[TXFred]

I've looked through other build threads, and what I have yet to find is good information about the correct size stepper motors to use with mini-lathe.

I've got a G540 control box ready to go, so I'm limited to its 48 volts, 3.5 amps.

I can put the best possible stepper on the Z, which is a Keling KL23H2100-35-4B. This is a 381 oz/in motor that works best at the volts and amps of the G540. The problem is, it's way too big to work on the X axis. I need something smaller and lighter for that location.

What are you guys using on your mini-lathes? I'd like to hear torque ratings and dimensions of the motor, specifically, the length.

Frederic

[doorknob]

I'm interested in seeing this also.

Seems to me that I remember one conversion that mounted the X stepper below the X axis, reversing it so that the shaft pointed away from the ways, and using a 1:1 timing belt drive, as a way of reducing the distance that the motor stuck out (but I'll have to look for the thread).

OK, I found the thread that I was thinking about, here are two of the posts from it:

http://www.cnczone.com/forums/623750-post1.html

and

http://www.cnczone.com/forums/625969-post13.html

His x axis motor looks pretty big physically, but of course that doesn't mean that he needed all of that torque for the application.

[JavaCnC]

This is copied out of a Mini Lathe CNC conversion PDF i have.
" Nema 23 Stepper motors near or greater than 200oz-in"
That set up uses the stock lead screws also. So if your switching out to balls screws you could go below 200oz a bit.

[rich_cree]

Mini Lathe CNC Conversion PDF? I'd like to see that, can you tell me where you got it from?

Thanks

Rich

[JavaCnC]

Mini Lathe CNC Conversion PDF? I'd like to see that, can you tell me where you got it from?

Thanks

Rich

Here you go.

Mini Lathe CNC Conversion

[blades]

I used KL23H276-30-8B from keling, and all the dimensions you could possibly want are given on spec sheets on their website. These motors are 282 oz motors. They are not as efficient or perfectly matched as the 381 oz motors, they will run at a slightly lower power, but they were PLENTY powerful for a 7x lathe, and ran flawlessly on a G540 (my conversion is the one doorknob posted links to. FULL THREAD HERE ). Also, an added bonus, they require no current limiting resistor on the wiring.
Personally, I don't understand the logic of using mis-matched motors on Z and X simply because you can fit a larger motor on Z. I also feel that 381 oz motors are serious overkill on this size lathe. My conversion was somewhat light-duty, not utilizing ball screws. The motors I used were more than capable of exceeding the torque the lathe was built for.

[TXFred]

Personally, I don't understand the logic of using mis-matched motors on Z and X simply because you can fit a larger motor on Z. I also feel that 381 oz motors are serious overkill on this size lathe.

Thanks for the feedback on your motor choice.

The logic of the mis-matched motors is just that of economy. I have a 381 oz in motor lying around unused, so it made sense to use it on the Z axis.

The reason I wanted smaller on the X is because the X motor sticks out and moves the center of gravity of the saddle. It's my belief that the CG should be on top of the ways.

I can always use a counterweight, but I like the way that you did yours. By slinging the motor down under, you likely kept the center of mass between the ways.

Frederic

[TXFred]

blank post

[fragger6662000]

on mine i used a 380 motor on z and 300ish on the x.
x was lead screwed and z had a 1605 ballscrew on it.

[cornbinder23]

How about this one stepper motor Its about .75" shorter than the 381's
and its a perfect match for the G540, and the BEST thing is its US MADE!!!

JTCUSTOMS

[blades]

The reason I wanted smaller on the X is because the X motor sticks out and moves the center of gravity of the saddle. It's my belief that the CG should be on top of the ways.

I can always use a counterweight, but I like the way that you did yours. By slinging the motor down under, you likely kept the center of mass between the ways.

Frederic

That was my feeling exactly, I wanted to keep the mass under the saddle, and I was also wanting to keep the footprint no larger than the original lathe (no motors sticking out anywhere).

[fragger6662000]

my recommendation would be to extend the cross slide by a 30-40mm so you can how tools with a little more projection and maintain the capacity of the machine this will gain you some more room for the stepper to be under slung. I did this on mine with in line motor mounting and did not have any issue with binding.

I would recommend getting rid of the compound slide and original tool post as this is where most of the problems occur in this machine.

7 x 12 lathe tool post modification - YouTube

With the mods i can hold +/-30um with out really trying.

Now it is a really good machine!

[TXFred]

That was my feeling exactly, I wanted to keep the mass under the saddle, and I was also wanting to keep the footprint no larger than the original lathe (no motors sticking out anywhere).

I ordered those same motors. I haven't decided exactly how I'm going to mount them, but I suspect that I'll be copying your design for the X axis. For Z, I need something more rigid than your design, so will probably set up a ballscrew in place of the current lead screw.

Frederic