OK, finding the PD for an exterior thread was too easy. In the best
spirit of McGyver, how can one measure the interior PD?

I'd like to verify the thread dimensions of this chuck adapter plate.

On 3/3/2010 10:15, Louis Ohland wrote:
4 threads in .504 thousandths. I'd say 8 tpi is pretty damn close.

Major diameter is 1.749 (D)

Pee Dee thread wire for use with 8tpi is .072", Constant for .072" wires
is .10775 (C)

Diameter over wires is 1.768" (M)

Formula to determine pitch diameter is E= M - Constant

E= 1.768 - .10775
E= 1.66025

Looking in Machinery's Handbook, pg 1668, Table 4:

1 3/4-8 UN Class 2A
Maj Dia Pitch dia
1.7477 Max 1.7327 Min 1.6665 Max 1.6590 Min

1 3/4-8 UN Class 3A
Maj Dia Pitch dia
1.7500 Max 1.7350 Min 1.6688 Max 1.6632 Min

If PD is 1.66025, it fits in Class 2A, but the Major diameter is 1.749
which is roughly 1.5 thou over. BUT... the adapter threads on about four
threads before it stops. I'm thinking the Major Diameter is not all that
critical.

On 3/3/2010 08:46, Louis Ohland wrote:
On 3/3/2010 00:00, Don Foreman wrote:

Put a sharp V threading bit in the toolholder and stick a DI on the
bed with a magnet or whatever. Visually align the point of the bit
with the crest (or the edge of a crest) of a spindle thread using a
10X loupe. Zero the DI that's tracking the carriage. Advance one
thread, optically aligning the point of the bit with the next crest.
Read the DI. You should now know the pitch to within a couple of
thou. You can measure the OD with a mike and the pitch dia with three
wires and a mike.

Don, you were helpful. Better quit that before you get into trouble...

Didn't think of measuring the crest to crest distance that way. I do
have a Mighty Mag not doing anything... Never used my Pee Dee thread
wires since shop operations 1 back in 96... Tried thread triangles last
night, and it didn't come up with a reasonable result.

OD has been determined with a digital caliper, multiple times.

To do list:

Measure crest to crest distance
Dust off thread wires and determine pitch diameter

Last step is drink heavily...

Grizzly answered back, they are researching it...