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Posted by Sherman in Idaho [72.47.9.37] on Sunday, October 28, 2012 at 17:45:45 :
I have a neat little horizontal mill that was built from scratch by hand by my great-uncle. The tooling that my grandpa managed to salvage after his brother's widow sold his whole machine shop to a junk man for $100 included a few odds and ends of collets, mills, etc, but is missing a lot of stuff because my grandpa wasn't a machinist and didn't know what to look for. I'm not sure why he even saved the mill.
Anyway, the machine was built to take tapered collets and bits with tapered shafts that have a threaded hole on the back end of them. A long drawbar goes in from the pulley end and threads into the back of the collet or bit and pulls it into the head. I've never seen anything like this on any modern machine. It was clearly not his own invention because there's one big end mill that's factory-made with that kind of shank on it. The taper per inch appears to be the same as a Morse taper, as near as I can tell by laying one of the old collets next to a Morse taper facing the opposite direction and measuring the combined width with calipers. The trouble is that the diameter of a #2 Mose taper is too small, and a #3 Morse taper is too big. I would like to find a collet or adapter that will let me use modern 1/2" straight shank tools in this old mill. I did make a 3/8" straight shank adapter by taking one of his old collets that had some oddball end on it and very carefully boring it out to exactly 3/8". I can't make an adapter from scratch because I don't have a taper jig for my lathe.
So, my question is, does anyone know what I should be looking for? It appears that I need a thing with a taper midway between a #2 and #3 Morse, with a female threaded back end (ideally 7/16-20, but I can make a different drawbar easily enough) and something on the business end that I can either put a 1/2" straight shank tool in or put in a collet for such.
I've been googling around, but since I don't even know how to describe what I'm looking for, I haven't found anything. Is anyone aware of what they might have used for tapered-shank milling machine tools back in the '30s and '40s that had a threaded hole on the back end of them?
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