[disneytoy2]

So,

In my current project, I'm sourcing parts for a 2000mm tall Z axis. I'm leaning towards a pulley belt drive based on a 25mm wide HTD8M Synchronous Belt. But I also saw some reasonably priced 20mm Ball screws in 2 meter length. (see attached jpg)

I don't need really fast speeds. I will be driving this with a Nema 34 Closed loop encoder stepper (8 N.m) driving a worm gear drive. (I haven't determined the gear ratio yet).

My thought is the worm gear reduction can't be back driven, so it will aid in holding the vertical position.

I'm leaning towards the belt, because It would allow me to adjust the Z height if my design needs.

The motion will mostly travel from the bottom up in apprx 1" increments. I don't really need sub mm accuracy.

What would be the pro's and cons going with Belt Vs. Ball Screw?

I think the 25mm HTD8M Synchronous Belt should be robust enough.

Also, I was thinking I could counterbalance if I go with the belt. Less work for the motor drive?

Thanks for any advice.

Randy

[Jim Dawson]

Sounds like a good application for a belt. Can't think of any downside to doing it that way.

[disneytoy2]

Thanks Jim. Just wanted to run things by the experts here:-)

[Jim Dawson]

My pleasure

[kawazuki]

Why have the worm screw or is that a necessity due to installation restrictions? If you are lifting something with stops every inch - I assume it will be attached to the belt somehow?
Would a rack and pinion work with stepper attached to the moving platform or head?

[he1957]

Seems we should attach the heavy duty rotary table to the equations :-)

Curious of the intended weight of what's to be carried on the 2 metre column?

Next question will be how to do another axis (sounds like it's a large/life size model makers machine) :-)...

[disneytoy2]

Yes,

This will be a 2 meter Z axis Clay printer. So essentially a large scale Scara style. The worm gear is for the gear reduction, perhaps 100:1 or so but won't know exactly until I have the parts to test. One of the advantages of the worm gear is it can't be backdriven.

The base is heavy so I'm looking for a axial bearing option that isn't crazy expensive. Not that I'd spend that much, but I was looking as some $5K+ bearings, ouch. I'll probably start out looking at an automotive option, Like a wheel hub assembly. That can be very inexpensive on ebay, relatively heavy duty. I just need to find a car truck guy to tell me which make/model vehicle has the largest wheel bearing.

Thanks

For all your input.

[Jim Dawson]

Anything that will support the weight of a car or truck will be more than enough to do what you want. A front hub assembly would work for your application. Here is one example https://www.amazon.com/Timken-HA5902.../dp/B0027AGFEG

The nice thing about these is that the hard work has already been done. It has a nice flat mounting flange on both the stationary and rotating sides. If you want bigger, here is one for a Dodge 3500 truck https://www.napaonline.com/en/p/PGRPBR930502

[spumco]

I just built a plasma table with the "Powge" belts and am very pleased with the performance. We used HTD5M-25mm for both the gantry and X-axis. Belts are stationary and tensioned with a threaded clamp plate at each end.

Properly tensioned, there is no backlash or 'spring' to the system. Unless we intentionally use some sort of lever or mechanical advantage to gronk on the gantry it's very stiff. And the 5M tooth seems perfectly capable of slinging the 30lb gantry at 1000IPM (or faster) without tooth jump or other issues.

Someone else can chime in, but the 8M pitch might have more cogging (less smooth tooth engagement) than a 5M pitch unless you get very large pulleys with lots of tooth engagement. The 8M teeth are, of course, capable of much higher loads than the 5M.

If you aren't concerned with speed then a guided counterweight on the back-side of the belt would help the motor and drive system. I'd suggest not trying to offset the entire weight of the head as this might lead to some 'fluttering' if there's any slop or lost motion. Maybe shoot for 50-75% of the head weight as a start.

And by 'guided' I mean the weight slides on a rail and doesn't bounce around tugging on the belt and drive system.

-R

[vegipete]

Number 40 or 50 roller chain might work fine too.

[disneytoy2]

Jim! Great info really appreciate that!

[disneytoy2]

Spumco, You are good. This sounds exactly the way I want to go. Counterweight, 5M 25mm belt. I'm ordering it today. Thanks!!!!