Cnc For Mini-lathe

[Billh50]

I have been toying with the idea of making my 7x 12 into a CNC. I have some questions that I think some on here can answer for me. By the way, I will probably do most of my shopping on ebay as I need to go as cheap as possible but still work good.

1) Type and Oz of Stepper is best for this but not real expensive.
2) Easiest software to learn.
3) Any links to beginner tutorials

 

[Wreck™Wreck]

If you require the tenth's accuracy that many hobbyists do you would be well served by looking into the cost and availability of the mechanical components of linear motion systems before the electronics and software.

Lead screws and nuts and the hardware to drive them Etc. This is of primary importance on a lathe X axis, in order to achieve .001" diameter accuracy you will need to hold .0005" positional resolution. In order to hold .0001" diameters will require .00005" positioning accuracy or better.

This will be a tall order on the cheap, the limiting factor is likely not the control but the hardware components and the base machine itself not including ambient temperature changes.

Give it a shot, all of the components will be rather small on a machine this size.

 

[ch2co]

Bill
What brand/ model lathe is this 7x12 machine? When I hear 7 x 12, I immediately think of Harbor Freight etc. quality machines.
With this quality of lathe, I would be worried that you would be putting a lot of money and effort into a machine that wouldn't
end up giving that good of results. On the other hand if it is a higher end machine then goferit!

CHuck the grumpy old guy

 

[Billh50]

It is a Homier and I can hold .001 with it. Nothing I do on it needs better than that. If I do occasionally need to be closer than .001 I usually polish it in.

 

[Billh50]

I already understand the lead screw items and accuracy problems with standard lead screws. My problem is with what type of stepper and torque requirements.

 

[Wreck™Wreck]

I already understand the lead screw items and accuracy problems with standard lead screws. My problem is with what type of stepper and torque requirements.

This depends entirely on how much power and feed speed are required, as far as power you will be limited by the machine construction itself.
If you plan on doing a good deal of non cutting moves, (rapid from the end of 1 cut to the beginning of the next) the max rapid speed is important especially if a tool changer is involved, I should imagine that 100 IPM rapids would be more then sufficient on such a small envelope machine.

I run a couple of Bridgeport 15 X 48 CNC lathes that have a max 100 IPM rapid speed, on longish parts the time adds up.

Even at a leisurely 100 IPM when testing a new program for the first time when it rapids at the chuck it causes much finger crossing on my part (-:

 

[JimDawson]

Even at a leisurely 100 IPM when testing a new program for the first time when it rapids at the chuck it causes much finger crossing on my part (-:

:+1:

 

[JimDawson]

My problem is with what type of stepper and torque requirements.

In this case I would be tempted to do a few tests to figure out what torque is required. Making a pulley that would attach to the lead screw and allow you to wrap a few turns of string around it and pull it with a spring scale would give you a pretty good idea of the torque requirement. Then at least double the value you get in that test to size the stepper motor.

There have been a few of the 7x12 lathes CNC'd by other folks, an internet search to see what has been done before is always a good starting point.

My theory on CNCing equipment is to over power the steppers, you can always cut them back with the DIP switches on the drive, but it's pretty hard to add more power if you undersize them. The cost difference is not much.

 

[Wreck™Wreck]

:+1:

Imagine the pucker factor when you have to push the GO button for the first time on one of these, Fanuc claims 1.5 G acceleration.

If not screwed to the floor it would try to walk itself right out of the building I suspect )-:

 

[Billh50]

I know how fast they can move. I have seen a few crash in the past. I remember one where a guy walked away when he pushed the button and the tool went straight into the chuck and just kept beating itself to death before he could hit the E stop. What was left wasn't pretty.