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Exact-Width Dado Jig

Cut dadoes to the desired width with the help of this handy shop aid.

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Comments (5)

Here's a jig for routing bookcase or cabinet-side dadoes that exactly match the thickness of your shelf stock. Better yet, no special bits are needed. Just use an ordinary straight bit and a guide bushing. (We used a 1" guide bushing and a 1/2" straight bit.) To start, cut a 3/8" rabbet 3/8" deep along the inside edge of both guide rails (A). Then complete the jig as shown in the drawing below. To customize the rails for a different bushing and bit, install them in your router, and trim the protruding lip of the rabbet in the guide rails, as shown in the Dadoing Detail. The remaining lip will now match your bushing/bit combo.

To adjust the jig for the exact width of your shelf stock, slip the jig over the shelf stock as shown in the Adjusting the Jig drawing. Pull the guide rails (A) tightly against the stock, and tighten the wing nuts. Slip the jig off the stock, and clamp the jig onto the piece being dadoed, centering the opening between the rails (A) over the marked dado on the side panel. Adjust the depth of cut with your router sitting on top of the rails. Start the router and make one pass with the guide bushing riding against one of the rabbeted rails. Make a second pass riding the bushing against the opposite rabbeted rail.

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Comments (5)

raybarker05 wrote:

I tried a pattern cutting bit. The dado was too wide. Seems the bearing wasn't quite the same size as the bit. Maybe a bad bit?? Don't know.

1/26/2012 09:15:44 AM Report Abuse

bjwisdom123 wrote:

Won't the bit cut into the side rail?

2/26/2011 03:36:54 PM Report Abuse

Eric Brigham wrote:

Good design. I might make one of these, but slightly tweaked: basically with a detachable base plate/lip on the guides (instead of that 3/8 reabbet) so I could use different size bits on the same jig.

12/4/2010 02:46:52 PM Report Abuse

jesse.roscoe wrote:

@harry_rutland: i liked your idea of using a pattern cutting bit instead, but then i thought of possible problems. suppose your 1/2 inch diameter bit has a 1 inch cutting length. if you want to make a shallow dado, you might end up with your bearing riding above your straight edge. and if you try to compensate by using thicker hardwood for your straight edges, then you'll be limited on how deep your dadoes can be(of course that part depends on your router's capabilities). just my 2 cents.

1/31/2010 11:06:11 AM Report Abuse

harry_rutland wrote:

Good idea, but why not use a pattern cutting bit? No offset calculations required.

11/2/2009 05:13:49 PM Report Abuse