G90 in the Lathe software (solved)

[jgrush]

Greetings -

I have a small lathe conversion and it appears to be working - steppers, gecko drives, encoder, limit/home switches all seem to be okay.

I used Intercon to create a simple threading example to test my spindle drive & encoder. - I basically set it up to turn down a 1" delrin rod to size and thread M10-1.25.
The Graph results looked reasonable. The first iteration of the program seemed to work okay but the feeds were really slow - my fault as it is set up metric and i am not used to that yet. I stopped it before getting to the threading diameter.

So I re-did it with faster feeds and depths of cut. It started out fine - doing the facing, then when it went to the straight turning to reduce the diameter, it made a single pass, then moved back to roughly Z0, then moved back to roughly Z20, then Z40 then Z60 until I run out of ways.
I looked at the code and it has a continuous string of G90 codes:

Starting at X 26 Z.0.5
G90 X25.0 Z-19.9
G0 X25.0 Z0.5
G90 X24.0 Z-19.9
G0 X24.0 Z0.5
G90 X23.0 Z-19.9
G0 X23.0 Z0.5
G90 X22.0 Z-19.9
G0 X22.0 Z0.5
and so on...

I looked up G90 in the manual and it refers to Outer/Inner Diameter turning cycle. It seems to make sense that Intercon would select this to reduce diameter and that all moves would be absolute as no U or W values are specified - as needed for incremental positioning.

Any ideas why it should behave that way?

[tblough]

Without the Intercon program to look at, I can only guess that you have programed a feed rate that is faster than the motors can move and it is loosing steps. The first moves to Z0 and then tries to cut at your unobtainable feedrate to Z-19.9. The controller sends the pulses, the motor can't move and the alarm output from the driver is not connected to the Acorn. Since the control thinks you have reached Z-19.9, it now sends enough pulses to retract to Z0.5 for the next pass.

These pulses then move you to Z20 since the move started at Z0 instead of Z-19.9. This cycle repeats until you run out of travel. To fix this, you need to do two things. First, connect the alarm output from each of your gecko drives to the Acorn - this will stop the machine if you overdrive your motors in the future. Second, you need to program a feedrate that is realistic for you drives, and the material being cut.

[jgrush]

Thanks Tom.

I came around to the idea that the feed rate was excessive a little while ago. I have the program providing css rates and I overdid it big time! I misplaced a decimal point!

I will look in to the alarms from the drives. - something of which I was not aware.
Best.

John