left hand threading??

[dvk]

quick question I could of course just experiment to figure this out, but I am in the process of making a small self centering vice, for my 4" rotory table, I am still milling in this project havn't gotten to my lathe work yet, so I'll ask a quick question I know you all could give me the answer to, to turn a LEFT hand thread on my lathe, do I need reverse spindle rotation ,carriage feed, or what is the combination, thanks in advance

Dave...

[x39]

Spindle rotation stays the same, feed is reversed. Start the cut on the head stock end of the thread, cutting towards the tailstock. A left handed threading tool is used.

[Al Messer]

Yep! I agree with what he says.

[rbregn]

I set everything just like I'm cutting a righthand thread, except I put my tool in upside down and reverse the spindle. That way you can still start at the tail stock end.

[x39]

rbregn- my problem with that method would be the fact that the cutting forces would tend to lift the carriage off the ways of the machine. Probably not a problem on a most lighter work, but if a person were to get into some heavy cuts it could present a problem. If feeding from the headstock toward the tailstock is impractical, perhaps one could reverse spindle rotation and place the tool cutting side up on the back side of the work piece, in feed towards the operator. That way the cutting forces would be towards the bed of the machine. Again, a left handed tool would be used.

[rbregn]

I never had a problem with the carrage lifting, the coursest pitch I've cut this way is 6tpi. But the smallest lathe I run is a 16" summit. I cut them alot when rebuilding turbine water pumps. all thier sahfts and couplers are left hand threads. But I could see a possable problem using a "lite duty"lathe.
By the way, what's the difference between a right and left hand single point threading tool? I use the same for both. You must have something special.
Rob

[x39]

<font face="Verdana, Arial" size="2">Originally posted by rbregn:


By the way, what's the difference between a right and left hand single point threading tool? I use the same for both. You must have something special.
Rob</font>

Nothing special at all. Even though the tool has a 60 degree point, I grind my tools so they have positive rake on the cutting edge. This keeps the tool from crowding the material as it cuts. I also relieve the leading face to follow the lead angle of the thread (more or less), sort of like the same form the tooth on a tap would have. Do you use inserts or grind your own? I can see where your method would work well with a Summit, that's a good heavy machine. Doesn't the 16" machine have something like a 3" spindle bore? I was thinking smaller. On many smaller machines, the only thing really holding the carriage in place is gravity.

[rbregn]

I use inserts. If you try inserts, get coated ones or you'll replace after every thread. Its one plase where coated inserts are well worth alittle more cost. Our 16" summit has a 3" bore and our 19" has a 4.062 bore and we mounted a chuck on the back side. That is really handy!
Rob

[darryl]

Left hand thread is easier in one way, in that you start the thread at the headstock, using normal rotation, and the tool just runs out off the workpiece. Still need reverse feed, though.

[x39]

<font face="Verdana, Arial" size="2">Originally posted by rbregn:
. Our 16" summit has a 3" bore and our 19" has a 4.062 bore and we mounted a chuck on the back side. That is really handy!
Rob</font>

Thanks for the pointer on the inserts. Dual chucks, man, you're making me jealous!