[zephyr9900]

Can anyone point me to any information on programming rear, or better yet, rear toolpost in conjunction with front?

I've read the one page in Using3Turn on rear toolposts, and Steve Blackmore's really good Mach3 Professional Turn PDF on setup unfortunately doesn't address rear toolposts at all. Neither does the Customizing Wiki.

I am planning to set up a small lathe with a rear toolpost for turning, and a front toolpost for cutoff, and a drill chuck in between, on a gang slide of sorts. Spindle will be unidirectional CW rotation, so the rear tool is upside down.

I'm familiar with lathe gcode (currently running TurboCNC on my Sherline lathe but will be tooling up with a new PC and Mach3,) but only with a front toolpost and a single tool. I have no idea how to handle arcs with the rear toolpost, for starters.

Anyway, I'll appreciate any guidance.

Best regards,

Randy

[Runner4404spd]

use the front tool post for turning and use the rear tool post for cutoff. this way all you have to do is program an x feed for the cutoff and locate its position in the z.

that way all of your standard coding works, except cut off will be in reverse. some also say that the rear cut off tool post is better on these small lathes as there is less chance to suck the tool under the material.

[zephyr9900]

Thanks for the reply, Runner. I realized that the lathe is a right-handed coordinate system, whether the tool is in front, in back, above or below the spindle axis, as long as Z positive is toward the "tailstock" and X zero is on the spindle axis.

You have given me the solution. I still plan to have the turning tool in back (actually, on top) but I will reverse the sense of the X axis movement in hardware. The gcode will act as if the turning toolpost is in "front" and I will do the parting as you suggest.

My current thinking for the lathe is pictured below. It does use a Sherline headstock (since I have the Sherline lathe already) but a pair of stacked THK linear ballscrew actuators for the Z and X axes. I will machine both "toolposts" into the gangslide itself, and the parting toolbit will have full support on its bottom edge. The lathe will be for turning .750" diameter maximum. I haven't drawn in the middle drilling toolpost yet. The lathe base will likely be a piece of 6"-square tubing filled with concrete.

Best regards,

Randy

[Andre' B]

Program the back tool just like the front tool but turn on the X mirror.

If your control does not do mirrors then all X, U and I values need to get the opposite sign, possitive/negative. All G2s become G3s likewize G3s become G2s.

[zephyr9900]

Program the back tool just like the front tool but turn on the X mirror.

Ah, excellent. I did not know about this function.

But reading the Mach handbook I see the G51 axis scaling command. It is modal so it looks like I could just do a G51 X-1.0000 before the rear tool operations, and then a G50 to cancel when I go back to the front tool.

Thank you for pointing me in that direction.

I still think that I will reverse the X sense in hardware so that the upper toolpost will be the "front" one.

Best regards,

Randy