View Full Version : Cross Slide / Compound / CNC Conversion

Bob La Londe
02-14-2012, 11:54 AM
Ok... I am in the planning stage of a CNC lathe conversion. The main Z is pretty straight forward. I can use machine to fit techniques and planning. The cross slide needs to have mounts and parts done a little differently, but a combination of precision and machine to fit techniques should get it done.

Where I run into a conundrum is planning the compound. I counsidered just locking it down and not putting a motor on it at all, but from what I have seen threading with the compound (manually) produces a much nicer result than threading with the cross slide. Does CNC software (Mach or LinuxCNC) allow for setting the compound to do the threading, or is that something that needs to be planned in CAM or manually in the math? Do most folks CNC thread using the compound, or is there a lathe threading G code or standard macro that advances the start point slightly on each pass so that you can cut with the leading edge of the tool bit like when manually threading?

I seem to recall reading somewhere that somebody was complaining that Mach just plunges the tool bit straight in further on each pass.

02-14-2012, 04:33 PM
LinuxCNC has a threading cycle, G76. It simply offsets the threading tool as you would if you had a compound set for threading.

Link here...

The EMC2 G Code Language (http://linuxcnc.org/docs/html/gcode_main.html#sec:G76:-Threading-Canned)

There is an option, Q, which allows you to specify the "compound angle", which isn't really the compound angle, it is the angle the threading tool moves forward on each pass.

I'm sure there was a better diagram on the site, but I can't find it.

02-14-2012, 04:47 PM
I'd be surprised if mach3 cannot move Z and X simultaneously to plunge in at the compound angle. I have never used it myself though. And I've never seen a lathe with a CNC'ed compound!


02-14-2012, 04:56 PM
Its called single edge cutting when threading and the tool moves over in the Z from the sync point the required distance, in a CNC control this is a simple Geometric calculation that depends on the amount the tool is indexed in the X.

Bob La Londe
02-15-2012, 04:00 PM
Well, upon doing more looking I see many CNC lathes don't have a compound at all. In fact it would just get in the way in many cases. I think I'll retain the mounting for it "just in case" but remove it and the stock tool post entirely in favor of cutting some t-slots in the cross slide for flexible gang tool mounting.

This is really a fun learning experience.

02-15-2012, 04:41 PM
I converted a 9x30 Lathemaster and removing the compound allowed more room to fit a larger QCTP.
It is actually for a lathe one size up, but it offers more rigidity.