A mini router plane is fantastic for leveling the bottom of grooves, pockets, etc. This build was an idea I'd had for some time, and finally I put it into practice. It could be improved upon, and I'll explain how later, but it works quite well as it was made, and really was simple to make.

Supplies

Mild steel plate (4mm (5/32") thick or more)

Fine thread nut and bolt (say 50mm (2") long)

Complimentary taper tap to thread a hole in the steel plate

Hardwood to make the base (preferably dense and oily)

Counter sink (HSS)

Small countersunk head slotted screws

Pilot and clearance hole drill bits for screws

Drill

Files

Gas torch and vegetable oil for heat treating cutter

Bench grinder or angle grinder

Sharpening stone(s) and strop, or alternative sharpening system

PPE, such as gloves, eye protection, face mask

Step 1: Mounting Plate

Any shape base could be used, but I opted for a rectangular one; this allows the router to be used against a straight fence to guide the cutter.

Mark out the base shape on the steel plate, and locate the position for the cutter post pass through hole (I positioned mine dead centre).

It's easier to drill and tap any holes before cutting the base shape out; the larger plate being easier to clamp if you don't have access to a machinists vise (I did have a vise, so photo's show some holes bored using that to secure the work piece)

Bore the holes for the cutter post, and the base attachment screws.

Thread the cutter post hole to accept the bolt from which the cutter will be made.

Counter sink the other holes a little. Only go so far that the screw slots just reach the surface of the plate.

Mark a hole above where the cutter will be, which will allow shavings to escape. Bore and file out.

Finally cut the base shape away from the steel plate.

Step 2: Cutter

Grind the bolt head into the shape of the cutter. Basically this is like a narrow chisel tip that slopes a little down from the end of the bolt stem.

Notice the bright and multiple forking sparks produced at the grinder. This indicates that the bolt is of high carbon or tool steel, and suitable for heat treating, which will extend the life of the sharpened tip.

If your bolt is suitable, heat treat the cutter by warming from the heal until the tip reaches a cherry red colour, and immediately quench it in a pot of vegetable oil. Continuously, swirl the heated cutter in the oil for at least two minutes, and then leave it in the oil to completely cool down.

Use whatever sharpening system you prefer to flatten and polish the bottom of the cutter, and hone the edge of the cutter tip. I prefer to finish by stropping the tip on a leather strop charged with polishing compound. The edge produced should be able to easily shave hairs from the back of your hand, but do be careful!

Step 3: Base

Cut a base from the hardwood, and make a hole in it to match the circle described by the cutter rotating in the post hole of the mounting plate. Extend this hole to match the shaving escapement hole in the plate.

Attach the base to the mounting plate, with the screws, and saw off most of the excess, then file the edges flush. If you didn't countersink the entire screw heads, now is the time to file the heads flush with the plate (done carefully, the heads will virtually disappear).

Mount the cutter by threading it through the mounting plate, and locking it in place with the nut.

Step 4: Testing

Test the router by extending the cutter marginally below the base and trying to take shavings from a board.

The idea is to take coarse shavings with the escapement hole above the cutter tip, until close to the desired depth. Then advance the cutter by fractions of a turn to take finer shavings until you reach the exact depth you want.

Thanks for checking out my Instructable :)