It appears that you're well ahead of the curve, Bob, as far as new machine
owners goes.. many just assume that what the chart shows reflects their only
options.

Another possibliity exists to expand the available number of threading
possibilities by adding just one more change gear to the set, as a number of
machine users have done on machines which rely on a set of gears to change
thread pitches.
Proxxon probably has replacement parts available.

And, don't know if it's too early to mention this, but, you may be seeing
other machine purchases in your (near) future.. so your ability to add new
features to existing machines becomes almost endless.

Metalworking on any scale, is full of inspirational ideas and nearly
infinite possibilities.. a very rewarding use of time, IMO.

--
WB
..........


"Bob S" wrote in message
...
On Tue, 6 Mar 2012 13:11:26 -0500, Wild_Bill wrote:

The desired inch/tpi thread pitches may be a bit more difficult if the
machine is made around metric scales on the dials and a metric leadscrew
pitch, but that doesn't mean that inch pitches can't be done.
I don't have the ability (software and I generally aren't on friendly
terms)
but some folks brighter than myself have created threading charts for
other
lathe models using spreadsheets or other methods, to show that many more
thread pitches can be attained than are shown in a lathe's threading
chart.

Good idea!

I went through the available combinations and found one that will give
36 TPI. There were also several other interesting combinations; 2/3 mm
pitch and 4/3 mm pitch sound like they ought to be good for
something...

No 26 TPI though.

So I started trying "what if" combinations. If I had a 26-tooth
leadscrew gear I would have 26 TPI to the same accuracy as all the
usual inch threads on this machine (.0463%). That would require gear
cutting, and I have several things to learn before I try that.

I can also get close (well under 1%) to 26 TPI with a spindle "gear"
of 17 or 19 or 22 "teeth". This "gear" is actually a timing belt
pulley, which is probably more difficult to make than a gear would be.

I didn't explore a new intermediate gear, since that is a double-layer
thing with a belt on one side and a gear on the other.

Bob