On Monday 15 June 2015 17:57:28 andy pugh wrote: > On 15 June 2015 at 20:33, Gene Heskett <ghesk...@wdtv.com> wrote: > > I've done quite a bit of googling, and read the older threads here, > > but the closest I've come is an included angle in the 14 degree > > area, or 7 degrees off axis in cnc terms. No one has discussed the > > effect of dissimilar metals that I have noted in skimming about 65 > > old messages or in the google outputs. > > It seems likely that the threshold angle is the arctan of the > coefficient of friction between the materials. > Looking in the tables, ( > http://www.engineershandbook.com/Tables/frictioncoefficients.htm ) > hardened steel on hardened steel, lubricated, has a mu of .11 so > should lock at angles below 6 degrees even with lubrication. > (which sounds plausible, though I am not sure about the lubrication of > a machine taper) > Dry aluminium on mild steel is listed as a mu of 1.05, so that > suggests it should lock at an angle of 45 degrees. > Its doubtfull I could get it clean enough for that, so I'd druther wedge it into place with a coat of copper colored neverseize & use the greased coeficients, which are not listed for that combo.
> Whether these would be half-angles or included angles I can't decide. I'm ambivelant too. So 7 degrees off the axis seems like a good first try. Thinking about the width, making 2, cyano glueed together, and then both sides machined in the center 5" to reduce its footprint width on the spindle sounds better all the time. Bonus points for machineing one side face with the encoders slots at the same time. ;-) Also a good way to get more precision there as my current encoder wheel is a 50 cycle wheel. With a 5i25 reading it, I could do 180 cycles and get 1/4 degree accuracy. Talk about overkill. ;-) There is lots of room for a 90 cycle disk on a 6" wheel. My 50 cycle is just a hair over 2" and took a mill of about .028" diameter to get close to a 50% duty cycle. Fragile little puppies at that size. Swimming in cutting oil because the brass sheet work hardened, but it worked if the right feed and a fresh mill per attempt. The last one was thinner alu, but was obviously harder stuff, it machined well so I quit and used it as the old screws in the mill were getting bad backlash again. That alu came out of a dishwasher door that had 2 panels in it, painted different colors so you could match the "kitchen decor". Too bad it was also a POS internally. Lasted about 3 years. So rather than price shopping, a Kitchen Aide replaced it, 6 or 7 years ago, still working like new. Sometimes you DO get what you pay for. 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) 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
