Making a taper attachment with a CNC

[BtoVin83]

I had a thought of using a stepper motor and controller to come up with a way to cut tapers on a lathe. I would mount the motor on the backside and use a sliding coupler to engage the crosslide shaft to cut taper or not, stock power feed would not change. How do I get started, explain as if I am in grade school as I know nothing about CNC

 

[British Steel]

You'll need some way to measure the Z direction movement, e.g. an encoder on the leadscrew or feed shaft, whichever is used for longitudinal feed, or perhaps (if you have a DRO) the Z axis scale. Then you'll need to run some calculations with e.g. an Arduino to convert from the Z travel to the desired X travel and from that to steps / direction to feed to the stepper motor's driver. Would be an interesting project, but by the point you have it working you'd almost have a full CNC lathe...
Take a look at LinuxCNC (free) and Mach3 (4? I don't keep up with it and it costs money!) which have most of the programming work done already so you'd just need PC, breakout board and stepper drivers/power supply which would leave you the interesting bit, adding the stepper(s) and tuning the system to your lathe.

Dave H. (the other one)
(who is blessed with a taper attachment as standard on his lathe)

 

[BtoVin83]

Ok explain to me as if I’m in kindergarten.

I think there are a couple of ways to do this, full on CNC where it knows it’s position in the X axis at all times. Another way would be just turn it on and have it programmed to make a certain number of revolutions per minute for instance. You would have to do the math each time you changed the feed rate but that would be doable.

If full on CNC you would need to have a scale the length of the bed or at least part of it. What resources do I need to peruse to try and understand the programming and interface portion of the issue. I can handle the layout and physical mounting part no problem.

 

[BtoVin83]

Another thing do DRO's have an output to interface for the positioning or will you need a special scale to determine the X axis position

 

[JimDawson]

Sounds like an interesting project.

First let's define the axes; Z is the carriage and X is the cross slide. The -Z direction is towards the the headstock. -X is towards the lathe centerline.

Yes, most modern DRO scales will output a signal that is compatible with an encoder input on most controlling devices.

In order to cut a taper you would have to electronically gear the X and Z axes together. In this case Z would be the master axis, and X the slave. So some number of Z encoder pulses would move the X axis some number of steps based on the desired taper angle.

It is possible to drive the stepper drive directly from the encoder output through a selectable counter network to do the gearing math. 3 or 4 decade counters would do I think. A step up from that would be some microprocessor like an Arduino that would be programmable. The next step up would be a Galil motion controller that has electronic gearing built in, available relatively cheap on Ebay.

So the required hardware would be:

A stepper motor
A stepper driver
Stepper power supply
Linear Encoder (DRO scale)
Some type of computational device.

Now that you have gone that far, you may as well add the second stepper and driver and make a real CNC out of it. In that case as @British Steel says Mach3 or LinuxCNC would be good options.

 

[BtoVin83]

Well no wonder I'm a hack machinist, I don't know my axes from 6 bits. Might be more trouble than it's worth and easier to just by the taper attachment. I just thought it might be interesting to do.