Wednesday, July 21, 2010

Machining Aluminum, Getting Experience

I discovered that the beautiful parts that I made a couple of days ago are just a bit short for the tripod in question.  (Fortunately, I discovered this before shipping.)  I discovered that what had been the franchisee for Metal Supermarkets in Boise has moved to Garden City, and become Gem State Metals, and I went there to get some 2" OD, .125" wall aluminum tubing.  Instead of boring from 1.47" to 1.73", I just bought tubing that was already 1.74", and made one quick pass with the emery cloth on the inside to make it pretty.

But I also suddenly found that the easy time I had three nights ago squaring the 1/4" wall aluminum tubing didn't work with .125" wall tubing.  Why?  Same alloy: 6061 T6.  It turns out that:

1. Getting very precisely centered in the lathe is far more important with aluminum than acetal--probably because the aluminum isn't self-lubricating.

2. Boring the inside of the tube requires a relatively low speed, but a heavier cut, to avoid "chattering," which often leads to the part being pulled from the chuck.  But squaring the tubing requires a medium to medium-high speed, and at least until you get an even end, very light cuts, typically .005"-.010".  I wasted a solid hour figuring this out.

Experience, unfortunately, is among the most expensive things to get.  I just hope that this experience turns into something economically useful, unlike most everything else with which I have developed an expertise.

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