Screwcutting not picking up in the same place

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Mr Ron
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Location: Vancleave, Mississippi

Re: Screwcutting not picking up in the same place

Post by Mr Ron »

Bill Shields wrote: Sat Oct 12, 2019 7:50 am I have been down this road....all the advise is good...but the practical solution is:

when doing metric threads..do NOT disengage the 1/2 nut at the end.

stop the lathe, run it in reverse to back the carriage up to the starting point.
How can you stop the lathe and reverse with the lead screw engaged? The carriage will still be "coasting" before stopping making it impossible to thread up to a shoulder. Unless the lathe will stop instantly, it won't work.
Mr.Ron from South Mississippi
John Evans
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Location: Phoenix ,AZ

Re: Screwcutting not picking up in the same place

Post by John Evans »

How can you stop the lathe and reverse with the lead screw engaged? The carriage will still be "coasting" before stopping making it impossible to thread up to a shoulder. Unless the lathe will stop instantly, it won't work.
Two opinions ,first-easiest is to thread towards the tail stock-second have one of those fancy quick retract tool holders like Multi-Fix tool posts use. A lathe with a clutch and brake like my Clausing 5914 is a help. For all metrics supposed advantages Imperial wins hands down when threading on a lathe.
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choprboy
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Re: Screwcutting not picking up in the same place

Post by choprboy »

Mr Ron wrote: Sat Oct 12, 2019 11:12 am How can you stop the lathe and reverse with the lead screw engaged? The carriage will still be "coasting" before stopping making it impossible to thread up to a shoulder. Unless the lathe will stop instantly, it won't work.
Well... you can use the disengage-engage method to thread up to a shoulder. Thread as normal and then disengage the half nuts at the shoulder and immediately stop the lathe (allowing the spindle to slow down normally). The reverse the lathe and re-engage the half-nuts on the same threading dial line as the first pass. As long as you do not allow the threading dial to fully rotate (or you keep count of dial rotations) you keep the same spot in the gear train/lead screw engagement.
earlgo
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Re: Screwcutting not picking up in the same place

Post by earlgo »

Years ago at the Colorado School of Trades where we had South Bend Lathes, we were taught to thread up to a shoulder, i.e. think of a barrel stub against a receiver, by disengaging the drive with the tool still in the cut, and then turn the chuck by hand until the tool was against the shoulder. Tools were HSS so the tip didn't break off when the cut stopped. Then one could back out the tool, reposition, and take another cut.
My ancient Sebastian and May lathe, circa 1880, has no thread dial, so it was engage the half nuts, cut, stop, retract, reverse, advance, cut, etc. Not the finest finish on the last threads, but serviceable. After a few threads, I installed a motor reversing switch for the reverse traverse. Cranking back by hand was a bit time consuming. :)
--earlgo
Before you do anything, you must do something else first. - Washington's principle.
spro
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Re: Screwcutting not picking up in the same place

Post by spro »

The Warco lathe looks a lot like my Enco. Warco is all metric and the Enco is functionally ~ Imperial. So threading hasn't been a big problem except with Metric. I used the transposing gears and clamped on the same # of the thread dial. Worked twice but usually split the thread. So it was to leave the half-nuts clamped but it isn't a big deal with these. The operation lever is at right side of apron REV-OFF-FOR. It is very quick.
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liveaboard
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Re: Screwcutting not picking up in the same place

Post by liveaboard »

I have no threading dial; I'm a reverser.
It's like everything, it takes a little practice.
Whenever possible I have an end groove the depth of the thread.
I shut off the power and pull the tool out with a quick turn of the cross slide wheel.
Sometimes, when things are tight, I reverse for a moment to stop the lathe. That took a while to get used to doing.
When cutting long threads, I reverse in a higher gear or motor speed. Most threads are pretty short and reversing just takes a few seconds.
Yes, I broke a few tips hitting shoulders. No pain, no gain!
spro
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Re: Screwcutting not picking up in the same place

Post by spro »

Yes.
charkmandler
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Re: Screwcutting not picking up in the same place

Post by charkmandler »

Thanks for all the thoughts and advise. Having used an imperial lathe for imperial threads for years I much prefer not having to leave the half nut engaged. Now with a metric lathe I have got used to leaving the half nut engaged when cutting imperial threads but would prefer to use metric threads when making threaded mandrels and be able to disengage the half nut. Looking in the 'tool box' that came with the lathe there are two small gears that fit on to the index and a table showing their corresponding pitch sizes.
It takes less than a minute to change these gears to be able to disengage the half nut when cutting metric threads. Also feels kinder on the 1ph motor.
Thanks
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