Timber Frame Tools

When making a swinging gate out of natural cedar timbers for my deck, I had the need to make round tenons on the ends of some cedar branches.  If I was doing a lot of them, it would have made sense to buy a dedicated round tenon cutter that is driven by a power drill.  These are very effective and fast, but they are a little pricey for anyone making just a handful of tenons.

I was looking for a more affordable and less noisy approach.  I found it through a video from a very clever Japanese woodworker.

He uses an inexpensive shinto saw rasp mounted to a block of wood.  The wood keeps the saw rasp at a right angle to the worktop and keeps the rasp from scraping up the worktop.  He marks the tenon with the circle representing the diameter of the tenon (either using a compass or circle template) and then rapidly cuts with the rasp down to the line.  He uses a flush cut saw to clean up the shoulders of the tenon  and it is done.  Very simple, fast and inexpensive.

The added bit of cleverness is that by shifting the workpiece a bit off plumb, the tenon  can be cut at an angle to produce angled joints.

Why not use an ordinary rasp?  A few reasons come to mind:

1. Most common rasps have teeth on the edges as well as on the faces.  This would cause the rasp to dig into the worktop jig and would make it pretty ragged.  The more you used it, the less precise it would become.
2. Ordinary rasps don’t have holes to bolt them to the block of wood (important for keeping the rasp square to the surface of the worktop).
3. Since these round tenons are often used on wood that is more toward green than dry, the saw rasps are less likely to plug up with wet wood fibers.