I ran across an article in Machine Design Mag that discusses thread forming in some rather interesting detail, including the reason for the "double threads" mentioned below.
http://machinedesign.com/article/don-t-come-unhinged-over-enclosure-design-1023 Making large molds from AL we always cut threads and then inserted helicoils or other hardened inserts; 6061-T6, QC7, cast plate, didn't matter, if it had to come apart it had hard inserts. Share and enjoy, Dave cogoman wrote: > We use thread forming in 6061-t6 all the time where I work, and the > threads are quite strong (even when the hole was a little oversize). > What hasn't been mentioned is that as the hole becomes larger, the > forming tap creates a pair of threads, or a double start situation. The > second start is not purposely made by the tap, and is not as smooth, but > in some cases is just as likely to be the thread the screw starts in as > the intended thread. It is annoying, because the unwanted thread binds > up much more than the intended thread, but sometimes the intended thread > is harder to find, and in a production situation you don't have the time > to be trying to find the right one. > Usually even in the unwanted thread, if a 4-40 slot head screw grabs > 3 turns, the 6061-t6 will hold better than the slot in the head of the > screw. I can crank it down very tightly. > > On the issue of TOP/BOTTOM posting I must comment. > > It seems to me that the subject line should give enough context for > people to know what the thread is about. If most people get enough > context from that, then quoting the relevant context from previous > messages below will help the one who tunes in without prior knowledge. > If context isn't needed, then I get to the relevant information first, > and I can move on. If I'm commenting on a specific issue, the whole > message is too much information. I just need to quote the two sentences > that apply to my message. > > Here I'm only commenting on forming taps, so I don't need to quote > any of the previous information on cutting taps. > > I understand the need for in-line posting when commenting on a number > of issues raised. > > Bottom posting doesn't bother me, but it doesn't seem optimum. The > thing that does annoy me is when commenting on one small point one > quotes the whole 80 lines of text, when only 2 to 5 lines actually > provide the context for the comment. > > Just my 2 cents. > >>>> In all this fuss over how to machine tap no one has mentioned thread >>>> forming. The few times I've tried it by hand it has worked well. >>>> >>>> True, but one has to be very careful with threadforming if thread >>>> strength >>>> >> is important: >> >> >> http://machinedesign.com/article/internal-thread-strip-out-tests-yield-surprising-results-0113?page=0%2C0 >> >> shows that thread strength is critically dependent on hole diameter when >> threadforming, much more so than for regular threading >> > ------------------------------------------------------------------------------ > The ultimate all-in-one performance toolkit: Intel(R) Parallel Studio XE: > Pinpoint memory and threading errors before they happen. > Find and fix more than 250 security defects in the development cycle. > Locate bottlenecks in serial and parallel code that limit performance. > http://p.sf.net/sfu/intel-dev2devfeb > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > > -- David M. Wright 168 Thompson Street Springfield, MA 01109 (413) 233-4730 ------------------------------------------------------------------------------ The ultimate all-in-one performance toolkit: Intel(R) Parallel Studio XE: Pinpoint memory and threading errors before they happen. Find and fix more than 250 security defects in the development cycle. Locate bottlenecks in serial and parallel code that limit performance. http://p.sf.net/sfu/intel-dev2devfeb _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
