This was a fun challenging project for my wood working Guru, friend. He had inherited a 21" Hegner Scroll saw from his Guru when he passed but the key for it was MIA. I just got a little Craftsman 16" scroll saw for my BD and he was all excited for me and gave me a lifetime supply of thin stuff he put together for me...beautiful stuff, Mahogany, Redwood, beautiful grained poplar, red/white Oak, Birch, etc...Oh My! On top of that 2 boxes the Grand Master had started with double inlay dove tails.
His Hegner is a piece of artwork in machine tools, IMHO and he wanted an old style "Skate Key" for it. You can get a new fangled key for <$20 but has a plastic handle and it just doesn't cut it with a $2k saw, IMHO.
Here is what the new fangled keys look like.
I did some research and found some pictures of the old style and he gave me the head that it fits to match the square drive and Off I went.
The shank is made from 1/2" W1 steel and turned the head down to about 7/16" (.44) then turned the center down to about 3/8". I mounted the 3/8 section in a tool holder on the lathe and used my cutoff arbor and a 3"x 3/64 cuttoff wheel to cut the notch for the key wings.
Doing the broach was a bit more tedious! The square was odd size (.105 AF) which equates to .1485 across corners, so I used a number 38 drill (.1015) knowing I'd need to open it a skosh. I then tried to make a broaching tool form a piece of tool stock but the Peanut (Mini Lathe) just didn't have the spizeringtom to get it done from the tale stock or the cross slide/compound. So I punted and used the Dremel and some tiny engraving bits to whittle it out to size. It was a Real Nice fit when I got it done despite the slight vortex affect you see in the pics. I chucked it back up in the lathe and put a shallow crown to it so it would slip in nice without looking or fiddling.
Next I had a piece of 1" x 1/16" CRS and cut the rough length and shaped it mostly on the belt sander. Center punched the 2 holes an drilled them. Mostly a lot of hand work to get the shape and fit into the shaft slot right. Then just silver brazed them together....then a lot more hand work to get it looking right.
The last thing I did was to heat treat the broached end to hold up to the hardened square head. Just heated it dark cherry with a Mapp torch and soaked it for a minute or two, then quenched in room temp water. A test with a file (All good) and little clean up and Whalah an old school Skate key for a Nice Scroll Saw and good friend!
One minor issue occurred when I heat treated it that I didn't think of. That was that the broach opened up maybe a thou or two, so it was a little looser than I originally had it. Basically because all the ducks lined up (grains tightened) in the structure it shrank the material, thereby opening the hole a tad. It works fine and he loves it but I will remember that next time I heat treat W1 for a fit like this.
Really enjoyed doing this project for a friend and hope others benefit from it here.