Wednesday, November 7, 2012

Steady part 2.

Still on the subject of steady rests for turning long whippy pieces. Now a lathe will turn to about .02 mm or a "thou," .001 of the width of Henry VIII's thumb. What a remarkable choice of a unit. Still, in those days the King's word was the law and we have not progessed much beyond that. Anyway, when you are turning long thin pieces the whip or spring in the piece far exceeds the accuracy of the cut of the lathe. If your lathe is good to .02 mm the thing will spring a whole mm so your accuracy is gone.

So I am trying to turn the threads off of a 1/4" threaded rod. My whole objective, as I related before is to put a leadscrew on the Taig lathe to allow me  precision adjustment along the bed. Taig uses a rack-and-pinion arrangement; cheap but inaccurate. But a 1/4 (6mm) rod is very whippy. I would rather use something around 18mm but I can't fit that through the bore of the Taig. So in this case we need steadies, and you might want (or not, but I will give it to you anyway) to see the completed arrangement.
We have both a fixed steady rest, which I described before, and a traveling steady bolted to the carriage. Both of these arrangements need refining, but they work. The traveling steady is a casting supplied by the Chalupy foundry, AKA John, but I did the pattern. And poorly. The more work you put into a pattern (wood) the less metal you have to move. Lesson learned.

The real problem in these rests is to machine the slots for the crews that hold these things down. In fact, the whole problem of machining metal is holding the work. The actual machining is easy, if only the work will stay put. So after many trials, unseemly language, and agony I came up with something that worked.

Here it is. The Taig has been fitted with the vertical milling attachment. An end mill sits in the 3-jaw chuck. An aluminum bar and some long screws provide vertical steadiness. Two pieces of steel square, barely visible, are held by clamps to my horizontal table. They keep the work form rotating around in the table. I wish I had an end mill exactly the width of the slot, but I broke it. You are not supposed to hold an end mill in a chuck but needs must when the Devil drives, as they say. You should use collets. But none of the Taig collets will hold my end mills. So into the chuck it goes.

 I finally got the blasted screw turned down. But alas, at last minute something went wrong and the hole in the mounting to pass the turned-down portion went wayward. I am in to re-making the mounting. Grrr.

After all this precision work it was comic relief to get Polecat, my mini-pole lathe (bungee lathe, actually) running  again.

It is nice. No motor. No fussing.  Immune to power failures. Excellent cardio workout. Just turn the thing! Made some improvements.

Polecat is doing a tool handle, of course. That's why I built it. Never can have enough tool handles. The handle happens to be for an Ulu. Whose? Ah, I won't tell.  Eat your heart out.

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