How to make a Router Plane
Router planes, also known as Old Woman’s Tooth or Hags Tooth planes, hold a blade below the sole of the plane and are used to rout out a recess or slot. They have generally been replaced by powered routers, but remain a handy tool for cleaning up a recess and create fewer ‘acci-dents’. They are also very easy to make.
To make one, first find a piece of hard, dense wood that is a few centimetres thick. Mine was a piece of macadamia wood about 3cm thick, and I would not want to go much thinner than this. Then mark out your favourite shape.
The shape doesn’t matter a lot. All you need is a block of wood with one perfectly flat face, a good sized hole, and some form of fastening mechanism. Some images on the web show a shape reminiscent of a ‘W’. This is the shape that I chose, and can be seen in the photo. In hindsight, handles with more finger room would have been better, and/or square sides would have permitted me to use a guide fence.
Cutting Out
I cut the blank to my chosen shape, and then rounded the various edges using a spokeshave and chisel. I used a 16mm (3/4”) and 25mm (1”) spade bits to drill out a tapered slot for the blade. This arrangement gives good visibility and finger access without compromising strength too much. I then drilled a ¼” hole through the back to take an eye bolt for holding the blade.
I made my own eye bolt from a piece of ¼” rod that I salvaged from a scrapped inner spring mattress. I first cut a piece of rod exactly several inches long and filed about an inch of rod to a half round cross section. I then heated it to red hot and forged the flattened end into a cup hook. Once forged to shape I cut the rod to length, threaded it, and chiselled out a recess in the plane body to fit the head of the hook.
You could also screw in a bolt from the front of the hole, or glue and screw a block of wood to the top of the plane, and then attach a holder to this if you want.
Applying a protective finish to the wood is a good idea, and my preferred option is a coat or three of boiled linseed oil followed by a good lathering of candlewax softened in turps. This creates a good utilitarian finish that seals the wood from humidity changes and lubricates the working surfaces.
Making the blades
The plane iron is an Allen key. Allen keys are made from high carbon steel, and make good cutting edges straight off the grinder, provided that you don’t ruin the temper by overheating (blueing) them. I made my first blade by cutting off the short end of a key at an angle, and squaring it up on a grinder (centre). This blade has a flat bottom and is difficult to use in a stopped recess like a mortise. I filed the bottom of the second blade at an angle (right) to remedy this, but this has created a weak point. I made the third (left) blade by heating and forging the blade to spread it and avoid the need to grind the sides of the key away. I also set the bottom of the blade at an angle to avoid the need to weaken the bend by filing. Once ground to shape, I rehardened the blade by heating it to a cherry red, quenching it in water, and then gently reheating it to draw the temper to a yellow/bronze. The exact temper colour is not vital, so long as the blade does not chip too easily (too hard) nor blunt too quickly (too soft). The temper colour is worth experimenting with, as steels of different grades do respond differently to the tempering process, and the guides found on the internet and in textbooks are generalisations that do not take specific alloys into account. Lastly, sharpen the blade, put it all together and you are ready to start using the plane.
A true 'hags tooth' blade does not have a toe on the blade, and points straight down like a chisel.
>> I have since found that you can also wedge a chip of wood behind the blade to set the angle, or angle the back of the hole in the plane body if you want to avoid all the metal working stuff. <<
Using the Router Plane
To true up something like a tennon, first take a block of wood with exactly the same dimensions as the piece you are working on (an offcut is ideal), and lay it along side so that both sides of the plane are supported. Then adjust the blade to depth, taking care not to take too thick a shaving. (A piece of thin cardboard or plastic set under the plane body can help in setting the shaving thickness.) Make incremental adjustments of half a millimetre or so until you reach the desired depth, and, as an Australian would say, Bob’s your Uncle.