Plywood Router Bits and Spiral bits

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Forum topic by rantingrich posted 01-03-2015 02:41 AM 1066 views 0 times favorited 8 replies Add to Favorites Watch
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372 posts in 1583 days

01-03-2015 02:41 AM

I have a new issue I have never come across. I plan to make more use of my New Dewalt router. I only have some round over bits at this time. I plan to do a lot of Cabinet work using plywood of course.

I need to buy some straight bits, the typical 1/4, 3/8, and 3/4 for now.

I have read some stuff about special router bits that are more closely matched to the TRUE dimensions of todays plywood. I do not know if that means the bits are larger or narrower than the typical 1/4, 3/8 and 3/4 plywood thickness.

1) Does anyone have any experience using these bit?

2) Does this issue exist for say typical Home Depot/lowes consumer Pine plywood AND the more expensive Birtch, Oak plys? Are ALL the different grades of Ply NOT exactly what the thickness should be and one should use these special Router bits?

I have noticed when using a Dado blade on my table saw say for 3/8 ply that if I set up the dado for exact;y 3/8 wides the ply is loose.

I also wish to buy some Spiral 1/2 shank straight cutting bits to do some Mortises. Any suggestions on brands there?


-- Rich

8 replies so far

View runswithscissors's profile


2927 posts in 2263 days

#1 posted 01-03-2015 02:52 AM

In their never ending quest to shave pennies off of costs (presumably), the manufacturers have taken to cheating the buyer out of abut a 1/32” of wood. So the bits for plywood are all narrower than the nominal size of the plywood. Grizzly has them, but I think all router bit makers supply them.

When you’re in at the Depot, check out the posted dimensions. Often they will give the actual thickness, such as 23/32” for nominal 3/4”.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

View kdc68's profile


2692 posts in 2514 days

#2 posted 01-03-2015 02:53 AM

Yes I own a straight bit set for plywood. These bits are 1/32” smaller than 1/4”, 1/2”, and 3/4”. If I find my “special set” won’t work with say 3/4” plywood, then I use a 1/2” straight bit and route a dado in the carcase, and route a rabbet in the shelf member that removes just enough material to leave a 1/2” tongue to fit the dado in the carcase.

I recommend Whiteside spiral bits

-- Measure "at least" twice and cut once

View Ger21's profile


1075 posts in 3369 days

#3 posted 01-04-2015 05:59 PM

You really need to measure the thickness of the actual plywood you’ll be using. In our shop, I’ve seen thickness vary by more than 1/32 between sheets, in a batch of 120 sheets from the same manufacturer.

-- Gerry,

View Fred Hargis's profile

Fred Hargis

5236 posts in 2731 days

#4 posted 01-04-2015 06:20 PM

I’ve same plywood vary in thickness within the same sheet. The plywood bits can be a little hit and miis, but they are probably better than using the nominal 3/4, 1/2 and 1/4” bits ( they are always undersized). But making yourself a correct width dado jig like the one in the link or any of the other 100’s that are available will also be useful. (copy and paste that link)

-- Our village hasn't lost it's idiot, he was elected to congress.

View oldnovice's profile


7380 posts in 3605 days

#5 posted 01-04-2015 07:11 PM

My neighbor gave up woodworking because of his health issues so he gave me a set of “plywood” bits. These are straight bits, in a wooden case, by an unknown manufacturer. They work fine but there is too much variability in plywood to guarantee a perfect fit.

Then again, I use a lot of Baltic birch and MDO which is still the actual thickness as labeled and does not require a “plywood” bit so these bits don’t get much use.

-- "I never met a board I didn't like!"

View Kelly's profile


2187 posts in 3182 days

#6 posted 01-04-2015 08:27 PM

IF you have the right dado jig, all you really have to worry about is making sure your bit is undersized from the dimension of the dado you want. For example, I might use a 1/2” bit to make a 23/32” slot.

Dado jigs that rely on a pattern bit allow you to use ANY bit, providing the bit is smaller than the slot.

You, likely, aren’t going to make the dado in one pass, so running up and back requires only a bit more effort and will not oversize the slot (up the left and back down the right). In truth, I’d rather make two passes with a 1/2” bit than a single one with a 3/4” or 23/32” bit.

You can buy bearings and collars, then slip them on the collet side of the bit to create a slot the diameter of the bit. Of course, this solution will not work with spiral bits. You’d have to buy a spiral pattern bit.

This is the jig I use:

View Bill White's profile

Bill White

5148 posts in 4198 days

#7 posted 01-04-2015 09:17 PM

Don’t EVEN get me started on ply quality. You’ve gotta measure, measure, hope, measure again. Then, the router bits may be off as well.
GOOD LUCK. Use good glue and shims.


View rantingrich's profile


372 posts in 1583 days

#8 posted 01-04-2015 09:20 PM

Yes this last summer I used a dado blade set for 3/8 Ply for a bunch of drawer bottom for my shop assembly bench and never thought about it.

Some of the plywood was so Sloppy loose while ply from another sheet was too tight to even fit in the dado

-- Rich

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