Belts or Balls getting me Screwed up! Help I need advice Please.

Hi everyone, I’ve had a major change of plan from my original design build. It’s sort of grown a tad from the original X at 700mm to 1500mm so that I can drop a quarter sheet of plywood or phenolic ( high pressure laminate ) which will save me having to do tile the cuts on lots of jobs. I also want to be able to engrave a standard door or a lump of 4” / 6” thick oak post.

I’m still working on the design at the moment but getting my head screwed up as to do I use belts or ball screws or both. Could I use belts to drive both the Y axis ball screws and use just one motor instead of synchronising 2 motors ? I was looking at using nema 23 - 425 Oz-in motors.

Attachment 12035

For the spindle I will be using an 1/2” router until I have enough funds to add a water cooled spindle. I’ve done a plan view so you can get an idea of what I would like to build, all steel framed and using SBR20’s for all the rails. X axis I was going to make up a lattice frame from aluminium extrusion and then laminate (epoxy) 2 sheets of 6 or 8mm plate to both sides, not sure how deep to make the beam but 6” or 8” (150 / 200mm)

As I want to be able to pass materials under the Y axis beams I was thinking of using 80x80x6mm with 50x50x3mm for the main frame, but might need to beef up the corners as this cnc will be floating on 4 corners. I welcome your input and won’t take offence but I may take the gate LOL

Lets me have your ideas as it’s easier to to make changes at the design stage and a lot less expensive. Failure to prepare is to prepare to Fail.

Mike :topsy_turvy:

First you'll get a stronger machine if you build it long and narrow rather than wide and short. It would also be easier to join ballscrews with a timing belt and use one motor and have the advantage of keeping screws in sync. Don't bother with timing belts only as they cost nearly as much as ballscrews by time you have bought belt and pulleys etc.
Also the ballscrews want to be 10mm pitch not 5mm if you planning on mainly cutting wood, if you need higher resolution then just put a ratio on the screws.

Also, the 425oz Nema 23 motors are about the worst choice in Nema 23 motors. They have very high inductance, which results in very low torque at higher rpm's.

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Originally Posted by Ger21

Also, the 425oz Nema 23 motors are about the worst choice in Nema 23 motors. They have very high inductance, which results in very low torque at higher rpm's.

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The ones people like to call 'nema 24' sometimes don't, for example:
Nema23 Stepper Motor 3.1Nm

(Mike: Don't take that as a recommendation yet - it may well be the motor you require, but you need to do more of the design before selecting motors)

That's not a 425oz motor, it's 439. The OP said 425, so I don't think he's referring to that motor. All the 425oz motors I've ever seen are high inductance.

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Originally Posted by Ger21

That's not a 425oz motor, it's 439. The OP said 425, so I don't think he's referring to that motor. All the 425oz motors I've ever seen are high inductance.

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The motor I linked to and the following one are probably the most popular ones on this forum:

SY60STH88-3008BF

That's 3Nm, so 424.8oz-in and 3.2mH... close enough for you?

I've measured the inducance of both motors and it does match the rating, within a reasonable tolerance.

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Originally Posted by JAZZCNC

First you'll get a stronger machine if you build it long and narrow rather than wide and short. It would also be easier to join ballscrews with a timing belt and use one motor and have the advantage of keeping screws in sync. Don't bother with timing belts only as they cost nearly as much as ballscrews by time you have bought belt and pulleys etc.
Also the ballscrews want to be 10mm pitch not 5mm if you planning on mainly cutting wood, if you need higher resolution then just put a ratio on the screws.

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Thanks for your input Jazz, I had looked at doing it the way you suggested and may well go back to longer / narrower machine. Ball screw pitch I'm not sure what you mean by "ratio on the screws" I do need to have the higher resolution as the laminate I want to cut needs a high tolerance. It's harder than a lot of allies to cut / drill, so do you think I would be better using the 1605 bs ? I'm going take what you've said about the machines orientation and work on another plan, I do know I can rename the axis x & y to fit my machine.

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Originally Posted by Jonathan

The motor I linked to and the following one are probably the most popular ones on this forum:

SY60STH88-3008BF

That's 3Nm, so 424.8oz-in and 3.2mH... close enough for you?

I've measured the inducance of both motors and it does match the rating, within a reasonable tolerance.

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Thanks Jonathan for the links to the motors. I've read your build logs with great interest well done. These are the motors / drive kit that I have been looking at �Germany Ship】4Axis Nema23 stepper motor 425oz-in Dual & Driver CNC control kit | eBay and within my budget, your views are welcome on the kit. I'm keeping well away from those 268 drivers offered with some kits.

Thanks to all for your valued input.

Mike :smile:

Virtually all of the 425oz motors available in the US and through Ebay (from China) are high inductance. The ones you linked to are not commonly available over here. So just make sure you know what you're getting.

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Originally Posted by Ger21

Virtually all of the 425oz motors available in the US and through Ebay (from China) are high inductance. The ones you linked to are not commonly available over here. So just make sure you know what you're getting.

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Thanks Gerry, I've not ordered any motors yet, but I will hopefully make sure I get the rights ones.
Mike

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Originally Posted by longy

These are the motors / drive kit that I have been looking at �Germany Ship】4Axis Nema23 stepper motor 425oz-in Dual & Driver CNC control kit | eBay and within my budget, your views are welcome on the kit. I'm keeping well away from those 268 drivers offered with some kits.

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Yes, those are the high inductance motors I'm talking about. They'd need close to 100V to get the best performance out of them, but they give you a 36V supply.

But listen to what Jonathan said. You shouldn't just arbitrarily choose motors and drives. They need to match your choice of screws, and the machine to get the best performance from them. In some situations, motors half the size will easily outperform larger, high inductance motors.