom surfaces are much uglier than before due to less repeatability and less rigid X carriage assembly.

As far as compromises go, i don't think i like this one all that much.

I'll try and find a balance between the two extremes, i guess...

-- 

Ante Vukorepa

Sent with Sparrow

[Ante Vukorepa]

Oh, and damping on the feet does help, but it depends on how you implement it.

Just a single layer of foam or a single layer of rubber or silicone doesn't do much or makes things worse.

Combining layers of different material helps, though. For example, foam, then silicone, then cork.

The idea is to have multiple transitions between materials with different spring constants and different dampening.

It seems like it also helps to have the feet mounted non-rigidly to the bot, with at least one degree of freedom, so they "eat up" the high impulse jerks.

-- 

Ante Vukorepa

Sent with Sparrow

[nop head]

Have you tried simply lowering the acceleration. I found my machine was slowly moving along the counter it was on so I lowered the acceleration from 4000 to 2000 and now it stays put.

[Ante Vukorepa]

I'm at 1000 right now. Was at 1500 before the whole ordeal.

I don't want to lower it any more than that, as i'll start getting blobbing at the corners (and lose detail).

-- 

Ante Vukorepa

Sent with Sparrow

[Chris Gibson]

Nop head, you push your printers too hard. It was trying to escape!!

[Laszlo KREKACS]

Hi,

First of all sorry for the late photo. I needed to take some microscope photo
alongside the macro photo what my camera can do.

The print is white, so hard to take a good photo,
but I can't see any reasonance what we were talking in the whole
thread, but I'll let you decide.

So here are the normal camera macro photos:
http://www.flickr.com/photos/48806889@N05/9046389119/
http://www.flickr.com/photos/48806889@N05/9046386285/
http://www.flickr.com/photos/48806889@N05/9046385015/
http://www.flickr.com/photos/48806889@N05/9048606654/
etc (see the flickr gallery or the wiki page)

And here are the microscope photos:
http://www.flickr.com/photos/48806889@N05/9046295045/
http://www.flickr.com/photos/48806889@N05/9046294727/
http://www.flickr.com/photos/48806889@N05/9048522342/
http://www.flickr.com/photos/48806889@N05/9048522156/

Ante, please update the wiki page with your later findings,
and there were some useful feedbacks too,
so would be nice to incorporate into the wiki page those comments also.

I added all the above photos to the wiki page:
http://wiki.arcol.hu/blog:printing-reasonance

Feel free to add text, delete some photos if you dont see it fit, etc.

Best,
Laszlo

ps: I loved all the useful comments in this thread, and I hope my
prints gives some more inputs to your issue.

[Ante Vukorepa]

Yeah, like i’ve said, the visibility of the ringing is heavily dependent on the filament used.

You probably won’t see any on white (i can’t see it on gray either, for example). Reflective, opaque filaments tend to exhibit it the most.

That said, your shots seem to be relatively light on ringing, regardless. I can count one distinct peak and one very slight, so in your case, the vibration seems to dissipate completely within two cycles.

Thanks for the photos!

And don’t worry, i intend to post the updates as soon as i take some photos of the changes.

Also, i’m waiting for two more items to experiment with (a stepper with a resonance damper and the anti-vibration mounts) to see if those have any additional effect.

-- 

Ante Vukorepa

Sent with Sparrow

[Ante Vukorepa]

(by the way, you seem to be getting quite a bit of unevenness in your layers, judging by the vertices... what are you using to drive your Z?)

-- 

Ante Vukorepa

Sent with Sparrow

[Laszlo KREKACS]

Hi,

On Mon, Jun 17, 2013 at 4:35 PM, Ante Vukorepa <o.or...@gmail.com> wrote:
> (by the way, you seem to be getting quite a bit of unevenness in your
> layers, judging by the vertices... what are you using to drive your Z?)

Currenlty I'm using trapezoidal threaded rod (like ACME rod), the Z is
really crappy.
I'm on the issue (and nailed it down to fundamental construction
error, what almost any reprap has).

That is another error, which can observe on *any* reprap print. Some
are more visible then others,
but almost all has crappy Z.

The Z layer height is pretty uniform, what is bad, is the wave form
along the Z axis.

Best,
Laszlo

[Ante Vukorepa]

Yup, i have the same problem, except at a much lower scale.

It’s not visible on the actual vertices, but becomes apparent in the texture (again, something you can see easily on reflective filaments but also on translucent ones, due to changes in refraction).

See here for example:

https://dl.dropboxusercontent.com/u/1702513/Z_variations.jpg

“Vertex" on the left, which is regular, vs. the actual visible variations in the texture on the right.

Contrast and unsharp mask enhanced to make it more obvious. (That’s 0.1mm layer height, though.)

Reason i’m asking is because i’m using a trapezoidal rod as well.

But in my case, since the X gantry is constrained by the aluminium extrusions and there’s really nowhere for it to go, i believe the effect truly is the result of a minute shift in layer height.

And more importantly, i believe the cause is the threaded rod itself (i.e. irregularities in the profile).

I’ve got a thicker, more expensive set of ACME rods stashed that i keep meaning to install, but never get around to (i need to devise and print a set of brackets for the nuts first).

-- 

Ante Vukorepa

Sent with Sparrow

[Laszlo KREKACS]

On Mon, Jun 17, 2013 at 4:32 PM, Ante Vukorepa <o.or...@gmail.com> wrote:
> That said, your shots seem to be relatively light on ringing, regardless. I
> can count one distinct peak and one very slight, so in your case, the
> vibration seems to dissipate completely within two cycles.

Could you edit my photos showing where you think it has this reasonance?
You made me curious, because I don't see at all, despite I even got a
microscope for real closeup photo.

If you want me, I can send you this test piece in an envelope.

Best,
Laszlo

[Laszlo KREKACS]

On Mon, Jun 17, 2013 at 4:57 PM, Ante Vukorepa <o.or...@gmail.com> wrote:
> Yup, i have the same problem, except at a much lower scale.

It only depends on your luck. Ie. if you disassemble and reassemble
the machine it
changes, either better or worse then before.

Trust me we have disassembled and reassembled more then 30 times in
the past 1.5 years,
we tried threaded rod, trapezoidal rod, and even ballscrew.

I think there is a fundamental issue in all of the reprap designs out
there (if you compare any regular CNC machine).
But who am I to judge others' designs:)

Best,
Laszlo

[Ante Vukorepa]

Here’s a contrast enhanced version:

https://dl.dropboxusercontent.com/u/1702513/Contrast.jpg

Like i’ve said, it’s minor.

-- 

Ante Vukorepa

Sent with Sparrow

[László KREKÁCS]

Hi,

What you marked on the photo is in the range of 0.1mm length.
I don't think the reasonance is that dense.

I will examine closer this evening when I get home, but I'm not convinced.

Laszlo

[Ante Vukorepa]

A lot of the less-reprappy designs out there are rather close to the design of “regular” CNC machines, but still exhibit this to some degree.

With traditional reprap designs it quite probably is an issue with the mechanics (i.e. too many degrees of freedom that can “swallow up” the irregularities in the Z drive train and turn them into X and Y undulations).

But i wouldn’t say it’s an issue with all the designs so much as with the tolerances required for 3D printing vs., say, milling (tolerances in the sense of tolerances needed for a visible defect, not a functional one).

And, more importantly, we all use machines with parts (namely threaded rods and nuts) that are orders of magnitude cheaper than what is used in most of the traditional CNC machines.

Just look at what a proper linear slide costs. Or a proper threaded rod with an anti-backlash nut :)

-- 

Ante Vukorepa

Sent with Sparrow

[Ante Vukorepa]

If that’s 0.1mm length, what layer height was that? :o

And yes, resonance can indeed be very dense. It depends on the speed and rigidity.

If the speed is high enough, you can even record audible frequencies.

-- 

Ante Vukorepa

Sent with Sparrow

[Laszlo KREKACS]

Hi,

> A lot of the less-reprappy designs out there are rather close to the design of “regular” CNC machines,

Show me *one* commercial CNC machine which uses two threaded
rod/trapezoidal rod/ballscrews for Z axis.

> And, more importantly, we all use machines with parts (namely threaded rods
> and nuts) that are orders of magnitude cheaper than what is used in most of
> the traditional CNC machines.

Not all of we...

>
> Just look at what a proper linear slide costs. Or a proper threaded rod with
> an anti-backlash nut :)

I know exactly how much it costs.
The old saying is still true: You get what you pay for.
You can't reasonably expect from a plastic corner piece to be rigid...

Best,
Laszlo

[László KREKÁCS]

On Mon, Jun 17, 2013 at 5:35 PM, Ante Vukorepa <o.or...@gmail.com> wrote:
> If that’s 0.1mm length, what layer height was that? :o

I will take a photo with a ruler later this week.

[Ante Vukorepa]

Most of them use *one* threaded rod for the Z axis.

At least those i’ve seen (mostly mills).

Some use it to move a linear slide, some use it to move a carriage along two smooth rods.

-- 

Ante Vukorepa

Sent with Sparrow

[Ante Vukorepa]

(or did i misunderstand and you meant lead screw vs. ball screw? ball screws aren’t really all that practical for reprap sized machines)

-- 

Ante Vukorepa

Sent with Sparrow

[Laszlo KREKACS]

it was only a sarcastic remark, that none of the commercial CNC
machines uses two drivescrews for one axis.
So it is pretty much a fundamental flaw imho, but to each his own.

(also the plastic structural parts are not helping either)


Best,
Laszlo

[Ante Vukorepa]

Ah. Gotcha.

And yes, plastic structural parts definitely do not help, although in some cases, they can dampen the vibration.

Anyway, since i have a drawerful of test cubes in my desk and a camera nearby, i took the photos of my worst vs. one of the later “fixed” samples next to a ruler.

Also, i should really be working, but this was too good an opportunity for procrastination to skip it ;P

https://dl.dropboxusercontent.com/u/1702513/bad.jpg

https://dl.dropboxusercontent.com/u/1702513/better.jpg

(note the lighting angle - it needs to be really oblique in order to reveal the surface oscillations)

-- 

Ante Vukorepa

Sent with Sparrow

[Laszlo KREKACS]

Hi,

Ante, I sent you my testprint in an envelope today. I hope you get it
within a few days.
You can examine it first hand, and make a conclusion:)
Also maybe you will be able to take better photos then me.

Best,
Laszlo

ps: Please, keep the wiki updated.

[Ante Vukorepa]

Wow, thanks!

No need to do that, hope it didn’t cost you too much.

I’ll take side-by-side photos when it arrives.

On a sidenote, i’ve received some new stepper drivers (TI DRV8825 based) so i plan to test what effect (if any) moving to 1/32 microstepping might have.

Also received the dampened stepper mounts, so planning on testing if there’s any effect from that as well.

I’ll post the conclusions on the wiki after i’m done with that.

-- 

Ante Vukorepa

Sent with Sparrow

[Laszlo KREKACS]

Hi,

On Tue, Jun 25, 2013 at 3:57 PM, Ante Vukorepa <o.or...@gmail.com> wrote:
> Wow, thanks!
> No need to do that, hope it didn’t cost you too much.

You are in the neighbourhood:)
Don't worry it is in a range of an icecream, and it's a hobby after all:)

> I’ll take side-by-side photos when it arrives.

Super!

>
> On a sidenote, i’ve received some new stepper drivers (TI DRV8825 based) so
> i plan to test what effect (if any) moving to 1/32 microstepping might have.
> Also received the dampened stepper mounts, so planning on testing if there’s
> any effect from that as well.

I'm really interested in your adventure!

Laszlo

[Laszlo KREKACS]

Hi,

Since Croatia will be part of the European Union from 2013 july 1st,
seems like I can ship to you up to 31kg for 15EUR from 1st of july
until 1st of September...
Also no more duty tax. Kind of simplify our life.

Laszlo

[Ante Vukorepa]

Yup, no duty, but there will be tax (i think - i’m not exactly sure how VAT is regulated between EU countries).

I hope the customs procedure will be faster too.

Anyways, i haven’t done much testing lately (or printing at all) due to work, but i did print one test cube with the new drivers in place.

The results were... truly bizarre:

https://dl.dropboxusercontent.com/u/1702513/weirdness.jpg

The increased unevenness in layers and the return of rippling is easy to diagnose - the ambient temperatures went up by a lot since my last tests (30-35 deg C) so things that used to be tight, very much weren’t when i printed that. But that’s not the part i’m finding weird, it’s the families of “exponential curves” on all the surfaces that i do :)

No idea what that is or where it came from. Note on the far right shot that they are vaguely symmetrical with the vertices of the “cube” as axes of symmetry.

I’ve started printing another one after this one, had to cancel it a few minutes or so in and go back to work, but that next one wasn’t exhibiting the same issue.

Very very weird.

-- 

Ante Vukorepa

Sent with Sparrow

[nop head]

A wild guess would be flow rate anomalies due to incorrect microstepping of the extruder. It is very difficult / impossible to achieve 1/32 stepping with those drivers.

[Ante Vukorepa]

Quite possible and my thought too.

I’ll know more when i get the time to do a few more test prints, at 1/8, 1/16 and 1/32.

If the issue pops up again, that is.

But regardless, it’s going to be interesting to see what effect the different microstepping ratios have on this particular driver.

BTW, Roy’s (Panucatt’s) DRV 8825 carrier boards have the decay pin broken out and a conveniently placed via nearby you can connect it to to pull it high, so i might give fast decay a try too.

-- 

Ante Vukorepa

Sent with Sparrow

[nop head]

It won't be able to get the current low enough with slow decay for the 1/16 step let alone the 1/32. With fast decay the ripple current is much higher. Since the chopper switches off on the peak, but the average is what sets the torque, you end with an offset which is similar to or maybe even more than the lower current steps.