Now in retirement, I have been given the oportunity fir out a small (miniature) metal lathe to CNC, just to keep busy.
It has to be functional, as well as instructional.
There are a few improvements it needs and what I need is what would be a practical range of spindle speeds be for something such as this,
The size is only 4" between centres with a max dia of around 4".
It is presently capable of making a decent cut in hardwood, aluminum, brass and light steel.
Right now it is fixed at 2kRPM, It also needs to be able to thread.
I am modifying it to take better (more professional) tooling.
Advice welcome.

 

Son of MrChips says about 2000-4000 rpm for wood and 100-2000 rpm for steel.
For cutting threads, the spindle speed will be very low and of course has to be synchronized with the Z-axis.

Look up cutting speed for the type of material, for example, 600 ft/min for aluminium:
https://littlemachineshop.com/reference/cuttingspeeds.php

Then look up the spindle speed:
https://www.omnicalculator.com/construction/spindle-speed

A good reference is Machinery's Handbook, available online as a pdf download.

 

That reminds me, I have this Unimat mini-lathe. I have always wanted to upgrade it to CNC also.

 

The problem that I have seen others run into is that neither required power nor required accuracy shrink nearly as fast as size.

 

I have retro fitted many a Machine tool to CNC over my career but never really got into the machining specs, I left that to the machine operator.

 

Max,
If you are still pondering, try: Log in to Model Engineer | Model Engineer & Workshop Magazine
Good luck............

 

Max,
If you are still pondering, try: Log in to Model Engineer | Model Engineer & Workshop Magazine
Good luck............

Thanks, I found the info I needed, so am working with it.

 

Nice project
For a small CNC lathe, try a variable speed range around 200–4000 RPM. Use low speed for steel and threading, and higher speed for aluminum or brass.
For threading, keep it very slow (50–300 RPM) and make sure it’s properly synced. Adding a spindle encoder will help a lot.
Focus on good torque at low speed and machine rigidity—that will matter more than just high RPM.

 

That reminds me, I have this Unimat mini-lathe. I have always wanted to upgrade it to CNC also.

View attachment 359770

That's not a mini-lathe ... that's a *micro*-lathe! ... and a rather nice one, I must say.

About 5 years ago, I bought a TAIG lathe. And although I was quite pleased with it mechanically speaking, I ended up completely replacing its controller with an Arduino GRBL and an interface software of my own design.
Those changes made a huge difference. Let me know if you're interested in said controller.

 

That's not a mini-lathe ... that's a *micro*-lathe! ... and a rather nice one, I must say.

About 5 years ago, I bought a TAIG lathe. And although I was quite pleased with it mechanically speaking, I ended up completely replacing its controller with an Arduino GRBL and an interface software of my own design.
Those changes made a huge difference. Let me know if you're interested in said controller.

Show us some photos. I would be thrilled to see it.

 

There you go.

I designed and built the Joystick myself. It's been extremely useful. Indispensable, I would say. Also, I added a zero-reference high accuracy limit switch. The machine is a real nightmare to use without it.

I bypassed the machine's internal controller (the black box that looks like a power regulator) and installed a GRBL Arduino, which cannot be seen in the pics because it's directly underneath the PCB. The PCB contains the Joystick interface circuitry, plus the encoders and rpm monitor circuits.

As you can see, the wiring is not what you'd call professional. But those are the original connectors and enclosures that were shipped with the machine. I did some cleanup and de-clutting here and there to make things look a little more organized, plus installed all of the electronic and electrical components on an MDF board, and simply screwed it to the wall to keep everything in place. I am now working on a complete machine of my own design, with slightly more capacity than this one.