Too tight plywood dado

[Alan S]

If you just cut the dado a bit narrow, as mentioned above, using a dado set in a tablesaw with a sacrificial fence to take a skim cut off the bottom of the shelf (or whatever fits in the dado) is a good idea.

If the problem is uneven plywood thickness, so you don't get a consistent fit into a constant width dado, you are better off taking material off the shelf in a different way. For example, a radial arm saw references off the opposite face, so you leave a constant thickness rather than take a consistent depth of cut. That's what you want here.

The radial arm cut is safer than a trapped cut in a router table, or trying to stand the work on end to cut between blade and fence on the tablesaw, but with a tall fence and featherboards, that might be a good method.

A rabbet plane might be easiest, checking where to cut with a go/no go gauge (a block with a test dado in it.)

[ebarker9]

Wow, thanks for all of the great suggestions. I do have "plywood width" router bits and a router that rides in a Festool-style (actually Makita) track so I may use that in the future for these type of operations but I feel like I'd need to make something along the lines of the Festool MFT table to get good repeatable results. I've used a similar router dado jig to what was posted previously but I don't have one wide enough for these plywood pieces and I don't think I'd use it enough to justify making a big one.

For now I think I'll give the sacrificial fence/rabbet approach a shot. That should have occurred to me previously. I don't have a radial arm saw and it's a wide piece of plywood (which doesn't help the alignment problem at all).

My hand tool collection is pretty embarrassing but one day that side rabbet plane will be a nice thing to have.

[daddo]

Be sure your wood is properly dried and not causing the problem.

[rwe2156]

I wouldn't try to use a side rabbet plane on plywood. I have one (WoodRiver) only because they were on sale but it will be a seldom used tool I fear.

I would do the shelf trimming several have described with an additional suggestion:

Score the plywood before cutting will give you a very crisp line.

And, of course, goes without saying: test cuts on scraps first.

[AHill]

Since all you need to do is widen the dado,you only need the two outer blades. Just sneak up on one of the sides. Use a piece of scrap ply to test the fit.