# Threading Revelation



## Surprman (Dec 22, 2015)

I have done a bit of threading with my SB 9C and have had variable levels of success.  Yesterday I was making a part for a friend and after getting most of the turning completed, I needed to single point turn a metric thread on in (I made a nice conversion gearset a while ago).  Anyway,  after a couple passes I had ruined the part because the tool did not track in the same path.  It was ugly and frustrating. I used the scrap to try out some things.  While I was playing I realized that my method was wrong.  I have no thread dial (those things are pricey!). I had been keeping the half nuts engaged and simply reversing the lead screw - by switching the transposing gear.  Yep.  That was the problem.  I realized that switching the gears with the lever sometimes throws off the chuck/leadscrew arrangement between passes.  Uggh -  that was embarrassing to realize.  I ran some tests by simply reversing the motor between passes.  It worked like a dream.  I applied the same technique to a rebuild of the original part and it came out great - best thread I ever made.  Hope this description will help somorone else out.
Rick


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## T Bredehoft (Dec 22, 2015)

Not too surprising, this same solution was discovered in the last two weeks in another thread. A new machinist couldn't understand when the same thing happened.


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## David VanNorman (Dec 22, 2015)

You must reverse the lathe. If you disconnect the spindle from the lead screw in any way you will sooner or later end up screwing up the thread. On an English thread if you you have a thread dial you can  take and open the thread lever , but if you don't have a thread dial you will be lost.


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## stupoty (Dec 23, 2015)

I used to mark the chuck and the lead screw with a sharpie and re line the lines up if i wanted to disingage the half but, slow but worked.

Stuart


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## brino (Dec 23, 2015)

T Bredehoft said:


> Not too surprising, this same solution was discovered in the last two weeks in another thread. A new machinist couldn't understand when the same thing happened.



Tom, that's the first thing that occurred to me to.
Here's the other thread:

http://www.hobby-machinist.com/threads/thread-crest-override.40895/

-brino


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## Surprman (Dec 23, 2015)

Thanks all!  I wish I had come across that thread earlier.  I did feel good about figuring out what I was doing wrong on my own, though.  I finished up the part this morning(the larger of the two parts in the first photo).  My friend wanted an Allen head put on the side opposite the threads.  I made up a broach out of an 8mm wrench (had to hit it with a Mapp gas torch to in harden the wrench material).  It worked ok, but my smallish arbor press was not up to the task on that size so I had to drill out the hole a little bigger (still works, but more round than hex).  I saw that you could do this with a rotary broach (which looks pretty cool), but those things are expensive!





Rick


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## brino (Dec 23, 2015)

on my (never ending) list is a rotary broach.

some clever folks here have done great things:
http://www.hobby-machinist.com/threads/rotary-broach.30404/
http://www.hobby-machinist.com/threads/a-simple-compact-rotary-broach.33032/
http://www.hobby-machinist.com/threads/project-rotary-broach.33003/

So many neat projects so few life times......
-brino


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