Thursday, February 21, 2008


I want to cut a bunch of thin grooves, about 1/2" apart, on a 30" length of 1" tube. Why would I want to do such a thing? That is a mystery that hopefully will be revealed in the future. I don't like to tell too much about a piece until it is done. However, at this moment, how hard could it be? Grab a length of tube, put it on the lathe, and cut some grooves, right?

The first problem is that my lathe (10" swing, vintage 1951) can almost, but not quite, take a 30" length of tube. OK, I'll change my design to 26". Still too long to fit in the chuck with a bull nose live center on the chuck. Hmm, maybe the new (to me) steady rest will be steady enough. Yes, I can see the smiles from all of you who know it is NOT steady enough. Wobbling away, way, way.

I then spent about 1/2 hour messing around with adjustments and a dial indicator to get it really centered in the rest. Still wobbles a bit even to my untrained eye.

All righty-rooty, change the design to 3/4" tube which will fit through my headstock. That should do it - and it does. Got the tube mounted on the lathe. This is a test piece so I just put on the first lathe tool that was at hand with an angled point.

Gee, is round tubing really round? Sort of, but not round enough to prevent the groove from being thin in some places and fat in others where the tube is slightly oval. If you look real close you can see I broke the very end of the carbide tip due to the initial interrupted cuts. By the way this test tubing was painted and the irregularity in the middle of the grooves in the picture is where the paint chipped.

Good thing I don't care how deep the groove is -- but it does have to look even. One contributor to the problem is the screw cutting tool. The triangular shaped cutting part cuts a fatter groove the deeper it goes. I need a rectangular shaped cutting tool rather than a triangle. The parting tool fits the bill but it is 1/8" wide and I want a groove that is around 1/32" wide.

Off to the industrial supply catalogs. Let's see .... groove tools, indexable groove tools, parting tools ..... Closest thing is a groove tool for cutting thin 'O' rings. Just the ticket, except for the tariff which is $43.12 plus shipping. Maybe if I wanted to do hundreds but I only want to do 40 or so grooves for a one-off. Order some rectangular HSS tool stock that will fit in my parting tool holder. Gotta make my own groove tool -- just like a real machinist. (to be continued).

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