If this is a 3/8 x 24 then I assume it is a UNF thread. As I understand it, UNF (and UNC) threads are part of the UTC system, but the specification for UNF and UNC threads is that UN threads typically have a flat root, with the option of a rounded root. The rounded root simply gives more clearance at the root, so is a benefit, but not a necessary feature. The root could be truncated H/4 from the theoretical vee at the bottom, to give the flat bottom, but the rounding extends beyond that, giving more clearance. Male UTC threads have a truncated flat top at the peaks, with a width equal to P/8 (or 1/8 of 1/24 of 1 inch, which is about 5 thou in imperial units. The reduction in theoretical OD is twice H/8. H is 0.866025404 x P, so about 72 thou. Your insert will cut beyond the flat root, so is fine in a normal duty thread. The pitch diameter measurement will guide you as to depth of cut.
UTC threads are metric, but expressed in imperial units, so the A60 insert, which I use myself, is a general purpose insert and may be a compromise between both systems, as well as across the range of pitches the insert can cut accurately. I have had no trouble with fit or finish using the A60 insert (or the A55 insert either). Marcus On 2 Jun 2017, at 16:36, tom-...@bgp.nu wrote: > There is a custom adjusting screw that I buy commercially and when I get them > the threads have a text-book geometry to them. That is, they have a small > flat top on the major diameter and small flat bottom at the minor diameter or > root. They are made to class 2 or perhaps even class 3. I know that these > screws I am getting commercially are made using single point carbide insert > tooling on a cnc lathe. > > I want to make a few of these myself and am cutting them using G76 canned > cycle on my Emco lathe (I have encoder on spindle, etc) using an Iscar > carbide insert 16ER A60 (link below). These are 3/8-24 thread and that falls > in the range of the TPI supported by the insert. We have spent time making > sure we have the tool lengths, etc dialed in as precisely as possible and are > trying to be very careful with our major diameter and thread depth, etc. > When measuring the threads we are within specification in terms of pitch > diameter and major diameter, etc but the geometry of our thread is very > pointy. That is the major diameter peaks are pointy (almost to the point of > being sharp) and the root appears to be quite pointy as well, seems to be > exactly like the pointy tip of the insert. So, the threads work fine for the > purpose but the geometry is bugging me. By the way, this seems to happen for > nearly every thread I have cut on the machine, but I haven’t cared as much in > the past as the screws have been for my own purposes, but this one will be > used in a product sent to customers. > > I am wondering if I am doing something wrong with the insert I am using or > what. Any thoughts? > > Iscar insert: > http://www.iscar.com/eCatalog/item.aspx?cat=5901944&fnum=113&mapp=TH&app=193&GFSTYP=M > > -Tom > > > ------------------------------------------------------------------------------ > 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 ------------------------------------------------------------------------------ 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
