AW Extra 2/28/13 – 11 Tips for Dadoes and Rabbets

11 Tips for Dadoes and Rabbets

Perfect Dadoes Without the Guesswork

By George Vondriska

Dadoes and rabbets are two of the most widely used joints in cabinetmaking. Cabinets, drawers and jewelry boxes all lend themselves to this simple but strong joinery.  I’ve been woodworking, demonstrating and teaching  woodworking  for a long time. Over the years, I have accumulated some great tips for making and using dadoes and rabbets. 

 

Proper terms

Some people get pretty worked up about using the right word for the right joint. Perhaps they have a point since imprecise use of terms can lead to confusion. So, to be precise, here are the proper definitions:

A dado is a U-shaped, square-bottomed channel cut across the grain (see photo, top right).  

A groove looks just like a dado, but runs with the grain. A lot of people call a groove a dado I think that’s OK – but imprecise. 

A rabbet is an L-shaped channel cut across or with the grain. A rabbet is always cut on the stock’s edge. 

Make a gauge block

Setting up a stackable dado head to fit your plywood can be fussy and time consuming but, you’ll significantly reduce the guesswork by making a dado gauge block.  

To make the block, cut a  23/32-in. wide dado in a board big enough to allow for six more dados with space between. Add a single .005-in. shim to the 23/32-in. set up and plow a second dado next to the 23/32-in. one. Continue adding shims and making dados in .005-in. increments until you get to a 3/4-in. dado. Mark the dadoes as you go. 

To use, slip your plywood into the test dadoes until you find the perfect fit. Then, read the number of shims needed. 

 

Click any image to view a full size version.

Best dado depth

For years, I made all my dadoes 3/8-in. deep in 3/4-in. plywood. If I made dadoes on opposite sides of a divider, however, I had to change their depth and recalculate shelf lengths just for that joint. 

I’ve since learned it’s a lot easier and just as strong to set the depth of cut for every dado to 1/4 in. This makes calculating shelf lengths a whole lot easier, and I never have to make special calculations for a double dado. 

Lock the height

Always lock the blade-height handwheel before cutting. Vibration can make the handle turn, changing the depth of cut. This change is often hard to observe until assembly time. A big oops, if you just cut dadoes for a  kitchen full of cabinets.  

Cut rabbets with a sacrificial fence

A sacrificial fence protects your stock fence from damage. I make my fence from melamine because its slippery. I cut a 3/8-in. x 3/4-in. groove to accept a commercial featherboard. A scallop cut in the face of the sacrificial fence allows me to bury part of the blade.  

A featherboard guarantees accuracy

A featherboard provides consistent downward  pressure on the material right over the blade. This will compensate for a slight warp in plywood and insure a consistent depth all along your rabbet. I always use a push block to keep something between my hands and the unguarded blade. 

What's the right fit?

A properly fitted joint should go together with hand pressure. At the same time it should be tight enough to lift a modestly sized assembly without falling apart.  

Stagger the teeth

Rim blade teeth and chipper teeth are meant to nestle between each other. If they touch you can chip or knock off a tooth when you tighten the arbor nut. 

Cut rabbets slightly oversized

I cut the rabbet at the top of cabinet sides slightly wider than the top’s thickness. The top is used to set the fence so the dado head projects 1/32-in. past the plywood. This positions the top just below the cabinet side after assembly. To make the side flush with the top, lay the cabinet on its side and make a quick pass with a flush trim bit. 

 

Don't over-glue

Often we tend to think, ”If a little is good, a lot has got to be better.” During glue-up, this is definitely not the case. 

A brush makes it easier to gauge the amount of glue you’re putting down and where you’re putting it. Spread a uniform film that’s just thick enough so you can’t see through it. Keep the glue in the bottom of the dado or rabbet but off the sides. I find this technique prevents excess glue from oozing out of the joint during assembly. 

Use a caul 'n card

Guarantee clamp pressure in the middle of the joint as well as the ends by putting a playing card or two between the caul and the cabinet.  Tightening the clamps bows the caul and puts clamping pressure along the entire joint.

Sources

Note: Product availability and prices are subject to change.

Woodworkers Supply, woodworker.com, 800-645-9292, 3/8-in. Glue brush #875-247; Benchdog Featherboard #103-322; Push block #95-410.

Amana Tool, amanatool.com, 800-445-0077, 5/8-in. diameter x 1/2-in. flush trim plungerouting
(pattern) bit #45462; 3/8-in. diameter 1/2-in cut length flush trim bit #47102.

This story originally appeared in American Woodworker September 2007, issue #130.



September 2007, issue #130


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