"SteveF" wrote in message
. com...
Let's say I have a small lathe (length) and need to make a threaded screw
longer than the max length of my lathe. Obviously this can be done in
theory by just threading one part, removing from the chuck, reinserting
further back in the headstock and continuing the thread. But in practice
can this be done with enough accuracy for something like a replacement
lead screw for a lathe? Yes, I am aware of parts on Ebay and long
threaded rods from MSC, etc. - this is more of a "how to use my lathe"
machining question.


Steve,
It's been about a quarter century since I've done this (CNC spoiled) but
I'll give it my best shot. First off set your compound slide at 30 degrees
and square up your tool and cut the first section of thread. In all
likelihood your lathe has a threading dial on it and you engage the feed at
the same number at every pass. If so, then what you need to do after you
rechuck the part is to engage the feed on the same number, feed up close to
a cut thread and shut the spindle off leaving the feed engaged. If your
lathe doesn't have a brake be careful as the carriage will continue to feed
as long as the spindle is rotating. Now use a combination of cross slide
travel and compound slide travel to nest the tool into the previously cut
thread. Note the numbers on your compound feed dial as they will be
different than your first thread section. Depending on how fussy you want to
be you can use an eye loupe or some Dykem, and rotate the spindle slightly
by hand to make sure the tool is lined up perfectly with the previously cut
section. Once you are satisfied that the tool is lined up with the thread,
back the tool out, disengage the feed, back the carriage up, start the
spindle and begin threading as normal by picking up the same number on the
threading dial.

HTH
Dan