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General Mach Discussion / Getting incorrect thread pitch with G76

« on: July 09, 2014, 05:47:35 PM »

I've been trying to cut a 13 TPI thread with MachTurn G76 and the pitch I'm getting is about 6% shorter than what I requested.  I'm running in metric mode so I use a P value of 1.954. While the thread is being cut the Feedrate DRO displays a value of 1.84 MM/REV instead of 1.95 and in when the thread is done the thread doesn't match a 13 TPI gage so I'm pretty sure the DRO is displaying what's actually happening. As far as I know there's no feedrate override in effect. I also tried a 20 TPI thread with a P of 1.27 and the DRO displays 1.20 MM/REV.

I don't know if this is related to the problem or not but although I've requested a spindle speed of 400 RPM the exact speed I'm getting is about 384 PRM which is about 4% slow. Mach does sync to the spindle so I don't think the speed difference is a problem.

I looked at code that's generated by the G76 macro and the G32 command is being passes a feed rate of 1.95 so the problem isn't in the macro.

FWIW I do have the "Use Spindle feedback in sync mode" box checked. Also my max feedrate is 1200 MM/MIN so I'm not trying to exceed that.

Can anyone think of what might be going wrong?

Thanks,
Drew

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General Mach Discussion / ANDing motor index pulse and a second switch to detect home position

« on: July 01, 2014, 11:57:59 PM »

Is it possible in Mach3 to "AND" two signals together to detect home position. My lathe has a proximity switch on the leadscrew pulley that pulses every 5mm and I'd like to add a second switch as something like a limit switch. I'd like Mach to detect home position when both of these switches are triggered. Can this be done in Mach or would it have to be some in hardware?

Thanks, Drew