What size steppers?

[cnczoner]

Hi,

What size stepper motors would I need to properly operate an HF 7x12? I noticed the left-right movement was stiffer than the fore-aft, so I'll probably use a more powerful motor there.

What about if I upgrade to a larger lathe later, such as a 9x20? What size motors would I need then?

Thanks,
-Neil.

[teilhardo]

I'd guess that 110 oz/in for the y and z axis and 170 for the x axis would suit your purposes just fine

-Tei

[cnczoner]

I assume these are for the 9x20 size? I can find decently-priced 125oz-in units. Think that will work for the X axis on a 7x10?

Thanks,
-Neil.

[teilhardo]

Hi Neil,
You know, I didn't notice it before but I have exactly the same lathe and am looking to retrofit it to. Do you have any designs in mind?
For the steppers, I would think that 125 oz/in would be fine for the z axis, but probably more like 210 for the x axis. You could use 125 oz/in on the x but you would have to gear it down and sacrifice some speed
-Tei

[cnczoner]

I've been analyzing and planning this before I purchase anything, so actual design I don't have yet. The mounting of the steppers was the biggest worry for me.

But I went down a local Harbor Freight recently and looked at the lathe in person. The handle for the crossslide was missing, which it made it easy to figure out how to mount the stepper. It should be as simple as bolting a plate to the surface that the steppers bolt up against, and then bolt the stepper to that plate with some standoffs. The only other thing required would be a coupler to connect the 2 shafts. I can only imagine the other 2 handles being the same way. (I'm not actually going to add a stepper to the cross-slide, btw).

But this is where I noticed that the X-axis was stiffer than the Y-axis.

For the electronics, I thought I would build my own drivers, or use the Linistepper or other similar driver. I'll probably also build my own controller and parallel-port interface, then use either TurboCNC (DOS) or EMC (Linux).

But that will happen later.

Cheers,
-Neil.

[RotarySMP]

For my 7x12 CNC conversions I used 187 ozin Vexta PK268-02A's for both Z (along the bed) and X (cross slide). Each is driven through a 1:2 timing belt reduction. These motors are plenty powerful enough. The cross slide is set up to rapid at 900 mm/min and the saddle at about 800mm/min. Not blindingly fast, but fast enough to not be an issue on such a small machine. Both leadscrews have been replaced.

I could rapid the saddle at nearly twice that speed at the headstock end, but the bed thickness is not consistant, and I had to slow down the rapids to prevent stalling at the tailstock end. Sooner or later I should address the bed thickness.

For a 9x20, you would probably want to go up to a 300+ ozin Nema 34 for the Z axis.

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[cnczoner]

Since the costs are adding up fast, I'm sticking with the components for the 7x10 for now. I have 142 oz-in bipolar stepper motors now, and intend to reduce that 1:2 (or more if necessary). I'll be able to change it later if I need to.

Thanks,
-Neil.