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Reversing carriage travel on a lathe when threading, two choices

Bill D

Diamond
Joined
Apr 1, 2004
Location
Modesto, CA USA
I understand about reversing carriage travel after each cut when single point threading on a lathe. Back cutter away from work before reversing etc.
My question is on my lathe I have two ways to do the reverse. One is I can reverse the motor and everything runs backwards. the other option is I have a reverse lever, not sure of the correct name, on the headstock. This keeps spindle rotation the same while it reverse the carriage travel direction.
I would not shift into reverse without first stopping the motor so no time saved. Is one method preferred over the other and why. It is just a 3hp motor so stopping each time is no big deal.
Bill D.
 
You will lose the the sync between the lead screw and headstock by using the reversing lever, don’t do that. Open the half nut and crank it back if you’re making imperial threads on an imperial lathe or reverse the spindle if you can’t (or don’t want to) open the half nut.
 
You will lose the the sync between the lead screw and headstock by using the reversing lever, don’t do that. Open the half nut and crank it back if you’re making imperial threads on an imperial lathe or reverse the spindle if you can’t (or don’t want to) open the half nut.
Have to reverse the spindle motor and do not open the half nut if machining metric threads on imperial lead screw lathe.
 
See a Utube of a guy cutting a coarse thread using his foot on a lever on the saddle to synch the cutting ......bare feet ,of course ,you just cant get the result in sandals.
 
He is talking about the tumbler reverse which reverses the direction of the lead screw ONLY. Even if you keep the half nuts closed, if you reverse the lead screw with the tumbler reverse, you WILL loose sync.

For the benefit of the OP and other novices:

In single point threading situations where you can not use the threading dial, you MUST keep the entire mechanical connection between the spindle (and the work mounted on it) and the threading tool exactly as it was for the first pass. If you interrupt that path at ANY POINT, you can and probably will lose sync.

The tumbler reverse on the head stock is intended to allow you to use either an even or an odd number of gears between the spindle and the lead screw OR to allow you to single point thread either a right hand or a left hand thread. It is NOT intended to be used to backup the lead screw when the threading dial does not function to synchronize subsequent threading passes.

There ARE two ways to back up while threading that preserve the synchronization. One is if you have a motor that has electric reverse controls. And the other is to MANUALLY turn the chuck or spindle backwards. Both of them require that the entire mechanical connection from work piece to the threading tool must be kept connected at all times.



Have to reverse the spindle motor and do not open the half nut if machining metric threads on imperial lead screw lathe.
 
So I did some threading today 12TPI on a inch leadscrew. I am having apron problems so I left the half nut closed. Reversing the motor seems much easier and logical. Yesterday I was doing it with half nuts closed and using the tumbler reverse. Maybe because it was an even thread count it stayed in sync.
Bill D
 
Reversing the motor without disengaging anything on the drive train is the only way to go. I have a 1916 Seneca Falls Star lathe that's never had a thread dial. Over the years I've made hundreds of internal and external threads without problems. The key is to back up the drivetrain until the tool is well behind the first thread. When the spindle and leadscrew are once again going the proper direction for threading all the drivetrain play will be in the same position it was on the first pass. Everything will line up perfectly and the threads will turn out fine.
 
So I did some threading today 12TPI on a inch leadscrew. I am having apron problems so I left the half nut closed. Reversing the motor seems much easier and logical. Yesterday I was doing it with half nuts closed and using the tumbler reverse. Maybe because it was an even thread count it stayed in sync.
Bill D
I think you got lucky.

I often do the motor reverse method, my half nut has a tendency to only half engage and then wipe the thread out.
 
I am thinking that 12 tpi is divisable by 4 and that made it stay in sync. I seem to think the leadscrew is either 4 or 6 tpi either of which divides into 12 nicely.
I will no longer push my luck. reversing the motor from now on it is
bill D.
 
Sir,
On an imperial leadscrew, cutting any multiple of leadscrew's TPI, you can engage half nut at any time. No need for any tricks.
Bob....not the cat.
 








 
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