Best Way to cut Dados in Plywood

[Dave Falkenstein]

...Are there router bits with guides on the top portion of the bit? The only router bits I've seen with guide bearings have the bearing on the bottom of the bit.

Can't you buy a base for your router that works with PC collars?


Template bits have bearings on top, like these:

http://www.holbren.com/manufacturers...rid=3&catid=66

Not sure I'd cut dados with a template bit, however. Check that out before buying.

Here's another interesting bit:

http://www.woodline.com/c-33-bearing...o-cutters.aspx

[glenn bradley]

This is exactly what I was looking for!!! Only problem I see is that my router (Makita 3612BR) doesn't have a collar. Maybe I can use a bit with a guide on it with a similar jig. Any ideas?

First let me say that on larger boards I always prefer to bring the tool to the board. Although the jig I built uses a collar and I feel this is easier and more consistent, the original jig I stole the idea from used the edge of the router plate as the guide. The trick here is to put a mark on your router so that the same point on the plate rides the guide edge for the whole cut. My previous jig worked this way.

The build would be about the same except you don't need the collar shelf and the jig would need to be wider to allow for the router plate riding 'inside' the guides as opposed to on top of them. The reason I redesigned it was I wasn't getting adequate support for the router and did not feel confident while making the cut but it was definitely workable.

[glenn bradley]

Jim - I'm going to be cutting cross cuts so I'll be using a router and making a jig. I saw the jig that Glen Bradley posted and it looks like the one I'd like to make. However, my router (Matika 3612BR) doesn't have a collet. Are there router bits with guides on the top portion of the bit? The only router bits I've seen with guide bearings have the bearing on the bottom of the bit.

There are top bearing bits commonly called pattern bits. They will not be spiral but in your case you will have to trade one advantage for another. I went with a 3/8" bit as it meets most needs and had to be consistent for the jig. If you build a different style jig, I would use the largest bit diameter that would allow two passes. Maybe something like:

http://www.holbren.com/product.php?p...6&cat=0&page=1

[Adam Slutsky]

Thanks, I think I'm set. I'm going to build a jig similar to yours and buy yet another router bit!

Thanks to everyone who helped me with this.

Adam

[Joe Chritz]

I thought I had a pic but I couldn't find one.

What I use doesn't use a guide, just a regular base and a straight bit.

Take a piece of hardboard about 10" wide. Glue and pin a straight piece of 3/4 plywood about in the center. Just so there is a tad more than from the edge of your router plate to the center. Once dry run the router down the hardboard, base against the plywood. You now have a zero clearancer router guide. Make a second one and you can clamp one on you line, stick a piece of scrap between the second one and a small piece of shim stock (I used old playing cards last time) and clamp the second. No way to mess up the dado unless the jigs slip, plus it fits perfect everytime.

With fast action hand clamps it is faster then it took to type this. Plus it is all scrap material to build normally.

I will take a pic after lunch but won't be back in until dinner time to post it.

Joe

[Dwain Lambrigger]

Adam,

I just fininshed a toybox and entertainment unit using 3/4 inch oak plywood. I made a few purchases to do this, as I am a beginning woodworker, and they made my life a lot easier.

1. An adjustable "all in one" straightedge clamp
2. All in one router plate attachment
3. Woodcraft 23/32 (could be wrong on the size) flush trim router bit. They bill these as "plywood" router bits

These cost me about 70 dollars all together, but I only have to cut the dado once, and it is perfect for the 3/4 ply dado, and with the router plate, the bit cuts smoothly through the wood. Also, the clamping straightedge is great for several purposes. I won't be buying a dado blade for a while as this setup works really well for me. As was said by woodworkers better than me, there are a lot of ways to do this, but this way works perfectly for me.

I hope this helps, and good luck!

[Adam Slutsky]

Dave: Why wouldn't you cut dados with a template bit? I can get another base plate for my router - I think Lee Valley even makes a gadget that will allow it to accept a guide bushing. I've considered purchasing it. But then I have to wait for that to come in the mail and the additional cost etc etc.

[Jesse Cloud]

If you go the router route, butt the two sides of the carcass together and cut both sides with the same setup. Guarantees same location on both sides and lessens chance for errors.

[Danny Thompson]

Here is the dado jig I built for my router. It does not require a bushing.

I ripped one 12"-wide and two 2"-wide x 4' long section of 1/2" plywood. I glued and brad-nailed one of the 2" strips to the 12" panel, approximately 2" from and parallel to the edge.

I then put my router against the 2" strip near one end and glued and clamped the other 2" strip so the router base was fit snugly between the two strips. I repeated this process on the other end and tested my alignment along the full length to ensure there was no wiggle room. With everything lined up, I brad-nailed the 2nd 2" strip in place.

Then I closed the ends of with two 2" wide strips of 1/2" ply custom fit to fill the gaps.

Last, I installed my 3/4" straight bit in my plunge router, clamped the jig to the bench so the target slot area was off of the bench, dropped the router into the jig, plunged, and routed the 3/4" slot for the full lenghth.

That's it. Now, to cut a dado, I sandwich the workpiece between the jig and my workbench, align, clamp, plunge and route.

[Bill Huber]

You really don't have to build a jig to cut dados with a router.
I have a jig now the Accurate Guide that I bought just for cutting dados, but they don't make it anymore.

Here is the way, if I remember right, I cut dados in plywood before I got my jig.

To start as was stated if you can put all the parts together and cut them at the same time is best, you know they will be lined up just right.

Use a straight edge, I used an All in One clamp, clamped to the board.
With a down cut spiral router bit of 1/2 in., make the first cut with the normal base plate of the router. The down cut bit makes a very clean top edge.
Now lay a spacer that has been cut to the thickness of the plywood minus the 1/2 in router bit, and make the second cut. Now if the fit is a little tight you can shim the spacer out with a playing card or just make a spacer that is a little wider.

Drawing1.jpg

[Dick Bringhurst]

Adam, they make router bits that will cut dados to fit standard plywood thicknesses. this would eliminate the need for the jig. Dick B.

[Adam Slutsky]

Simple enough! I guess I could add another piece below and perpendicular to the slot so that it would be easy to line up the jig and the plywood.

[Adam Slutsky]

yes, but I still want to use more than a straight edge since I'm prone to screwing things up. Also, from what I've read in this forum it seems all plywood is not created equal and thicknesses vary. I like the idea of setting the jig based on the thickness of an existing piece of plywood.

[Joe Chritz]

Here is a quick pic of what I have been using. Obviously it would need to be clamped down with some hand clamps of some kind.

Not fancy but pretty fast and infinitely adjustable.

Joe

[Danny Thompson]

Adam,

Good idea about the strip on the bottom to help keep it square. I forgot to mention that I sanded the edges smooth and hit the inside edges of the 2" plywood strips with a little wax to ensure smooth operation.