So how do you adjust for undersized plywood?

[Joseph Ezerskis]

I'm making the NYW router table, and went and cut all the pieces to size. I checked the plans for the rabbit & dado dimensions and saw the note about adjusting the plans for undersized ply. I checked the baltic birch ply I'm using (11 void-free ply) and found it's 0.708". I'm glad I didn't cut any of the dado's yet! So I'll adjust the dado blade set smaller.
Will the difference cause any problems with the carcass or joints? Is this a big enough difference to cause problems with all the drawers? I think there are something like 6 small bit + 2 large bit + 3 storage drawers = 11 total.
What have you guys done to compensate for something like this?
thanks,
Joe

[Jim Becker]

Plywood is almost universally undersized and you need to adjust your dados and rabbits accordingly. Always remember that plans are only a guide...you need to do "field measurements" throughout project construction to insure that things fit. With plywood, I find it useful to work with centerlines for locating the positions of interior panels in cabinet work and be sure to measure carefully for anything that needs to intersect them. This is where traditional techniques, such as story sticks and direct measurement shines.

[Richard Gillespie]

I agree completely with what Jim Becker said. I'd like to add however, I leave drawer faces oversize until the last moment. I can then make whatever adjustments I have to.

[David Brown]

but I tried, hey it is almost FRIDAY!

[Joseph Ezerskis]

:D :D :D yeah! No problem if it was MDF. In fact that's one of it's selling points!

[Mark Singer]

A digital caliper is the key to comparing thicknesses, dados, blade settings and heights...it is the best $25 you will spend!
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=25269&item=3810965697&rd=1

[Chris Padilla]

Agree. I have a pair of calipers (dropped them!! :mad: ...bought another pair) and they are indespensible in the shop. I got the kind whose primary measuring is in 1/64"...quite helpful.

[Joseph Ezerskis]

Mark & Chris, thanks for the reply. I had picked up the HF caliper.That's how I got the .708". I'm going to follow Jim's advise and centerline the dado's and go with the flow. I don't want to decrease the ¼" deep dado's anymore.I figure I'll still have some slop around the cleats and the drawer fronts. What do you think of edging them in red oak glue veneer? That should be thin enough.
Thanks again,
Joe

[Dale Thompson]

Joseph,
You can also buy "undersized" router bits for the "new" plywood. As I recall, all sizes are 1/32" under nominal. (ie. 3/4 = 23/32, 1/2 = 15/32, 1/4 = 7/32 etc.). As I recall, the three bit set was not that expensive. I think that this is what they call "new math". Either that or "more profit". :)

Dale T.

[Jim Becker]

You can also buy "undersized" router bits for the "new" plywood. As I recall, all sizes are 1/32" under nominal.
It would be nice if it all was consistantly 1/32" under, but I found variation between sheets when I was doing the kitchen project. I even had one sheet where there was variation in the thickness on the same sheet! Fortunately, my Forrest DadoKing without shims is pretty much a shoe-in for the undersided plywood. I just slap it on and cut.

[Todd Burch]

Undersized plywood is a pain. And, as to what has been eluded to above, inconsistently sized is even a bigger pain.

As far as rabbet and dado depths, I don't get hung up on having it exactly 1/4" deep, or 1/2" the thickness deep, etc. I go for easy measurements and cutting for final dimensions.

If I have a case that is supposed to be 24" wide, outside dimensions, and I will use dados for the top and bottom fixed shelves, I want to be able to remember my measurements as I cut. So, I have a top & bottom shelf that is 3/4" narrower, or 23 ¼" wide. I cut those first. Then, I want 3/8" deep dados in both shelf sides, right? Wrong! What I REALLY want is 3/8" thick material LEFT after I dado. So, I dado until I have 3/8" material left in the bottom of the dado. Then, if the dado is 3/8" deep, 11/32", 5/16" - it doesn't really matter. Noone orders a case specifying they want 3/8" deep dados.

Also, I typically cut the outer 1/2" to 1" of sheet goods off, if sheet layout will allow it, especially 1/2" baltic birch ply. Too many times I have had sheets that were 7/16" thick right at the edges where the wide sheet sander rounded the corners over. Also, cutting the edges off will get rid of burnishing and dirt and grit and knicks/chips/splits you get from handling and sliding sheets around.

If I have a sheet of ply that has a bulge in it, I might belt sand or hand plane it out and put that side where noone will ever see it (like the bottom of a fixed bottom shelf).

For drawer bottoms, if I have the time to jack around with shims when I dado, I will for a nice tight fit top and bottom. If not, or if the client isn't paying for top-notch quality, when I glue up the drawer, I will turn the freshly assembled drawer box upside down, press down on the drawer bottom to remove any gaps that might be seen inside the drawer box during use, and pin or staple it there while the glue sets. Any gap is now on the bottom of the drawer.

[Howard Acheson]

Keep in mind that true Baltic Birch is manufactured in metric thicknesses. That explains why 3/4" doen't measure 3/4".