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Waste board tolerances

Posted: Mon May 25, 2020 2:34 pm
by Roland J
I have the Shapeoko 3XXl with a 3/4 MDF 32" x 32" waste board with tee-nuts attached at 4 corners and at the 5 centerpoints to the factory waste board that I have been trying to resurface to be able to v-carve on. Needless to say I don't believe everything is going my way, or I'm expecting too much accuracy, but I have resurfaced this thing till it's about worn out.
Started with a feeler gauge and 1/4 end mill checking the 9 points without much success, so I bought a dial indicator and mounted it to the router, and started checking the board with following readings starting at NE .000 N.012 NW.003 W.016 SW -.010 S -.001 SE -.013 E -.011 & C -.003. coming back NE indicator read .000, I marked the spots with each reading and randomly checking got the same readings.
I took the center point as a starting point and r, an a surfacing toolpath with a .008 depth of cut, with the following results, starting at the center as .000 W -.015 NW -.014 N -.013 NE -.013 E -.012 SE -.014 S -.016 SW -.015 W -.015 and back to C reading .000.
The tramming is very good as there are visible marks or deflections on indicator as it passes across to indicate a ridge. Did notice that you can't lean on machine bed as you can change readings by a couple of thou. though.
Looks to me like that I went from random slopes to a .013 dome. I guess what I want to know is if this is as close as it gets, or what needs adjusted, just call it close enough and shim work pieces. What got me looking into this was a profile cut that in 8 " across on the x axis cut 0 into spoil board and .006 on the opposite side.
Any thoughts or helpful hints will be appreciated as I'm lost once again.

Re: Waste board tolerances

Posted: Tue May 26, 2020 2:26 am
by WillAdams
Start by stiffening up the machine itself --- the easiest way to do this is to set the machine on a sheet of insulation foam --- alternately, work up some way to level it sitting on a torsion box (and then use the threaded holes for the leveling feet to secure it to the torsion box.

Then add a spoilboard on top of the MDF baseplate (optional: replace the MDF with something more stable --- at a minimum, if you haven't sprayed the MDF to seal it, do so now). Tram the spoilboard, then check for level.

Re: Waste board tolerances

Posted: Tue May 26, 2020 2:26 pm
by Roland J
Thank's Will for the reply Will give your recommendations a try. Any improvement will be better than having a dome in the center.