"jim rozen" wrote in message
...
In article , Harold & Susan Vordos says...

I don't like thread mikes. Never have, although they are fine for home
usage, probably even so good as to be considered over-kill. My personal
preference is to use wires, not even triangles. Both thread mikes and
triangles have the potential to measure a thread off the pitch diameter
when
there's the slightest error in thread form. That's not true with wires.

Harold I cannot argue with using the best method for the job, even
at home, but it would seem to me that the wires cannot meausure
properly if there *is* an error in the thread form. For example,
what if the threads were cut to some odd angle, say, 63 degrees
or so. Unless one used a comparator to actually measure the thread
angle, wouldn't the wires give some reading that would allow
one to *think* the threads were properly formed when in fact
they were not?

What role do thread gages play in all this?

Jim



I fully agree, Jim. The tolerance of the thread form is very much a part
of the equation, and it's relatively narrow. Certainly 3 degrees would
be WAY out of tolerance. It's been a lot of years, but I seem to recall
that the thread form is held to +/- 15 minutes. I think it's safe to say
that most of us, especially us older dudes, can't even see it on a thread
gage unless we're grinding a relatively large threading tool with broad
faces.

The harsh reality is that the wires *will* be measuring at the pitch
diameter, it just won't be right because of form error. I think you can
see that. The problem with triangles is they bear anywhere but at the
pitch line if the angle is off, and it makes no difference which way.
Mikes are slightly different because they have a truncated spindle and anvil
as I recall. If the thread form is too narrow, they will make contact near
the major diameter instead of at the pitch line. Wires always measure the
pitch line, even with bad form.

Actually, thread gages pick up thread form error to some degree.
Considering the no go is generally truncated, if a go gage fits, but the
form is off, the no go is likely to go on as well, depending on the thread
form angle. Other features may be off, so it won't go. Because the gage
checks angle to some degree, when you finally get a thread to fit the gage
that is off form, it is usually off so far in other features that the no go
betrays the bad form. If you kick this around in your head a bit, I think
you'll see what I'm talking about. Ring gages, in particular, are very
effective at determining many features, although they may not describe the
degree of error that may exist. They actually check all major features,
major diameter, pitch diameter and minor diameter, and by variations in how
they fit, thread form. When a go gage fits well, but the no go does, too,
you know something's amiss. All you have to do is determine what's wrong.
There's nothing like having a comparator to help in working with threads
when it's important that they be right.

Harold