[rdhopkins]

Hi everyone,

Since finding CNCzone and building two CNC routers, I've really got the CNC bug and ended up buying a CNC lathe for no real reason other than the challenge of retrofitting it to work with a modern PC.

I intend to perform a complete conversion, including full control of the spindle, feedback from the spindle encoder for RPM and threading as well as handling all the control panel inputs on the lathe and the turret toolchanger.

To achieve the amount of I/O and control I need, I have developed my own Modbus board using a PIC microcontroller. Other than this and the parallel breakout board, I intend to use all the original drivers and other electronics in the lathe. This is a bit of a challenge for a software engineer like me! My experience with electronics is fairly limited.

I've made pretty good progress. I thought some of you may be interested in seeing details of the conversion which you can see on this page.

I hope you find it interesting!

[Rob G.]

Great post.

They are fun little lathes & well made, dovetail bed with recirculating ball screws.

I kept the manual controls (motor, dir, jog, override etc...) as they are more convenient than pressing the PC keys.

My main complaint is that the system has very poor earthing, it also runs hot so I added a small fan which actually removes the hot air from the enclosure !!

Opto-isolating is mandatory with high voltage and bad earthing !!!

The GE motor drive also has a 10V analogue feedback signal, but sensing the spindle optos is easy.

Cheers,

Rob

[rdhopkins]

Hi Rob,

I haven't had a chance to do much to my lathe for a couple of months now but hope to get back to it soon.

I did notice that it runs a little bit warm but my model has two fans in it already which seem to cope OK.

I'm no electronics engineer but I have managed to develop an interface that allows the front panel buttons to be handled by the software on the PC. This is not quite as nice as having the lathe itself handle the panel but it was a fairly simple and usable solution.

With regards to the spindle sensing optos, I am using the original slotted disk to sense the speed. The pulse generated by this disk is too small for Mach 3 to use so I monitor the sensor using a PIC which then increases the pulse width and forwards it onto the PC. It seems to work OK!

Roy

[Rob G.]

Hi Roy,

Does the Mach 3 software need an external timer circuit ?

I wrote my stuff using Quickbasic V4 (yes the ultimate software for quick & dirty Electronic Engineers !!).

However, the BIOS timer is only about 10ms resolution (if I remember right) so I had to add a programmable timer to generate interrupts on the printer port.

I had bought an AVR micro controller board to mount inside the lathe for smarter serial interfacing and running lower level routines locally but I have never got round to setting it up.

Your post is starting to jog my memory !

Cheers,

Rob

[rdhopkins]

Hi Rob,

Mach 3 does not require an external timer. I'm not sure how it generates pulses of the correct frequency because, as you say, the system timer is not all that quick (in fact, I think it generates pulses 18.2 times per second) but it seems to do a pretty good job at keeping it steady so long as you don't do much else on the PC.

I use the output pulse and direction outputs from Mach 3 to drive the X and Z axes (and will also use it for the tool changer). Everything else is under the control of my processor board which interfaces with Mach via a serial Modbus interface. It's a bit tricky to setup but does seem to work.

I also have plans to include more logic in the processor board in the lathe, particularly regarding the manual control of the lathe but I'm not sure if I'll ever get the time to get around to it!

Roy