In 2011 I posted an article on a kerfing chisel, a tool used to deepen the kerf in half-blind dovetails.
The idea for this came from a method used by Tage Frid, who used either a scraper blade or, as I viewed in a video, a section of bandsaw blade. The kerfing chisel was my effort at making a specific tool, rather than buggering up a prized scraper blade.
In the years since, I am aware of two similar tools, the first was by Ron Bontz and the second by Rob Cosman. Both are shaped like saws, complete with brass backs and scraper plates. They do the same thing.
Over the years I have received many queries how to make a kerfing chisel, and this posed a problem since I had made it from a steel gardening trowel/spatula. These can be difficult to find. I have been thinking of other ways to make this easier for anyone interested in rolling their own. This is what I came up with ...
At the moment I am testing out a few different sizes ...
Top is Jarrah and bottom is Hard Maple.
A few others ...
The parts include a scraper blade (these are 0.03" thick). I was curious to see whether this would create a problem when dovetail saws have a 0.026" kerf (0.02" plate plus 0.003" set, which is considered "fine"). A ferrule is made from brass tube.
Turn the handle, and then saw the slot for the blade using a bandsaw. Place the handle on a V-jig to hold it steady. Ensure that the shaft matches the depth of the ferrule (so that is bottoms out against the end of the handle). Epoxy everything together.
So why is a kerfing tool so useful that it warrants being made into a specialised tool?
Here is a half-blind pin board socket being sawn. Note the diagonal angle, which leaves half the socket ...
This is where the kerfing chisel is used: First clamp the ends of the pin board. The edge of the blade is squared (not bevelled like a chisel), but it has the potential to split or cleave a board. The clamp helps prevent this.
Tap the blade into the kerf, to full depth, moving towards the boundary line a little at a time - be especially careful with the outside kerfs, where there is less support.
I have been doing this for a decade and may have had 2 or 3 splits in all this time, mainly from being careless.
When chopping into the socket, the deepened kerf will make it easier to split out the waste ...
The blue tape makes it easier for older eyes to see lines ...
Cleaning out the waste is significantly easier ..
Removing waste leaves clean sides to the sockets ...
This is saw-to-saw cut ...
Regards from Perth
Derek