On 2012-03-08, Wild_Bill wrote:

[ ... ]

The percentage of error is quite small when measuring the minor diameter of
fine pitched threads on a part with a caliper.. if the user has an existing
example of the threaded part they want to duplicate, then measuring becomes
a matter of comparison of measurements, not to an exact size specification.

Except that you usually don't want the minor diameter, but
rather the pitch diameter which is about half-way down the thread
(depending on the shape of the root of the thread).

[ ... ]

On short threaded sections such as 4 turns of a fine thread on an optical
filter ring, there won't be much room for the measurement tool to make a
measurement.

Yes -- here is probably the place where thread wires of an
appropriate size and a micrometer is the best bet -- unless you have a
standard to test it in.

[ ... ]

Eventually most HSMs encounter threads which are unfamiliar to them, and may
not appear to match any commonly available published standards.
Microphone stand connectors,

FWIW -- the standard US microphone stand connector is 5/8-27,
which is a problem for many because only some lathes with a quick-change
gearbox include that pitch. My 12x24" Clausing does. I think that the
typical South Bend does not.

optics, military/aircraft hardware standards
may all have minor differences for no apparent reasons.

Weird threads for military connectors are usually because a
finer thread does not cut as deeply into the wall of the connector
shell. If you were to use a standard thread for say a 2" diameter, it
would be *way* too deep in a connector shell, cutting deeply into the
area where the pins are located. :-)

As long as the machine user has an existing part (not just low tolerance
specs listed on a page), almost any matching part can be made depending of
course, upon experience and the required number of tricks up one's sleeve.
I'll not likely ever be an expert at cutting threads, so I usually always
have a "known good" mating part sitting within reach when I'm threading on a
lathe.. and carefully sneaking up on the final cuts works very well for me.

Yes -- as long as you do have something to test it against.
However, if you are making something to thread into another part which
is across the continent from you -- there is where the ability to use
the measuring tools wins.

Chucking and threading thin hollow parts can require some additional methods
that don't usually apply to solid stock workpieces.. but there are plenty of
methods to minimalize problems.

One thing which helps significantly with thin-walled parts is a
6-jaw chuck. Even better is one with two-piece jaws, for which you can
make some pie-wedge soft jaws.

Lastly.. threading dies may seem like a logical shortcut/substitute for the
learning process of cutting threads on a lathe, but in general, they aren't.

They just lead to the "I can't do this because I don't have the
right tap or die." excuse. Far better to be able to define your own
thread at need.

And then there's that gratification thing, again.

Indeed so.

Enjoy,
DoN.

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