On 1/24/2012 11:34 PM, Jon Elson wrote: > Kent A. Reed wrote: >> At best I'm a dilettante with machine tools and certainly I'm no expert >> with a lathe. That not withstanding, long, long ago, I was taught to cut >> a tapered thread on a manual lathe by shifting the tailstock over. It >> seems to me this would necessarily mean the thread pitch was measured >> "along the hypotenuse" since the line of motion of the saddle is >> parallel to that hypotenuse. >> > Right. and in fact it is wrong, by the definition of the thread pitch. > BUT, it is a small > enough error in most tapered threads as to not cause any problem. >> Not being able to imagine (I said limited brain, remember) how else they >> cut tapered threads on a lathe in the old days, I expect the standard >> specifications (ASME B1.20.1, fer instance) of the times would reflect this. >> > The proper way to do this is with a taper attachment, which WILL cut the > exact taper > parallel to the spindle axis. > > I think it is all in Machinery's handbook, of you have one of those. > > Jon > >
Well, yes I do, Jon, 26th ed. to be exact, but do I know how to use its index properly? Apparently not since I looked in all the wrong places before I posted my query. Now that I'm in the right section, American Pipe Threads, I see enough material reproduced from ASME B1.20.1 that I'm doubly glad I didn't pony up the 21USD to ASME's website so I could peek under their skirts. For all that, I don't see an explicit "definition of the thread pitch" in this section. There's use of "threads per inch" and of "pitch" or "p" but it isn't until the figure over Table 4 that I find an indication the thread pitch is measured along the axis and then only because of the orientation of the witness lines for the dimension labelled "2p". Quite a difference from all the explicit material in the screw thread sections. It's enough to make an old pedant like me pull some of what's left of the hair even though, practically, the error is quite small. Mechanics have persuaders, e.g., lengths of pipe to extend wrench handles, to take care of this (at which point my technician would exclaim "good enough for government work"). Once others had clued me in on the taper attachment it was easy to find illustrations on the Internet that make it obvious that using it one would cut the taper parallel to the spindle axis. Thanks, all. Regards, Kent ------------------------------------------------------------------------------ Keep Your Developer Skills Current with LearnDevNow! The most comprehensive online learning library for Microsoft developers is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, Metro Style Apps, more. Free future releases when you subscribe now! http://p.sf.net/sfu/learndevnow-d2d _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
