Well I might be retrofitting a decent sized lathe that had the drive gears for the threading stripped out, don't ask me how. What we're looking at now is setting the lathe up for CNC and just ripping out the thread gears and feed gears. This isn't a problem really if you're not doing much with the machine. My main question is how to set the retrofitted machine up to be able to do threads. There has to be somekind of encoder on the chuck/spindle to tell the computer where it is and the computer then has to be able to tell the servo for the carrage drive where to be. My best guess is there is an encoder attached to the spindle and that would connect into an input of some sort on the breakout board. Any help would be greatly appreciated.

Carl

Carl, It depends on what system you are thinking of using to retrofit, yes for threading you require an encoder which should be driven off of the final spindle shaft for best results and a CNC system that will recognize and able to implement the threading G-codes. Also it is preferable to have maybe one gear reduction as well as direct drive for turning at really low spindle rpm, the motor is then not rotating at really low rpm. It also depends on what kind of spindle drive you have. DC, Variable AC or Standard AC Induction motor.
BTW one nice feature of CNC threading is the ease of using single edge cutting on a thread and taper out at the end using the G76 function if the control has it.
Al

From what I understand is all it needs is to read the rpm acurately. over at turbocncs website they have an encoder and information about it. Just make sure to run the spindle speed pretty slow, cnc threading is one of the coolest things I have seen on a lathe:p

Jon

I'm not sure how accurate the RPM is on the spindle, that's why I was thinking that having an encoder on there would be the best bet and the timing would have to be dead on. Does anyone have any good examples of CNC lathe threading or do any of the cheaper manufactures of drivers have any examples or information. I'd like to keep this project fairly cheap to show that it can be done on a budget to my instructor. I'll have more info once school starts up on monday and if it is a go for conversion. If it is you guys will see the step by step progress.

Carl

If this is a manual lathe as it appears to be and you mention a 'fair size' , you will need alot more than some software, for accuracy you will need to change the acme screws for precision ballscrews and then you require X & Z servo's and amplifiers. Also is the present spindle motor at fixed rpm and speed controlled through a gear box? Which is OK you just need to make sure the spindle encoder is on the final chuck shaft.
Most CNC software packages have the routines built in as canned routines such as the G76.
Al

A spindle encoder is definitely required for multi-pass single point threading. For tapping only, you could get away with a floating tap driver, and an accurate rpm reading. As Al pointed out, ballscrews are a must, too, although I can sort of imagine using the ordinary leadscrew with the halfnuts lever wired closed :D