On Thursday 21 May 2020 21:46:50 John Dammeyer wrote: > So I popped over to a friends to borrow a carbide 3 cutter face mill. > Alas the MORSE Taper draw bar fitting wouldn't work with my R8 to MT3 > adaptor. But the more rounded cutters gave me the idea to use my > green wheel on the carbide brazed cutter I was usingin the mid size > fly cutter holder. > > No difference really other than the cast aluminium tended to melt onto > the tip more easily. I had clamped a failed casting into a large > vise. > > Having seen my friends fly cutter bits (modified carbide inserts) I > started thinking about the amount the 1/4" shank cutter protruded. I > found a 5/16" HSS tool bit and touched up the tip. Then screwed it in > place. Ultimately I ended up using a set screw (long story) but all I > can say is Wow! > > http://www.autoartisans.com/mill/TestFlycut_1.jpg > > http://www.autoartisans.com/mill/TestFlycut_2.jpg > > Silky smooth. No light past a straight edge laid across it. With my > eyes closed dragging fingernail across it I can't feel the pass > transitions. Milling done by moving X axis. Last pass was 0.003" > DOC, 390 RPM, 2.1 IPM. About 2"diameter fly cutter. Overlap about > 0.2" between passes. > > So I suspect the 1/4" tool bit vibrated like heck as it grabbed and > cut the work and that's what did much of the scratching on the > retreating edge. > > John
More than likely the 1/4" tool was borderline dull, and flexing sideways, tipping its face. I have also found, when doing alu, that an HSS bit can be made much sharper than carbide on the powered rouge waterstone I sharpen wood plane blades with giving a much smoother finishing cut than carbide inserts ever thought of. Carbide inserts can be sharpened but take a huge toll on the rouge if not using a feather touch, taking a long time to get the mirror edge that HSS can be done to in just a few minutes. But you absolutely must have active coolant flow, mist working better than a liquid dribble, to keep the air away from your just cut surface to reduce the alox formation behind the cutters passage, which in turn eats the edge off your tool as it comes back around on thenext revolution. Its that quick if left dry, even with carbide as the alox from burning alu is harder than your carbide. That alox formation behind the cutting edge in less than a thousandth of a second is also the majority of the heat generated when cutting alu, far more than the friction of the cut, that heat is carried away by the chip being removed. Alu, in the presence of the 21% airborn oxygen is a very active metal, keep it sealed with a mist directed at the back face of your cutting tool so its wetted and sealed as quickly as possible behind the edge of your cutting tools passage. So I do roughing passes with carbide, but finishing passes with HSS. Another alu cooling method might be done by boxing the machine up in an air tight enclosure, and flooding the enclosure with dry nitrogen. That of course has its problems with operator safety, and doesn't work as well for steel though, due to nitrogen embrittlement and the flooding gas costs lots more. I probably should not have mentioned it except I've been around it since the '60's as its used to pressurize transmission lines on broadcast towers. Dried air is cheaper, but 50 yo copper still looks brand new when nitrogen is used in it, and the connection failure rates are vanishingly smaller. > > > _______________________________________________ > 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
