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bradtal
01-25-2008, 06:04 PM
Hello All-

Ok, here's the deal. I hand-build a Jrgo machine and it was been working fine. I use Mach 3 and I used the "Set Steps Per Unit" axis configuration for each of the axis. I told each axis to move a certain distance, measured the distance with a digital micrometer, and entered in the "moved" distance value.

Anyways, it looked like everything was fine. I started cutting pieces for my Joes2006, but during assembly, I noticed the some holes were not lining up (like 1/8 inch or more off).

So, I just ran a test on my machine. I cut 1 x 6 rectangles (inside and outside profiles) and 1 & 2 inch diameter circles. In the X axis, the rectangles measure at .997 (pretty darn close), but in the Y direction, the rectangles measure at 6.1 (instead of 6.0). Also, the 1 inch circles measured .998 in the X-axis, but 1.07 in the Y direction, so the circles are not perfectly round.

So, I reran all the "Steps per Units" tests on all the axis. I reran the cutting of the rectangles and circles and got the same (or within 0.002) results.

So, any ideas here? The only thing I could thing of is to "tweak" the Y-axis settings, cut a test, then tweak again until I get the right numbers. But that would take many, many cuts and tests (I would think).

Thanks for your help.

Brad

BobF
01-26-2008, 08:24 AM
bradtal,
you can calculate the steps per inch and put that in mach.
motor steps per revolution X threads per inch X micro steps. Example
most motors are 1.8 degrees per step or 200 steps per revolution
my machine has 1/2" 8tpi 2start screws for effective 4 revolutions per inch
I use 1/2 step micro stepping.
200 X 4 X 2 = 1600 steps per inch.
just adjust these numbers to match your screws and micro stepping settings.

PhillyCyberJoe
01-28-2008, 10:02 AM
Bradtal,
I had the same exact problem with my machine as well.

I discovered a crack in the z axis HDPE router holder plate. That was a result of trying to force the 2" U bolts through and the outward stress cracked a corner. I didn't think it would cause much problem, until after I did the same kind of test that you did. I cut a new plate and used 1.5" U bolts which went in with no fighting and my problem went away.

The take away message here is that you might have a tiny bit of slop in your z axis due to the above. If you take the router holder off and just try moving the HDPE side to side, you might find a a problem there.

Just my two cents.

Joe