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Nema 23 vs Nema 17 for the engineering challenged

Posted by Endante 
Nema 23 vs Nema 17 for the engineering challenged
June 13, 2012 12:48AM
My wife and I have started designing a CNC/3D printer hybrid. I over engineered some structural designs so now my YZ assembly is a bit weighty (to say the least). dual 20mm linear shatfs with pillow blocks...I failed to look into the weight per meter before buying eye rolling smiley

I planned all along on using Nema 23's for the z axis and haven't decided on Nema 17's or 23's for X or Y, and still deciding on Nema 17's or 11's for the extruder.

I also like the looks, and thought that has gone into the design of the PrintrBoard.

Can anyone with more experience and or knowledge shed some light here. Am I over thinking this as well?
I have listed some assumptions I am working with and would appreciate any input what-so-ever. (even if it's a "You idiot, read this!" winking smiley )

1) I haven't seen many mixed motor builds discussed, and am assuming that is due to limitations in regulating power supplies in order to deliver the different current/voltage profiles for the different motors.

2) And I suspect that if I am correct in #1 then this is even more of an issue when using a unified controller/driver board like the PrintrBoard.

3) Also I haven't been able to find any documentation on the PrintrBoard, or Polulo as to whether or not you can drive Nema 23's with them without burning them up (Polulo specifically mentions using Nema 17's but not that it is a requirement/limitation).

4) I do know that Simply stating Nema 23 and/or Nema 17 is not enough of a consideration, as these numbers are more a designation of footprint than power needs, however what specs do I need to be most concerned with when I am trying to source these, especially if I am looking at trying to mix them in a build?

Thanks, I appricate any insight you can offer.
~Michael "Endante"
Re: Nema 23 vs Nema 17 for the engineering challenged
June 13, 2012 05:33AM
You can drive NEMA23's with a Pololu and they won't burn out because they control the current. But you probably won't get any more torque than a high torque NEMA17 because the limiting factor is usually the maximum current the Pololu can supply rather than the motor.

There isn't a problem mixing motors. The only thing they share is the power supply and that simply has to have enough current to drive all of them.

Re: Nema 23 vs Nema 17 for the engineering challenged
June 13, 2012 02:43PM
Most reprap's provide less that ideal Voltage to the Nema17 motors they use, but most aren't running them anywhere near their torque or speed limits.
While you can likely drive Nema23's with pololu drivers, I'd guess you'd end up limiting their torque significantly.

It is not unusual in the CNC world to mix Nema 23 and Nema 34 motors, ideal voltage is primarily a function of motor inductance, and it's relatively easy to mix drivers on a breakout board to match different current demands.

What are you looking to mill/route? The structural requirements for the Milling/Routing side will likely determine how much weight you need to throw around.
Re: Nema 23 vs Nema 17 for the engineering challenged
June 13, 2012 10:21PM
Thanks to both of you.

The CNC router is expected to be cutting Acrylic, Delrin, Oilon, NS woods up to the hardness of White Oak or Purple Heartwood.

I have had some thought of possibly aluminium but nothing harder than that, and I don't really have my heart set on the aluminium.
Re: Nema 23 vs Nema 17 for the engineering challenged
June 14, 2012 08:00AM
... the milling abilities are mostly defined by the tool-bit-diameters and cutting speed per volume - I've milled steel sheets and ceramics on an Isel-CNC-mill, that's explicit not recommended for harder materials than plastics (or maybe aluminium).

With small hard alloy bits with diameters below 1 Millimeter, a spindle with >20000 rpm's and some hundred microns cutting depth you can handle any material, when your frame is sturdy enough (or damped), so it won't start to shake apart by resonancies ...

Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]
Re: Nema 23 vs Nema 17 for the engineering challenged
June 14, 2012 01:57PM
I agree, you can mill almost anything on any machine with enough RPM and small enough DOC.
Having said that, I think it's important to understand what you want to mill, how much material you expect to remove, and how patient you are.

With a 40lb CNC'd Sherline cutting AL you're reduced to DOC's in the 0.015 range and speeds ~10ipm, that makes any significant material removal a SLOOOOWWWW process.
It's much less of an issue if you're primarily routing wood, though I'm not convinced you wouldn't want more torque than most Nema17's offer.
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