South Bend Lathe Threading problem
 

I am learning to cut threads on my SB Heavy 10 Lathe. I put a piece of
plastic rod in the chuck and a pen in the tool holder to simulate
thread cutting. However I am having trouble matching up the actual TPI
vs what the lathe is set for. At first I tried to replicate 10 tpi. I
set the gear to the correct slot, put the sliding gear "in" and put my
3 position gear selecter in the "center". The result was much more than
10 tpi and more that I could count. So I set it for 5 tpi and tried
again. This time I got about 15 tpi. I have my Bull gear pin "out" and
my back gear "in" and my flat belt on the middle pully.

What am I doing wrong? Could I have metric gears? I bought the lathe
used and dont know its history.

Any ideas on what to try?
Thanks
Steve

Steve-

Sounds like you might be using the power carriage feed instead of the half
nuts. On my SB heavy 10, which like yours has the single lever gear box,
the power feed is one third the speed of threading. In other words, the
setting for 5 tpi corresponds to a longitudinal feed (with the power feed
clutch engaged instead of the half nuts) of .0669 inches per revolution, or
just about 15 tpi. If you don't have one already, you ought to pick up a
copy of the SB publication "How to Run a Lathe". Originals and reprints are
readily available on ebay and elsewhere for modest cost.

Hope this helps,

-Bill Fill
Olympia, WA


"gtslabs" wrote in message
oups.com...
I am learning to cut threads on my SB Heavy 10 Lathe. I put a piece of
plastic rod in the chuck and a pen in the tool holder to simulate
thread cutting. However I am having trouble matching up the actual TPI
vs what the lathe is set for. At first I tried to replicate 10 tpi. I
set the gear to the correct slot, put the sliding gear "in" and put my
3 position gear selecter in the "center". The result was much more than
10 tpi and more that I could count. So I set it for 5 tpi and tried
again. This time I got about 15 tpi. I have my Bull gear pin "out" and
my back gear "in" and my flat belt on the middle pully.

What am I doing wrong? Could I have metric gears? I bought the lathe
used and dont know its history.

Any ideas on what to try?
Thanks
Steve

Bill is correct of course, but be certain that your gear selection is also
correct on the left side of your lathe. You will find a stud gear selection
guide on the front of your quick change gearbox. Make certain you are using
the correct stud gear which is mounted on the drive side of the gearbox. The
large gear is a 40 tooth and the small gear is a 20 tooth. The gears are
mounted together. The choice is made by inverting the gears. Also make
certain that you have an inch lead screw as opposed to a metric pitch. I
believe the inch screw is 8 TPI. A good clue is that the thread indicator
has 4 major divisions, if the leadscrew is inch.
Steve

"Bill Fill" wrote in message
...
Steve-

Sounds like you might be using the power carriage feed instead of the half
nuts. On my SB heavy 10, which like yours has the single lever gear box,
the power feed is one third the speed of threading. In other words, the
setting for 5 tpi corresponds to a longitudinal feed (with the power feed
clutch engaged instead of the half nuts) of .0669 inches per revolution,
or just about 15 tpi. If you don't have one already, you ought to pick
up a copy of the SB publication "How to Run a Lathe". Originals and
reprints are readily available on ebay and elsewhere for modest cost.

Hope this helps,

-Bill Fill
Olympia, WA


"gtslabs" wrote in message
oups.com...
I am learning to cut threads on my SB Heavy 10 Lathe. I put a piece of
plastic rod in the chuck and a pen in the tool holder to simulate
thread cutting. However I am having trouble matching up the actual TPI
vs what the lathe is set for. At first I tried to replicate 10 tpi. I
set the gear to the correct slot, put the sliding gear "in" and put my
3 position gear selecter in the "center". The result was much more than
10 tpi and more that I could count. So I set it for 5 tpi and tried
again. This time I got about 15 tpi. I have my Bull gear pin "out" and
my back gear "in" and my flat belt on the middle pully.

What am I doing wrong? Could I have metric gears? I bought the lathe
used and dont know its history.

Any ideas on what to try?
Thanks
Steve

In article .com, gtslabs
says...

What am I doing wrong? Could I have metric gears? I bought the lathe
used and dont know its history.

See what Bill commented above.

Are you using the half nuts to engage the leadscrew?

If so, then somebody may have put a non-standard
gear in the train.

Jim


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please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
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I had the same confusion with my SB 11", and, as Bill suggests, when I used
the half nuts instead of the carriage feed, things got a little easier. It
also took me a little bit to figure out that there is a stop built in and
the half nut lever won't move and engage the half nuts unless I pull the
cross feed "button" out. I don't know if your H10 is like this, but I
figured I'd mention it.

Peter

"gtslabs" wrote in message
oups.com...
I am learning to cut threads on my SB Heavy 10 Lathe. I put a piece of
plastic rod in the chuck and a pen in the tool holder to simulate
thread cutting. However I am having trouble matching up the actual TPI
vs what the lathe is set for. At first I tried to replicate 10 tpi. I
set the gear to the correct slot, put the sliding gear "in" and put my
3 position gear selecter in the "center". The result was much more than
10 tpi and more that I could count. So I set it for 5 tpi and tried
again. This time I got about 15 tpi. I have my Bull gear pin "out" and
my back gear "in" and my flat belt on the middle pully.

What am I doing wrong? Could I have metric gears? I bought the lathe
used and dont know its history.

Any ideas on what to try?
Thanks
Steve

In article . net, Peter Grey
says...

I had the same confusion with my SB 11", and, as Bill suggests, when I used
the half nuts instead of the carriage feed, things got a little easier. It
also took me a little bit to figure out that there is a stop built in and
the half nut lever won't move and engage the half nuts unless I pull the
cross feed "button" out. I don't know if your H10 is like this, but I
figured I'd mention it.

It's a good point, and his 10L is like that. There's a lockout
to prevent engaging the longitudinal feeds and the halfnuts
at the same time. If one were able to do this (and some old
machines lack such a lock-out) it has the effect of putting
two power transmission paths in parallel, and because they
have two different ratios, it will lock the driven gear and
blow up the weakest link in the driveline.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================