Cutting dados in 23/32 plywood? Cannot find 3/4" plywood...

[Justin Green]

Has anyone tried assembling casework out of the Chinese plywood that is the 18mm or 23/32" thickness?

The lumber yard where I purchased plywood last time has switched to buying the chinese made plywood and it is 18mm. I'm using a router and a guide to cut dados, but my bit is 3/4". The last project I built was with 3/4" and the shelves fit nice and snugly into the dados, and helped me assemble the project squarely.

Has anyone else run into this problem? I suppose I could special order an 18mm straight router bit, but this is just a bit frustrating. We have both big box hardware stores here and neither of them carry true 3/4, and the other lumber yard doesn't carry 3/4 anymore, either.

[Jaze Derr]

I didn't know that ANYONE made true 3/4 plywood anymore.

I would recommend sizing your dado to the true width using a scrap piece, and then using a 1/2" bit and making it in two passes. Build an adjustable dado jig for perfect fit dados, no matter what size stock.

[James Phillips]

Use an under-sized bit and sneak up in it. THere are tricks to make it repeatable. Use a straight board as your guide and cut a shim for the second cut instead of moving the board.

[Eric DeSilva]

Whiteside, among other manufacturers, provides undersized plywood bits in a lot of different sizes...

[Howard Acheson]

You have basically two choices. One is to cut your dado with two passes moving the guide board a hair between passes. Second, is to buy a new 23/32" router bit. Most router bit manufacturers offer that size or a set of three undersized bits so you can deal with nominal 1/4", 1/2" and 3/4" plywood.

[glenn bradley]

+1 on two passes. I have a couple sets of undersized bits but, the ply is so inconsistent, they are far from the perfect fit they advertise (no fault of the bit). I use a 3/8" upcut spiral and a jig (http://www.sawmillcreek.org/showthread.php?46406-Auto-Adjust-Router-Dado-Jig-Pics) for almost all dados involving sheet goods.

[Justin Green]

Thanks for the recommendations. The last project I worked on was just 6 months ago. Some built-in shelving for my wife's closet. As far as I could tell, it was true 3/4, and my 3/4 bit made the right size dados for a snug fit. I think the plywood was aspen?

Anyways, I suppose I will just order the bit, or a few of them.

[Greg Wease]

Another way to deal with variable thickness of plywood is to cut a rabbet on the end and fit into a smaller dado, say 1/2".

[Bobby Knourek]

23/32'' router bit at 19.00 delivered would save alot of time.

[Van Huskey]

Two passes or an undersized bit. I have pretty much gone to 2 passes as undersized bits only work (tight) about half the time.

[David Hawxhurst]

+1 on the two pass method.

[Joe Scharle]

Build yourself one of these and you won't have to even measure the dado. Like most have said, 2 passes. Also, works great for sliding DTs. Just open one end slighty and make one pass with a 1/2" DT bit.

http://www.ncwoodworker.net/pp/data/194/thumbs/Dado_Jig.JPG (http://www.ncwoodworker.net/pp/data/194/Dado_Jig.JPG)

[Mike Cutler]

Build yourself one of these and you won't have to even measure the dado. Like most have said, 2 passes. Also, works great for sliding DTs. Just open one end slighty and make one pass with a 1/2" DT bit.

http://www.ncwoodworker.net/pp/data/194/thumbs/Dado_Jig.JPG (http://www.ncwoodworker.net/pp/data/194/Dado_Jig.JPG)


Yeah baby,,,, I'm going to be making one of those.
I like it.!!
Thank's Joe.

[Rob Sack]

There's a company in Atascadero, CA called Her-Saf that makes great panel routers. They have a whole line of 1/2" shank router bits that will accomodate undersized plywood. Their bits include a 23/32 diameter bit, and they have other sizes for accomodating various "3/4 inch" panels besides just the 23/32 so that you can get dados that accept panels of varying thicknesses perfectly. They also have a system that I use that includes a universal 1/2" shank that is threaded to accept a wide variety of cutters, which allows me to fine tune a dado to accomodate the exact thickness of whatever panel I am working with.

[Ernie Miller]

Take a look at this website for a good dado jig. (http://www.newwoodworker.com/autodadojigpln.html) Easy to build and a lot cheaper than buying multiple undersized bits and hoping they make a correctly sized dado.

Ernie

[steven c newman]

If you have to use a tablesaw for dados, try using a few shims. For a 3/4" wide dado set-up, remove one chipper. Add a shim between the rest to get to the plywood's thickness. When done, label the shims with the size of the corrected dado, plus how many chippers were used.

DAMHIKT note: The old dado set I have (VA 6") is worn down enough that it already makes a dado the correct size. Non-carbide teeth, cutting way too much oak/ash, took a bit of the set off those old steel teeth.

[Chip Lindley]

Finally, mention of a stack dado set! Works great on the TS, or RAS, unless dados need to be stopped.

But, that adjustable dado jig for the router is a handy, dandy thing to have. Adjust the jig to the thickness of the Chi-Ply you are using, and every two-pass dado will be perfect!

[johnny means]

I prefer to make all my dadoes the same, say 1/2", then rabbet all the mating parts to fit. This ensures that any thickness variations have absolutely no affect on the fit of my joints. BTW Appleply makes true 3/4 ply, but you will bleed for it.

[David Cefai]

I have read that the official spec for plywood allows for a substantial undersize but hardly any oversize.

I live in a metric country and can confirm that the ply I buy is always thinner than the nominal dimension. The 18mm plywood referred to in this thread is probably a nominal 19mm and the OP's next purchase could easily come in at 17.5mm!

[abram godshall]

i just recently got the woodline router jig which does the double pass routine but have yet to use it. has anyone else used it and any comments on its performance?

[Rob Sack]

If you have to use a tablesaw for dados, try using a few shims. For a 3/4" wide dado set-up, remove one chipper. Add a shim between the rest to get to the plywood's thickness. When done, label the shims with the size of the corrected dado, plus how many chippers were used.

DAMHIKT note: The old dado set I have (VA 6") is worn down enough that it already makes a dado the correct size. Non-carbide teeth, cutting way too much oak/ash, took a bit of the set off those old steel teeth.

The Forrest stacked dado is intentionally slightly undersized and includes shims to fine tune the width of a dado.

[Bobby Knourek]

for small odd jobs, the two pass concept is sound.

Larger jobs find consistant material thickness and if the 23/32'' standard bit wont fit the bill...
Then send the size to www.woodworkerstoolworks.com (http://www.woodworkerstoolworks.com) and they will custom tip the bit at the same price as a new one.
You can even send in your worn out bits for a retipping and for half the money receive a better cutting tool than some of the imports are when new.
They use a radial relief grind, rather than a straight back grind, as well as a increased hook angle.
All work is guarrenteed.

[Kent A Bathurst]

I prefer to make all my dadoes the same, say 1/2", then rabbet all the mating parts to fit. This ensures that any thickness variations have absolutely no affect on the fit of my joints.

Bingo. Makes a cleaner-looking joint as well, IMO.

[Bill Huber]

I guess that I am one of the lucky ones that found an Accurate Guide. My dados come out just right every time, I just don't see why the company disappeared, they had a good product.

http://www.newwoodworker.com/reviews/accurateguidervu.html

[Rick Fisher]

The Baltic birch we get is still full dimension, but most other ply is sanded or metric.

The Dado stack with shims is the simplest choice..

[Curt Harms]

I bought 5 sheets of plywood from Industrial Plywood in Reading, PA. All 5 sheets were a full 3/4" by 49" by 97". When cut they stayed flat and with NO voids. Flat sawn R/O one side, birch the other. Around $70/sheet. This was a couple years ago. The point being that full 3/4" plywood does exist but you probably won't find it at a borg.

[abram godshall]

yesterday i used for the first time my dado-max with the blue max clamp using a festool router and it worked great! highly recommend it. you can buy it from woodline. i used it for 3/4" ply and it was easy to setup, learn and calibrate.

[Rod Sheridan]

Aren't the plywood standards for North America metric?

I was under the impression that all hardwood plywood made in NA was to metric thicknesses.

19mm would be almost exactly 3/4" and 18mm would be very close to 23/32".

Anyone work in the sheet goods industry and have some info on this?

Thanks, Rod.

[Jaze Derr]

Take a look at this website for a good dado jig. (http://www.newwoodworker.com/autodadojigpln.html) Easy to build and a lot cheaper than buying multiple undersized bits and hoping they make a correctly sized dado.

Ernie

I just made one of those this weekend! :) haven't used it yet, though. Used someone else's plans, but they are pretty much all the same thing.

[Paul Johnstone]

+1 on two passes. I have a couple sets of undersized bits but, the ply is so inconsistent, they are far from the perfect fit they advertise (no fault of the bit). I use a 3/8" upcut spiral and a jig (http://www.sawmillcreek.org/showthread.php?46406-Auto-Adjust-Router-Dado-Jig-Pics) for almost all dados involving sheet goods.

I'm not trying to nitpick, but I think you'd get much better results with a downspiral or a compression spiral bit.
The upspiral has a tendency to lift up/tear the plywood veneer as you are making the dado. I learned this the hard way.

[Norman Hitt]

I'm not trying to nitpick, but I think you'd get much better results with a downspiral or a compression spiral bit.
The upspiral has a tendency to lift up/tear the plywood veneer as you are making the dado. I learned this the hard way.

Downcut not necessary with "this" jig, since the guide edges are clamped directly flush to the cut lines, therefore the jig itself works similar to the splinterguard on a tracksaw. To see what I mean, clamp a short piece of plywood to the bottom of a piece of hardwood or MDF with a good square edge along the bottom and then make a pass along the edge with an upcut spiral bit and then unclamp the two and check the cut edge of the plywood.

Another plus for this type of jig is that sometimes plywood will have a slight bow in it (or even a large bow) that make it difficult to get an even depth across the length of the dado when cut on a tablesaw with a dado blade because of the difficulty of keeping the plywood pressed down flat on the tablesaw as it is pushed across the saw to make the cut. With this jig you can clamp the jig down over a panel keeping the panel flat resulting in an even depth dado across it's length.