[[email protected]]

Sorry for the long subject line folks,
Anyway, it seems that camera lens threads are all, or mostly all,
75mm pitch. Cutting metric threads on an inch lathe is of course a
hassle. 34 TPI would be close enough but my gearbox doesn't have a 34
TPI option. Looking at the change gears that came with my lathe (which
has a quick change gearbox), I figured that there must be some
combination of two gears and the quick change gearbox that would get
me close enough to the inch equivalent of .75mm. It turns out that I
have a 30 tooth gear and a 32 tooth gear and that the ratio between
these gears, times 36 TPI, which my lathe does have, results in a
pitch only .0001 different than .75mm, calculated to 5 places. My
lathe has two ratio settings for both the headstock gearbox and the
threading gearbox. The headstock gearbox output is either 1:1 or 2:1
in relation to the spindle. The threading gearbox input is either 1:2
or 2:1. So, in order to get the .75mm pitch I set the headstock
gearbox to the 2:1 ratio and the quick change (threading) gearbox to
36 TPI. The change gears are mounted so that the headstock gear is the
32 tooth gear and the quick change gearbox gear is the 30 tooth gear.
The ratio between the 32 and 30 tooth gears is 1:1.06666666667. The
pitch of 36 TPI is .02778 and .75 mm is .02952. 1.066666667 times
02778 is .02962, which is only .00010 more than .02952(.75mm). I'm
pretty certain that all lathes with quick change gearboxes will have
even ratios of spindle revs to quick change gearbox input revs, so as
long as a 32 tooth gear drives a 30 tooth gear (or any set of gears
with a 1:1.0666666667 ratio), through an idler or not, you should be
able to cut a .75mm pitch thread and still release the halfnuts after
each pass. I'm sure someone has already posted this info on usenet but
I needed this today and thought it might be useful to someone else.
Especially considering the ubiquity of asian lathes.
Cheers,
Eric

[Jim Wilkins]

On Feb 18, 9:59*pm, wrote:
...It turns out that I
have a 30 tooth gear and a 32 tooth gear and that the ratio between
these gears, times 36 TPI, which my lathe does have, results in a
pitch only .0001 different than .75mm, calculated to 5 places. ...
Eric

Good idea.

My lathe's gearbox chart was missing so I made one up with a
spreadsheet. I changed a copy of it to show the metric modulus for
each pitch and experimented with gear ratio multipliers to get exact
values.

Jim Wilkins

[[email protected]]

On Thu, 19 Feb 2009 05:23:36 -0800 (PST), Jim Wilkins
wrote:

On Feb 18, 9:59=A0pm, wrote:
...It turns out that I
have a 30 tooth gear and a 32 tooth gear and that the ratio between
these gears, times 36 TPI, which my lathe does have, results in a
pitch only .0001 different than .75mm, calculated to 5 places. ...
Eric

Good idea.

My lathe's gearbox chart was missing so I made one up with a
spreadsheet. I changed a copy of it to show the metric modulus for
each pitch and experimented with gear ratio multipliers to get exact
values.

Jim Wilkins
Thanks. I hope it helps someone else out. Now that I figured that one
out I'm gonna try for some other common pitches.
ERS

[Don Young]

wrote in message
...
Sorry for the long subject line folks,
Anyway, it seems that camera lens threads are all, or mostly all,
75mm pitch. Cutting metric threads on an inch lathe is of course a
hassle. 34 TPI would be close enough but my gearbox doesn't have a 34
TPI option. Looking at the change gears that came with my lathe (which
has a quick change gearbox), I figured that there must be some
combination of two gears and the quick change gearbox that would get
me close enough to the inch equivalent of .75mm. It turns out that I
have a 30 tooth gear and a 32 tooth gear and that the ratio between
these gears, times 36 TPI, which my lathe does have, results in a
pitch only .0001 different than .75mm, calculated to 5 places. My
lathe has two ratio settings for both the headstock gearbox and the
threading gearbox. The headstock gearbox output is either 1:1 or 2:1
in relation to the spindle. The threading gearbox input is either 1:2
or 2:1. So, in order to get the .75mm pitch I set the headstock
gearbox to the 2:1 ratio and the quick change (threading) gearbox to
36 TPI. The change gears are mounted so that the headstock gear is the
32 tooth gear and the quick change gearbox gear is the 30 tooth gear.
The ratio between the 32 and 30 tooth gears is 1:1.06666666667. The
pitch of 36 TPI is .02778 and .75 mm is .02952. 1.066666667 times
02778 is .02962, which is only .00010 more than .02952(.75mm). I'm
pretty certain that all lathes with quick change gearboxes will have
even ratios of spindle revs to quick change gearbox input revs, so as
long as a 32 tooth gear drives a 30 tooth gear (or any set of gears
with a 1:1.0666666667 ratio), through an idler or not, you should be
able to cut a .75mm pitch thread and still release the halfnuts after
each pass. I'm sure someone has already posted this info on usenet but
I needed this today and thought it might be useful to someone else.
Especially considering the ubiquity of asian lathes.
Cheers,
Eric
I like your thinking on the gear ratios. Be very careful about opening the
half nuts as the success of that has to do with the pitch of the leadscrew,
the thread dial gear, and the pitch being cut. I do not believe that your
system will reliably re-engage the feed without loosing its synchronization
if you allow the dial to go all the way around.
A metric thread re-synchronizes with an inch leadscrew every 127 turns of
the spindle so a 0.75MM thread synchronizes every 3.75 inches. If your
thread dial goes around to the next starting point when you move the
carriage 3.75 inches you are good to go. About the only one I know will work
is 0.8MM which synchronizes every 4 inches and that is the distance for a
32T gear on a 8TPI leadscrew. Of course if you are not using a 127 tooth
gear your error multiplies for each revolution of the dial also.

I think the best way, if you really need to open the half-nuts, is to just
watch the dial and back up the lathe so it does not go around.

Don Young

[Don Young]

"Don Young" wrote in message
webinternetservicesprovideinc...

wrote in message
...
Sorry for the long subject line folks,
Anyway, it seems that camera lens threads are all, or mostly all,
75mm pitch. Cutting metric threads on an inch lathe is of course a
hassle. 34 TPI would be close enough but my gearbox doesn't have a 34
TPI option. Looking at the change gears that came with my lathe (which
has a quick change gearbox), I figured that there must be some
combination of two gears and the quick change gearbox that would get
me close enough to the inch equivalent of .75mm. It turns out that I
have a 30 tooth gear and a 32 tooth gear and that the ratio between
these gears, times 36 TPI, which my lathe does have, results in a
pitch only .0001 different than .75mm, calculated to 5 places. My
lathe has two ratio settings for both the headstock gearbox and the
threading gearbox. The headstock gearbox output is either 1:1 or 2:1
in relation to the spindle. The threading gearbox input is either 1:2
or 2:1. So, in order to get the .75mm pitch I set the headstock
gearbox to the 2:1 ratio and the quick change (threading) gearbox to
36 TPI. The change gears are mounted so that the headstock gear is the
32 tooth gear and the quick change gearbox gear is the 30 tooth gear.
The ratio between the 32 and 30 tooth gears is 1:1.06666666667. The
pitch of 36 TPI is .02778 and .75 mm is .02952. 1.066666667 times
02778 is .02962, which is only .00010 more than .02952(.75mm). I'm
pretty certain that all lathes with quick change gearboxes will have
even ratios of spindle revs to quick change gearbox input revs, so as
long as a 32 tooth gear drives a 30 tooth gear (or any set of gears
with a 1:1.0666666667 ratio), through an idler or not, you should be
able to cut a .75mm pitch thread and still release the halfnuts after
each pass. I'm sure someone has already posted this info on usenet but
I needed this today and thought it might be useful to someone else.
Especially considering the ubiquity of asian lathes.
Cheers,
Eric
I like your thinking on the gear ratios. Be very careful about opening the
half nuts as the success of that has to do with the pitch of the
leadscrew, the thread dial gear, and the pitch being cut. I do not believe
that your system will reliably re-engage the feed without loosing its
synchronization if you allow the dial to go all the way around.
A metric thread re-synchronizes with an inch leadscrew every 127 turns of
the spindle so a 0.75MM thread synchronizes every 3.75 inches. If your
thread dial goes around to the next starting point when you move the
carriage 3.75 inches you are good to go. About the only one I know will
work is 0.8MM which synchronizes every 4 inches and that is the distance
for a 32T gear on a 8TPI leadscrew. Of course if you are not using a 127
tooth gear your error multiplies for each revolution of the dial also.

I think the best way, if you really need to open the half-nuts, is to just
watch the dial and back up the lathe so it does not go around.

Don Young


I noticed on another group that you indicated your success at opening the
half nuts was due to you actually cutting a 36TPI thread. Because of the
gear change you are actually cutting a 33 3/4 TPI thread. Your thread dial
will work for this if its gear has teeth equal to 4 times the leadscrew
pitch and you always use the same point on the dial. This requires 4 inches
for the gear to go around and will work correctly for threads that are a
multiple of 1/4 TPI. Good work!!

Don Young

[Davebt]

Don Young wrote:
"Don Young" wrote in message
webinternetservicesprovideinc...

wrote in message
...
Sorry for the long subject line folks,
Anyway, it seems that camera lens threads are all, or mostly all,
75mm pitch. Cutting metric threads on an inch lathe is of course a
hassle. 34 TPI would be close enough but my gearbox doesn't have a
34 TPI option. Looking at the change gears that came with my lathe
(which has a quick change gearbox), I figured that there must be
some combination of two gears and the quick change gearbox that
would get me close enough to the inch equivalent of .75mm. It turns
out that I have a 30 tooth gear and a 32 tooth gear and that the
ratio between these gears, times 36 TPI, which my lathe does have,
results in a pitch only .0001 different than .75mm, calculated to 5
places. My lathe has two ratio settings for both the headstock
gearbox and the threading gearbox. The headstock gearbox output is
either 1:1 or 2:1 in relation to the spindle. The threading gearbox
input is either 1:2 or 2:1. So, in order to get the .75mm pitch I
set the headstock gearbox to the 2:1 ratio and the quick change
(threading) gearbox to 36 TPI. The change gears are mounted so that
the headstock gear is the 32 tooth gear and the quick change
gearbox gear is the 30 tooth gear. The ratio between the 32 and 30
tooth gears is 1:1.06666666667. The pitch of 36 TPI is .02778 and
.75 mm is .02952. 1.066666667 times 02778 is .02962, which is only
.00010 more than .02952(.75mm). I'm pretty certain that all lathes
with quick change gearboxes will have even ratios of spindle revs
to quick change gearbox input revs, so as long as a 32 tooth gear
drives a 30 tooth gear (or any set of gears with a 1:1.0666666667
ratio), through an idler or not, you should be able to cut a .75mm
pitch thread and still release the halfnuts after each pass. I'm
sure someone has already posted this info on usenet but I needed
this today and thought it might be useful to someone else.
Especially considering the ubiquity of asian lathes. Cheers,
Eric
I like your thinking on the gear ratios. Be very careful about
opening the half nuts as the success of that has to do with the
pitch of the leadscrew, the thread dial gear, and the pitch being
cut. I do not believe that your system will reliably re-engage the
feed without loosing its synchronization if you allow the dial to go
all the way around. A metric thread re-synchronizes with an inch
leadscrew every 127
turns of the spindle so a 0.75MM thread synchronizes every 3.75
inches. If your thread dial goes around to the next starting point
when you move the carriage 3.75 inches you are good to go. About the
only one I know will work is 0.8MM which synchronizes every 4 inches
and that is the distance for a 32T gear on a 8TPI leadscrew. Of
course if you are not using a 127 tooth gear your error multiplies
for each revolution of the dial also. I think the best way, if you really
need to open the half-nuts, is
to just watch the dial and back up the lathe so it does not go
around. Don Young


I noticed on another group that you indicated your success at opening
the half nuts was due to you actually cutting a 36TPI thread. Because
of the gear change you are actually cutting a 33 3/4 TPI thread. Your
thread dial will work for this if its gear has teeth equal to 4 times
the leadscrew pitch and you always use the same point on the dial.
This requires 4 inches for the gear to go around and will work
correctly for threads that are a multiple of 1/4 TPI. Good work!!

Don Young

Has anyone any idea how/if these threads (in particular the 0.75mm one for
lens filters) might be cut on a Myford ML7 (NOT a Super7) with a gearbox?

Dave (UK)

[Jim Wilkins]

On Feb 20, 10:47*pm, "Davebt" wrote:


Has anyone any idea how/if these threads (in particular the 0.75mm one for
lens filters) might be cut on a Myford ML7 (NOT a Super7) with a gearbox?

Dave *(UK)-

0.75mm = 0.0295275"
0.0295275" * 127/120 = 0.0312499" modulus, 1/0.0312499 = 32.000064
TPI.

Set the gearbox for 32 TPI with a 127/120 compound in the train
instead of an idler. 120 and 127 tooth, 16DP change gears cost around
$100 apiece in the USA. 100 is better for the standard screw pitches.
I found 120 with the spreadsheet method mentioned in a previous post.

Jim Wilkins

[F. George McDuffee]

On Sat, 21 Feb 2009 03:47:20 -0000, "Davebt"
wrote:

Don Young wrote:
"Don Young" wrote in message
webinternetservicesprovideinc...

wrote in message
...
Sorry for the long subject line folks,
Anyway, it seems that camera lens threads are all, or mostly all,
75mm pitch. Cutting metric threads on an inch lathe is of course a
hassle. 34 TPI would be close enough but my gearbox doesn't have a
34 TPI option. Looking at the change gears that came with my lathe
(which has a quick change gearbox), I figured that there must be
some combination of two gears and the quick change gearbox that
would get me close enough to the inch equivalent of .75mm. It turns
out that I have a 30 tooth gear and a 32 tooth gear and that the
ratio between these gears, times 36 TPI, which my lathe does have,
results in a pitch only .0001 different than .75mm, calculated to 5
places. My lathe has two ratio settings for both the headstock
gearbox and the threading gearbox. The headstock gearbox output is
either 1:1 or 2:1 in relation to the spindle. The threading gearbox
input is either 1:2 or 2:1. So, in order to get the .75mm pitch I
set the headstock gearbox to the 2:1 ratio and the quick change
(threading) gearbox to 36 TPI. The change gears are mounted so that
the headstock gear is the 32 tooth gear and the quick change
gearbox gear is the 30 tooth gear. The ratio between the 32 and 30
tooth gears is 1:1.06666666667. The pitch of 36 TPI is .02778 and
.75 mm is .02952. 1.066666667 times 02778 is .02962, which is only
.00010 more than .02952(.75mm). I'm pretty certain that all lathes
with quick change gearboxes will have even ratios of spindle revs
to quick change gearbox input revs, so as long as a 32 tooth gear
drives a 30 tooth gear (or any set of gears with a 1:1.0666666667
ratio), through an idler or not, you should be able to cut a .75mm
pitch thread and still release the halfnuts after each pass. I'm
sure someone has already posted this info on usenet but I needed
this today and thought it might be useful to someone else.
Especially considering the ubiquity of asian lathes. Cheers,
Eric
I like your thinking on the gear ratios. Be very careful about
opening the half nuts as the success of that has to do with the
pitch of the leadscrew, the thread dial gear, and the pitch being
cut. I do not believe that your system will reliably re-engage the
feed without loosing its synchronization if you allow the dial to go
all the way around. A metric thread re-synchronizes with an inch
leadscrew every 127
turns of the spindle so a 0.75MM thread synchronizes every 3.75
inches. If your thread dial goes around to the next starting point
when you move the carriage 3.75 inches you are good to go. About the
only one I know will work is 0.8MM which synchronizes every 4 inches
and that is the distance for a 32T gear on a 8TPI leadscrew. Of
course if you are not using a 127 tooth gear your error multiplies
for each revolution of the dial also. I think the best way, if you really
need to open the half-nuts, is
to just watch the dial and back up the lathe so it does not go
around. Don Young


I noticed on another group that you indicated your success at opening
the half nuts was due to you actually cutting a 36TPI thread. Because
of the gear change you are actually cutting a 33 3/4 TPI thread. Your
thread dial will work for this if its gear has teeth equal to 4 times
the leadscrew pitch and you always use the same point on the dial.
This requires 4 inches for the gear to go around and will work
correctly for threads that are a multiple of 1/4 TPI. Good work!!

Don Young

Has anyone any idea how/if these threads (in particular the 0.75mm one for
lens filters) might be cut on a Myford ML7 (NOT a Super7) with a gearbox?

Dave (UK)

-------------
Calculation of the required gears is the easy part.

Given that these threads are generally to a shoulder and that you
cannot disengage the half nut when using inch/metric change gears
you will most likely want to get or make a spindle hand crank for
threading. The threading tool will also be critical given the
small size of the thread. More than likely you will need to
grind a special tool with one side straight and the other side 30
degrees for a 60 degree included angle. This will let you get up
next to the shoulder.
for an example see
http://www.midwayusa.com/viewproduct...tnumber=607918


Be sure to set the compound/top-slide to 29 to 30 degrees and
advance the tool using this so the bulk of the cut is to the
front. It can also be helpful to cut a relief all the way around
the part next to the shoulder, one thread wide.


For some ideas on the hand crank see
http://mcduffee-associates.us/machin...ndle_crank.htm

Be very careful not to turn the lathe on with the crank
installed. It will whack the c**p out of you and/or shake the
lathe off its table/mounting pads. On the Emco we always popped
the spindle belt off [after the first time].

a cross slide stop may also be helpful. see
http://mcduffee-associates.us/machining/thrdstp01.htm
Use the crosslide to retract the tool to crank back to the start
position. A stop will help avoid loss of zero.

Good luck and let the group know how you make out and any
shortcuts you discover.


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).

[[email protected]]

On Thu, 19 Feb 2009 22:20:53 -0600, "Don Young"
wrote:


"Don Young" wrote in message
dwebinternetservicesprovideinc...

wrote in message
...
Sorry for the long subject line folks,
Anyway, it seems that camera lens threads are all, or mostly all,
75mm pitch. Cutting metric threads on an inch lathe is of course a
hassle. 34 TPI would be close enough but my gearbox doesn't have a 34
TPI option. Looking at the change gears that came with my lathe (which
has a quick change gearbox), I figured that there must be some
combination of two gears and the quick change gearbox that would get
me close enough to the inch equivalent of .75mm. It turns out that I
have a 30 tooth gear and a 32 tooth gear and that the ratio between
these gears, times 36 TPI, which my lathe does have, results in a
pitch only .0001 different than .75mm, calculated to 5 places. My
lathe has two ratio settings for both the headstock gearbox and the
threading gearbox. The headstock gearbox output is either 1:1 or 2:1
in relation to the spindle. The threading gearbox input is either 1:2
or 2:1. So, in order to get the .75mm pitch I set the headstock
gearbox to the 2:1 ratio and the quick change (threading) gearbox to
36 TPI. The change gears are mounted so that the headstock gear is the
32 tooth gear and the quick change gearbox gear is the 30 tooth gear.
The ratio between the 32 and 30 tooth gears is 1:1.06666666667. The
pitch of 36 TPI is .02778 and .75 mm is .02952. 1.066666667 times
02778 is .02962, which is only .00010 more than .02952(.75mm). I'm
pretty certain that all lathes with quick change gearboxes will have
even ratios of spindle revs to quick change gearbox input revs, so as
long as a 32 tooth gear drives a 30 tooth gear (or any set of gears
with a 1:1.0666666667 ratio), through an idler or not, you should be
able to cut a .75mm pitch thread and still release the halfnuts after
each pass. I'm sure someone has already posted this info on usenet but
I needed this today and thought it might be useful to someone else.
Especially considering the ubiquity of asian lathes.
Cheers,
Eric
I like your thinking on the gear ratios. Be very careful about opening the
half nuts as the success of that has to do with the pitch of the
leadscrew, the thread dial gear, and the pitch being cut. I do not believe
that your system will reliably re-engage the feed without loosing its
synchronization if you allow the dial to go all the way around.
A metric thread re-synchronizes with an inch leadscrew every 127 turns of
the spindle so a 0.75MM thread synchronizes every 3.75 inches. If your
thread dial goes around to the next starting point when you move the
carriage 3.75 inches you are good to go. About the only one I know will
work is 0.8MM which synchronizes every 4 inches and that is the distance
for a 32T gear on a 8TPI leadscrew. Of course if you are not using a 127
tooth gear your error multiplies for each revolution of the dial also.

I think the best way, if you really need to open the half-nuts, is to just
watch the dial and back up the lathe so it does not go around.

Don Young


I noticed on another group that you indicated your success at opening the
half nuts was due to you actually cutting a 36TPI thread. Because of the
gear change you are actually cutting a 33 3/4 TPI thread. Your thread dial
will work for this if its gear has teeth equal to 4 times the leadscrew
pitch and you always use the same point on the dial. This requires 4 inches
for the gear to go around and will work correctly for threads that are a
multiple of 1/4 TPI. Good work!!

Don Young



Greetings Don,
I do engage the half nuts only at the number 1 position every time. I
should have said that the QC gearbox was set at 36 TPI and I was
actually cutting close to 34 TPI as you noted.
Cheers,
Eric

[Davebt]

Don Young wrote:
"Don Young" wrote in message
webinternetservicesprovideinc...

wrote in message
...
Sorry for the long subject line folks,
Anyway, it seems that camera lens threads are all, or mostly all,
75mm pitch. Cutting metric threads on an inch lathe is of course a
hassle. 34 TPI would be close enough but my gearbox doesn't have a
34 TPI option. Looking at the change gears that came with my lathe
(which has a quick change gearbox), I figured that there must be
some combination of two gears and the quick change gearbox that
would get me close enough to the inch equivalent of .75mm. It turns
out that I have a 30 tooth gear and a 32 tooth gear and that the
ratio between these gears, times 36 TPI, which my lathe does have,
results in a pitch only .0001 different than .75mm, calculated to 5
places. My lathe has two ratio settings for both the headstock
gearbox and the threading gearbox. The headstock gearbox output is
either 1:1 or 2:1 in relation to the spindle. The threading gearbox
input is either 1:2 or 2:1. So, in order to get the .75mm pitch I
set the headstock gearbox to the 2:1 ratio and the quick change
(threading) gearbox to 36 TPI. The change gears are mounted so that
the headstock gear is the 32 tooth gear and the quick change
gearbox gear is the 30 tooth gear. The ratio between the 32 and 30
tooth gears is 1:1.06666666667. The pitch of 36 TPI is .02778 and
.75 mm is .02952. 1.066666667 times 02778 is .02962, which is only
.00010 more than .02952(.75mm). I'm pretty certain that all lathes
with quick change gearboxes will have even ratios of spindle revs
to quick change gearbox input revs, so as long as a 32 tooth gear
drives a 30 tooth gear (or any set of gears with a 1:1.0666666667
ratio), through an idler or not, you should be able to cut a .75mm
pitch thread and still release the halfnuts after each pass. I'm
sure someone has already posted this info on usenet but I needed
this today and thought it might be useful to someone else.
Especially considering the ubiquity of asian lathes. Cheers,
Eric
I like your thinking on the gear ratios. Be very careful about
opening the half nuts as the success of that has to do with the
pitch of the leadscrew, the thread dial gear, and the pitch being
cut. I do not believe that your system will reliably re-engage the
feed without loosing its synchronization if you allow the dial to go
all the way around. A metric thread re-synchronizes with an inch
leadscrew every 127
turns of the spindle so a 0.75MM thread synchronizes every 3.75
inches. If your thread dial goes around to the next starting point
when you move the carriage 3.75 inches you are good to go. About the
only one I know will work is 0.8MM which synchronizes every 4 inches
and that is the distance for a 32T gear on a 8TPI leadscrew. Of
course if you are not using a 127 tooth gear your error multiplies
for each revolution of the dial also. I think the best way, if you really
need to open the half-nuts, is
to just watch the dial and back up the lathe so it does not go
around. Don Young


I noticed on another group that you indicated your success at opening
the half nuts was due to you actually cutting a 36TPI thread. Because
of the gear change you are actually cutting a 33 3/4 TPI thread. Your
thread dial will work for this if its gear has teeth equal to 4 times
the leadscrew pitch and you always use the same point on the dial.
This requires 4 inches for the gear to go around and will work
correctly for threads that are a multiple of 1/4 TPI. Good work!!

Don Young

Has anyone any idea how/if these threads (in particular the 0.75mm one for
lens filters) might be cut on a Myford ML7 (NOT a Super7) with a gearbox?

Dave (UK)