On Sunday 04 June 2017 21:56:46 Jon Elson wrote: > On 06/04/2017 08:22 PM, [email protected] wrote: > > I have to increase the depth a couple thou and re-cut the thread > > to cut it deep enough. > > Due to machine spring as well as workpiece deflection, a second pass > without even changing the X depth will take off some material. So, if > you turn it down, measure, and then feed in a few thousandths in Z and > cut again and get the desired depth, that will get you a too shallow > cut if you try to cut at the same Z depth on the next part. > > Jon
This I think is one of the reasons for G76 H parameter, where it makes H passes at the final depth, often called spring cuts. And I've noted that since I installed the shop made toolpost holder, replacing the springy compound, and tapered gibs on TLM, that the ending spring cuts aren't taking off a cut to speak of during the spring cuts, so machine rigidity does make a difference. I'll be somewhat surprised if, when I make my first threads on the sheldon, I see an actual cutting action after the first H pass. Even w/o tapered gibs, the huge H pattern to its carriages footprint should be more rigid than TLM's very narrow carriage footprint with the tapered gibs. But first I need to do the poor mans set-true on that 3 jaw, its running about 3 thou eccentric. I think it can do better. If not, I'll have to buy a 4 jaw independant and big bore backplate. 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> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
