# Question: Is it safe to plane plywood?



## Dyidawg (Feb 24, 2010)

I have cut 3/4" dado in the side of a vertical piece and the 3/4" plywood piece doesn't fit. Is it safe to plane down the piece by 1/16" or try to widen the dado cut? The dado was cut with my router since I don't have the proper blade for my table saw.

Thanks


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## North40 (Oct 17, 2007)

You're okay if it's a decent quality ply. I worry about what might be inside of cheap ply. But if you plane it down, you'll loose the veneer and be into the core … I don't know if you care about that. You can definately widen the dado by reseting your router guide slightly - there are lots of router dado jigs that are designed specifically to make two passes to get the correct width dado.


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## CarlBert (Apr 13, 2010)

Widening the dado seems to be the simple solution. Whether you made it with a dado blade or a router, it is still much easier to widen it then to plane down the plywood. Unless you are in a situation where you can't widen it, though I can't imagine one. In that case I would then narrow just the edge of the plywood that is going to sit in the dado with a dado blade or router. This way you don't risk ruining the whole piece.


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## manumurf (Mar 4, 2010)

Route a shallow rabbet on the end of the shelf(horizontal piece) to allow it to fit.

You could even stand the piece on end and do the rabbet on the Table Saw if the board isn't too long. Set the blade height to the dado depth and the rip fence to the width of the dado. Take it off the bottom of the shelf.


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## Beginningwoodworker (May 5, 2008)

I am not sure!


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## rwyoung (Nov 22, 2008)

Michael Murphy hit it. Make a housed dado by rabbeting the "shelf" just a little bit to fit the existing dado. In the future, you can make a dado say 1/4" to 1/8" narrower than your shelf then just get in the habit of rabbeting the shelf piece.

If necessary, scribe a knife line on the shelf piece first to cleanly cut the top layer of veneer if you have problems with chipout.

To widen a dado, you can go back with the router and take another pass but it is dicey business to keep it clean and tight. There are special hand planes (Stanley 95 & 96 as well as modern versions from Lie-Nielson and Lee Valley/Veritas) that can cleanly widen a dado.

Another option is to build and use on of the custom width dado jigs for your router to use in the future. Simplest version consists of two shop-made T-squares, 3/4" material is a good choice. Use a bottom bearing router bit slightly narrower than the desired finished dado. By sliding these two T-squares along your workpiece (pinch the shelf between to set the exact width) and running the router on top with the bearing against the "trunk" of the T-square you can make a perfect width dado.

One last comment, plane, scrape or sand your shelf piece to finish quality FIRST before taking any measurements for fit.


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## Gofor (Jan 12, 2008)

Depends on which piece was easier to work with and handle. Resetting the router (or using the table saw) to widen the dado if the vertical piece is easier, and rabbeting the cross piece if the horizontal is easiest.

That said, I have never run across a piece of 3/4 ply that was thicker than 3/4" (some were only 1/64th over 5/8ths but never oversized). If the problem is due to warped ply, I would clamp a straight board to it to get it to fit into the dado.

On the few occasions where I do use a router to cut a dado, I always use a narrower bit and make two passes to get the best cut on each edge, as well as lets me exactly adjust the width.

Go


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## bigike (May 25, 2009)

you might be better off sanding so you won't go throught the veneer or you can widen the dado with the router use tape on a straight edge to move the router very little.


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## manumurf (Mar 4, 2010)

I built cabinets for years, did a lot of dadoes. Used a Her-Saf Panel router for most of them. They had bits that were a size + a few thousandths of an inch, like .753. instead of .75. That was so you could actually get a .75 piece into it without using a giant hammer. They were intended for use with engineered panels like melamine or MDF.

Manufactured panels like Particle Board or MDF or Melamine can have predictable thicknesses. Usually they are pretty close to the the target, say .75" or .625" because they are made by pressing the material to a set thickness.

Plywood is not as predictable. It is made of laid up sheets of material with the grain going in opposite directions to one another with glue in between. You can have "3/4" plywood " as thin as .68" or up to .74 but usually it is in the range of around 11/16" thick. Variations in veneer thickness, platen pressure, glue viscosity, moisture content, sanding pressure and quality all tend to make the Plywood thickness unpredictable. Since you can't predict the thickness, and even that thickness tends to vary when you get to the outer edges of the panel (and we know we want to use it all) you can get thickness variations in pieces from the same sheet. That is the reason you want to use a dado width of something narrower (say 5/8" wide) and rabbet the end of each panel to be the correct thickness to fit the dado.

Or just butt joint and nail or screw the thing together. But then we wouldn't have anything to discuss.


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## Jim Jakosh (Nov 24, 2009)

I would widen the dado rather than mess with the plywood. It might splinter unless you score it first. If you have the cabinet to a point that you can't get the route back in to recut the dado wider, you have no choice but to cut down the plywood a bit to make it fit. Score it first if you do!!

In the future, measure all the boards first that will fit in a dado. These days you never know what you will be getting for wood. A lot of plywood is smaller than nominal and you could have had a real sloppy fit.


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## Catspaw (Dec 15, 2007)

I pretty much cut a test peice first. As was stated, plywood varies. And of course, 3/4 plywood is not 3/4. So usually a 3/4 router bit will make a loose dado.

You can plane plywood, for sure. But the other solutions stated here are better.


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