beginner lathe conversion .

skeeter wrote:

2 I have repowered it with a inverter duty motor and ac drive . so my spindel speed will will be controlled by me at the ac drive itself .

It is fairly easy to have LinuxCNC control the inverter. This then allows you to run constant surface speed mode, and to do rigid-tapping with taps held in the toolpost.

I am making an add on feature that will support an X and Y axis . that I want to drive with steppers because they are cheaper these I would like to drive with new acme screws and nuts

Something like the old Anilam "Lathemate"? Not a bad plan, and it means you can use the lathe in manual mode still. (Possibly at the same time...)
I would consider ballscrews, even the cheap ones are likely to work better than acme screws. The cheap ones are quite cheap: www.zappautomation.co.uk/mechanical-prod...-ballscrew-4703.html

My goal is to use linux cnc to cut threads, profiles, cams and tapers am I correct in assuming that linux cnc will do all of these functions

Profiles, tapers and threads are standard and easy. Cams are possible:



but a bit of custom configuration was needed. Both threading and cam profile cutting need some kind of encoder on the spindle. These are often home-made slotted discs.

what size steppers should I use

My 9x30 lathe uses Nema23. They work fine, both axes can stall the spindle. I wouldn't mind a bigger motor on the Z for pushing toolpost-mounted drills. I would suggest looking hard at the new closed-loop stepper systems, an example here: www.ebay.co.uk/itm/CNC-Hybrid-Closed-loo...&hash=item461fd4f7c8

skeeter wrote:

Hi, Andy . What are the advantages of this servo system ?

Because the drives know where the motor has actually got to, it can either recover lost steps, or trigger a fault output if it can't recover position. This is rather an improvement, especially on a lathe where you can sometimes lose steps and not notice (running too hard into a shoulder, for example)

this will have it's own saddle cross slide compound and tailstock essentially a lathe with out a headstock.

You don't need a compound slide on a CNC. It's better to have a stronger cross slide. It might be advantageous to use the original tailstock (if there is one)

The encoder you mentioned i have one already on the spindel for a tach. Can I take the signal fron this and use for the software requirements or will I need another one These is simply a hall effect transister I think

Threading need an index pulse once per rev. That is the bare minimum. More pulses + index is better. For rigid-tapping you need index + quadrature to sense the spindle direction as well as the speed.

If not what is the encoder you recommend ?

I ended up using a commercial encoder, geared 1:1 to the spindle, after experimenting with laser-print and home-made. But only because it turned up very cheap.
An opaque disc with a set of radial slots, with one slot longer than the others for the index detector, and then some slot detectors similar to uk.rs-online.com/web/p/products/171-1830...n=PSF_438299|QVTN-LL works well for many people. (That particular sensor has two channels, so does quadrature in one device).
You would need to choose the number of slots to match you intended PC interface. The parallel port can only generally count reliably at 10kHz, so if you have a 3000rpm spindle you only want about 100 slots. This is one reason not to use a standard encoder as they often have many more slots than that. If you are using a PCI card or EPP-interfaced FPGA card then that limit is removed. (I am using a Mesa 7i43 on my lathe which counts at 10Mhz)

Do have any cad programs that you would cecommend for me to use either free or very cheap ? Then next a way to convert to gcode ?

I don't tend to us CAM on the lathe, I typically use a set of macros I have set up ( www.linuxcnc.org/index.php/english/forum...s/26550-lathe-macros ) But CamBam claims to have a lathe mode.
Some people have made the (free) add-in to (free) Inkscape work, but I didn't. www.cnc-club.ru/forum/viewtopic.php?t=35
FreeCAD is nearly there: www.freecadweb.org/wiki/index.php?title=CAM_project and the CAD part is quite well developed.
Lots of other options exist, Autodesk Fusion might be worth a look. I have a full license for Inventor, so quite like that as the interface is vaguely familiar. That's Windows/Mac only though. CamBam, Inkscape and FreeCAD all run on Linux too.