coping with cope & stick joinery and diet plywood

[Stan Calow]

Its been a while since I've made frame & panel doors using plywood panels. My router bits leave an honest 1/4" groove, while the best "1/4 inch nominal" oak plywood I can find around here is anywhere from 13/64" down to 3/16". Even my old "1/4" undersized plywood bit" was 15/64", which is what I expected to find. I see newer bits are 7/32".

How do you deal with a gap like that without a lot of cover up work? Not sure I trust shipping from somewhere.

Or should I wait a few more years when 1/2" will equal !/4"?

Thanks for input.

[Jim Becker]

Plywood is actually metric sized in most cases which is why the "nominal" doesn't match the expected. Some cutters either compensate directly or are "stackable" so you can use a groover that's more matched to your sheet goods. About the only thing you can "reliably" buy that's true 1/4" is MDF and that may transition at some point, too...you never know!

[Steve Jenkins]

If you can get mdf core instead of veneer core it wil be really close to 1/4

[Stan Calow]

Thanks. The MDF core stuff I can find is 13/64", which still leaves a visible gap. I do want to use my bit set. I'm not concerned about rattling, but about the visible gap. I consider using veneer strips, quarter round, or other thin pieces to fill or cover the gap, but that's a bit more fussing than I want to do.

[Jamie Buxton]

I bought a stacked dado set from Forrest which goes down to 3/16" wide. It works, but it wasn't cheap. There are also now adjustable slot cutter router bits which will get down to that thickness. I don't remember the manufacturer. There's been a thread recently about them, or google.

[roger wiegand]

Sounds like you either need a different router bit or to make the panels out of solid wood where you can cut the edge to size. I cut my door panel grooves on the table saw so I can make them the exact width I need without having to accumulate a whole collection of router/shaper bits.

[Jim Becker]

I kinda agree with Roger. And you are not alone in this...I have two cope/stick bit sets that are of fixed design and are more or less obsoleted since I bought them a couple decades ago, despite limited use. When I recently bought a T&G set, I made sure it was a stackable design to hopefully avoid this issue into the future. I think that sheet goods are not going to go back to the old full Imperial dimensions...

I'll also note that one possible solution is to lay up your own panels by veneering both sides of an "undersized" panel to get close to the 1/4" that your cutters support.

[Warren Lake]

3/8 and back cut makes a better door

[Jim Becker]

3/8 and back cut makes a better door
Yet another EXCELLENT suggestion!

[Rich Engelhardt]

Or should I wait a few more years when 1/2" will equal !/4"?

First off - - I use a Whiteside set w/a 7/32" cutter.
Even that can be loose with some 5mm stuff, so, I use spaceballs to make sure the panels are centered & put a few dabs of glue on the panels.

2nd - - I hear you loud and clear about the sizing of plywood & can NOT for the life of me understand why we, as a collective, are unable to do anything about it.
Better grades of plywood must be a sort of thing that woodworkers are about the only people (outside of cabinet shops) buy.
If we all got together and just flat out told the plywood industry we're fed up with the under sizing & boycotted buying plywood, I bet we could force them into stopping.
I know,,,there's two chances of that happening - - - Slim and None & Slim just left town.....it's nice to dream though...

[Warren Lake]

and while you re doing that tell them to cut 4/4 to the same thickness as when I started.

[J.R. Rutter]

You could laminate 2 layers of your thin plywood and back cut it. Pro: 2 A faces, works for any undersized material. Con: extra work, 2x the $.

I had my cutter sets done with 6mm tongue and groove. Most species of mdf core veneered panels at a nominal 1/4" fit nicely. Some species, like alder, come in at a true 1/4" and need a slight back cut. I do that with a radius back cutter set up so that the cut edges of the veneer barely fit into the edges of the groove.

[Stan Calow]

Thanks guys for sharing your thoughts. I'll manage to deal with it on this one time project. If I need to do it again, I'll look for a bit set with a smaller groove., which I didnt think existed. I thought about cutting back thicker plywood or planing down solid pieces (don't want raised panels) but time is a factor on this one.

I understand the metric size issue, and wouldn't complain so much about 15/64" as being close enough, but I just think calling 3/16" as 1/4" is downright deceitful. At 3/16" a panel is pretty close to cardboard to me.

I'm almost as disappointed as to how few places there are to look for any good plywood in my area.