Error in movements when switching between mm and inch

06 Sep 2017 16:11 #98587 by MDM3D
MDM3D created the topic: Error in movements when switching between mm and inch
So I discovered noticed something odd when i was checking my machines movement when i told it to move 5mm through axis using the fixed increment size my machine moves almost exactly 4.999 mm according to a very nice digital indicator and 10.000 mm when jogged another 5mm. Awesome! But when I moved jogged by .5 inches I moved .5016 inches and when I jogged again I measured 1.0028 inches switch back to mm jogs and the machine move the correct amount as specified in the jog window. I repeated these jogs several time to make sure that this wasn't a fluke.

My axies are all the same movement is exact when given mm commands and off when given inch commands. the machine is configure as a mm machine 1605 ballscrews with 200 step per rev steppers at 10x micro stepping which should give me 2000/5 = 400 steps per rev which is what the .ini file shows.

Is this a rounding error or am I missing something? Thanks in advance.

I can force my post to output gcode in mm for now but it would be nice for the machine to not care what units were given.
06 Sep 2017 17:06 #98589 by Todd Zuercher
Todd Zuercher replied the topic: Error in movements when switching between mm and inch
Could you try your test again but this time use MDI commands to do your inch jogging?
G20 G91;
Then try
G20 G90;
G0 X0;
Are the results from both of the above tests the same? Are they closer to correct?

Not sure how you could have a rounding error, 1" would be 2032 steps/rev, and a 1/2" jog should come out to an even 1016.
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