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Discussion Starter · #1 ·
Now I know that 3/4 plywood is typically only supposed to be 23/32". However, I recently bought the Freud plywood dado router bit set and cut my very first dados with my hand held router. I had all my pieces cut to size and went to dry fit the assembly together. I have some beautiful 13 ply maple plywood and went to fit it in the dados and learned that it is actually 3/4". There was no way it was going to fit into the dado slot. Luckily, I had some 3/4 oak ply that I was able to cut to fit the dados, but come on! When is 3/4 ply 23/32 and when is It 3/4??? Is there any reason to this madness?

Btw, I had to hit the oak ply with a mallet to get it to seat into the dado. I really like the Freud set and nice tight dados.

Jeremy
 

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Plywood thicknesses can and do vary. Even though most plywood is typically 23/32 and 1/2" ply is typically 15/32, you should still measure it. Then do a test cut on scrap to ensure it does fit properly. Sometimes it's smaller then the typical dimensions as well. You're lucky though your plywood was thicker; a simple shaving in the dado would have made it fit correctly instead of it being too loose in the joint.
 

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I've had some that varied within the piece. This is more typical with Chinese ply, since it looks like they simply piles the veneers together and then try to force press them thickness. One occassion, I will now cut my dadoes too tight, and then rabbet the ply to fit...sure seems silly to have to work around such things.
 

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I've gotten maple plywood that was a thin as 11/16". I never run a dado a standard size. I allways measure the plywood I'm using at the time and then set up the dado to fit. It's possible the 23/32" plywood you were using was exposed to high humidity long enough that it swelled to 3/4" or it may have been domestic plywood which runs 3/4".
 

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Plywood thickness might depend on where you buy it, and how it's marked. Not all manufactures adhere or use a standard grading system. Domestically, plywood is generally graded into three groups. Decorative, construction, and shop.

The words "cabinet grade" are plywoods not graded by the HPVA. It is grading that uses an alpha character for both sides. It refers to plywood that could be suitable for building cabinets.

If you buy plywood that is marked "ANSI/HPVA", it has been marked as it applies to specific manufacturing standards. If domestic, it's likely ¾" thick, and likely you have face veneers .0625, or .040. The face veneer is marked with an alpha character A-C, and the back veneer is marked with a numerical character 1-4. Each of the grades has it's minimum standards for that grade. Decorative plywood is classified with this grading system.

Construction grades will have an alpha character for face values, and the backs can be numerical, or an "X" for "exterior".

Plywood marked otherwise is available for sale, and could have a variety of markings depending on the country of origin. Many just use an alpha character for both sides, but the overall grading may not comply with the standards set forth by the HPVA. That plywood generally falls into the "construction" category. The face veneers could look very nice, and be considered suitable for cabinetry, but there could be quality problems such as varying thickness, voids, odor, out of square, undersized (L-W).

Most plywood suppliers carry plywoods in varying species of face veneers that are referred to as "shop" grade. This plywood is accepted as being for whatever use you feel like using it for, but it's understood that it does not fall into the regular grading as "decorative" or "construction". These plywoods are like seconds, sold with the caveat that anomalies are present.

Plywood thickness should be checked.






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I've had plywood from the same stack vary in thickness enough to throw me off. Now I recheck each piece and take nothing for granted.
 

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Plywood thickness should be checked.
There's 2 different types/sizes of router bits for making dados in plywood. The regular dimension sizes, 1/2", 3/4" etc. like these:
http://www.infinitytools.com/4-pc-Plywood-Dado-Router-Bit-Set-1_2-Shank/productinfo/00-152

And the undersized bits like these:
Amazon.com: 3-Piece Undersized Plywood Dado Bit Set With 1/2" Shank, Whiteside# 470: Home Improvement

You will probably need both sets, since plywood varies so much from source to source and depending on the type, quality and grade.

That's the disadvantage of using one "exact" size" bit rather than the next size smaller bit and making 2 passes using a jig set up to fit your plywood dimension perfectly. Search - router dado jig and you'll find one.

 

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Discussion Starter · #9 ·
Thanks for the link. Now I have another jig to make. It's funny that I have been spending so much time making jigs and things for my shop that its hard to find time to do the projects that I have on my list. At least it gets me in my shop cutting wood and I have really enjoyed that.
 

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Thanks for the link. Now I have another jig to make. It's funny that I have been spending so much time making jigs and things for my shop that its hard to find time to do the projects that I have on my list. At least it gets me in my shop cutting wood and I have really enjoyed that.
Ha! Get used to it. I put off making jigs and storage. My work has been so so without a good jig. I always think to myself "a jig would be nice right now", but I never make it. Or "if I had that jig I could make that", but I don't. I'm finally now starting to add more storage and rearrange and wow is it amazing how much it cleans things up. I now have less on my workbench :)
 

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I have a jig similar to the one in the video. That video was my inspiration.

While not exactly like the one Marc made, it does work well for me. I have my adjustment knobs on top.

Sometimes I use the pattern bit to hog out the dado in several passes. Other times I use a guide bushing and a bit. I get good results both ways.
 
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