On Monday 05 June 2017 05:30:10 andy pugh wrote: > On 5 June 2017 at 02:22, <tom-...@bgp.nu> wrote: > > Currently I do that by cutting a diameter with the threading tool. > > I measure that with a micrometer and I enter the DRO value in the > > tool touch off for that tool (I have a routine that leaves the tool > > at the diameter after cutting so this works). But I am wondering, I > > don’t have a DIAMETER value in the tool table for the tool. Should > > I? Is a zero (or non-existant) radius value causing Linuxcnc to > > think the tool is longer than it really is when cutting? > > How do your numbers compare with line 502 of this spreadsheet? > https://docs.google.com/spreadsheets/d/1m5zkO9-SbQaYWbTPlQXJ2VA73Ys8Wg >WDrPk_rEukHc0/edit?ts=57064122#gid=0 > > (This is a version of the table I complied 20 years or so ago, but > modified to include the effects of crest and root flattening/rounding) > > The DXF file of the inserts shows a 0.05mm radius, whereas as the > web-page table shows 0.06mm. In either case the tip is rounded, not > flat. > > You might consider drawing the thread in CAD, with the exact profile > for the thread and grade required, and then fit an exact drawing of > the insert into it. That might answer the question of how to touch-off > and what to. > > It is an interesting puzzle, and I am another who will admit to > "creeping up" on one-off threads.
Even the "creep up" can lead to fit problems. I cannot buy an insert truely suitable for cutting a 50 TPI thread, all are tip profiled for much coarser threads, and rarely is the tip profile correct for a thread 3x finer than a 16 to 20 TPI thread. So the nuts I might make for a 50 TPI thread, I expect to have to drive with spanners, well lubed, as they'll need to round off the sharper tips of each the first time assembled. Yet 3 trips later, they'll need some thread-locker magic to stay put. Neither actually has a full bodied width of tooth. Whats needed is an HSS insert with a sharp tip that might be flattened about half a red one on a wet rouge stone. Cheap enough to bin when its dull w/o shedding a tear because the carbide version is so outragiously priced. The insert makers are not serving the market with what the market needs. 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
