3/4" slot in plywood -- route or dado?

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I really need to route it because I need to plunge into it and don't want the slot the total length of the board.
Been a long time since I've done this, so can't remember if I can route that wide a slot (3/4") -- just 1/4" deep or even less, just enough to fit another piece of 3/4" plywood into.
Do they even make a 3/4" bit or would I have to do multiple passes for both the width and depth? (yuk).
thanks
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mkr5000 wrote:

Sure assuming your router is up to the task.
Altho w/ today's ply you'll more than likely want a 23/32" bit specifically for the purpose.
Even there you'll want to make a test cut and see if that matches the specific piece sufficiently well.
So, all in all, you may well want to consider one of two options -- use the narrower bit and make the cut in a couple of passes to ensure the proper fit or,
b) cut a rabbet on the inset piece of a specific thickness and use the proper bit size for it instead.
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You can buy a router bit for plywood, it's 23/32 as is 3/4 plywood. Always good for me.
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On 1/16/2010 12:12 PM, mkr5000 wrote:

Plywood is not 3/4" thick, and yes, there are bits that are sized for the thickness of modern plywood, generally around 23/32 for 3/4" plywood.
However, using a jig and a piece of the actual ply to set up the jig, can give you the exact dado size for a much better fit.
Leon has a jig that is excellent for cutting the dado to the exact fit, but I can't remember where the file is located.
I'm sure someone will jump in here with a url to it.
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I've posted a dado jig to ABPW.
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Assuming the OP is not using cabinet grade plywood you are correct. However, if the project does involve cabinet grade plywood then a 3/4" piece of plywood is 3/4" thick.
Gordon Shumway
Our Constitution needs to be used less as a shield for the guilty and more as a sword for the victim.
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wrote:

After working with probably 50 sheets of cabinet grade 3/4" plywood in the last few years, specifically Oak veneer plywood, I can tell you that 3/4" cabinet grade plywood is not 3/4" thick. It is very close to 23/32" as witnessed by my tape measure just now. At least in Texas it is that way and had been for years.
Now I will say that recently I have seen cabinet grade 1/4" oak veneer plywood that appeared to be a full 1/4" thick at Lowe's. I was shocked.
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wrote:

I haven't used 50 sheets of plywood in these last years, but I can tell you that's it's been well over 30 years since I've actually seen plywood that's exactly 3/4" thick. Between imperial and metric measurements, plywood in Canada has been every conceivable thickness except 3/4".
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Around here, 5x5 Finnish birch comes off the pile in 3/4" sheets.
Lew
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wrote:

Actual 3/4? What I get is typically closer to 18-19 mm IIRC.
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"Leon" wrote:

Yes, actual 3/4" for 13 ply.
Also, 1/4", 1/2" (9 ply) and 5/8" (11 ply).
All bets off on 4x8 shts.
Lew
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Cool..All I can find is actual metric.
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Same here, although it's actually just enough below 3/4" that it fits a 3/4" dado just nicely, merely needing the edge broken. Another reson to use the good stuff.
I don't use cheap ply much, certainly not for making cabinets out of. Repeatable results like this are just one reason. The only ply I've used lately has been some cheap Chinese stuff (sorry) for dy-lining the refurbed workshop, and the thickness of that wasn't even consistent from one end of the board to the other.
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"Andy Dingley" wrote:

According to one of my ply suppliers, the Chinese are shipping pure crap or at least they were.
I'm reminded of the old saw about the seller usually knows the value of what they are selling.
Lew
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On 1/16/2010 2:14 PM, Gordon Shumway wrote:

Actually, there is no "grade" of plywood termed "cabinet grade".
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Touch.
Gordon Shumway
Our Constitution needs to be used less as a shield for the guilty and more as a sword for the victim.
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On 1/16/2010 2:48 PM, Gordon Shumway wrote:

:) I buy a _lot_ of plywood.
As an example, the last 3/4" "hardwood plywood" I bought for a large kitchen project was "A-1 grade" Red Oak and was just a tad over 23/32" thick (.73) ... on a good day. :)
Since hardwood ply varies in thickness from lot to lot, even from the same manufacturer, I try to buy plywood for a full sized kitchen all at one time, and from the same stack, so that I can at least try to get an even average thickness.
AAMOF, and Leon will verify this, I ALWAYS carry a "project dado guide" in my truck for the projects that are currently in progress ... this is nothing more than cutoff stile with the project dado size cut in it that matched the thickness of the first lot of plywood bought for that particular project:
http://www.e-woodshop.net/files/projectdado.jpg
That way, and because I make all the face frames first, I can insure that any extra plywood that needs to be bought, from a different lot, stack, or retailer, will actually fit the pre-cut dadoes in the face frames already made up.
I do wish that this thickness variable wasn't in play, but it must be taken into account when doing any production type fabrication. :)
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wrote:

Seems like Hardwood Products refers to cabinet quality and paint grade.
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They're all right about the nominal vs. actual thickness of ply. Bits ... here ... among other sources:
http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/setstrgt.htm
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As mentioned, Leon... Oh that's me. I have designed a jig to route a slot to be exactly the width of any thickness piece of wood that you would want to fit the dado.
But! If you simply want to do the deed and be done you can use the principal that my jig uses and be done with it pronto.
What you will need,
1. A "Top Bearing" straight cut pattern bit. I was able to pick up cheap ones 1/2" in diameter for around $5-6 each a few years ago. 2. Two straight edges the length of the dado you want to cut and preferably at least 1/2" thick. Plywood works well for this.
What to do.
1. Clamp one straight edge exactly where you want the edge of the dado to be located. 2. Use a piece of the actual material that is going to fit in the dado and stand it on edge next to the board you just clamped. 3. Clamp the second straight edge up next to that piece of scrap. Basically what you end up with are two straight edges defining exactly where the dado will be and exactly the width of the material that will fit in the dado. 4. Remove the scrap material. 5. With the top bearing bit in your router plunge down between the straight edges until the bearing is below the top surface of the straight edge. Use both straight edges to guide your cut. The top bearing will ride along the inside edges of the straight edges. You will have to make a couple passes but do not move the straight edges until the dado is complete. When finished the scrap should fit perfectly into the dado.
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