Making rabbets with a router

I’m making another rack. I promised I’ll write about the finish of the first, tung oil, and shellac, and I will get to it eventually, but I want to write this before I forget.

As I mention in the rack post, all the joints are rabbeted, and with the first rack I did some with a table saw and a dado blade, and then some were impossible to do on the table saw, so I did them with a router. Also, the dado blade was tearing out some wood, so it really makes sense to do it all with a router. Here are my best rabbets:

Some aren’t as pretty and smooth but they’re pretty close, and with the glue and the piece that goes in the joint, it’ll all be invisible. These were done separately, meaning that the long edge was done first, and then the shorter one. I then squared the rounded corner with a chisel. I thought I took a picture, but I guess I didn’t. It came out pretty well I thought.

So here’s my method for making rabbets, but before I get into it. Yes, it’s safe to use a router on Baltic Birch plywood. I do not know if this will work with regular hardware store plywood, and I don’t know if it’ll work on Oak plywood that has a very thin top – I can see that tearing like crazy, but it works very well on the Baltic Birch, as you can see.

Width of the rabbet:

Pretty self explanatory, it is the horizontal distance in the pictures. I hemmed and hawed about how to set that distance in the best way, and here’s what I came up with. I measured the distance from the edge of the router base to the edge of the bit. It measured exactly 2.5″, and I’m sure it’s specific to this router (Porter Cable 690) and bit. So if I set my guide/fence at 2.5″ from the edge of the piece, then the bit will just slide along it. So now I add the thickness of the piece of birch. This birch is pretty close to being 3/4″ thick, but it’s not – it’s about 0.715″. Now I add the two measurements together (2.5″ + 0.715″ = 3.215″) and set my digital caliper to this length. Then I use my caliper to set the depth on my adjustable square. So basically, I use the caliper like I would measure depth (of course the measurement is locked in) and adjust the square so it’s perfect. Then I make two shallow passes with the router and check if the width is right by placing a piece of birch on it. I like it to be dead on (it almost never is) or for the piece to be a little shallower than the edge of the rabbet. So if the piece is really 0.715″ thick, then the width of the rabbet is maybe 0.715″. The excess can then be trimmed away with a flush bit with a ball bearing.

Depth of the rabbet:

First and foremost, do multiple shallow passes. I probably do 5-10 passes to get the depth. Try and remove a 19″ stretch of 3/8″ thick of Baltic Birch in one pass and your blade will dull and your joint will suffer.

I set the depth like I set the width. Measure 3/8″ on the caliper, and copy that to the square. My first rabbet will be exactly that and I’ll measure how far the bit sticks out by placing the square on top of the bit and see how the ruler end touches the base. When I have rabbets that are a corner, I do one edge first (mentioned that earlier), and make it 3/8″. Then for the depth of the other end of the corner, I just keep lowering the bit down, and I see how it sits on top of the rabbet I have already done. Obviously, power is off and the router is unplugged. I keep comparing and I like erring on the side of caution, meaning that it’s ok if the new edge is a little taller.