I bought the RF-30 mill. It was cheap enough, but I was hesitant about
whether I would get any use out of it, but then I figured its got to be
better than either of my drill presses and the price was a lot less than any
good drill press. The seller threw in some tooling and an old 8.5 by 18 HF
31316 lathe to get me to close the deal.

I figured out the basics of the mill pretty quick. Its biggest limitation
is the rigidity of the quill. It is way better than either of my drill
presses and still quite a bit better than the cheap mill drill I use as a
"better" drill press. However at full extension I can feel atleast a few
thousandths deflection with the quill locked. A couple quick runs with a
face mill on aluminum pretty much confirmed this from the fair finish
quality. Basically its exactly what I expected. The vises, mills, several
chucks, several collets, clamping set, etc were a nice little bonus.

About the "free" lathe.

I didn't think a whole lot of the lathe, but figured it had to be worth a
couple hundred bucks. Its not bad, but not great Somebody must have worked
on it at one time because the center line of the chuck is pretty close to
parallel with the ways. The tailstock is adjusted pretty darn close too.
There is where the good news ends.

The pulley's were jacked around for maximum speed. I think two of the
pulleys are actually reversed on the shafts to give greater speed increase.
Its enough that it bogs down the motor on startup. It claims it only has a
3/4 HP motor, but once it gets going its unstoppable. I mean it will hog a
..06 deep thread in one pass in 1" aluminum rod. Badly, LOL, but it does
it. (its way to fast for thread cutting the way it is.)

Anyway, the speed was jacked up to use it for wood turning. I know because
everything was full of sawdust.

If anybody has one of these things I'ld sure appreciate a picture of the
pulleys and belts, and the size of the belts. They are certainly not the
original belts if I am correct about the pulley setup. The way they are now
its impossible to slow the machine down enough to do real (or surreal) metal
work.

The next bad news. The saddle itself is sloppy on the ways. The ways
themselves don't look bad or even worn, but the way to adjust the saddle is
not immediately apparent. I'm sure I'll figure it out eventually, but a
scan of the original manual or atleast the exploded parts diagrams would
sure be nice.

More bad news. Some of the threads listed in the gear chart are impossible
to cut. No kidding. If I try to install the gears for one thread I tried I
found one gear would not reach the threading drive gear, and the other was
so big it would hit the pulley. I think somebody figured out the ratio when
it was originally built and never bothered to check if the gears would fit.
LOL.

One small bit of good news. After I got the compounded apart, sawdust
cleaned out, relubed, and reassembled it I found its slightly more rigid
than the mini lathe. Of course that doesn't help until I figure out how to
tighten up the saddle on the ways.

Pictures? Manual? Anybody?

I already posted on CNCZONE in the manual section, and on the 8x18 lathe
group on Yahoo.

Now for a scary thought. I'm considering CNCing it, but in a way to retain
manual operation. LOL (it really is better than the mini lathe in some
ways)

"Bob La Londe" wrote in message
...
I bought the RF-30 mill. It was cheap enough, but I was hesitant about
whether I would get any use out of it, but then I figured its got to be
better than either of my drill presses and the price was a lot less than
any good drill press. The seller threw in some tooling and an old 8.5 by
18 HF 31316 lathe to get me to close the deal....

The next bad news. The saddle itself is sloppy on the ways. The ways
themselves don't look bad or even worn, but the way to adjust the saddle
is not immediately apparent. I'm sure I'll figure it out eventually, but
a scan of the original manual or atleast the exploded parts diagrams would
sure be nice.

More bad news. Some of the threads listed in the gear chart are
impossible to cut. No kidding. If I try to install the gears for one
thread I tried I found one gear would not reach the threading drive gear,
and the other was so big it would hit the pulley. I think somebody
figured out the ratio when it was originally built and never bothered to
check if the gears would fit.
Pictures? Manual? Anybody?

Does any of this look like yours?
http://littlemachineshop.com/Info/Images/44859Parts.pdf

jsw

http://manuals.harborfreight.com/man...1999/31316.pdf

-----
Regards,
Carl Ijames
"Bob La Londe" wrote in message ...

I bought the RF-30 mill. It was cheap enough, but I was hesitant about
whether I would get any use out of it, but then I figured its got to be
better than either of my drill presses and the price was a lot less than any
good drill press. The seller threw in some tooling and an old 8.5 by 18 HF
31316 lathe to get me to close the deal.

I figured out the basics of the mill pretty quick. Its biggest limitation
is the rigidity of the quill. It is way better than either of my drill
presses and still quite a bit better than the cheap mill drill I use as a
"better" drill press. However at full extension I can feel atleast a few
thousandths deflection with the quill locked. A couple quick runs with a
face mill on aluminum pretty much confirmed this from the fair finish
quality. Basically its exactly what I expected. The vises, mills, several
chucks, several collets, clamping set, etc were a nice little bonus.

About the "free" lathe.

I didn't think a whole lot of the lathe, but figured it had to be worth a
couple hundred bucks. Its not bad, but not great Somebody must have worked
on it at one time because the center line of the chuck is pretty close to
parallel with the ways. The tailstock is adjusted pretty darn close too.
There is where the good news ends.

The pulley's were jacked around for maximum speed. I think two of the
pulleys are actually reversed on the shafts to give greater speed increase.
Its enough that it bogs down the motor on startup. It claims it only has a
3/4 HP motor, but once it gets going its unstoppable. I mean it will hog a
..06 deep thread in one pass in 1" aluminum rod. Badly, LOL, but it does
it. (its way to fast for thread cutting the way it is.)

Anyway, the speed was jacked up to use it for wood turning. I know because
everything was full of sawdust.

If anybody has one of these things I'ld sure appreciate a picture of the
pulleys and belts, and the size of the belts. They are certainly not the
original belts if I am correct about the pulley setup. The way they are now
its impossible to slow the machine down enough to do real (or surreal) metal
work.

The next bad news. The saddle itself is sloppy on the ways. The ways
themselves don't look bad or even worn, but the way to adjust the saddle is
not immediately apparent. I'm sure I'll figure it out eventually, but a
scan of the original manual or atleast the exploded parts diagrams would
sure be nice.

More bad news. Some of the threads listed in the gear chart are impossible
to cut. No kidding. If I try to install the gears for one thread I tried I
found one gear would not reach the threading drive gear, and the other was
so big it would hit the pulley. I think somebody figured out the ratio when
it was originally built and never bothered to check if the gears would fit.
LOL.

One small bit of good news. After I got the compounded apart, sawdust
cleaned out, relubed, and reassembled it I found its slightly more rigid
than the mini lathe. Of course that doesn't help until I figure out how to
tighten up the saddle on the ways.

Pictures? Manual? Anybody?

I already posted on CNCZONE in the manual section, and on the 8x18 lathe
group on Yahoo.

Now for a scary thought. I'm considering CNCing it, but in a way to retain
manual operation. LOL (it really is better than the mini lathe in some
ways)

"Carl Ijames" wrote in message
...
http://manuals.harborfreight.com/man...1999/31316.pdf


Thanks. I appreciate that.




-----
Regards,
Carl Ijames
"Bob La Londe" wrote in message ...

I bought the RF-30 mill. It was cheap enough, but I was hesitant about
whether I would get any use out of it, but then I figured its got to be
better than either of my drill presses and the price was a lot less than
any
good drill press. The seller threw in some tooling and an old 8.5 by 18
HF
31316 lathe to get me to close the deal.

I figured out the basics of the mill pretty quick. Its biggest limitation
is the rigidity of the quill. It is way better than either of my drill
presses and still quite a bit better than the cheap mill drill I use as a
"better" drill press. However at full extension I can feel atleast a few
thousandths deflection with the quill locked. A couple quick runs with a
face mill on aluminum pretty much confirmed this from the fair finish
quality. Basically its exactly what I expected. The vises, mills,
several
chucks, several collets, clamping set, etc were a nice little bonus.

About the "free" lathe.

I didn't think a whole lot of the lathe, but figured it had to be worth a
couple hundred bucks. Its not bad, but not great Somebody must have
worked
on it at one time because the center line of the chuck is pretty close to
parallel with the ways. The tailstock is adjusted pretty darn close too.
There is where the good news ends.

The pulley's were jacked around for maximum speed. I think two of the
pulleys are actually reversed on the shafts to give greater speed
increase.
Its enough that it bogs down the motor on startup. It claims it only has
a
3/4 HP motor, but once it gets going its unstoppable. I mean it will hog
a
.06 deep thread in one pass in 1" aluminum rod. Badly, LOL, but it does
it. (its way to fast for thread cutting the way it is.)

Anyway, the speed was jacked up to use it for wood turning. I know
because
everything was full of sawdust.

If anybody has one of these things I'ld sure appreciate a picture of the
pulleys and belts, and the size of the belts. They are certainly not the
original belts if I am correct about the pulley setup. The way they are
now
its impossible to slow the machine down enough to do real (or surreal)
metal
work.

The next bad news. The saddle itself is sloppy on the ways. The ways
themselves don't look bad or even worn, but the way to adjust the saddle
is
not immediately apparent. I'm sure I'll figure it out eventually, but a
scan of the original manual or atleast the exploded parts diagrams would
sure be nice.

More bad news. Some of the threads listed in the gear chart are
impossible
to cut. No kidding. If I try to install the gears for one thread I tried
I
found one gear would not reach the threading drive gear, and the other was
so big it would hit the pulley. I think somebody figured out the ratio
when
it was originally built and never bothered to check if the gears would
fit.
LOL.

One small bit of good news. After I got the compounded apart, sawdust
cleaned out, relubed, and reassembled it I found its slightly more rigid
than the mini lathe. Of course that doesn't help until I figure out how
to
tighten up the saddle on the ways.

Pictures? Manual? Anybody?

I already posted on CNCZONE in the manual section, and on the 8x18 lathe
group on Yahoo.

Now for a scary thought. I'm considering CNCing it, but in a way to
retain
manual operation. LOL (it really is better than the mini lathe in some
ways)

"Jim Wilkins" wrote in message
...

"Bob La Londe" wrote in message
...
I bought the RF-30 mill. It was cheap enough, but I was hesitant about
whether I would get any use out of it, but then I figured its got to be
better than either of my drill presses and the price was a lot less than
any good drill press. The seller threw in some tooling and an old 8.5 by
18 HF 31316 lathe to get me to close the deal....

The next bad news. The saddle itself is sloppy on the ways. The ways
themselves don't look bad or even worn, but the way to adjust the saddle
is not immediately apparent. I'm sure I'll figure it out eventually, but
a scan of the original manual or atleast the exploded parts diagrams
would sure be nice.

More bad news. Some of the threads listed in the gear chart are
impossible to cut. No kidding. If I try to install the gears for one
thread I tried I found one gear would not reach the threading drive gear,
and the other was so big it would hit the pulley. I think somebody
figured out the ratio when it was originally built and never bothered to
check if the gears would fit.
Pictures? Manual? Anybody?

Does any of this look like yours?
http://littlemachineshop.com/Info/Images/44859Parts.pdf

Thanks Jim. Maybe, except this one does not have a quick change gear box
and many of the newer models do. Thanks for the link.

FWIW, most of the small import lathes can cut many more thread pitches than
are shown on labels or in manuals.
Then, there are some improvised/alternate gear combinations that are within
a RCH of being right on the nose (sniff).

I put a pdf file in one of the old dropbox archives which shows many pitches
for the popular 9x20 lathe models, so if your machine is a kinda-sorta copy,
and you have the same gears to select from, you're in good shape there.. not
too important though, I guess, if you CNC it.

There are likely to be Yahoo groups related to the RF and clone mill models,
so someone may be able to steer you to groups for your new machines.

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


"Bob La Londe" wrote in message
...
I bought the RF-30 mill. It was cheap enough, but I was hesitant about
whether I would get any use out of it, but then I figured its got to be
better than either of my drill presses and the price was a lot less than
any good drill press. The seller threw in some tooling and an old 8.5 by
18 HF 31316 lathe to get me to close the deal.

I figured out the basics of the mill pretty quick. Its biggest limitation
is the rigidity of the quill. It is way better than either of my drill
presses and still quite a bit better than the cheap mill drill I use as a
"better" drill press. However at full extension I can feel atleast a few
thousandths deflection with the quill locked. A couple quick runs with a
face mill on aluminum pretty much confirmed this from the fair finish
quality. Basically its exactly what I expected. The vises, mills,
several chucks, several collets, clamping set, etc were a nice little
bonus.

About the "free" lathe.

I didn't think a whole lot of the lathe, but figured it had to be worth a
couple hundred bucks. Its not bad, but not great Somebody must have
worked on it at one time because the center line of the chuck is pretty
close to parallel with the ways. The tailstock is adjusted pretty darn
close too. There is where the good news ends.

The pulley's were jacked around for maximum speed. I think two of the
pulleys are actually reversed on the shafts to give greater speed
increase. Its enough that it bogs down the motor on startup. It claims it
only has a 3/4 HP motor, but once it gets going its unstoppable. I mean
it will hog a .06 deep thread in one pass in 1" aluminum rod. Badly, LOL,
but it does it. (its way to fast for thread cutting the way it is.)

Anyway, the speed was jacked up to use it for wood turning. I know
because everything was full of sawdust.

If anybody has one of these things I'ld sure appreciate a picture of the
pulleys and belts, and the size of the belts. They are certainly not the
original belts if I am correct about the pulley setup. The way they are
now its impossible to slow the machine down enough to do real (or surreal)
metal work.

The next bad news. The saddle itself is sloppy on the ways. The ways
themselves don't look bad or even worn, but the way to adjust the saddle
is not immediately apparent. I'm sure I'll figure it out eventually, but
a scan of the original manual or atleast the exploded parts diagrams would
sure be nice.

More bad news. Some of the threads listed in the gear chart are
impossible to cut. No kidding. If I try to install the gears for one
thread I tried I found one gear would not reach the threading drive gear,
and the other was so big it would hit the pulley. I think somebody
figured out the ratio when it was originally built and never bothered to
check if the gears would fit. LOL.

One small bit of good news. After I got the compounded apart, sawdust
cleaned out, relubed, and reassembled it I found its slightly more rigid
than the mini lathe. Of course that doesn't help until I figure out how
to tighten up the saddle on the ways.

Pictures? Manual? Anybody?

I already posted on CNCZONE in the manual section, and on the 8x18 lathe
group on Yahoo.

Now for a scary thought. I'm considering CNCing it, but in a way to
retain manual operation. LOL (it really is better than the mini lathe in
some ways)

"Wild_Bill" wrote in message
...
FWIW, most of the small import lathes can cut many more thread pitches
than are shown on labels or in manuals.
Then, there are some improvised/alternate gear combinations that are
within a RCH of being right on the nose (sniff).

I'm going to have to find that. Remember where I should start looking?



I put a pdf file in one of the old dropbox archives which shows many
pitches for the popular 9x20 lathe models, so if your machine is a
kinda-sorta copy, and you have the same gears to select from, you're in
good shape there.. not too important though, I guess, if you CNC it.

I was thinking that, but every once in a while I will want to "feel" what I
am doing I suspect or thread something quick without waiting for the
computer to boot up. Then it mighbt be faster to wait for the computer than
to change gears. LOL.




There are likely to be Yahoo groups related to the RF and clone mill
models, so someone may be able to steer you to groups for your new
machines.

There are a number of RF-30 conversions out there, but I was thinking about
leaving it manual. I've already got the Taig and the Max NC for small
stuff, and the Hurco for big stuff. The biggest thing I might do to it is
see how I can improve the quill. Then again I might CNC it, but set it up
to be manual as well. For now its staying manual.




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


"Bob La Londe" wrote in message
...
I bought the RF-30 mill. It was cheap enough, but I was hesitant about
whether I would get any use out of it, but then I figured its got to be
better than either of my drill presses and the price was a lot less than
any good drill press. The seller threw in some tooling and an old 8.5 by
18 HF 31316 lathe to get me to close the deal.

I figured out the basics of the mill pretty quick. Its biggest
limitation is the rigidity of the quill. It is way better than either of
my drill presses and still quite a bit better than the cheap mill drill I
use as a "better" drill press. However at full extension I can feel
atleast a few thousandths deflection with the quill locked. A couple
quick runs with a face mill on aluminum pretty much confirmed this from
the fair finish quality. Basically its exactly what I expected. The
vises, mills, several chucks, several collets, clamping set, etc were a
nice little bonus.

About the "free" lathe.

I didn't think a whole lot of the lathe, but figured it had to be worth a
couple hundred bucks. Its not bad, but not great Somebody must have
worked on it at one time because the center line of the chuck is pretty
close to parallel with the ways. The tailstock is adjusted pretty darn
close too. There is where the good news ends.

The pulley's were jacked around for maximum speed. I think two of the
pulleys are actually reversed on the shafts to give greater speed
increase. Its enough that it bogs down the motor on startup. It claims
it only has a 3/4 HP motor, but once it gets going its unstoppable. I
mean it will hog a .06 deep thread in one pass in 1" aluminum rod.
Badly, LOL, but it does it. (its way to fast for thread cutting the way
it is.)

Anyway, the speed was jacked up to use it for wood turning. I know
because everything was full of sawdust.

If anybody has one of these things I'ld sure appreciate a picture of the
pulleys and belts, and the size of the belts. They are certainly not the
original belts if I am correct about the pulley setup. The way they are
now its impossible to slow the machine down enough to do real (or
surreal) metal work.

The next bad news. The saddle itself is sloppy on the ways. The ways
themselves don't look bad or even worn, but the way to adjust the saddle
is not immediately apparent. I'm sure I'll figure it out eventually, but
a scan of the original manual or atleast the exploded parts diagrams
would sure be nice.

More bad news. Some of the threads listed in the gear chart are
impossible to cut. No kidding. If I try to install the gears for one
thread I tried I found one gear would not reach the threading drive gear,
and the other was so big it would hit the pulley. I think somebody
figured out the ratio when it was originally built and never bothered to
check if the gears would fit. LOL.

One small bit of good news. After I got the compounded apart, sawdust
cleaned out, relubed, and reassembled it I found its slightly more rigid
than the mini lathe. Of course that doesn't help until I figure out how
to tighten up the saddle on the ways.

Pictures? Manual? Anybody?

I already posted on CNCZONE in the manual section, and on the 8x18 lathe
group on Yahoo.

Now for a scary thought. I'm considering CNCing it, but in a way to
retain manual operation. LOL (it really is better than the mini lathe
in some ways)

I noticed you mentioned your new lathe doesn't include a QCGB, and I
thought: Oh, wunnah those.
Still, there may be a Yahoo group, or someone that knows about the headstock
gearing and leadscrew size/pitch etc.

I'm not so swift with the math required to do the gear ratios/leadscrew
pitch math.. so I just mount a dial indicator and count the spindle
rotations to double-check the setup before committing to chip cutting.

The 9x20 models have the gearbox, but here is where a chart can be found in
the 2004 archives..
http://www.metalworking.com/dropbox/...retired_files/
9X20Lathe_threads.pdf

Link to other comments in RCM archived messages can be found by searching
for..
Expanded threading chart for 9x20 lathes NOPOL

http://groups.google.com/group/rec.c...h+th is+group

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


"Bob La Londe" wrote in message
...
"Wild_Bill" wrote in message
...
FWIW, most of the small import lathes can cut many more thread pitches
than are shown on labels or in manuals.
Then, there are some improvised/alternate gear combinations that are
within a RCH of being right on the nose (sniff).

I'm going to have to find that. Remember where I should start looking?



I put a pdf file in one of the old dropbox archives which shows many
pitches for the popular 9x20 lathe models, so if your machine is a
kinda-sorta copy, and you have the same gears to select from, you're in
good shape there.. not too important though, I guess, if you CNC it.

I was thinking that, but every once in a while I will want to "feel" what
I am doing I suspect or thread something quick without waiting for the
computer to boot up. Then it mighbt be faster to wait for the computer
than to change gears. LOL.




There are likely to be Yahoo groups related to the RF and clone mill
models, so someone may be able to steer you to groups for your new
machines.

There are a number of RF-30 conversions out there, but I was thinking
about leaving it manual. I've already got the Taig and the Max NC for
small stuff, and the Hurco for big stuff. The biggest thing I might do to
it is see how I can improve the quill. Then again I might CNC it, but set
it up to be manual as well. For now its staying manual.




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


"Bob La Londe" wrote in message
...
I bought the RF-30 mill. It was cheap enough, but I was hesitant about
whether I would get any use out of it, but then I figured its got to be
better than either of my drill presses and the price was a lot less than
any good drill press. The seller threw in some tooling and an old 8.5 by
18 HF 31316 lathe to get me to close the deal.

I figured out the basics of the mill pretty quick. Its biggest
limitation is the rigidity of the quill. It is way better than either
of my drill presses and still quite a bit better than the cheap mill
drill I use as a "better" drill press. However at full extension I can
feel atleast a few thousandths deflection with the quill locked. A
couple quick runs with a face mill on aluminum pretty much confirmed
this from the fair finish quality. Basically its exactly what I
expected. The vises, mills, several chucks, several collets, clamping
set, etc were a nice little bonus.

About the "free" lathe.

I didn't think a whole lot of the lathe, but figured it had to be worth
a couple hundred bucks. Its not bad, but not great Somebody must have
worked on it at one time because the center line of the chuck is pretty
close to parallel with the ways. The tailstock is adjusted pretty darn
close too. There is where the good news ends.

The pulley's were jacked around for maximum speed. I think two of the
pulleys are actually reversed on the shafts to give greater speed
increase. Its enough that it bogs down the motor on startup. It claims
it only has a 3/4 HP motor, but once it gets going its unstoppable. I
mean it will hog a .06 deep thread in one pass in 1" aluminum rod.
Badly, LOL, but it does it. (its way to fast for thread cutting the
way it is.)

Anyway, the speed was jacked up to use it for wood turning. I know
because everything was full of sawdust.

If anybody has one of these things I'ld sure appreciate a picture of the
pulleys and belts, and the size of the belts. They are certainly not
the original belts if I am correct about the pulley setup. The way they
are now its impossible to slow the machine down enough to do real (or
surreal) metal work.

The next bad news. The saddle itself is sloppy on the ways. The ways
themselves don't look bad or even worn, but the way to adjust the saddle
is not immediately apparent. I'm sure I'll figure it out eventually,
but a scan of the original manual or atleast the exploded parts diagrams
would sure be nice.

More bad news. Some of the threads listed in the gear chart are
impossible to cut. No kidding. If I try to install the gears for one
thread I tried I found one gear would not reach the threading drive
gear, and the other was so big it would hit the pulley. I think
somebody figured out the ratio when it was originally built and never
bothered to check if the gears would fit. LOL.

One small bit of good news. After I got the compounded apart, sawdust
cleaned out, relubed, and reassembled it I found its slightly more rigid
than the mini lathe. Of course that doesn't help until I figure out how
to tighten up the saddle on the ways.

Pictures? Manual? Anybody?

I already posted on CNCZONE in the manual section, and on the 8x18 lathe
group on Yahoo.

Now for a scary thought. I'm considering CNCing it, but in a way to
retain manual operation. LOL (it really is better than the mini lathe
in some ways)

"Wild_Bill" wrote
...
I'm not so swift with the math required to do the gear ratios/leadscrew
pitch math.. so I just mount a dial indicator and count the spindle
rotations to double-check the setup before committing to chip cutting.
--
WB

If the spindle and leadscrew turn at the same speed the lathe will cut the
leadscrew's pitch. For other threads the gear-up or -down ratio equals the
pitch ratio. Finer threads require a slower leadscrew so it gets the larger
gear.

For example my leadscrew has 8 threads per inch. To cut 3/8-16 the leadscrew
has to be reduced to half speed with 2:1 ratio gears, like 48 and 24 or 64
and 32, whatever fits.

jsw

Yep.. see what you're sayin' Jim, although on my larger machine, there is a
2-range speed selector in the headstock for changing between fine and coarse
leadscrew feeds (plus a stack of change gears, but no QCGB).
So, there's the additional gear ratios, and trying to mentally sort it out
on the fly is a bit overwhelming for me anyway.

Luckily for me, I had the pleasure of communicating with a very sharp
participant named Ted Edwards, in the old days here on RCM, and he had
written a program to simplify any pitch that the SOG stack-o-gears is
capable of.

I'm a bit hostile toward software, and respect those who can use it to solve
problems or create easy solutions for the not-so-bright-ones such as myself.

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


"Jim Wilkins" wrote in message
...

"Wild_Bill" wrote
...
I'm not so swift with the math required to do the gear ratios/leadscrew
pitch math.. so I just mount a dial indicator and count the spindle
rotations to double-check the setup before committing to chip cutting.
--
WB

If the spindle and leadscrew turn at the same speed the lathe will cut the
leadscrew's pitch. For other threads the gear-up or -down ratio equals the
pitch ratio. Finer threads require a slower leadscrew so it gets the
larger gear.

For example my leadscrew has 8 threads per inch. To cut 3/8-16 the
leadscrew has to be reduced to half speed with 2:1 ratio gears, like 48
and 24 or 64 and 32, whatever fits.

jsw

"Jim Wilkins" wrote in message
If the spindle and leadscrew turn at the same speed the lathe will cut
the leadscrew's pitch. For other threads the gear-up or -down ratio
equals the pitch ratio. Finer threads require a slower leadscrew so it
gets the larger gear.
jsw

"Wild_Bill" wrote Yep.. see what you're
sayin' Jim, although on my larger machine, there is a 2-range speed
selector in the headstock for changing between fine and coarse leadscrew
feeds (plus a stack of change gears, but no QCGB).
So, there's the additional gear ratios, and trying to mentally sort it out
on the fly is a bit overwhelming for me anyway.

Luckily for me, I had the pleasure of communicating with a very sharp
participant named Ted Edwards, in the old days here on RCM, and he had
written a program to simplify any pitch that the SOG stack-o-gears is
capable of.

I'm a bit hostile toward software, and respect those who can use it to
solve problems or create easy solutions for the not-so-bright-ones such as
myself.
WB

You deal with the fine and coarse feeds by assuming they are two
interchangeable direct-drive leadscrews of appropriate pitch. An 8 TPI
leadscrew geared to half speed is equivalent to a 16TPI one driven at
spindle speed. It might be easier to think in terms of how far the carriage
moves per spindle rotation, half of 1/8" is 1/16" in this case.

My South Bend has a spindle-speed 40 tooth gear on the tumbler stud driving
a 56 tooth on the gearbox input through an 80 tooth idler. I have no idea
what some of the gears in the box are, I only know that when I set it to cut
8 threads per inch the 8 TPI leadscrew and the spindle turn at the same
rates.

The threading chart was missing and I had to reconstruct it from a barely
legible photo.

The left-hand lever clearly doubles the threads per inch with each step,
starting at 4TPI and ending at 256. The right-hand one's progression was
less evident as some positions cut standard threads at only at one
left+right combination, like 11-1/2 and 27 TPI for pipe threads. The top row
of my chart is 4 4.5 5 5.5 5.75 6 6.5 6.75 7 7.5

When I bought the lathe I was making optical components which are all
metric. I entered the coarsest right-hand-lever thread pitches given above
into the columns of a spreadsheet and made the rows progressively double
them, corresponding to the positions of the left-hand lever. Then I tried
several combinations of metric transposing gears to see if multiplying all
the cells by the transposing gear ratio of N/127 gave useful optical thread
pitches. 100/127 is South Bend's standard but I had more hits on the finer
pitches with 120/127.

jsw