Z-Rods

[Henning]

Hi and Hello to the new Group!

I have same questions and ideas for the Z-Rods.
First of all: There are four z-rods: a threaded and a non-threaded on
either side - correct?

Z-Threaded-Rod:
On the to it's fixed using two couplings and six zip-ties - works fine.

[Henning]

Ok - first fail in the mailing list:
Pressing [TAB] does not introduce a tab, but changes focus on the web-
page - next [Enter] sends your post.

Where was I:

> I have same questions and ideas for the Z-Rods.
> First of all: There are four z-rods: a threaded and a non-threaded on
> either side - correct?
>
> Z-Threaded-Rod:
> On the to it's fixed using two couplings and six zip-ties - works fine.

^-- top/stepper
On the bottom/basis it is fixed: None?
Makes sense, because the x-ends will hold it.

Z-Non-Threaded-Rods:
Their purpose is to stabilze the x-ends - correct?
On the top they are fixed by - inserting them into the hole of z-motor-
mount - doesn't sound so stable.
On the bottom they are fixed by - another middle threaded x-rod and
fixed using two bar-clamps like here:
http://www.flickr.com/photos/46125284@N03/5372668795/in/photostream/
???
Do we have space for this middle x-rod?

Why do we need such a large pipe for the nut traps on the x-ends?

Suggestion:
Why don't we get rid of the non-threaded z-rods?
Mount the Z-Steppers on the base, and fix the z-rods using 608-
bearings inside z-motor mount and some washers and nuts on the top.
Advantage: reduce space by getting rid of the steppers on top, reuse
empty space on the basis for the steppers, get rid of 2 non-threaded-z-
rods and 1 threaded middle-x-rod.
Disadvantage: Instability. RLY? By keeping the nut trap pipes in the x-
ends and mounting a nut in the basis and the top of these pipes -
things could be pretty stable. Another issue: the z-stepper-mount
would be mounted on the bottom y-threaded-rod - and could twist around
it. Issue?

What do you guys think?

Henning

[Christopher Olah]

On Sun, Jan 23, 2011 at 2:48 PM, Henning <tut...@gmail.com> wrote:
> Ok - first fail in the mailing list:
> Pressing [TAB] does not introduce a tab, but changes focus on the web-
> page - next [Enter] sends your post.
>
> Where was I:
>> I have same questions and ideas for the Z-Rods.
>> First of all: There are four z-rods: a threaded and a non-threaded on
>> either side - correct?

Yes.

>> Z-Threaded-Rod:
>> On the to it's fixed using two couplings and six zip-ties - works fine.
>            ^-- top/stepper
> On the bottom/basis it is fixed: None?
> Makes sense, because the x-ends will hold it.
>
> Z-Non-Threaded-Rods:
> Their purpose is to stabilze the x-ends - correct?
> On the top they are fixed by - inserting them into the hole of z-motor-
> mount - doesn't sound so stable.
> On the bottom they are fixed by - another middle threaded x-rod and
> fixed using two bar-clamps like here:
> http://www.flickr.com/photos/46125284@N03/5372668795/in/photostream/
> ???
> Do we have space for this middle x-rod?

We did, but it is no longer necessary if we go with my new designs for
z-motor-mount.

http://christopherolah.wordpress.com/2011/01/24/hacklab-reprap-coolness-2/

> Why do we need such a large pipe for the nut traps on the x-ends?

No idea why they're there. Well... I suspect it maybe to make it
easier to put the nuts and threaded rod through, but it's not
necessary. Redesigning x-end-* is next on my list of things to do.

> Suggestion:
> Why don't we get rid of the non-threaded z-rods?
> Mount the Z-Steppers on the base, and fix the z-rods using 608-
> bearings inside z-motor mount and some washers and nuts on the top.
> Advantage: reduce space by getting rid of the steppers on top, reuse
> empty space on the basis for the steppers, get rid of 2 non-threaded-z-
> rods and 1 threaded middle-x-rod.
> Disadvantage: Instability. RLY? By keeping the nut trap pipes in the x-
> ends and mounting a nut in the basis and the top of these pipes -
> things could be pretty stable. Another issue: the z-stepper-mount
> would be mounted on the bottom y-threaded-rod - and could twist around
> it. Issue?
>
> What do you guys think?

I'd be concerned about stability, but I don't have any empirical
grounds for that. We should test it. It would simplify my designs for
z-motor-mount even further.

I'd also be concerned about the added stress on the motor/coupling.
And about the nuts binding. It seems to me like loose threaded rod
would help avoid that which makes me concerned about changing things.

> Henning

Christopher

[Whosawhatsis]

The smooth bearing rods are important to keep the axis straight.
Remember, the Z leadscrews turn and may not be entirely straight. You
don't want Z-wobble like on a cupcake.

On Jan 24, 10:59 am, Christopher Olah <christopherolah...@gmail.com>
wrote:

> http://christopherolah.wordpress.com/2011/01/24/hacklab-reprap-coolne...

[Henning Meyer]

2011/1/24 Whosawhatsis <whosaw...@gmail.com>:

> The smooth bearing rods are important to keep the axis straight.
> Remember, the Z leadscrews turn and may not be entirely straight. You
> don't want Z-wobble like on a cupcake.

Are you sure about not being entirely straight? It seems that might be
a problem of the coupling - maybe we have to improve this.
Even if they wobble: The x-ends are mounted to both: loose coupling
via pla-bushings to smooth and thight coupling via nuts to threaded
rods. I doubt that the wobble will be reduced effectivly this way.

Henning

[Whosawhatsis]

The leadscrews can't cause wobble because they are only constrained at one end. If they're not straight, the loose end will just swing around. If you capture it in a bearing, it can swing the carriage around in the middle of the rod, and you would have to do this if you were going to get rid of the bearing rods.

[Christopher Olah]

> Are you sure about not being entirely straight? It seems that might be
> a problem of the coupling - maybe we have to improve this.

This was more of an issue before Rob redesigned the coupling. He
managed to achieve fairly good self-straightening.

On the other hand, if you have your motor mounted with your extruder
(ie. no bowden cable) there's going to be a lot of impulse when you
reverse directions on x. I wouldn't expect the couplings to hold out
against that by themselves.

But I thought you were proposing to attach them to a bearing at the
bottom as well? That would go a long ways to solving that problem.

> The x-ends are mounted to both: loose coupling
> via pla-bushings to smooth and thight coupling via nuts to threaded
> rods.

It may be worth mentioning that we are planning to ditch the pla
bushings for a new vitamin: teflon sliders. These will attach much
more tightly while also reducing friction and removing the `have a
machine that prints PLA' requirement.

[Whosawhatsis]

What you should really do is make it modular. Prusa's design can already be used with PLA bushings or with dummies that are the same shape externally, but have brass (or, presumably plastic) vitamin bushings inserted. The ideal design would maintain this option, and would also allow for use of linear bearings. This modularity allows machines to be built quickly and inexpensively, and then later upgraded easily.

[Christopher Olah]

This is a good point. Since the plan is for full circle bushings,
we'll need to redesign the PLA bushings... Laser cut bushing options
may also be possible.

[Henning Meyer]

> But I thought you were proposing to attach them to a bearing at the
> bottom as well? That would go a long ways to solving that problem.

I'm thinking about it. I want to keep the bearing count as low as
possible though. Maybe I just give it a shot.

[Henning Meyer]

> It may be worth mentioning that we are planning to ditch the pla
> bushings for a new vitamin: teflon sliders. These will attach much
> more tightly while also reducing friction and removing the `have a
> machine that prints PLA' requirement.

About the Teflon-Sliders - I'm currently trying to source them in
Germany, which seems suprisingly hard - is an inner diameter of 8 mm
sufficient, or should I go for 8,5 or 9 mm?

[Whosawhatsis]

9mm would be way too big. something like 8.1-8.2 is probably best. Better to get 8mm ID and ream them out a little if necessary.

[Christopher Olah]

Whatever matches your smooth rod.

[Whosawhatsis]

Well yes, it does depend on the rods you use. For 5/16" rods, 8mm ID bushings should be perfect.

[Strelly]

I have done some work with teflon bushings on my oversized huxley, I
haven't specially documented it in my blog (strelly3d.blogspot.com)
but I have had great success with them.

instead of trying to source them from overseas at expense, it could be
easier to get a few people with hobby lathes to churn out a few, I did
8 bushings in about 20 mins.. And that was being lazy!

[Rob]

<side tracked by shiny over-sized huxley/>

Dam that is a nice x assembly! My x-carriage is similar to that although I've not done all the material minimizing you've done.. is that for injection molding or something?! So shiny! The x-idler, again is very similar to what we're doing - just thinner and without the internal supports/shell design.

How big is the over-sized huxley going to be?

It's funny that in minimizing the prusa and maximizing the huxley we have ended up in such parallel development.

The only major difference, other then the shell design (did i mention how nice that was?), is how i'm attaching the vitamins. For the rods I'm going to zip tie them down into half-cylinders instead of set-screwing them (down with screws!) and the idler pulley is just mounted to a cylindrical extrusion of plastic which it can be glued on to.

Cheers,

Rob

PS. really glad to hear teflon bushings work well. I haven't tested them at all so this hacklab-reprap design was going to be one big gamble on them working well!!

[Strelly]

Cheers! I made my x-carriage minimized as I have to pay by the ccm
when using my uni’s 3d printer! It also makes me think of a slightly
more ingenious design to maximise the function of the part. I also
printed MarcusWolson’s (sp) shelled mini-mendel and filled the shells
with casting resin.. which worked very well. That was my intention
with the x-idlers, but they turned out to be strong enough.. so I
didn’t need to fill them.

The oversized Huxley is has a build area of just under 200x200mm, but
I have yet to start printing as I need to make the final few parts for
the extruder.

I like the idea of using zip-ties to constrain the x-rods.. much
simpler! Also keen to see how your idler puly turns out too.

Although my Huxley hasn’t even been power on, the Teflon bushings are
sliding nicely and i think they will outlast a set of PLA bushings.
The only problem I found with using a circular bushing is that the
rods need to be perfectly constrained, or the carriage will jam (a
common problem!). Once setup correctly however they are really smooth
and there is no play in the assembly.

Looking forward to seeing some more of the developments you guys are
making!

[Christopher Olah]

Wow! It's awesome that you've printed one!

As far as I know, you are the first person to print the new x-end-*
pieces; there certainly isn't a pair at hacklab yet. I started, but
skeinforge was being stupid that day.

Post some pics? ;)