What is the formula for cutting threads for odd numbered threading,I
have to cut a screw @27 t.p.i.?Even numbered threading is easy to figure
from the gear chart but not the odds.

On Thu, 02 Jul 2009 00:52:36 -0400, Time Traveler wrote:

What is the formula for cutting threads for odd numbered threading,I
have to cut a screw @27 t.p.i.?Even numbered threading is easy to figure
from the gear chart but not the odds.

The HF 33684.pdf manual labels the top gear A. A drives B.
C is the gear on the shaft with B. C drives D, which turns
the 16-pitch lead screw. The tpi formula is 16*B/A*D/C,
so you get the same tpi when A and C are interchanged with
each other, or when B and D are interchanged with each other.
For 27 tpi, use gears ABCD = 20 45 80 60, per gears.c
program. 16*(45/20)*(60/80) = 27.

--
jiw

Thank you for the advice.

On 2009-07-02, Time Traveler wrote:
What is the formula for cutting threads for odd numbered threading,I
have to cut a screw @27 t.p.i.?Even numbered threading is easy to figure
from the gear chart but not the odds.

That may be because the supplied gears don't include what you
need.

Well ... you seem to be assuming that everyone knows the specs
of the HF 7x10 and its accessories -- or that only those who do will
answer.

First off -- in my 12x24" Clausing, to cut 27 TPI, I simply
select it from the quick-change gearbox.

But many quick-change gearboxes do not offer 27 TPI -- it is
(for whatever reason) a relatively uncommon thread -- mostly seen in
3/8-27 electrical threads for mounting lamp sockets derived from old gas
light fittings, and the somewhat larger 5/8-27 thread used for
microphone mounts -- perhaps from the same origin.

What you need to know is first the pitch of the leadscrew. You
should have that in your manual -- or be able to measure it.

Then calculate how far you need to move per rotation of the
spindle (1/27th of an inch, or 0.037037").

Now -- assuming that your leadscrew pitch is say 10 TPI (Sounds
reasonable for a 7" lathe, but it could easily be something else), that
gives you 0.100" per full rotation of the leadscrew, and divide that
into the distance you *want* to move (0.037037") to get how much of a
rotation you need the leadscrew to turn to produce that, That turns out
to be 0.37037 rotation.

So -- the ratio is 1:0.037037 or 2.7:1. Convert this to get
integers on both sides, which becomes 27:10.

So -- you now need to find a combination of gears (taking into
account all gears from the spindle to the leadscrew) which will give 10
turns of the leadscrew for 27 turns of the spindle, or perhaps 54:20
would give more reasonable gear choices and is the same ratio in
reality.

Now -- it comes down to *you* knowing what gears *you* have, and
figuring out whether any combination which will physically fit into the
headstock can be made from what gears you have available.

It may turn out that you will need to *make* a 54 tooth gear to
mesh with an existing 20 tooth gear in your set.

There have been people who have written programs (spreadsheets
or C programs or BASIC or whatever) which when fed a list of the
available gears will tell you which you need to use. Maybe one of those
will post.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 3 Jul 2009 01:32:50 GMT, "DoN. Nichols"
wrote:

On 2009-07-02, Time Traveler wrote:
What is the formula for cutting threads for odd numbered threading,I
have to cut a screw @27 t.p.i.?Even numbered threading is easy to figure
from the gear chart but not the odds.

That may be because the supplied gears don't include what you
need.

Well ... you seem to be assuming that everyone knows the specs
of the HF 7x10 and its accessories -- or that only those who do will
answer.

First off -- in my 12x24" Clausing, to cut 27 TPI, I simply
select it from the quick-change gearbox.

But many quick-change gearboxes do not offer 27 TPI -- it is
(for whatever reason) a relatively uncommon thread -- mostly seen in
3/8-27 electrical threads for mounting lamp sockets derived from old gas
light fittings, and the somewhat larger 5/8-27 thread used for
microphone mounts -- perhaps from the same origin.

What you need to know is first the pitch of the leadscrew. You
should have that in your manual -- or be able to measure it.

Then calculate how far you need to move per rotation of the
spindle (1/27th of an inch, or 0.037037").

Now -- assuming that your leadscrew pitch is say 10 TPI (Sounds
reasonable for a 7" lathe, but it could easily be something else), that
gives you 0.100" per full rotation of the leadscrew, and divide that
into the distance you *want* to move (0.037037") to get how much of a
rotation you need the leadscrew to turn to produce that, That turns out
to be 0.37037 rotation.

So -- the ratio is 1:0.037037 or 2.7:1. Convert this to get
integers on both sides, which becomes 27:10.

So -- you now need to find a combination of gears (taking into
account all gears from the spindle to the leadscrew) which will give 10
turns of the leadscrew for 27 turns of the spindle, or perhaps 54:20
would give more reasonable gear choices and is the same ratio in
reality.

Now -- it comes down to *you* knowing what gears *you* have, and
figuring out whether any combination which will physically fit into the
headstock can be made from what gears you have available.

It may turn out that you will need to *make* a 54 tooth gear to
mesh with an existing 20 tooth gear in your set.

There have been people who have written programs (spreadsheets
or C programs or BASIC or whatever) which when fed a list of the
available gears will tell you which you need to use. Maybe one of those
will post.

Good Luck,
DoN.
=======
For occasional use see
http://littlemachineshop.com/product...ProductID=1523
metal also available at 3X the price see
http://littlemachineshop.com/product...3447&category=
for separate gears see
http://littlemachineshop.com/product...oduc t+Search

If you are new to machining/mini lathe see
http://littlemachineshop.com/product...3111&category=
for free see
http://ec1.images-amazon.com/media/i...L000048646.pdf




also see
http://www.titaniumstudios.com/toolj...angegears.html
http://www.varmintal.com/alath.htm
more good stuff
http://www.varmintal.com/aupda.htm


Let the group know how you make out.



Unka' George [George McDuffee]
-------------------------------------------
He that will not apply new remedies,
must expect new evils:
for Time is the greatest innovator: and
if Time, of course, alter things to the worse,
and wisdom and counsel shall not alter them to the better,
what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman.
Essays, "Of Innovations" (1597-1625).

Thank you Don for your input.The workaround was to use a friend's lathe
with the capability of 27 tpi.I didn't have the correct gear for my
lathe.I needed to make a connector for a faucet that had a 13/16 x27
threading.It all worked out.