2008/5/22 Jon Elson <[EMAIL PROTECTED]>:
> Glenn R. Edwards wrote:
> > Jon,
> > I hope it doesn't appear as though I am jostling you for the final word,
> > however you pointed out a major difference between us hobbyists and
> > professionals. A professional must deliver a part in spec 100% of the
> time
> > ( six sigma- don't get me started...) no matter if the part was cut in
> the
> > cold morning or during a hot afternoon, if the part was mounted at the
> > center of the table or if mounted near the edge, if the machine was being
> > run by your best operator or the guy you hired yesterday.
> >
> > A tap can wear, but so can a thread mill cutter and probably faster.
> > However, thread milling introduces two additional tolerances that tapping
> > does not. Each of those tolerances can (and eventually will) produce an
> > unacceptable thread. A loose fitting thread can have a LOT less pull-out
> > strength than a properly formed thread. And, you might not be aware of a
> > loose thread unless you have a GO NO-GO gage. In my day job, I want
> tapped
> > holes from the machine shop (In fact, I am getting quite accustomed to
> > roll-tapping and the superior strength thread it produces). During the
> > weekend, I will enjoy making my own threaded holes with a thread mill.
> Yup, I have to say I do not do aerospace work, or much where a
> mechanical failure would endanger life or limb. And, I am not a
> job shop where all my parts wind up passing under the scrutiny
> of my customer's incoming parts inspector.
>
> On the other hand, I buy a lot of stuff that is SUPPOSED to be
> tested, and I have a little pill bottle full of screws with no
> threads or no recess in the head, and such like.
>
> My guess is that thread milling with a worn cutter will result
> in an under-size internal thread or an oversize external one, in
> either case the parts can't be assembled, rather than a
> too-loose thread.
>
> Jon
>
You've got the same problem with a worn tap.
Don't worry about thread mills, I know some uge industries that uses them in
full production. VCE, Scania, Saab Aerotech to name a few. They wouldn't use
them for the same reason as I would. They use them for cost and speed, I
would use them because they are fun. :)
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