The next step in the build is to mount the tabletop onto some legs. I wanted to make the height of the scanner comfortable for me while sitting. I should be able to hold my arms out straight ahead or slightly down and touch the top of the platen. For me, that makes the top of the platen about 29 inches from the floor, making the top of the table 21 inches from the floor.
I spoke with Lewis at NextFab for some advice, since I have no experience in building stable tables. The best I did was ten years ago when I took a 4' x 8' piece of plywood and stuck some 2" x 4" legs on. I added some bracing after I realized that it was unstable, and it sort of worked. But I wanted something a little more stable from the beginning.
He suggested building an "apron" around the bottom of the tabletop, made of 3/4" plywood, 3" wide. I decided to leave a 1" lip around the perimeter. My tabletop measures 30" x 23 1/2" -- I cut the plywood to slightly under 24" because I didn't want to assume one edge was perfectly parallel with the axis of the laser. So I subtract 2" from each dimension to get 28" and 21 1/2". That latter dimension is very close to my desired leg height, so I decided to use 21 1/2" for the legs as well.
I cut two strips 3" wide and 28" long, then ten strips 3" wide and 21 1/2" long. Two of each go into the apron. Now, if you're not like me, you've discovered a little problem already. If I were to place the strips like this: |_| then I'd get 21 1/2" plus twice 3/4", which is 23". That gives a 1/4" lip, not the 1" I wanted! What I should have done was make the 28" strips smaller by twice 3/4", or 26 1/2".
So instead I just placed the strips alternately. I ended up with a lip of 5/8", which is fine. Just don't forget the thickness of the plywood strips!
To attach the strips, first mark a pencil line 5/8" from the edge (or however big the lip is) on the bottom of the tabletop. Run a thin bead of wood glue inside the line, and put the strip on top. Clamp in three places:
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Now mark a pencil line 5/8" plus half of 3/4" along the top from the edge. More generally, lip plus half the apron plywood thickness. This is where your screws must go:
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Drill pilot holes through the top -- it helps to use a very small square to make sure you're drilling perpendicular to the top -- then countersink for the screw heads, and screw together.
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Once all four sides are on, use a looooooooong clamp to squeeze the sides together. Drill pilot holes, countersink, and screw:
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Use only one screw at the top, because we will later be drilling holes through the apron near the corners.
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We now have a very sturdy tabletop.
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