Ply thickness RANT

[John Moorhead]

Folks -

Okay, Sunday afternoon.... Just finished a glue up, and don't really want to start a finishing project... So, how about a "shop job"? Sure, he thinks - How about building that set of drawers for the bench? Maybe get the crap off of the bench and into some drawers? Maybe? Got enough poplar and pine on hand? Yep, good! Got 1/2" plywood for the gallery? Yep, good! Not so fast, bubba....

Okay, I have several sheets of 1/2" ply... I take a look see, and remember that I got a set of plywood thickness bits from Grizzly as a Christmas gift.... Good chance to try 'em out making dadoes for the ply. HA!

Okay, WTF? I have 1/2" plywood. One sheet is 1/2" right on the money. Okay.. odd, but okay.. The other partial sheet is 23/32... That's what I was expecting. The third partial is just *under* 7/16, and the last sheet is something that is none of the above, although it *IS* exactly 9mm.

'Scuse me, but how the FAQ is this? I don't want to cut multiple width dadoes - that's a recipie for disaster.

Am I now to expect that 1/2 ply, er, 23/32 can't be relied upon, and I should expect something between 3/8" and a full 1/2"? This is NUTS. Especially at close to 50 bucks a sheet.

How does your scrap bin measure up? This really is a pisser....

John Moorhead

[Jim Bailey]

I feal you're pain (PITA actually). I just did the same thing today - went to cut a couple drawers out of cut off 1/2 ply from my scrap bin. Didn't bother to check it - all the stuff was from a recent trips to the borg. Two different sizes I didn't discover until the drawers didn't go together right. What as pisser. And of course there wasn't enough left to cut more - truly Murphy at work.

jim bailey

[Upscale]

No insult intended, but where have you been hibernating? Imperial measure, metric conversions and 1/2 dimensions in between both measurement systems have been flooding the market for several years now. Not sure if that's how it is down in the USA, but up here in Canada it's called Pot-Luck sizing as far as I'm concerned.

Personally, I think all the router bit manufacturers made some kind of back room deal to sell more router bits.

[Ba r r y]

Beat the conspiracy! Use the smallest size bit with a pantograph style dado jig to cut them all.

We'll show THEM!!

Barry

[John Moorhead]

Upscale -

Ho-kay.... Blame the victim - I've gotten used to 23/32" plywood which was

*apparently* at the time, supposed to be the *actual* thickness of the "1/2" ply after it had been finish sanded. Fair enough... But *why* now, are there a total of FOUR "sizes" of 1/2" thick stock? What kind of control at the mill gives you 1/2", 23/32", 7/16" and 9mm all grouped under 1/2" thickness....This is NUTS!

I think this follows the progression that 1" thick stock "means" somewhere between 11/16 and 3/4" - ah, EXCEPT for Redwood. 1x redwood had been somewhere between 11/16" and 5/8" except that now I get rough sawn boards that are *just* over 9/16". At this rate 6/4 will really mean "veneer" in a few years...

At the prices they're getting, I don't really care HOW thick it is, call it

1/2" and make it ONE thickness, between 3/8" and a 1/2"... I'll deal with it, but for chrissakes, don't make me play a shell game every time I want to knock together a gallery or box. Jeeezus!

I haven't had to get this creative with a ruler since I started measuring my dick!

John

[John]

Ain't modern technology great. I have two sheets of 3/4 $100+ mahogany that are not the same. If the veneer was any thiner, they would have missed. If you sneeze while sanding, you may ruin the whole project.

[Mike W.]

I've not been WWing for so long, but I agree. I've already run into this issue twice. I did get a nice tip from a magazine or online newsletter on the same day I had the first problem. I can't remember what the outlet was, and I know the extra work sucks, but it did work. Basically cut a slot in the ply and insert a larger-than-kerf strip to expand the size on that edge. It worked perfectly both times... both were shop fixtures so the innaccuracy didnt mean so much.

Thats a work-around.. and no excuse for the problem, especially when, as you say, you spend $50 a sheet. The alternative is to keep that micrometer with you when you head out to buy the sheet goods.

Thanks.

[Guess who]

Solution, old technology: Plant as many trees as you cut; more if you want to supply the rest of the world.

Problem: (No solution) Greed. Selfishness of a now generation.

We have about a dozen new walnut plantings. By the time they are of a useable size, our great great grandchildren might be able to build stuff. Hopefully they'll plant more before they run out again. The squirrels help, but they are losing the battle against pesticides and artificial fertiliser.

It's just come back to bite us in the backside ...again. Stop clearcutting, and learn to farm the trees. They used walnut and oak for firewood when clearing for the fields now farmed. They didn't know better; we should.

[Ed & Sue Beresnikow]

While I agree with the frustration over plywood thickness variations I think we need to keep some perspective here.

Isn't a 23/32 thk sheet a thin 3/4 inch or fat 11/16? Not really in the

1/2 inch range?

Plywood these days is manufactured to metric thickness specifications and unfortunately also allow the variations that we trip across. Much is dependant on the type and then the finish quality including sanded and unsanded.

In the case of 1/2" ply it will be sold from 11 thru 12.5 mm (~7/16" thru ~1/2") and at 3/4" the range is broader with 23/32" being smack center at 18.5mm. Check any ply manufacturer site for details.

Sadly none of this is of help when trying to complete a project using left overs and often even with separately purchased panels. I have seen a few tips to use tapered shims to tighten panel to dado fit but this doesn't fit my mind as a 'quality' solution.

... or as is always said double or more measure panel thickness before cutting the dado one by one ... groan :-(

Ed

[Frank Ketchum]

Don't do that when I have just taken a drink of beer! I guess that is the explanation for your last name.

Frank

[Todd Fatheree]

OK, I'll pile on. This happened to me not long ago, but for me, it was on "identical" sheets that I purchased at the same time. I didn't realize until I was about to glue up that I had basically two different thicknesses. I had done my test fits from pieces that were from one sheet and then cut all the dadoes based on that. I'm with the other comments...I don't care if it's 15/32 or 12mm, just make it consistent within a reasonable tolerance.

todd

[John Moorhead]

D'oh! Yes, 23/32 is "3/4"... I just had it on the brain... I guess I mean

15/32, or perhaps 29/64 or 59/128ths, ad nauseum...

I guess I'm getting the same disease the lumber mfrs have... you heard what I said, but you weren't listening to what I *meant*... rrrr...

My rant still stands, tho'...

[John Moorhead]

Okay, sure, *now* I'm greedy to boot! I'd venture a guess that over a year the total amount of wood used in project by rec'rs as a part of the whole is probably less than the volume of sawdust produced at furniture mills on one afternoon in Vietnam.

Many of us have woodlots, others buy locally from millers or locally. You want now that we should plant a forest full of saplings and will the whole mess 3 generations down the line with all of our tools to boot? What do we do then - sit in the corner and whimper?

I use FSC or sustainable woods when they are available and I was a cheap SOB

*LONG* before it became ecologically hip to do so...

Now, go put your on your Birkinstocks, hop in your Prius and hie yourself down to Starbucks. Then head over to the compassion center for a group hug and stragety sessions for '08. Do this if you wish, but don't you *dare* make assumptions on my behalf!.

If you don't have anything to contribute other than telling me to plant some trees (D'oh!) then pardon me in advance, but STFU!

Lordy!

John Moorhead

PS: As an aside, I wonder how much paper got wasted printing up flyers and posters for Earth day? So much for mindfulness... Bless their pointy widdle heads...

[Mark & Juanita]

... snip

Don't you mean 15/32? 23/32 would be for 3/4?

+--------------------------------------------------------------------------------+ The absence of accidents does not mean the presence of safety Army General Richard Cody +--------------------------------------------------------------------------------+

[JeffB]

Having experienced your exact problem, and not possessing the "plywood" sized router bits, I've been very happy with the router jig

- manufactured by Accurate Woodworking Tools It automatically sizes the dados to the exact thickness of the plywood (or other stock) that you have, using a standard 1/4" or 1/2" router bit.

No connection to either company, just a satisfied woodworker.

[Todd Fatheree]

It

Well, that's all well and good, if all of your pieces are the same size (but just not all 1/2" or 15/32" or whatever). When you're making a cabinet, it's really tedious if all your dadoes have to be sized individually. DAMHIKT.

todd

[JeffB]

If you've got different thicknesses of stock - ply or otherwise - the only way to make good fitting dados is to cut them (or shim them to) slightly different widths. Even if you have different thicknesses of ply, this little jig will allow you to cut snug dados - of varying sizes, if necessary - very quickly. Try doing that with a dado stack or special sized router bit...

I know it would be easier if ply was of consistent thickness, but sometimes it just isn't. There can be thickness variations within a single sheet!

[Another Phil]

Ed:

Thanks for the Plywood industry info.

I had always assumed the plywood thickness problem was caused by that North American Treaty thing (NAFTA ??) and the high volume of Plywood being imported from Canada. (Canada being on metric standard, and exporting to Asian countries also.) Being a low volume plywood buyer, I just noticed the problem back in the 90's when NAFTA was passed and put two and two together and I guess I got 6.

I was wrong. Sorry Canadians, I guess it is not your fault after all.

Phil

[Prometheus]

I feel your pain... How about putting a rabbet on the edge of the ply to get it to a consistant thickness as a technique? Not only makes takes the guesswork out of the dado width, but the shoulders cover up any little nicks the router might happen to make if you get a little shaky at the wrong moment.

Aut inveniam viam aut faciam

[WillR]

I will file your note along with the recent letter from Newt Gingrich.

:-)