Newbie- SOLVED - Backlash compensentation causing problems while moving 2 axes

[Hirudin]

As the prefix to this thread says, I'm a newbie, so hopefully I just missed something easy or obvious and this problem can be fixed. Sorry, I'm long winded... hopefully below is enough explanation to make a diagnosis...

Machine...
I have a TAIG mill using Gecko 203v drivers, Keling KL23H276-30-8B steppers, and a Keling 48 volt / 12.5 amp power supply.

Computer...
I set up my computer in "Standard PC" mode (fresh format and install of Windows XP with SP3 and all updates) and it is only used to run Mach3 and get files from a USB flash drive (no other software is installed and it's not connected to the internet). I don't remember all the specs, but the processor is an AMD 2800+ (32 bit, single core at ~2.2 ghz IIRC). I've run the driver test and it ran perfectly all the way up to 100 khz.

My problem...
It worked just fine for a while, then stopped. Here's where it went from working to broken. I made the description red so it's easy to skip if you don't want to read it.

I started milling my first "real" part today. Everything was working beautifully until the machine refused to work correctly at all. Long story (read below) short: attempting to move two axes at once will make one axis stall. The stalled axis motor will keep "trying" to turn, but it wont move. It is as if the acceleration is too high or there is a physical barrier stopping the axis from moving.

It first came up while milling a circle, it started at 12 o'clock and started moving counter clockwise, when it got the the 9 o'clock position instead of continuing around to 6 o'clock it went directly into the center. I managed to stop the machine without anything being screwed up. Figuring I had the mill too deep in the aluminum I remade my g-code to take cuts at half the depth as before, re-zeroed the machine and started it again. It pretty much did the same thing except it made it around to 6 o'clock before heading for the center this time. Also, I wasn't able to stop it as quickly this time (I gotta get an e-stop button wired up) and it ended up going a little further.

Not to be discouraged, I set it up again, this time the problem showed up earlier, on the top/right of the part (see the attached photo). At this moment the machine was barely cutting any metal at all (maybe a thousandth off this 1/4" piece of aluminum).

I did a dry run. "Cutting air" as they say. The machine made the same error, even without any force being put on the cutter.

I experimented quite a bit... The only thing I could do to correct the problem is to turn OFF backlash compensation. With backlash compensation turned off, I could run BOTH the X and Y axes at ~100 IPM (and 20+ acceleration) without any issues. With backlash compensation turned ON I could be moving the X axis at 21 IPM and as soon as I make the Y axis move (at 2 IPM!) the X axis would stall. If I made the X axis move at 20 or less IPM I could seemingly make the Y axis go as fast as I want (all the way up to ~100 IPM!).

I don't think it's the motor, the drive, or the axis as I switched the pins for the X and Y axes (in the "Ports and Pins" configuration in Mach3) and the same thing would happen but with the axes reversed (the Y would stall if I tried to move the X at the same time).

Recap...
X@21 & Y@2 = no go
X@<20 & Y@100 = works fine
X@100 & Y@100 (both at 20+ acceleration) with backlash compensation OFF = works fine
Swap pins for the X and Y axes = no change in behavior

Anyone know what the problem may be? Please don't tell me I cannot compensate for backlash any more!

[ger21]

If you have CV mode on, turn it off. It typically doesn't work well with backlash.

Also, you probably need to play with the Shuttle Accel setting in the General Config screen. It controls the backlash comp speed. Not sure how to set it, but there's some info in the CV docs here.

http://www.machsupport.com/docs/Mach3_CVSettings_v2.pdf

[Hirudin]

I think that's what it needed, thanks ger21! Specifically the shuttle wheel setting. I hate to go so far from the default (0.004) but I guess it needed to be bumped up to 0.1.

The CV mode setting didn't seem to change anything, but I'll probably leave it off anyway.

I knew I shouldn't have written that super-long post and just truncated it to something like "Unless I turn off backlash compensation my machine will not move in arcs. Help!".

I messed with my settings while fiddling with it, now I'll have to measure the backlash again... this time if it's under a thousandth I think I'll just leave it at "0". Smooth motion with very little backlash is preferable to little pauses with slightly less backlash IMO.