Plywood makes me angry....

[drumpriest]

Anyone notice that 3/4" ply, which used to be 23/32" is now quite a bit UNDER 23/32"?!?!?!?

It is a big enough pain in the butt to deal with 23/32" maths, let alone dealing with .691" or .702" per side!

GAH!

end vent.....

[cabinetman]

Depends where you buy plywood. I can still buy veneer core 3/4" with .0625 hardwood veneer faces. It isn't cheap and it doesn't come from the big box stores.
.

[LarryG]

Anyone notice that 3/4" ply, which used to be 23/32" is now quite a bit UNDER 23/32"?!?!?!?

Yes, I've noticed. Worse, the amount by which the thickness is "under" varies. Three or four years back, I had a project that needed a bit more material than one full 4x8 sheet would yield, and bought a supposedly-matching 2x4 "Handipanel" to make up the difference. Big mistake. I hadn't done that much arithmetic since grade school.

These dimensional discrepancies are one reason I think a set of undersized plywood bits are a bad investment. If you get lucky, the bit matches your material; if not, you're scrood. It's a lot easier, and the bit collection can be a little smaller, to just use an ordinary straight bit and make two passes to get the required width.

[docrowan]

Why is it that they went away from .750" plywood in the first place? Cost savings to produce cheaper plywood? Or does it match up with some metric thickness the rest of the world uses?

Another thing that is irritating is 3/4 MDF is still .750". One would think if they cheaped out the plywood they would cheap out the MDF as well.

[Uncle Cracker]

Heck, it's even worse when you consider that even variations in humidity can also cause ply thickness to change.

[vaking]

Why is it that they went away from .750" plywood in the first place? Cost savings to produce cheaper plywood? Or does it match up with some metric thickness the rest of the world uses?

Another thing that is irritating is 3/4 MDF is still .750". One would think if they cheaped out the plywood they would cheap out the MDF as well.

They are cheap and that's why they import plywood but not MDF. The rest of the world is metric and uses 18mm plywood. 18mm translates into 0.708". 23/32 is a very rough approximation. It is 0.718" rather than 0.708. If you want better numbers - use 45/64" or even 91/128". That gives you 0.703" and 0.71" respectively. This does not apply to MDF for a very simple reason. MDF is a cheap material made of scrap and it is heavy. For MDF transportation cost is higher than cost of manufacturing, which means MDF is mostly manufactured locally. Good quality material like plywood makes sense to transport, MDF does not.
I agree with Larry that plywood bits are a bad idea. If you really want to go this route - get an 18mm bit. Be prepared, however, that it may need router with metric collet.

[bthere]

I've gotten kicked on a couple of projects when two sheets of plywood are needed and they aren't the same thickness. It adds a whole lot of time and effort to get everything to work. To help get around this, one thing that I've started doing is taking a scrap board that has a couple of "standard" dadoes cut in it and then go through the stack of ply until you get sheets that fit the dadoes.

[cgallery]

To help get around this, one thing that I've started doing is taking a scrap board that has a couple of "standard" dadoes cut in it and then go through the stack of ply until you get sheets that fit the dadoes.

Not a bad idea, but I've had plywood where the thickness varied by 1/32" through the sheet. I think the name of the game is, "you can't win."

[chopnhack]

agreed, that is why I have sworn off BORG ply for anything other than shop or construction purposes. Our time has value too!