Imperial thread on metric lathe!

[Steve]

Hi Folks
I have recently acquired one of the little 7x12 minilathes. Its the
metric model and came with a small box marked "gear wheels for imperial
threads". I want to cut a 32tpi on some 1" brass bar.
I note on the `Little Machine Shop minilathe manual` that to cut 32tpi
I need gear wheels 20,any,any,40 in the order A,B,C,D on the gear
mounting. Will this give me 32tpi without a different leadscrew?. I see
that to cut metric threads with an imperial lathe a 127 tooth gear is
reqd, is there a similar requirement for cutting imperial threads on a
metric lathe?.
Cheers
Steve

[Tim Wescott]

Post by Steve
Hi Folks
I have recently acquired one of the little 7x12 minilathes. Its the
metric model and came with a small box marked "gear wheels for imperial
threads". I want to cut a 32tpi on some 1" brass bar.
I note on the `Little Machine Shop minilathe manual` that to cut 32tpi
I need gear wheels 20,any,any,40 in the order A,B,C,D on the gear
mounting. Will this give me 32tpi without a different leadscrew?. I see
that to cut metric threads with an imperial lathe a 127 tooth gear is
reqd, is there a similar requirement for cutting imperial threads on a
metric lathe?.
Cheers
Steve

One inch is 127/5 mm, so to be exact you need that 127 tooth wheel.

But there are other change gear combinations that come close. If you
can get the ratio close enough that the error due to the change gear
ratio is significantly less that the error due to your lathe's
inaccuracies then you're doing as well as you ever can. If you can get
the ratio close enough that the error due to the change gear ratio, plus
the error due to your lathe's inaccuracies is less that the tolerance
you have to build to, you're doing well enough.

It would be interesting to do the math on your change gears, to see just
how close it comes.

[F. George McDuffee]

On 10 Nov 2006 11:42:23 -0800, "Steve"

Post by Steve
Hi Folks
I have recently acquired one of the little 7x12 minilathes. Its the
metric model and came with a small box marked "gear wheels for imperial
threads". I want to cut a 32tpi on some 1" brass bar.
I note on the `Little Machine Shop minilathe manual` that to cut 32tpi
I need gear wheels 20,any,any,40 in the order A,B,C,D on the gear
mounting. Will this give me 32tpi without a different leadscrew?. I see
that to cut metric threads with an imperial lathe a 127 tooth gear is
reqd, is there a similar requirement for cutting imperial threads on a
metric lathe?.
Cheers
Steve

===================
To cut exact metric threads with an inch lead screw or inch
threads with a metric leadscrew you must have a 127 tooth gear.
==>The operational word here being exact.<==

Because of size limitations it may not be possible to install a
127 tooth gear, or one may not be available for your machine.
Some combinations of [compound] gears will result in a very close
approximation to the required 1.27:1, for example 70/55 which
produces 1.2727. In many cases the this be so close the lead
screw will have more error than the conversion gearing. [ hint
-- an Excel or similar spread sheet can be very helpful to
determine just what threads you can cut with the gears you have.]

In other cases a "strange" inch or metric thread will be a "close
enough" fit. For example, 32 TPI is 25.4/32 or 0.79375 m/m pitch.
If you are engaging only a few threads a 0.80 mm pitch may be
"close enough.

Be reminded that the thread dial will most likely not work
correctly when you you use a 127 tooth gear or one of the
approximation compounding sets, so you will have to leave the
half-nut engaged.

IIRC -- The Little Machine Shop has lead screw / half nut kits to
convert between inch /metric threading. This may be your better
option.


Unka' George (George McDuffee)
..............................
Only in Britain could it be thought
a defect to be "too clever by half."
The probability is that too many people
are too stupid by three-quarters.

John Major (b. 1943),
British Conservative politician, prime minister.
Quoted in: Observer (London, 7 July 1991).

[Half-Nutz]

Post by F. George McDuffee
On 10 Nov 2006 11:42:23 -0800, "Steve"

Post by Steve
Hi Folks
I have recently acquired one of the little 7x12 minilathes. Its the
metric model and came with a small box marked "gear wheels for imperial
threads". I want to cut a 32tpi on some 1" brass bar.
I note on the `Little Machine Shop minilathe manual` that to cut 32tpi
I need gear wheels 20,any,any,40 in the order A,B,C,D on the gear
mounting. Will this give me 32tpi without a different leadscrew?. I see
that to cut metric threads with an imperial lathe a 127 tooth gear is
reqd, is there a similar requirement for cutting imperial threads on a
metric lathe?.
Cheers
Steve

===================
To cut exact metric threads with an inch lead screw or inch
threads with a metric leadscrew you must have a 127 tooth gear.
==>The operational word here being exact.<==
Because of size limitations it may not be possible to install a
127 tooth gear, or one may not be available for your machine.
Some combinations of [compound] gears will result in a very close
approximation to the required 1.27:1, for example 70/55 which
produces 1.2727. In many cases the this be so close the lead
screw will have more error than the conversion gearing. [ hint
-- an Excel or similar spread sheet can be very helpful to
determine just what threads you can cut with the gears you have.]

70:55 is a 14:11 ratio. Maybe a 28 : 22 gear set,
Another combinaion to consider is the 80:63 combination. This is even
more accurate. And can be made from a 20:21 and 4:3 ratio. Common gears
that you might have.
Pete

[Robert Roland]

Post by Steve
7x12 minilathes.

There is at least one free software out there that will find the
closest matches for you. You choose whether you have a metric or
imperial leadscrew and what thread pitch you want, and program spits
out one or more gear combinations that will usually get you within a
percent or two.

You may find it in the files section of one of the Yahoo groups for
the mini lathes. There's one group named 7x10, which is 90% politics
and religion, and another group named 7x12, which is much less noisy.
The 7x10 and the 7x12 are essentially the same machines, so both
groups may be of use to you.

[Steve]

Thanks for the replies guys.
I don`t know if a 127 tooth gear is available for the minilathe but the
suggestions made will help a lot. Have to `suck it and see` how
accurate the actual thread will need to be.
I need to make an adaptor for a firewire camera I`ve ordered o connect
it to the eyepiece of my telescope 1" 32tpi to 1.25" OD .The brass bar
is actually 1.5" diam. The threaded part might only need to go into the
camera body half inch or so.
Thanks again
Steve

[Eric R Snow]

Post by Steve
Thanks for the replies guys.
I don`t know if a 127 tooth gear is available for the minilathe but the
suggestions made will help a lot. Have to `suck it and see` how
accurate the actual thread will need to be.
I need to make an adaptor for a firewire camera I`ve ordered o connect
it to the eyepiece of my telescope 1" 32tpi to 1.25" OD .The brass bar
is actually 1.5" diam. The threaded part might only need to go into the
camera body half inch or so.
Thanks again
Steve

It may be that the threads are a 55 degree form, rather than 60
degrees. Microscope threads are all 55 degrees. At least all the ones
I've done. Not only that, the camera lenses I've had to adapt to were
also 55 degree threads.
ERS

[Stecica]

RMS threads are 55 degree cuts; the C mount is 60 degree 1 " x 32tpi of USA origin, UNEF United Extra Fine

[Bob La Londe]

Post by Stecica
RMS threads are 55 degree cuts; the C mount is 60 degree 1 " x 32tpi of
USA origin, UNEF United Extra Fine.

I think we may have set a new record.

[Bob La Londe]

Post by Bob La Londe

Post by Stecica
RMS threads are 55 degree cuts; the C mount is 60 degree 1 " x 32tpi
of USA origin, UNEF United Extra Fine.

I think we may have set a new record.

This Zombie thread is old enough to vote.

[Stecica]

Sorry, Unified (not united

[Tim Wescott]

Post by Steve
Thanks for the replies guys.
I don`t know if a 127 tooth gear is available for the minilathe but the
suggestions made will help a lot. Have to `suck it and see` how
accurate the actual thread will need to be.
I need to make an adaptor for a firewire camera I`ve ordered o connect
it to the eyepiece of my telescope 1" 32tpi to 1.25" OD .The brass bar
is actually 1.5" diam. The threaded part might only need to go into the
camera body half inch or so.
Thanks again
Steve

If it's a C mount the male threads on those usually span about 1/8" or so.

[F. George McDuffee]

On Fri, 10 Nov 2006 17:08:49 -0800, Tim Wescott
<***@seemywebsite.com> wrote:
<snip>

Post by Steve
I need to make an adaptor for a firewire camera I`ve ordered o connect
it to the eyepiece of my telescope 1" 32tpi to 1.25" OD

<snip>
From a functional standpoint do you actually need threads or
would a plastic adapter made from nylon or delrin or even pvc
pipe turned for about a 50% depth-of-thread be adequate?

Many times we get fixated on the end product rather than the
function.

This sounds like there should be an adapter commercially
available. Have you checked with the camara and teleoscope
manufacturer, and the bigger camara supply places [Porter's?] How
about some of the shops in the small classified ads in the photo
magazines?


Unka' George (George McDuffee)
..............................
Only in Britain could it be thought
a defect to be "too clever by half."
The probability is that too many people
are too stupid by three-quarters.

John Major (b. 1943),
British Conservative politician, prime minister.
Quoted in: Observer (London, 7 July 1991).

[w***@gmail.com]

Post by Steve
Hi Folks
I have recently acquired one of the little 7x12 minilathes. Its the
metric model and came with a small box marked "gear wheels for imperial
threads".
I note ...to cut 32tpi
I need gear wheels 20,any,any,40 in the order A,B,C,D on the gear
mounting. Will this give me 32tpi without a different leadscrew?. I see
that to cut metric threads with an imperial lathe a 127 tooth gear is
reqd,

So, doesn't that mean that you will be removing the 127 tooth gear when
you install
the 20,x,x,40 gears for imperial threads? I don't see the problem; my
old
MiniMat lathe cut fully compliant threads both inch and metric (after
the gear fiddling).

[F. George McDuffee]

Post by w***@gmail.com

Post by Steve
Hi Folks
I have recently acquired one of the little 7x12 minilathes. Its the
metric model and came with a small box marked "gear wheels for imperial
threads".
I note ...to cut 32tpi
I need gear wheels 20,any,any,40 in the order A,B,C,D on the gear
mounting. Will this give me 32tpi without a different leadscrew?. I see
that to cut metric threads with an imperial lathe a 127 tooth gear is
reqd,

So, doesn't that mean that you will be removing the 127 tooth gear when
you install
the 20,x,x,40 gears for imperial threads? I don't see the problem; my
old
MiniMat lathe cut fully compliant threads both inch and metric (after
the gear fiddling).

============
Actually the 127 tooth gear will be compounded with a 100 tooth
gear [or some compound train to give the same effect].

What is the pitch or TPI of your lead screw?

Unka' George (George McDuffee)
..............................
Only in Britain could it be thought
a defect to be "too clever by half."
The probability is that too many people
are too stupid by three-quarters.

John Major (b. 1943),
British Conservative politician, prime minister.
Quoted in: Observer (London, 7 July 1991).

[Stealth Pilot]

On Fri, 10 Nov 2006 22:28:05 -0600, F. George McDuffee

Post by F. George McDuffee

Post by w***@gmail.com

Post by Steve
Hi Folks
I have recently acquired one of the little 7x12 minilathes. Its the
metric model and came with a small box marked "gear wheels for imperial
threads".
I note ...to cut 32tpi
I need gear wheels 20,any,any,40 in the order A,B,C,D on the gear
mounting. Will this give me 32tpi without a different leadscrew?. I see
that to cut metric threads with an imperial lathe a 127 tooth gear is
reqd,

So, doesn't that mean that you will be removing the 127 tooth gear when
you install
the 20,x,x,40 gears for imperial threads? I don't see the problem; my
old
MiniMat lathe cut fully compliant threads both inch and metric (after
the gear fiddling).

============
Actually the 127 tooth gear will be compounded with a 100 tooth
gear [or some compound train to give the same effect].
What is the pitch or TPI of your lead screw?
Unka' George (George McDuffee)

unka george the ratio is 100:254 or halving both to get lowest
denominator 50:127

he needs a 50 tooth gear as well not a 100.

it is based on 1"=25.4mm

Stealth Pilot

[Trevor Jones]

Post by Stealth Pilot
unka george the ratio is 100:254 or halving both to get lowest
denominator 50:127
he needs a 50 tooth gear as well not a 100.
it is based on 1"=25.4mm
Stealth Pilot

As often as not, the gears come together, the 100 pinned to the 127
gear. This was the standard metric trnsposing gear from several tool
companies.

Whether you use the 100:127 ratio or 50:127 ratio only makes a little
difference. It will all get factored into the gear train.

Most of the transposing gear screwcutting charts I have seen used the
100:127 set, or skipped that alltogether and utilised 21 and 63 tooth
gears for somewhat less precise conversions.

The charts I can recall seeing all related to an 8 TPI leadscrew. I am
not fluent enough in the math to tell off the top of my head if halving
the 100 tooth gear to a fifty would allow direct use of the same
geartrains on a 16 TPI leadscrew or not by that simple substitution.

If you have the room to fit the 127 tooth gear on the leadscrew,
without it hitting the table, then you also have room to fit the 100
with it.
Further to all that, the use of the 100 toth gear provides the ability
to make a possible geartrain as opposed to an impossible one, wich works
correctly on paper, but cannot be physically produced due to the gear
pairs interfering on each other. I would expect some difficulty in that
respect out of a 50/127 pair.

Cheers
Trevor Jones

[Don Young]

Post by Steve
Hi Folks
I have recently acquired one of the little 7x12 minilathes. Its the
metric model and came with a small box marked "gear wheels for imperial
threads". I want to cut a 32tpi on some 1" brass bar.
I note on the `Little Machine Shop minilathe manual` that to cut 32tpi
I need gear wheels 20,any,any,40 in the order A,B,C,D on the gear
mounting. Will this give me 32tpi without a different leadscrew?. I see
that to cut metric threads with an imperial lathe a 127 tooth gear is
reqd, is there a similar requirement for cutting imperial threads on a
metric lathe?.
Cheers
Steve

From this discussion I suspect that your lathe does not have a metric
feedscrew. I suspect it is 16TPI. SouthBend made both imperial and metric
lathes. They recommended that a lathe to cut both metric and imperial
threads should have an imperial leadscrew.

Don Young

[F. George McDuffee]

On Fri, 10 Nov 2006 22:12:48 -0600, "Don Young"

Post by Don Young

Post by Steve
Hi Folks
I have recently acquired one of the little 7x12 minilathes. Its the
metric model and came with a small box marked "gear wheels for imperial
threads". I want to cut a 32tpi on some 1" brass bar.
I note on the `Little Machine Shop minilathe manual` that to cut 32tpi
I need gear wheels 20,any,any,40 in the order A,B,C,D on the gear
mounting. Will this give me 32tpi without a different leadscrew?. I see
that to cut metric threads with an imperial lathe a 127 tooth gear is
reqd, is there a similar requirement for cutting imperial threads on a
metric lathe?.
Cheers
Steve

From this discussion I suspect that your lathe does not have a metric
feedscrew. I suspect it is 16TPI. SouthBend made both imperial and metric
lathes. They recommended that a lathe to cut both metric and imperial
threads should have an imperial leadscrew.
Don Young

===============
If he does indeed have the inch leadscrew (which the 20,X,X40
suggested change gears suggests), he should be good to go.

If he wants to cut metric, rather than fool around with strange
change gearing, get the metric leadscrew kit.

see:
http://littlemachineshop.com/products/product_view.php?ProductID=1691


Unka' George (George McDuffee)
..............................
Only in Britain could it be thought
a defect to be "too clever by half."
The probability is that too many people
are too stupid by three-quarters.

John Major (b. 1943),
British Conservative politician, prime minister.
Quoted in: Observer (London, 7 July 1991).

[Trevor Jones]

Post by F. George McDuffee
If he does indeed have the inch leadscrew (which the 20,X,X40
suggested change gears suggests), he should be good to go.
If he wants to cut metric, rather than fool around with strange
change gearing, get the metric leadscrew kit.
http://littlemachineshop.com/products/product_view.php?ProductID=1691

Now that's a darn fine idea, and you can hardly complain about the
price, either.

That would be a good buy even if you had to doctor up an outboard end
extension to fit it to one of the longer versions.

Cheers
Trevor Jones

[F. George McDuffee]

On Sat, 11 Nov 2006 16:20:56 GMT, Trevor Jones

Post by Trevor Jones

Post by F. George McDuffee
If he does indeed have the inch leadscrew (which the 20,X,X40
suggested change gears suggests), he should be good to go.
If he wants to cut metric, rather than fool around with strange
change gearing, get the metric leadscrew kit.
http://littlemachineshop.com/products/product_view.php?ProductID=1691

Now that's a darn fine idea, and you can hardly complain about the
price, either.
That would be a good buy even if you had to doctor up an outboard end
extension to fit it to one of the longer versions.
Cheers
Trevor Jones

=================
Check the website. They have kits to fit the longer lathes.


Unka' George (George McDuffee)
..............................
Only in Britain could it be thought
a defect to be "too clever by half."
The probability is that too many people
are too stupid by three-quarters.

John Major (b. 1943),
British Conservative politician, prime minister.
Quoted in: Observer (London, 7 July 1991).

[Steve]

Hi again chaps
Not quite sure whats going on with my little lathe. I`ve just checked
the leadscrew and it is 16tpi. All the badges and labels show thread
pitches in mm, the guy I bought it off said its a metric lathe so what
makes it a `metric` lathe exactly as opposed to the imperial version of
this lathe?. It came with gear wheels
2x20,2x80,2x60,1x50,1x45,1x35,1x30 so with the `imperial` leadscrew I
appear to have then I should be fine with the 32tpi.
I notice in some of the ads for the minilathe a `metric` add on kit to
cut metric threads with an imperial lathe?????. Confusing or what!!.
regards
Steve

[Jon Elson]

Post by Steve
Hi Folks
I have recently acquired one of the little 7x12 minilathes. Its the
metric model and came with a small box marked "gear wheels for imperial
threads". I want to cut a 32tpi on some 1" brass bar.
I note on the `Little Machine Shop minilathe manual` that to cut 32tpi
I need gear wheels 20,any,any,40 in the order A,B,C,D on the gear
mounting. Will this give me 32tpi without a different leadscrew?. I see
that to cut metric threads with an imperial lathe a 127 tooth gear is
reqd, is there a similar requirement for cutting imperial threads on a
metric lathe?.
Cheers
Steve

well, 20 x x 40 sounds like it just slows the feed down by 2 x.
Oh, maybe the 20 x x 40 is the feed setup for a machine with an
Imperial leadscrew.

If you just set the lathe for .8 mm pitch, that works out to
31.75 TPI, which is pretty close, 0.7% error.

What is the leadscrew pitch on the lathe? How many teeth are
on the spindle drive gear? From that info, you can figure out
the gears needed.

The 127 : 100 gear set is ideal as 2 X 127 is the familar 254
(as in 25.4 mm / inch) But, it could be hard to fit a 127 tooth
gear into a small lathe unless the gear pitch was really fine.

Jon