Saturday, April 5, 2008

Getting the Hang of Machining 6061 Aluminum

What may have aggravated the problems was that mill vise was mounted to a tilting table (which lets you put the workpiece at any angle from 0 to 90 degrees). The tilting table wasn't quite as stationary as it should have been--I noticed that one of the holddowns was either breaking or broken. Even a little bit of motion of the tilting table, in conjunction with the leverage problem I previously mentioned of trying to machine a piece much taller than the vise jaws, would cause shaking. This would then allow the workpiece to vibrate up, and grab the cutting tools.

One of the suggestions was to build a "vise stop"--and here's an example of how to make and use such a device specifically for the Sherline mill vise, just like the one that I have. The primary purpose of a vise stop is to make it easy to put multiple workpieces at the exact same position relative to the cutting tool each time. Thus, you figure out where zero is on the first article, and you don't have to rezero your mill when you put the next workpiece in the vise.

The suggestion for using the vise stop was that it would prevent motion in the X-axis, while the vise prevents motion in the Z-axis. I can see using one on each end of the mill vise to prevent motion in either direction. I still think some taller vise jaws might help.

Anyway, I clamped down the tilting table a little more rigidly, and now I can mill the way that it is supposed to be done. There are still limits--don't try to take off more than .020" in conventional milling, and perhaps .005" in climb milling, but I only had a couple of stoppages while making some really, really beautiful cuts.

It's unfortunate that the early cuts were made with less knowledge, so I have a pretty clunky and ugly piece with a few finely machined sections. Oh well: remember IBM's motto about mainframe operating systems: build two; the first one to throw away.

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