On Monday, August 15, 2011 07:49:47 AM John Thornton did opine: > That does sound pretty weak, perhaps more hole than should be done on a > mini mill. > > John > > On 8/15/2011 6:40 AM, andy pugh wrote: > > On 15 August 2011 12:28, John Thornton<bjt...@gmail.com> wrote: > >> If you want perfectly round holes get a boring bar. > > > > In some cases a boring bar will work less well than > > backlash-compensated spiral milling. > > > > And in the case of a Mini Mill (and this is a Mini Mill) the > > head/column stiffness is very different in X and Y directions, so you > > get ovality even with the slides locked. This can be partially > > compensated by taking tiny finishing cuts. When I built that new Z drive for my HF Micro Mill, I carved the bearing recesses in those alu blocks that you can see in the pix on my web page, with a 4 flute spiral upcut TiN plated solid carbide bit, switching to a fresh one for the last 2 or 3 passes.
Working with the backlash comp (adjusting that without having to reboot emc each time would be a god send) I was able to fit those ball thrust bearings that support the turning nuts to a snug, couldn't quite push them in by hand fit. There is still about a .0002" ridge detectable at the xy reversal points when the bearings were pushed back out so I could take the measurements that make the grease zerk's align with a small hole in the bearing race (and it does, I can grease them with no problems), but the feel of turning the bearing in my hand vs once seated, remained the same. Aware of the higher flex in the X direction, the column was locked down tightly once the Z position was arrived at, and the last cuts made with about a .0002" inch increment in the size per pass and the cut was kept swimming in cutting oil to slow the alox formation that dulls tools. Literally swimming, it was sitting on a sheet of thin plywood that held the cutting oil in the hole quite nicely. Maybe I was lucky, it worked. OTOH, my measuring tool at the time was a fairly fresh 6" dial caliper with .001" graduations, not golden by any stretch. I generally use a digital version now, but IMO they are sloppier. Maybe I got lucky, but it worked. As an ex Bro-in-law was fond of saying, it was good enough for the girls I go with. ;-) And my Z drive can now bore holes with emc as it has about 155 pounds of push. The OEM lashup of the Micro Mill binds to the column badly enough that it wasn't capable of more then 5 or 6 pounds of push, so the drill would sit and burn up. Cheers, gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Money may buy friendship but money cannot buy love. ------------------------------------------------------------------------------ uberSVN's rich system and user administration capabilities and model configuration take the hassle out of deploying and managing Subversion and the tools developers use with it. Learn more about uberSVN and get a free download at: http://p.sf.net/sfu/wandisco-dev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
