Squaring up my machine

[analogman]

I am just finishing up my aluminum based data-cut machine and looking for any suggestions on how to square it up.

I have a "pretty good" 8" machinists square, but it is not a $400 Starett or Browne and Sharpe. I heard some people take a carpenters square to the machine shop for squaring.


Anyways, any help is always much appreciated.

thanks

[stevespo]

I'd like to hear people's techniques as well. Here is what I have done:

Square the gantry vertically to the workboard/table with a good square and some feeler gauges. Square the spindle (Z) to the workboard/table, front/back and side/side.

When you're happy with the Z, focus on the X/Y. The best way I've come up with is to drill (4) 1/4" holes, one in each corner of my worktable. Use some dowel pins, and measure the distance between the diagonals with a piece of scrap and a dial caliper. When these two measurements are "equal", the table is square as well.

If they are not equal, you can shim/adjust/etc the table/gantry, plug the old holes, drill 4 new ones and re-measure. It may take an iteration or two, but you can get very, very close this way - a few thousands over a 40 inch span is close enough for me. With my type of gantry, I haven't figured out a better method, but I'm sure there is one out there somewhere.

I then level my workboard with a large diameter bit. If the surface is nice and smooth (no stair stepping) then the Z turned out accurately as well. If there is a rough surface, recheck the Z and resurface the board to be sure. The MIT machine shop videos have some nice techniques for squaring milling machines and vises, which you may be able to apply here.

http://techtv.mit.edu/videos/127-machine-shop-4

Steve

[BobF]

If you use a spoil board or don't mind cutting the table. Cut a large L in the table. I cut this anyway with a 1/8" bit and use a pair of 1/8" aluminum strips as a square corner for work setup. One side follows the long axis, the other the short.
Once you have made the cut, use the largest accurate square you have to check it. If your carpenters square is accurate, and your table is this large or larger, use it to check. Adjust as needed.

[jsheerin]

Another way is to cut a large square with your router. Measure across the diagonals - they should measure the same.

[analogman]

I saw an interesting post on another site. The guy cut a 12x12" square. Measured the diagonals for squareness, measured the side lengths to ensure no missed steps. Since it was water jet there was no concern for Z axis.

This method was criticized for the corners may not be accurate due to rounding. With a wood machine, this may not be a big deal.