direct drive with bowden

[Bill Schwanitz]

Anyone have experience with direct drive and bowden setups? I'm switching from a direct drive straight to the hot end and having some issues.

Basically, I can push the filament through the ptfe tube and once it hits the hot end, there is just too much friction/resistance. I get some extrusion but for some reason I end up just grinding the filament.

If I push filament through by hand I can feel there is some resistance. I can't tell if the issue is with the extruder, the switch to bowden, temps or ( more likely ) a combination.

I'm using an mk7 stainless steel from qu-bd. the mk7 is directly attached to the stepper, no gearing.

Hot end is pico, 1.75mm

abs from ic3d, printed tons of this without issue ( on a jhead )

  - printing at 235

extruder is http://www.thingiverse.com/thing:215010

  - I had to manually tweak this a bit, the bearing was pressing in to the opposite side

  - With the filament firmly put up against the drive gear, stepper off, I can't push the filament without bending it so its very tight

  - Tried various degrees of tight/loose

My gut tells me that with switching to a bowden and the semi-flexibility of the tubing + the pressure from pushing the filament through the hot end its just too much for the non-geared setup to overcome. I end up just grinding the filament to a nice fine dust ;)

I have the parts for a wades extruder - probably give that a go soon-ish. Curious what others have to say.

Bill

[Charles Haase]

From what I have seen, there are people doing Bowden with direct drive, so I can't say that's the main problem. Here is what I would check:

- is filament diameter in spec?

- is tube inner diameter in spec?

- any bulges in the filament (I've seen this happen before)?

- are any curves in the PTFE tube as gentle as possible?

- can you increase current to the motor (though if you're getting stripping then the motor is still turning and you just don't have enough clamp force against the hobbed bolt/gear area)?

- have you tried extruding slower?  I think steppers make more torque at lower speeds. 

 -Charles

Sent from my TRS-80.

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[Larry Knopp]

Yep Bill...

Bowden's are a PITA to get *right*.

All of what Charles asks is right on.

One other thing...  what hob do you have?  Could be not enough bite in addition to friction in the tube/filament.

Good Luck!

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[Bill Schwanitz]

Charles,

The filament diameter is basically within spec. I don't have any issues putting it in the hot end manually and when I can get the extruder to not seize up, it does push fine. Like I said, I've printed with the ic3d stuff for a while ( on my 4th spool ). I had no trouble printing this role on my old j-head, only have about 1/8 spool left. I measured it at 1.73 at its smallest, and 1.76 in a spot or two - I put 1.74 in the slicer config.

The inner tube does not seem to be an issue. When I feel the filament through I don't notice any friction ( well not much, it pretty much glides in ).

I have tried increasing and decreasing the current. When I go too high, the motor gets pretty hot - hot as in been printing for 8 hours hot ;) ( ok, maybe I just admitted I was running my stepper too high previously? ;) )

I posted a pic of my setup on dropbox, https://dl.dropboxusercontent.com/u/86313544/ob1.jpg. Forgive the wiring mess, I'm still tidying up ;) I just moved the electronics over from another frame ( yes Larry, that y axis on my old frame really sucked ;) I think this one is going to be a little better! )

I'll have this printer with me at the meetup wednesday. I'm hoping its printing better by then.

Also for an interesting ad-on, when I switched the hot end back to the j-head, same thing. I'm 99.9999% sure this is a split/tie between going to a bowden setup ( other half being the new extruder setup ). The motor and drive gear are un-changed so I know that part works. Also using the same ramps board, drivers etc.

The hob I'm using is http://store.quintessentialuniversalbuildingdevice.com/product.php?id_product=142 . Other than the drive gear being a very tight fit on the stepper shaft, its actually done fairly well. I do wonder if there is just not enough bite on the drive gear. I think this is the drive gear one of the other guys had been looking at/recommending - http://wiki.arcol.hu/product:mini-hyena-v20.

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[Charles Haase]

The only other thing I can think of to try is to apply a fan to the motor. Maybe the motor is heating up, transferring heat through the hobbed gear, and softening the filament. All of this seems highly unlikely to me, but it could be worth a shot. I have never run a Bowden, but heat creep from the cold end up the filament caused stripping issues for me until I added a fan. 

-CH 

Sent from my TRS-80.

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[Bill Schwanitz]

Does anyone have a stepper motor with built in gears which I could borrow wednesday while at the meetup? I want to try using the geared stepper with my mk7 drive hob, curious if that makes any difference

[Larry Knopp]

Hmmm.

I use almost the exact same hob on my 1.75 bowden setup on my "Mini MendelMax", with direct drive, and "only" a NEMA 14 motor.

Your 17 surely has more "ooompf" and isn't the problem (it doesn't sound as if it is slipping and stripping, but rather that it is unable to overcome the resistive force).

One thing you didn't mention...  what diameter hot-end tip?  (Amazing how much more back-pressure you get from a .35 compared to a .50)

Make sure you get the clamping on the filament as tight as you can, to ensure really good bite.

Looking at the picture of your setup, my first thought is that the bowden tube is too long and it's location isn't optimal.

I would recommend moving the drive motor to one of your side uprights and shortening the bowden tube. And, I believe most critically, creating the simplest/shortest curvature you can.

The twist and length of the current configuration looks to me to just be presenting too much opportunity for friction as the printhead moves.  Especially the higher up in a print it gets.

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[Larry Knopp]

You mean a stepper with a gearhead?

I only have NEMA 14 sized.  Which would require a completely different mounting system.

Sorry.

(Oh, and unfortunately I won't make the Meetup this week either...)

[Bill Schwanitz]

Charles,

Interesting. I have a fan available - I'll give it a try!

[Bill Schwanitz]

Larry,

Correct a stepper with a built in gear along the lines of http://store.makerstoolworks.com/extruders-and-parts/geared-nema17-stepper-motor/

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[Larry Knopp]

Ahyup.

I have Nema14, couple different ratios that we played around with, but no 17's.

Sorry man!

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[Bill Schwanitz]

Well,

Tried a fan setup to see if that helped. No such luck.

I also tried switching to PLA, same thing.

I did find something interesting out. If I manually start flowing filament and then start up an long extrude ( 200mm or so ) and force the flow/insert the bowden tube I get a nice even flow of filament. Once the extrude is complete, I hit extrude again ( maybe 5 or 10 seconds ) and it just grinds on the filament.

Any ideas? I tried setting up my wades extruder but I don't have the right springs. I can probably make it work though, thats my next idea/attempt.

[Larry Knopp]

I'm still betting on too much friction in the tube / tube length.

Any idea on the specs of the motor?

As an experiment, if you have any extra ptfe tubing, try dismounting the extruder and shorten the tube.  Hold the thing by hand even, and see if it'll extrude evenly.

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[Charles Haase]

One more idea... check to see if the PTFE is over tightened, making it squeeze the filament on either end. 

-CH 

Sent from my TRS-80.

[Bill Schwanitz]

I'll check the tubing. I have the printer with me for the meetup tonight.

I switched late last night to a wades extruder and only had enough time to test a simple push of filament through the hotend, no actual printing. The filament flowed very very smoothly including no delay on the second push which previously would result in the jamming/grinding.

Now, this also includes a new hobbed bolt. It does use the same stepper motor, so ;)

More testing tonight - hopefully I can get prints running tonight!

bill

Charles,

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[Larry Knopp]

The gearing on the wades = mech. advantage

Hopefully that's your fix!

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[Bill Schwanitz]

Sadly, no ;(

[Larry Knopp]

Man.

Same deal...  stripping and grinding?

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[Bill Schwanitz]

yup ;(

I went to a non-bowden setup on the wades extruder and that works well enough to push a fair amount of filament ( 600-700mm so far, at varying speeds ). Sadly, the x carriage I have is only for the bowden setup. I'm going to try to get a print of the wades/x carriage combined which I had not printed previously.

If anyone is interesting/willing to help me out I'd be much appreciated - http://www.thingiverse.com/thing:49663. I only need the extruder frame, I have the gears ( assuming they are the same ratio/size for the wades I already have assembled ). Happy to pay for the cost

[Bill Schwanitz]

Follow-up to my bowden woes

my bowden setup is done, using a wades and was able to re-print the extruder and parts necessary to get my setup working. Asside from a loss of X/Y due to the bulk of the extruder I'm happily printing again.

Stuart was kind enough to get me the thing I references in my last post in PLA. Incidentally, that extruder held up fairly well - I was surprised. I was very concerned of heat creep from the hot end and warping of the PLA. That did not happen at the hot end ( I hacked on some cooling ;) ) but the stepper motor was very interesting to peel off when I was done. The PLA had softened enough to glue itself in place. Thankfully it did not warp much so I was able to get things functional.