On Saturday 04 July 2020 21:12:57 Jon Elson wrote: > On 07/04/2020 04:26 PM, Gene Heskett wrote: > > IIRC no sparks, 200 or so revs, could just barely hear it touching, > > peeled two strips down to the alu about 1/4" wide. Not at all > > impressed. Up to that point, I was watching a very thin cloud of > > steel dust drifting away in the work light and figured it would get > > to where it should be in about half an hour. I wound up doing it on > > the bench grinder with a glass of water to keep from burning my > > fingers. > > Unless you are whetting the edge on a scalpel, no need to > use diamond to shape a lathe tool. > > A coarse alumina wheel will do a fine job. > > Jon > That depends on how long you want that edge to last. On a wood plane iron, nothing compares to the edge that 12,000 grit rouge wheel leaves. I touch it up about yearly, and a touch is all it needs. On a piece of 3/8 HSS tool steel cutting alu, that mirror like finish goes away much quicker because alox is the 2nd hardest abrasive we have. That, and if cutting dry, the heat of oxidation of the chip coming off is 98% of the heat generated. The heat from the chip sliding off the top of the tool is nothing compared to the heat generated by the rapid burning of the freshly cut alu surface, both on the bottom of the chip as the airborn oxygen attacks it, and on the workpieces freshly exposed surface. If you can put the work in a dry nitrogen atmosphere, you can machine alu at 20x faster rates, and the swarf still won't burn you until its flown thru a couple foot of normal air. Water, delivered as a mist, possibly with other contaminants, even though its 2 parts oxy, is harder for the alu to oxidize rapidly than plain dry air. And if directed at the back edge of the tool, can easily extend the life of a carbide tool by 5 to 20x, depending on how fast you can get the alu wet behind the passage of the cutting edge. Microseconds count. So high pressure air pushing that mist is the key, not so much the quantity of water or mix delivered. As an experiment 20 years back, I had to make bearing spacer block to move a blower bearing out of the groove cut in the shaft by 50 years of its spinning in the fafner eccentric collar. About an inch thick and 5" square, I rigged a mister using safflower oil, all this on the only mill I had at the time, the teeny little hf I had cnc'd. Took about 4 hours working on a block bandsawn from a 7"x7"x24" of solid alu I'd found at one of our recycle places and stolen for a 40 dollar bill. And misted about 3 oz of oil. That block never got warm. But with that much oil in the air, I couldn't see the 16 foot length of the shop building and my lungs complained for several days. Its still under that bearing today, but that whole 1956 transmitter was turned off forever at midnight June 30, 2008.
Proving to me that keeping airborn oxygen away from the alu makes machining it much easier. But making that environment was harder than I thought. And hard on the human involved. I can certainly see why machining centers pump coolant by the hundreds of gallons peer hour, unless you get legionaires growing in the sump, much easier on the humans nearby. > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
