Birds Mouth Router Bit

Reading a past issue of WoodenBoat magazine I discovered the birds mouth joint. It is used to make hollow spars (masts, booms, etc...). I got to thinking this would make a wonderfully light shaft for a double paddle. One problem though, I don't have a bench saw... well not one accurate enough to do this kind of joint. Lee Valley sells router bits to cut this joint but then I though hummm for an eight sided spar the angle is 90deg, right? So with that in mind I started making my own router bit with a 90deg cutting face.

I made the body out of H13 steel (wonderful stuff) and I've silver soldered two bits of carbide on it. You can see in the photo I was kinda messy with the silver. No worries though it'll clean up nice. Then it's on to the cutter grinder to give the carbide bits their cutting shape and clearances.

One of the wonderful things about H13 is that when you're soldering get the body to a nice red heat. Once the soldering is done clamp the piece in a heavy vice and it'll act as a heat sink. Now if the part cools down fast enough (not too fast or the soldering 'll have stresses in it) it will harden to 40/45 Rc. That's the perfect hardness and toughness for a tool shank and body. Wonderful isn't it!