Strange Behavior

I have a Sherline 4400 Lathe, CNC, Sherline parallel port driver board.
kernel 4.19.0-17-rt-amd64
linuxcnc 2.8.2-11-g6a3d0a434

I created a .ini using stepconf. Seemed OK in testing.

I completed making a part and wanted to move away to measure. The Z-axis was at 0.1000, near the chuck jaws.

I did G90 G00 Z4. The axis moved about 1/2 inch and the stepper started missing steps (howling) like the axis was blocked. Power off. Inspecting the bed and leadscrew showed no problem. The handwheel revealed no obstruction.

Moved back to the starting position. Homed Z-axis. I did G90 G00 Z4. Same problem. Power off, wiggled the handwheel, no obstruction. Homed the Z-axis and did G90 G00 Z4. The z-axis moved a couple inches and started missing steps like the axis was blocked. Again, found no problem

I restarted linuxcnc with the Sherline .ini, etc. All normal. The moves as above showed no problem. No missing steps, moved the entire length of the z-axis with no problem.

I restarted using the stepconf .ini, etc. Same problem with missing steps.

It appears that something is causing linuxcnc to issue incorrect step and/or direction commands.

I believe this is something I did in creating the configs. But, what?

What information may I supply to help diagnoise this problem?

Tom Dean
 

Attach your hal and INI files - that's the first step.

Make a copy in your config folder and rename them xyzhal.txt and xyzini.txt - the forum doesn't allow .hal and .ini files to be attached.

Once you do that and you're waiting for someone to have a look at the files... the first place to check is your INI file.  Look at the AXIS and JOINT sections (probably AXIS_Z and JOINT_1 for a lathe) and see if the MAX_VELOCITY and MAX_ACCELERATION values in both locations look reasonable.

Keep in mind that those values are in units/second, not units/minute.  Hard to get used to for some folks.

Do the math for those values - does it translate in to a 'sane' Z-axis rapid speed for your lathe, or have you inadvertantly told it to go a billion inches/mm per minute during a G0 move?

Did this work before you experienced this current problem?  i.e. have you changed something recently or is this your first go at moving the lathe around and making chips?  Can you command a G0 move for the X-axis successfully?


 

I would say that your rapid speed is set too high and your acceleration as well.

It's probably fine if your feeds are really slow, but once you get out of low speed towards the speed of your rapid, you're accelerating too fast. That howl is the stepper stalling and skipping steps.

I would go back into stepconfig spend some time testing acceleration and top speeds. Then knock about 25% off what seems to be working as your top speed in stepconfig as your final rapid setting.

I believe this is true. The lathe did not exhibit this behavior before I tried stepconf. I compared the stepconf .ini to the original sherline.ini and the values are much higher.
I will play with these values before I post the hal and iini files.

Thanks for the replies.
Tom Dean