Thursday, August 28, 2014

Life is a grind

Well, the bandsaw vise is working. I still need some blade adjustments to bet the thing to cut perfectly square. But this is for another day.  Today's post is about a grinder. Specifically I have a 4mm carbide end mill to deal with, for my Proxxon mill. The largest size collet I have for that mill is 3.2 mm which is 1/8" in RGU. So I propose to cut the shank down to 3mm to fit my next collet. I tried very hard to cut it down to 3.2 mm and failed. I cut a taper into it. Slipped in the collet.

Now you might say "you have a lathe, dummy! Just turn the shank down! Piece of cake!" Alas, the end mill is carbide. If I tried to cut it with even a carbide tool, I would ruin the shank, certainly the tool, and maybe even the lathe. Not an option!

The only way to do this with my equipment is with a toolpost grinder. But nobody makes one for the Taig. So I improvised one. I started with some 1/4" - 6.3 mm steel square bar from Lowe's. Nice nickel finish on it, too. The Taig toolpost takes this size. Ten second's worth of time with Handy Bandy cut it off. Then I milled the ends square.

 The basis for this gadget is the Dremel chainsaw sharpener. This gadget is lousy for chainsaw sharpening. But the Dremel screws into it. It is amazingly a metric thread, M19x2, which I cannot cut. It's very large and I have no such tap. So I bolted the sharpener bracket on my piece of bar. I put a dial indicator on the Dremel and on the chuck. Chuck ran out (was off center) .06 mm and the Dremel only .03. I was impressed by the Dremel. It took a lot of fiddling to get the holes in the bracket right in line.
In the end, it took a long time. The grinder does not like big cuts. Furthermore if the grinder axis is off-center you will grind a taper on the shaft. So you have to measure the shaft at root, middle, and end and adjust the toolpost accordingly. There is no way I can get a dial indictor into this setup, I sure tried enough, but no room. I practiced on a broken drill bit until I got the angles right. I wore out 3 grinding wheels in the process. Carbide is very hard. Also things tend to move. So it's grind, measure, reset, go again. Took, essentially, a full day.

But it worked. The new shaft fits, just, the 3mm collet, so I have a 4mm endmill at my disposal on Cecil B. de Mille.

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