Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: spinningwood on July 21, 2011, 11:16:24 PM
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While trying to fix another issue I happend to notice that the dro doesn't match the gcode when I stop the program during a run. They are all off by a small amount. A search of the web only turned up a suggestion to check backlash settings. I have backlash compensation turned off so I don't think that's my problem.
I did some air runs of old jobs and now see that those files had dro / gcode mismatch as well. The pieces cut fine, but I cut artwork not jet engine components and I don't measure the finished project.
Is this normal behavior for Mach? Is a setting(s) I should be checking?
Thanks.
Ed
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Ed,
It may be due to the resolution of your system. For instance my controller is ½ step and with 4tpi lead screws each step is 0.000625 inch. So if the G-code is in 4 or 5 decimal places it is unlikely that Mach can drive to that exact position. Mach will drive to and display the step that is the nearest to the commanded G-code. For example if I step in 0.001 increments the DRO will show steps such as .0000, .0006, .0019, .0025, .0037, .0050…. etc. As you suspect it’s quite likely normal and not a poblem.
Al
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Hi Al - Thanks. That sounds like a reasonable explanation. I'm going to single step through a job when I get a chance and see if that's what looks like is going on.
Ed
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Looks like you were right on with your answer Al. I learned something new as well by single stepping through a job. When you stop a job the gcode stops at the next line to be executed, not the last line that executed. Everyone else probably already knew that, but I didn't.
When I compared the DROs to the line before where it stops, the gcode and DRO are either right on or off by a tiny amount. Exactly like you would expect based on resolution limits.
So much to learn with Mach! Good thing I enjoy learning new things. Mach keeps me really happy in that respect.
Thanks again for the help.
Ed
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:)