Please help!

I need to know how to make 8 threads per inch on a tos trencin type sv18ra.
Nobody in the shop can figure it out. I have looked all over for reference
material that would help, with no luck. Any help would be greatly
appreciated.

Thank you

Jon

Jon wrote:

Please help!

I need to know how to make 8 threads per inch on a tos trencin type sv18ra.
Nobody in the shop can figure it out. I have looked all over for reference
material that would help, with no luck. Any help would be greatly
appreciated.



Does it have a metric or imperial leadscrew? Most imperial leadscrews on
larger lathes are 8 TPI, so all you need is a 1:1 ratio between the
spindle and
the leadscrew. That should be easy to accomplish.

If the leadscrew is metric, only, then it gets more difficult. Some
lathes have
transposing gear sets that can be inserted in the gear train to make an
approximate
conversion between metric and imperial threads. But, because it is an
approximation, and the basic leadscrew thread is the wrong pitch, you
have to back up the lathe to wind the carriage back to the starting point.
You cannot disengage the half nuts until you are done with the thread.

Jon

What is a tos trencin type sv18ra?
8tpi is generally a pretty easy setting for a lathe to do if that is what it
is. You do need a cutter with the right shape tho.

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink less.
Works evevery time it is tried!

On Wed, 16 Jul 2003 13:40:02 -0500, Jon Elson wrote:
If the leadscrew is metric, only, then it gets more difficult. Some
lathes have
transposing gear sets that can be inserted in the gear train to make an
approximate
conversion between metric and imperial threads.

If the transpose gears are 127 tooth and 100 tooth, it isn't an approximation.
It is *exact*. 127x2 is 254 which is the *exact* number of millimeters in an
inch by definition.

Gary

On Wed, 16 Jul 2003 21:49:40 GMT, (Gary Coffman) wrote:
On Wed, 16 Jul 2003 13:40:02 -0500, Jon Elson wrote:
If the leadscrew is metric, only, then it gets more difficult. Some
lathes have
transposing gear sets that can be inserted in the gear train to make an
approximate
conversion between metric and imperial threads.

If the transpose gears are 127 tooth and 100 tooth, it isn't an approximation.
It is *exact*. 127x2 is 254 which is the *exact* number of millimeters in an
inch by definition.

Er, ah, decimal point decimal point, but it still is exact.

Gary

Gary Coffman wrote:

On Wed, 16 Jul 2003 13:40:02 -0500, Jon Elson wrote:


If the leadscrew is metric, only, then it gets more difficult. Some
lathes have
transposing gear sets that can be inserted in the gear train to make an
approximate
conversion between metric and imperial threads.



If the transpose gears are 127 tooth and 100 tooth, it isn't an approximation.
It is *exact*. 127x2 is 254 which is the *exact* number of millimeters in an
inch by definition.

Gary



The thread will come out exact, assuming the QC box has the right
selection, since
the metric way is thread pitch, while us imperial types do threads/unit
of measure.
But, you STILL have to back up without disengaging the half-nuts,
because the
leadscrew pitch doesn't repeat every inch.

Jon

"Bob May" wrote in message ...
What is a tos trencin type sv18ra?
8tpi is generally a pretty easy setting for a lathe to do if that is what it
is. You do need a cutter with the right shape tho.


Sorry, it is a lathe. Made in Slovakia, sometime in the '70s. I have
access to the right cutter, I just wonder if it is possible to set
this machine to cut 8 threads per inch without modifying it and if so
how.

Thank you

Jon