Planing a slope on a small sheet of plywoodD

[Vince Shriver]

I'd like to cut a slight slope in to a sheet of 3/4" plywood (27" Left to right, 12" top to bottom). I want the thickness to finish out at somewhere around 1/2"-3/8" at the top and 3/4" at the bottom. I would use my 15" planer, but I've never planed down plywood before and am hesitant to do so. I have the Byrd cutters in the machine. It only needs to be "good" on one side. Should I go ahead with it, or is it just a bad idea?

[Marty Schlosser]

There's a few problems I can see with this. First is the core material chipping away as you machine away the face veneer and engage into the core. Cores made from veneers layered perpendicular to each other (that's what many call "ply core" or "veneer core") will most likely fare poorer than most other commonly available core type plywood, simply because every second veneer layer will be going cross grain to the line of the planer knives. To my way of thinking, chip core - because of its larger sized chips - will fare a bit better, followed by cores made of the finer material (particleboard core). However, if you can purchase lumber core plywood, you would be much better off, as that style of core in a 3/4" thick panel, is made of an approximate 1/2" to 5/8" thick main core of solid wood - with a cross grain veneer on each face to help stabilize the core, followed by the face veneer on each face, running parallel to the central core. Because you're only dealing with one layer going perpendicular to the cutters, it should have a greater likelihood of surviving intact. I think, though, that regardless of the core type, it's fortunate that you have a Byrd style of cutterhead, because those smaller knives will work out better than the traditional 2 or 3-knife head cutterhead. Expect, nonetheless that there will be quite a bit of chipping. Expect, as well, that your cutterhead cutters will be going through quite a bit of glue layers, which isn't that good for them.

You'll also have to make yourself a tapered sled to place under the piece of plywood as it goes through the planer.

Then, when it's all said and done, you'll have a piece of tapered plywood which unless you apply a veneer layer to the machined side, will warp on you.

So, perhaps there's a better way... and that's to forego using plywood entirely and glueing up a solid panel then running that through your planer on your tapered sled.

Keep us posted as to how this comes out.

[Rich Engelhardt]

Instead of cutting down 3/4" why not build it up out of thinner, like 1/4" or 1/8" thick plywood and shims?

[Lee Schierer]

The glue in plywood is going to be really hard on your blades and as others have mentioned, when the knives hit the layers at 90 degrees to the face grain you are going to get a really rough cut and lots of tear out. I would suggest the build it up from thinner pieces method and use a belt sander with a coarse grit to obtain the taper.

[Jamie Buxton]

Planing plywood is really hard on the knives. I'd start with plywood that is your minimum thickness (1/2"-3/8"), and add lumber to the edges on the back side to get to your maximum thickness (3/4"). Then I'd do the tapering to the lumber. You could do the tapering with your planer, or even with a hand plane. Or you might could taper the lumber before you glue it on to the plywood.

[Peter Quinn]

Forget the knives, when you take that much material out of a sheet of man made material, it's going to go crazy. No way this will stay flat, may easily curl beyond usable. I'd rethink the whole thing, perhaps easier out of solid wood which may not stay straight but often fairs better when tapered because there is no cross banding issue to contend with.

[glenn bradley]

This sounds like one of those rare uses for a hand held belt sander and some patience. I'm not quite picturing this right "I want the thickness to finish out at somewhere around 1/2"-3/8" at the top and 3/4" at the bottom." Are you trying to make an edge like a raised panel door might use? How wide is the taper from 3/8" to 3/4"? If it is only a couple of inches, a tall fence on the tablesaw and running the material on edge could be you solution.

[Vince Shriver]

Glad I posted this; thanks for your thoughtful input. I'll glue up a solid panel and go from there.