Squaring shopbot issues

[bruce_taylor]

Doing a little work to check my squareness. Cut a piece 5 X5 and it is square at 7.057 corner to corner both ways. But it is 5.004 front to back and 4.96 side to side . What could be causing this?? any ideas??
As always thanks for the help.
Bruce

[nat_wheatley]

Bruce,

If you haven't read Gary Campbell's article on this, I'd recommend it. It's titled 'Tuning Up the PRS Gantry' and is located about 1/4 of the way down this page:

http://shopbottools.com/garysmusings.htm

[tmerrill]

If your corner to corner measurements are the same I would say your gantry is square.

I would experiment with making small changes to your X and Y unit values (keep good notes) and see if you can bring the measurements to 5" in both directions. Use the VU command for this.

Also be sure you're not seeing any bit deflection. Try to do this test with a large diameter bit. I recently did the same test that you did and used a 1/2" downspiral bit with piece of corian I had laying around. Didn't have to worry about any effects due to the grain of the wood.

Tim

[bruce_taylor]

I have found it is the same at several locations on the table x to x .004 short y to y .004 long . Every piece square to with in .001.
Haven't looked into the unit values yet, Going that way next going to check a couple more little things just to rule out the hardware side before I dive into changing unit values . Anyone have any success with changing unit values and what did you do ?
Thanks