# How to Make dadoes for undersized 1/4 inch plywood



## MT Stringer (Aug 15, 2012)

I think I have mentioned this method before, but here goes anyway.

The culprit is 1/4 inch plywood. These days, it is less than 1/4 inch thick. And it can vary from one supplier to another.

There are several ways to cut a groove for this size to fit.

Make one pass on the table saw, then adjust the fence and make a second pass.
Use router bits made specifically for undersized plywood.

There is another method that I have found to work great. I used two 7 1/4 inch circular saw blades from the big box store. These are just the garden variety 24T blades made for ripping, and cost less than $10 each. Sandwiched in between the two blades are a pair of shims from my stacked dado set.

The blades are 1/16th inch thick. The combo of both blades and the shims make for a good fitting groove. If the thickness of the plywood changes some, I can change out a shim to adjust the width.

Here is my solution in action when mounted on the little DeWalt DWE7480 compact portable table saw. Makes for a smooth groove. :grin:

Hope you find this info useful.
Mike


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## hawkeye10 (Jul 28, 2015)

Great idea Mike. We are going to hve to come up with a title for you. You keep comming up with good solutions. I always look forward to your next post.


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## MT Stringer (Aug 15, 2012)

Thanks Don. I need to mention that I checked the blades for the maximum rpm...8500. So I was good to go.


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## JIMMIEM (Apr 4, 2010)

Good tip!!!! Thank You!!!!!!


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## 4DThinker (Feb 16, 2014)

Great tip! 

When I have 6mm plywood (.236") and no 6mm bit I'll use a 3/16" router bit and make one pass for the plywood. I'll typically go 3/16" deep as well. Then I'll lower a 3/16" bit in my router table, snug the fence up to it, and cut a shallow rabbet on the edge of the plywood to leave 3/16" to go in the slot. Not hard to get a nice fit, and the shouldered edge can be left on the bottom or side where no one will see it. 

A 3/16" piece of key stock set atop the bit and raised until flush with the plywood thickness is how I get the height set for a great fit. 

4D


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## Garyk (Dec 29, 2011)

A word of caution: I have the Whiteside bits for undersized plywood. Had a project for my granddaughter a while back and without thinking used the undersized bit. Works real well IF the ply is undersized but I was using cabinet grade stuff so the 3/4 ply really was 3/4. Had to switch bits and start over. Just saying...........but at my age small lapses of attention are normal.


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## The Hobbyist (Apr 25, 2015)

Wouldn't it be better to route the edge of the plywood down to a uniform 3/16" and then cut a dado groove with a 3/16" bit, making a nice, tight joint?


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## DaninVan (Jan 1, 2012)

*Three of a Kind*



MT Stringer said:


> Thanks Don. I need to mention that I checked the blades for the maximum rpm...8500. So I was good to go.


Have you tried it with 3 stacked blades, Mike?
Plus shims, would cover a lot of width spacing in around the 3/8" mark(?)...
Still a bargain. Rather than sharpening the blades, just relegate them to the circ. saw after they lose their like new sharpness.


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## DaninVan (Jan 1, 2012)

I tried one of my new 60 tooth thin kerf CMT 8" circ. saw blades on my TS (10"). It cut a beautifully clean and thin kerfed dado. I meant to measure the width of the kerf. 
Need to remember the printed side of the circ. saw blades is reversed to a TS blade. I almost put it on the normal way but realized my mistake in time. 
Nice tool to have in your arsenal, especially if you're cutting thin strips. Cuts waaaay down on the wastage!


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## MT Stringer (Aug 15, 2012)

The Hobbyist said:


> Wouldn't it be better to route the edge of the plywood down to a uniform 3/16" and then cut a dado groove with a 3/16" bit, making a nice, tight joint?


Why? IMHO, that's too much work, especially for 18 drawers. One single pass over this setup per piece and no messin' with the bottom at all.

Just sayin'


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## MT Stringer (Aug 15, 2012)

DaninVan said:


> Have you tried it with 3 stacked blades, Mike?
> Plus shims, would cover a lot of width spacing in around the 3/8" mark(?)...
> Still a bargain. Rather than sharpening the blades, just relegate them to the circ. saw after they lose their like new sharpness.


I only bought two blades.  I might have the original blade that came with my Makita circular saw, but right off hand, I don't know where it is. :frown:


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## DaninVan (Jan 1, 2012)

"...but right off hand, I don't know where it is."
No idea what you mean. 
(In my dreams)


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## DaninVan (Jan 1, 2012)

I just noticed...
Your motor is on the left, looking from the front? Direct drive?
The picture completely threw me:


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## MT Stringer (Aug 15, 2012)

DaninVan said:


> I just noticed...
> Your motor is on the left, looking from the front? Direct drive?
> The picture completely threw me:


Yep. Motor on the left. Same as the Grizzly, just not direct drive.


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## MT Stringer (Aug 15, 2012)

DaninVan said:


> I just noticed...
> Your motor is on the left, looking from the front? Direct drive?
> The picture completely threw me:


Check out this pic. See that yeller arrow? It is on the knob that secures the riving knife.


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