Really novice question about dados?

[Teri McCarter]

I need to route a dado in a board to allow for another piece of plywood 11/16" to insert into the dado very snug. What size router bit would I use? We have a 3/4" bit but it is exactly that and you get slight gappage. Do I need to buy a 5/8" to get the desired result.
Please help!
Thanks,
Teri

[Mike Cutler]

There are router bits specifically for plywood thicknesses. Amana, Whiteside, and Freud have them. I'm sure that other maunufactures have them also.
Absent of a dedicated router bit, you might want to look at the MicroFence router jig. Very expensive, very accurate. It would allow you to start with an undersize bit, and sneak up on the exact width necessary.

[glenn bradley]

I have a set of "made for plywood" bits. The problem is plywood will be inconsistent. I had a fat 1/32" difference between two pieces of Baltic birch ply out of the same bundle. This small variance only really bothers me when it's time for a dado or rabbet. I made this jig in about an hour (plus overnight for the glue to dry) to solve my problem. Maybe something similar would work for you.

http://www.sawmillcreek.org/showthread.php?t=46406&highlight=Auto+Adjust

[Charlie Plesums]

I have the 23/32 router bit that is supposed to work for 3/4 inch plywood, but there is still a lot of variation in the plywood. Therefore, much of my dado work is with a 1/2 inch bit, with a separate setup for each side of the dado. The plywood still varies an embarrasing amount across the length of the dado, so when I glue up, I sometimes shove a putty knife in the side that will show less, to force the shelf (or whatever) to the more attractive position.

[Allen Bookout]

I really like that jig Glenn! I am going to build one tonight to use tomorrow.

Well forget that. I did not notice how late it is getting. I do not like to bother my neighbors past nine oclock with my power tools.

[Rob Bodenschatz]

Do it Glenn's way. I built a similar jig a few months ago & it works perfectly. You'll get a lot of good use out of it.

[Bob Aliano]

If you have a Table or Radial Arm Saw you can make progressive cuts to exactly the dado width you want. You can also sneak up on the correct width with an undersize router bit, say half inch in this case.

[Teri McCarter]

Thanks everybody. I really like that jig and I may just try making one. Howie, that trick is pretty cool and quick.

[Howie French]

Teri...

lets see if I can explain this right, I saw this trick in FWW.

if you are using a 1/2" bit, set your guide 1/2" further away from your
intended dado, then place a piece of 1/2" stock against your guide.
Then rout your dado with your router against the 1/2 " piece.

Now, remove the 1/2" piece and replace with stock the exact same thickness
as your intended dado. Now rout a 2nd pass. The result should be a dado
the exact thickness you intended (the width of the second piece you padded
out the guide with)

The trick is the first pass must be made with a smaller bit then the intended dado width.
So in my example you could use a 3/8" bit, just make sure all of my references to 1/2"
are changed to 3/8"

Does this make sense ?

Good Luck, Howie

[CPeter James]

You got it right. A great idea, why didn't I think of it.

CPeter

[Byron Trantham]

I saw a article recently about cutting datoes and it seems to work fine. If you want to cut a "3/4"" dato use a 1/2" router bit. Align the straight edge so the bit cuts one side of the dato. Now take a sample of the material going into the dato and lay it against the guide and the router against the material and finish the dato. The width should be dead on for the material you are trying to use regardless of the thickness.

[Charlie Plesums]

I saw a article recently about cutting datoes and it seems to work fine. If you want to cut a "3/4"" dato use a 1/2" router bit. Align the straight edge so the bit cuts one side of the dato. Now take a sample of the material going into the dato and lay it against the guide and the router against the material and finish the dato. The width should be dead on for the material you are trying to use regardless of the thickness. I bet if I followed your directions exactly, I would have two 1/2 inch dadoes with 1/4 inch between them.

I believe your trick would work if your first cut had a "filler" the width of the cutter (1/2") and the second cut had a "filler" that is a sample of your material going into the dado (3/4" in this example), thus moving the cutter over 1/4 inch (rather than 3/4 inch), plus or minus the variation in the actual plywood thickness.

[Byron Trantham]

I bet if I followed your directions exactly, I would have two 1/2 inch dadoes with 1/4 inch between them.

I believe your trick would work if your first cut had a "filler" the width of the cutter (1/2") and the second cut had a "filler" that is a sample of your material going into the dado (3/4" in this example), thus moving the cutter over 1/4 inch (rather than 3/4 inch), plus or minus the variation in the actual plywood thickness.


This why you paid the big bucks!:D I need someone to keep me in line. The idea is great though albeit changing bits is a pain.

[Hoa Dinh]

Teri...

lets see if I can explain this right, I saw this trick in FWW.

if you are using a 1/2" bit, set your guide 1/2" further away from your
intended dado, then place a piece of 1/2" stock against your guide.
Then rout your dado with your router against the 1/2 " piece.

Now, remove the 1/2" piece and replace with stock the exact same thickness
as your intended dado. Now rout a 2nd pass. The result should be a dado
the exact thickness you intended (the width of the second piece you padded
out the guide with)

The trick is the first pass must be made with a smaller bit then the intended dado width.
So in my example you could use a 3/8" bit, just make sure all of my references to 1/2"
are changed to 3/8"

Does this make sense ?

Good Luck, Howie

Teri,

Howie sums up the process well.

But since you mentioned you were a novice, and even for not-so-novice, I think a word of caution is in order....

Change the order of the two routing passes if needed so you don't "climb cut."

Follow the order of the steps described by Howie only either (1) the guide is on the left side of the router and you are pulling the router, or (2) the guide is on the right and you are pushing the router.

If either (3) the guide is on the right and you are pushing the router, or (4) the guide is on the left and you are pulling the router, reverse the order of the two passes. In other words, route with the scrap piece as the spacer first, and then route with the 1/2" thick spacer.

Someone please check this for me. I hope I didn't mess up the direction when writing this.