Messages

1

General Mach Discussion / Re: Getting incorrect thread pitch with G76

« on: July 10, 2014, 11:04:17 PM »

I guess that's one way to do it. However to me it seems odd to think of a motor index when everything is in terms of the spindle; spindle speed, spindle index, etc. The pulley on my machine's motor is 85% the size of the one on the spindle so I actually though that I should have had a value of .85 (or maybe 1/.85) for the pulley 1 ratio. But since my index is on the actual spindle that would have messed up the feed per rev. I'm able to setup my VFD to tale care of the .85 difference. Oh well, at least it's working now and I appreciate all the help.

Drew

2

General Mach Discussion / Re: Getting incorrect thread pitch with G76

« on: July 10, 2014, 06:43:47 PM »

Thanks Hood and Rich. That fixed it. But it does seem to imply that Mach thinks the Spindle Index is before the "pulleys". Kind of strange but Hey! as long as it's working!

I'll be sure to check out the "Threading on The Lathe" doc. Thanks or the pointer Rich.

Drew

3

General Mach Discussion / Re: Getting incorrect thread pitch with G76

« on: July 09, 2014, 11:21:05 PM »

I'm not exactly sure of the version number but it was downloaded from Newfangledsolutions last week.

The problem with getting very accurate spindle speed is that I'm using a VFD and adjusting the analog output of the CNC4PC C11 interface board is pretty touchy. That and at low RPMs the VFD/motor combination isn't very stable. I was under the impression that with with a spindle index pulse Mach would adjust the feedrate to the spindle speed. With in reason of course.

According to the MachTurn_1.84 manual section 5.4.6.6, exact spindle speed is not likely to be important. Maybe tomorrow I'll try turning on the spindle Closed Loop Spindle PID control and see if I can tune it yo make things better.

Drew

4

General Mach Discussion / Re: Getting incorrect thread pitch with G76

« on: July 09, 2014, 07:25:25 PM »

Thanks Hood. The xml is attached.

Drew

5

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

6

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

« on: July 02, 2014, 10:35:03 AM »

Thanks again :-)

One final question. It looks like the majority of proximity switches are listed as taking between 6 and ~30 volts, will they run off of 5V? That's the voltage that's going to my current switch and I'm wondering if it's something special.

Drew

7

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

« on: July 02, 2014, 03:12:07 AM »

Thanks Peter.

From cruzing Amazon I see that switches can come in NO or NC configurations. My current switch is 3-wire but I don't know if it's NO or NC. In the 3-wire series example in the PDF are the switches NO?

Drew

8

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