Author Topic: Jig: Very simple very accurate way to make dados with a router, fast setup  (Read 2857 times)

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Offline martin felder

  • Posts: 115
I found a new way to make dados (could also apply to rabbets).  I can take and post pictures.  I like the option of making a mark-scribe on the workpiece using some of the Woodpeckers squares as to where I want the dados.  I can be sure it is square and I like the marking being visible.

Then, I use a Festool 1400 loaded with a 7/16 downcut spiral.  It is my experience and understanding that the downcut spiral has the least plywood tearout, but not as good of a chip evacuation as the uncut (benefit of the dust collection on the Festool).  I set the bit for 1/4 depth (could be adjusted). 

I place a rectangular block of wood up against another block of wood (the simple "jig" that is exactly the width of the distance between the edge of the rounded part of the base plate and the bit.

I line up the 2 pieces of wood to the marked line.  Very precise.  Then I clamp the block farthest from the line to my workpiece (hold down clamps) and then remove the "jig" block.

When I run the router along the edge of the clamped block, no tearout, and the cut is right on the marked-scribe line.  However, then I need to make another pass if I do not want it to be 7/16.  That is where these come in!

https://www.metals4uonline.com/tool-steel-flat-bar-stock-o1-SFLTSO1932x932

You can get metal bars in 18 inch length that are whatever thickness you want.  Say I want to make a dado for 3/4 plywood.  I use a 9/32 metal bar along the "fence" of the clamped bar, and on the second pass, the final width is the width of 3/4 plywood.  I can use different metal bars for different widths.  For example, 5/16 for a true 3/4. 

Very easy.  Very accurate.  Not too much wood removed on a single pass.  Also, I could not find a downcut spiral in plywood sizes, and so with this 1 bit, I can made dados from 7/16 to 3/4 with anything in between.  Just a couple blocks of wood, 1 bit, a couple clamps, and some metal spacer bars. 

For me that is better than a Festool track guide, Micro-fence, dado blades and shims. 

Just a personal preference.  FYI.


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Offline martin felder

  • Posts: 115
I got the idea for my "jig" from this excellent video



I used a straight bit from Whitesides, and got quite a bit of tearout compared to a downcut spiral.



Maybe I need a new straight bit!  However, I liked the idea of a downcut spiral with dust collection, which is supposed to produce the best cut in plywood, and if you want a dado for 3/4 plywood (23/32), you can't get downcut spiral in that size (or you can, but I failed to find one).  So, for my own version of this jig, I did something a little different.

First thing is I marked where I want the dado as shown (pencil to see, but scribe for more accuracy).



Then, I took a board and cut it to exactly the width of the distance between the edge of the Festool router and the edge of a 7/16 downcut spiral.



Then, I put it up against another board, to be the fence, and clamped that down to the workpiece as shown



That is a bit unlike the other jig in that the 2 pieces are not connected.  I then remove the wood spacer board and make the first cut.



One thing I like about that is that the entire baseplate is on an even surface as opposed to less than half.  My first cut is 7/16 wide and very smooth.  I can make it more than 1/8 deep without removing too much material on the first pass given that it is not the full width.

Then, I bought some spacer bars as shown.



With the 9/32, when I put that up against my clamped fence, that gives me on the second pass, a final width of 7/16 plus the 9/32 - 23/32 for 3/4 plywood



If I wanted a full 1/2 or 5/8 or 3/4, I would just use a different metal spacer bar, but the same bit and the same wood spacer.

The jig in the video is certainly simple and excellent.  One pass and your are done!  For me this is not better, just different and a personal preference variation. 


Offline eeeesh

  • Posts: 24
I basically do it the same way, but I just cut strips of wood instead

Offline ChuckM

  • Posts: 2789
Another no-math approach:

Drill bit shanks can work in place of the metal blocks.
« Last Edit: December 22, 2019, 03:59 PM by ChuckM »


Offline mkasdin

  • Posts: 475
You could set up a (gauge) block front and back behind a Festool track with a spacer to add to the exact width of cut using a couple of homemade wood shims. Then using a Festool router and guide rail run the dado. On the final exact width pass, just move the spacer out and push the guide rail flush to the gauge blocks. I’m not sure what Lewis was doing with the shallow dados? I’m pretty sure you need about 1/4” of depth to have adequate glue surface. I wouldn’t use drywall screw, except for drywall. I’m not big on pocket hole joinery, some people swear by it! The strips of wood are okay. Using an mft you could index the dado....
« Last Edit: October 08, 2020, 02:28 AM by mkasdin »