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I have 5' x 5' sheets of baltic birch plywood having a thickness close to 3/4" at 23/32" so it's missing 1/32".

I want to glue 4 pieces together using yellow PVA glue.

I'm currently designing a multi-station workbench with 3"x3" legs (3/4 x 4 = 3") but since the material is 23/32 the total thickness would be (without gluing) 23/32 x 4 = 92/32 = 2 7/8 so I'm missing 1/8 !

However does glue add some thickness between the 4 pieces? I'm counting on the fact that it would result in getting close to an overall thickness of 3"... am I right?

Thanks!

Update:

Trying to fit posts with rails, all of them consisting of 4 pieces joined together. Each piece, before being glued together, is cut with the necessary shape for either a mortise or tenon.

This match is easy:

This one I am not sure:

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    The thickness of a PVA glue layer should be negligable, assuming you used a sanw amount of glue and clamped the pieces while the blue dried. – keshlam Aug 29 '16 at 13:28
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    Why do the legs need to be exactly 3" square? Work with the size they end up with, whatever it is. If you were doing this in solid wood due to planing or sanding differences you could have maybe a 1/64" discrepancy between legs and it wouldn't make any real difference to the finished piece. – Graphus Aug 30 '16 at 7:06
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using the proper amount of glue will not fill in the remaining 1/8", not by a long shot. The thickness of each layer, once fully dried, should be microns, not even hundredths on an inch.

In general, I would caution you against trying to calculate these sort of dimensions beforehand, and just use the actual workpiece dimensions as you progress with the project... it'll be much less frustrating! variations in dimensions on (or even greater) than the order of glue film thickness can be caused by humidity changes, so what's the point?

  • Ok, that's what I was afraid. I will have to rethink my design in regard to dimensions. – Stécy Aug 29 '16 at 14:02
  • other adhesives, notably epoxy, can be used very successfully to fill gaps. But trying to fill precisely a 1/8" gap can be really tough, especially by hand. I suppose you could overfill and then mill down to final dimension, but that's also hard when dealing with plywood... again, best to glue up, then use the final dimension going forward. – aaron Aug 30 '16 at 12:19
  • I'm trying to join a post consisting of 4 pieces where the two middle ones are previously cut as a mortise. A rail, also having 4 pieces, with the two middle pieces are cut to be the tenon. When matching the "faces" of the post and the rail I have no problem. The complication happens when I match a face with a side then the first two pieces in the post will have the mortise cut in differently. – Stécy Aug 30 '16 at 13:57
  • I've updated my question with some drawings. – Stécy Aug 30 '16 at 14:24
  • I see. Definitely do what's easy if that's possible! If you have to do the second option, then mill the mortise to fit the tenon. Normally you would mill a tenon to fit a mortise, but I think this is a good exception to that rule. – aaron Aug 30 '16 at 17:30

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