Dual stepper for Z-Axis?

Discussed here are the various tilt/ slide and Z-Axis mechanisms
Finhead
Posts: 276
Joined: Fri Jan 31, 2014 12:56 pm

Dual stepper for Z-Axis?

Postby Finhead » Sat Feb 01, 2014 6:45 pm

Reading around on the forum last night and found that the Z-Axis needs to be fairly strong on these machines to basically tear the resin from the vat floor every layer, is that correct? So I see some are using Nema 23 Motors for there Z-axis, is it also possible to use a dual Nema 17 like quit a few RepRaps do? I ask this because I already have the motors and the RAMPS 1.4/Mega 2560 boards from a different build and would like to use what I have if I'm able to. :)

Thanks
Clinton

johnrpm
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Joined: Sun Dec 01, 2013 5:25 pm
Location: UK

Re: Dual stepper for Z-Axis?

Postby johnrpm » Sat Feb 01, 2014 8:11 pm

I think the leadscrew would make a difference, with a fine pitch it should be ok, but a 5mm pitch ballscrew may
not, depends on the surface area as well, I would try the 17 with a fine pitch screw and oilon nut, then change it if you hit problems,, but thats just my opinion.
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Finhead
Posts: 276
Joined: Fri Jan 31, 2014 12:56 pm

Re: Dual stepper for Z-Axis?

Postby Finhead » Sat Feb 01, 2014 9:39 pm

Ok that sounds like a plan. I was actually going to try something a little different than a lead screw.
I'll try one motor and see how it goes, if not should be easy to replace it with 2 instead.

Thanks
Clinton

johnrpm
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Joined: Sun Dec 01, 2013 5:25 pm
Location: UK

Re: Dual stepper for Z-Axis?

Postby johnrpm » Mon Feb 03, 2014 4:10 am

I was actually going to try something a little different than a lead screw

What was you going to try?, it may be a better idea?.
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Finhead
Posts: 276
Joined: Fri Jan 31, 2014 12:56 pm

Re: Dual stepper for Z-Axis?

Postby Finhead » Mon Feb 03, 2014 12:11 pm

johnrpm wrote:What was you going to try?, it may be a better idea?.


May not be but I have all the parts here to try it out so thought I would.
My large (400mm build area) Deltabot uses reels with Specrta 65lb line for all the axis movements and it works great, cheap to gather parts for and quite.
So I thought I would try the same on the Z axis on this machine. Just not sure one Nema 17 has the power to pull the resin from the build plate, might try a top down instead since that should work perfectly fine with a low power stepper. Just need to find some information on how exactly to build one. lol

sitzme
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Joined: Wed Dec 04, 2013 12:19 am
Location: Colorado

Re: Dual stepper for Z-Axis?

Postby sitzme » Mon Feb 03, 2014 12:42 pm

You may find that it can take a lot of force to break the part loose from the vat bottom. The other considerations are how repeatable your Z move will be and the addressable resolution. For example, if the finest move you can command is .075 mm you definitely can't do a .05 mm layer. You also might have trouble getting a repeatable .075m layer. Try to plan for some kind of backlash in the system. There are ways to mechanically eliminate a lot of it or you can accept the limitation of the machine and use it as is. There are a lot of compromises available. One option you have is to use a lead screw with a belt drive or gear head. You give up speed for torque. If time is an issue buy a bigger motor/drive, otherwise you can work with just about any size motor if you gear it down. The belt or gear drive is a potential source of backlash so beware. Also keep in mind that the accuracy of the lead screw is an issue. Threaded rod is a fastener, and not designed for use as a lead screw. It is done a lot but with some loss of accuracy. Just another compromise to be aware of. There are a lot of components available on eBay, and McMaster Carr just to name 2.

Finhead
Posts: 276
Joined: Fri Jan 31, 2014 12:56 pm

Re: Dual stepper for Z-Axis?

Postby Finhead » Mon Feb 03, 2014 12:56 pm

Thanks, I'm well aware of backlash. I ave built a few DeltaBots, have a ReplicatorXL as well as built a 3'X4' CNC Router using Ball screws on all axis with 30mm linear rails. Like I say it would just be a experiment since I have all the pieces here and can lathe out various reel sizes etc for resolution since I also have a 10X18 lathe and RF45 mill in my garage, I'm set to experiment. :) Just wanted a starting point what was why I was curious if 2 motors would be useable with the software side, reading further looks like it is controlled with standard RepRap firmware so a none issue. Thanks for the input and I'll be sure to post my findings.

Clinton

johnrpm
Posts: 128
Joined: Sun Dec 01, 2013 5:25 pm
Location: UK

Re: Dual stepper for Z-Axis?

Postby johnrpm » Mon Feb 03, 2014 2:53 pm

Thanks for the input and I'll be sure to post my findings.

Please do, I think build logs with pictures help others more than anything else, I add my stuff but progress is very slow as other projects need finishing first.
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sitzme
Posts: 58
Joined: Wed Dec 04, 2013 12:19 am
Location: Colorado

Re: Dual stepper for Z-Axis?

Postby sitzme » Tue Feb 04, 2014 10:02 am

Hi Clinton. It sounds like you have a good handle on the hardware requirements. Ultimately, it is going to depend a lot on the area of your build plate. Mine is a large build area so I am using a 5:1 gearhead and NEMA 23 motor. I thought it would be too slow but am finding that it releases better when the initial move is slow so I am running it well under the max speed. My lead screw is about a .1" pitch. Looking forward to hearing about your progress.