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Author Topic: X Axis Scaling Problem  (Read 1953 times)

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X Axis Scaling Problem
« on: September 27, 2015, 06:00:19 PM »
Hello, my machine is scaled and cuts squares and circles accurately. When I try to cut a figure into a plaque the x axis movement when left of center appears to be scaled down. The resulting carving looks kind of egg-shaped. I've tried using the center of the part for zero and I've tried using lower left corner for zero and both have this issue. This is a new machine running Mach3 with a parallel port. I have tried some older code I used successfully with another machine and it has the same egg shaped output on this machine. If I look at the toolpath tab and compare the X extents of the code with what actually is carved it's obvious that anything left of center is scaled downward. The final carving doesn't have any jagged edges or signs of the machine "hiccupping. It's what I would expect to see if there were some sort of leadscrew compensation on the x axis. There is no compensation employed and the x axis works as it should when done manually and compared against a ruler. The toolpath looks OK in Mach3 but doesn't follow what is actually being carved. Does anybody have any ideas? It's one of the Chinese import machines. I was thinking the controls would need to be replaced when I bought it but they seem to work OK other than this problem.  Thanks for listening to my frustrated ranting!

Offline RICH

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Re: X Axis Scaling Problem
« Reply #1 on: September 28, 2015, 04:28:32 AM »
Confirm that  the steps per unit of the X axis are correct in motor tuning. This can be done using the calibrate axis feature of Mach.

Attach your xml file that you are using and someone will have a look.
RICH
Re: X Axis Scaling Problem
« Reply #2 on: September 28, 2015, 06:23:24 AM »
Thanks for the response. The XAxis is scaled and seems to work correctly. I attached a photo of the problem as well as the xml file for the machine. In the photo, the outer circle is correct and centered on the x. The inner circular pocket is skewed. The cut starts in the center at the x but moves +x on the part. The resolution in the photo isn't high enough to make out the circular machining marks but it definitely starts in the center. Again, the XAxis is set up properly. I've used Mach3 for a few years and am confident it works fine but in this case I'm not so sure. The toolpath preview in Mach3 looks normal however the actual toolpath on the part is not. I can't see where the stepper controls would do this. If I had another suitable PC my next step would be to install Mach3 on it and give it a try. I've reloaded Mach3 on the existing PC and that didn't correct the problem. By the way, the toolpath was generated with Aspire. I have checked this machine against known good toolpaths used in the past and the problem follows this machine. This is a new machine with Mach3 running on a spare WinXP Pro PC.  Thanks again for any thoughts or ideas!
Re: X Axis Scaling Problem
« Reply #3 on: September 28, 2015, 06:26:06 AM »
Here are the files

Offline RICH

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Re: X Axis Scaling Problem
« Reply #4 on: September 28, 2015, 08:07:32 AM »
Post the gcode file.

RICH
Re: X Axis Scaling Problem
« Reply #5 on: September 28, 2015, 06:25:42 PM »
Here's the GCode file that generated the skewed circular pocket.

Thanks,
Marty

Offline RICH

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Re: X Axis Scaling Problem
« Reply #6 on: September 29, 2015, 06:22:55 AM »
The pocket file you posted starts at X & Y=0.

Where does the larger circle code start?
If it also starts at X&Y=0, and if you are running the files separately, the you may have created a work offset and that is the reason the second one is  it is offset.

RICH
Re: X Axis Scaling Problem
« Reply #7 on: September 29, 2015, 06:36:24 AM »
Rich,

Thanks for your help. The finished part isn't really offset. It starts at X0Y0. The problem is any X movement less than X0 seems to travel less. The result is a circle that is "ballooned" to the right. If I had a more complicated finished part to show you would see that the left half of the finished part would be shrunk while the right half would be about normal. When I do a simple shape or manual move along the X axis the movement is correct. I'm almost to the conclusion that this somehow has to be a PC issue. I've tested known good code from previous setup and it doesn't work on this machine. Knowing Mach3 works and that the stepper drivers aren't smart enough to do this leaves the PC.
Re: X Axis Scaling Problem
« Reply #8 on: October 03, 2015, 05:24:20 PM »
Rich,

Finally found the X axis flexible motor coupling although tight didn't fit the ballscrew properly. When driving +x it wrapped the coupler tighter and gripped pretty good. When moving -x it tended to unwrap the coupler and slipped a bit. Only found that when I decided to swap the X and Y motors to see if that was the problem.