When the cutter reaches the center of the tenon, it stops cutting, therefore it will repeat the size indefinitely to within about .002” every time and it only takes seconds instead of minutes to precisely size a tenon!
To use the tenon tool adapter: First, true up the tenon by rough turning the tenon leaving 1/16” stock for the tenon cutter to cut. (I simply turn the tool upside down and use the scraper as a scraper). I then simply place the bottom of the guide finger on the tool rest. Then guide the tenon tool onto the tenon and let it cut until it stops.
Remember that the “guide finger” rubs on the bottom of the tenon, so the friction will tend to pull the tool into the cut, so it is best to hold back on the tool as it cuts. In order to reduce the friction, rub the top of guide finger with wax (parafin/candle wax) or a bar of soap to act as a lubricant. You don't have to do this for every tenon and it won't coat the tenon with wax. You will quickly learn when and how often to lubricate it. (Rub some on your tool rest occasionally too, to make your tools slide easily.)
To adjust the tool size: The guide finger is bent/milled at a 30° angle, so make a test cut. Measure the size with a vernier/micrometer and assess the size the tool is cutting. If it is cutting small, move the adapter back the appropriate amount. (If the tenon is 0.008” small, move the adapter back 0.008”.)
I use a 1/2" round nose scraper and grind it to a square nose at anywhere between a 70 and 45 degree angle. The steeper 45 degree angle gives the scraper more of a shear rather than scraping cut.
To care for the tool: The adapter is soft mild steel, so treat it with care. Don’t drop it or bang it around and put nicks/dings in it. The thin plating will wear off, so rub it with wax before putting it away so it doesn’t rust and it will be pre-lubricated for the next use!
I've had a few days to make tenons of many sizes. The tool works wonderfully. I thought the claim of reproducible size within .002" was optimistic - as you know, it does it time after time.
John Wolf; May 23, 2014
This tool is an adaptation of an antique production turning tool that went out of production about 75 to 100 years ago. The original tool was a dedicated tenon cutter. This newly designed tool is an adapter used in conjunction with a standard or heavy 1/2” square nose scraper so you can remover the adapter and use the scraper by itself.
A Bedan tool may be too thick to work.