8mm vs 10mm (topic shifted to lead screws)

I'm working on a repstrap type build, made using the copious amounts of random stuff in my garage. I've got the main part of the frame built, and I am currently sourcing the parts that I can't scavange locally. Which brings me to the linear rods.

I was wondering is there would be a benifit to using 10mm rod? That sounds a bit silly, because the obvious benifit would be that it's stronger and less prone to flex. But what I was wondering is, is it worth it?

Really, what I'm wanting to know (having never put my hands or eyes on a reprap in person) is if I would see a benifit in stability if I go with 10mm, over 8mm? Or is the 8mm as solid as they need to be?




**edited title**

Edited 1 time(s). Last edit at 06/25/2013 05:11PM by TheJones.

If I had my time again, i'd go with 10mm over 8mm. 10mm vs 8mm gives you over 50% increase in cross-section area (pi x r squared). Also, you want your Z rods to be thick enough to resist any flex of your leadscrews.

Same here.

Thicker rods won't eliminate imperfections in the Z axis due to leadscrew wobble, it might help a bit, but if the leadscrews don't run straight, the Z-nuts won't ride on the same place inside the nuts, when the leadscrews turn, this will result in non linear motion in the Z direction.

I used 16mm hardened steel rods on my repstrap, in the hope that it would improve quality. It probably did since I removed the lateral motion of my X-axis, but I still had problems with ribbing on my prints because the Z axis wasn't moving linear, becayse my leadscrews wasn't running completely straight.

If you have to choose, you're better off spending your money on real leadscrews instead of thicker rods.

I was thinking of going with a nema 17 with a lead screw shaft, but the ones I saw have an 8 pitch. Unless my math is wrong, that equates to 2.5 steps for 0.1mm of movment. That just seems crazy considering the fact that I got "meh..." responces when I suggested a 2 pitch (at 10 steps per 0.1mm).

The best price I can find for them is $36 each on robotdigg.com(making it $72 for the Z axis). Which is a little more than I was planing to spend, but not by much. So the cost isn't a deal breaker.

The only thing keeping me from buying them is the 8 pitch. I heard that maker bot uses them in their replicators, but I don't know. I might just stick with my original plan of using a 14-2 rod. It seems simpler all around.

Edited 1 time(s). Last edit at 06/25/2013 05:23PM by TheJones.

Remember that you normally use microstepping on reprap's, and many other cnc machines for that matter, this gives smoother operation and a more quiet machne.
With 1/8 microstepping you have 1600 steps/rev, on a normal 1.8 deg stepper, this should be ore than enough, even on 8 pitch.

But 36$ isn't bad considering that you also get the motor, and you dont have to fit the rod.

Ralf Wrote:
-------------------------------------------------------
> Thicker rods won't eliminate imperfections in the
> Z axis due to leadscrew wobble, it might help a
> bit, but if the leadscrews don't run straight, the
> Z-nuts won't ride on the same place inside the
> nuts, when the leadscrews turn, this will result
> in non linear motion in the Z direction.
>
> I used 16mm hardened steel rods on my repstrap, in
> the hope that it would improve quality. It
> probably did since I removed the lateral motion of
> my X-axis, but I still had problems with ribbing
> on my prints because the Z axis wasn't moving
> linear, becayse my leadscrews wasn't running
> completely straight.
>
> If you have to choose, you're better off spending
> your money on real leadscrews instead of thicker
> rods.


thats design error, i have no wobble with leadscrews....

once i have seen tutorial for assembling prusa, and guy is doing meassures, watch now, with box from arduino, hello!!!
and most sad part, kids are following that...


8 vs 10 mm...il go with 12

then you can sav manipulate with machine with no flexing... more is better,,,if motors can handle it

12mm in all honesty over that small distance of movement would be overkill. 10mm is what you should go with along with some integrated leadscrew NEMA17s, can't go wrong with that IMO.

woo Wrote:
> thats design error, i have no wobble with
> leadscrews....

I don't think you got me right..

Bent leadscrews will give you non linear motion in the Z direction, allmost no matter how rigid your printer is.

It is easily within reach to have perfect prints from normal threaded rods as leadscrews, it's just a question of straightening the threaded rods, or carefully finding the most straight ones when buying.

But as kburr wrote, the solution with NEMA17's with integrated leadscrews, is a sure winner.

Has anyone found NEMA17's with an integrated 10mm leadscrew? I see the 8mm ones everywhere but have not found a comparable 10mm setup to buy? Are there any major issues using couplers? I know TAZ does this on their z-axis with big leadscrews...

Why do you need 10mm lead screws though? That'll make the effects of a slightly bent screw worse, since your z axis smooth rods will have to resist a thicker lead screw. 8mm lead screws are very standard, most printers use them and they work fine. I wouldn't rely on microstepping to boost resolution, it doesn't, but the resolution you get is more than good enough. Just use appropriate layer heights, not the 0.1mm, 0.2mm layer heights everyone uses because they're nice round numbers.

If you purchase online and have no easy way to return than go with 10mm since there's less chance you get faulty one.

I'm currently tweaking and tuning a leadscrew delta it uses 8mm screws with 8mm lead so that on 1.8 deg motors running at 1/16th microstepping it's 400 steps/mm which is 5 times the resolution of 20t pulleys and gt2 belts. It seems to work fairly well, but each axis has a linear rail so it's quite good at resisting any lateral force from non-straight leadscrews, next step add some antibacklash nuts.

Perhaps even devise a way of attaching them to the carriages so that lateral movements are not transfered to the carriages only vertical movements, would have to be a very close tolerance part though to prevent lash/backlash.

Edited 2 time(s). Last edit at 03/03/2018 07:40AM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions