Any safe way to thread away from my chuck on a South Bend 10K?

[Illinoyance]

It's my understanding that 3C collets (more readily available than 6K) can be used in a 10K by using the 3C to MT2 adapter for the 9" lathes. This will limit you to 1/2" dia. though where use of 6K will go up to 5/8ths.

I have a MT3 spindle adapter for 3C collets. I made an extension for the drawbar that fits 3C collets. It is not as convenient as using thr 6Ks but my set of 6Ks are in 1/16" steps. Last time I checked a single 6K from Hardinge was $168. I can get 3Cs in 1/64 increments a lot cheaper. Metric, too.

 

[Illinoyance]

Back to the original question. It is unwise to thread in reverse on any lathe with a threaded spindle. Torque generated by threading COULD cause the chuck to unscrew. For small diameter threads it is probably OK if one accepts the risk. For work held in a collet it is perfectly fine to thread in reverse.

 

[Ken226]

For anyone intimidated by cutting metric threads to a shoulder, with inch leadscrew and thread disl, I've been doing it for many years using the method below.

It lets you use both your inch thread dial, and to disengage the half nut at the shoulder.

Adom is quick at it, but he slows down later in the video and shows better shots of the method.

Adoms like a robot doing that. Very fast.

I run the lathe at a much slower rpm, disengage the half-nut, then leasurely back out the cross slide. For me, I back out the cross slide 1 full turn before reversing the spindle.

When the spindles running in reverse, re-engage the half-nut on the same thread dial setting that you started the thread on. When back to the start of the cut, run the cross slide that 1 full turn in, back to zero. Then take the next pass, thread dial in the same spot as the first pass

The important thing, is after you disengage the half-nut at the end of each pass, don't let the spindle run long enough for the thread dial to make a full revolution past your mark.

Back out the cross slide, and stop the spindle, then reverse it so you can engage the thread dial on the same mark. As long as the thread dial didn't go a full revolution, the same mark will mean the same thread, in exactly the same spot.

 

[twooldvolvos]

Please watch Joe Pieczynski's video on threading in Reverse Direction gear on youtube.

I wish I could use this technique but my understanding is that it is unsafe running a lathe like my South Bend 10K in reverse since the chuck is screwed on and I risk it unscrewing with tool pressure. Am I missing something?

 

[twooldvolvos]

No, the wording of my answer was unfortunate - "If you have collets for your machine, their use would make threading away from the chuck safe". What I should have said is, "If you have collets for your machine, their use would make threading away from the headstock safe". You remove the chuck to use your collets. If you have the correct size collet, it is the best thing to hold your work with, both toward the headstock and toward the tailstock.

When practicing threading, be sure to support the work from BOTH ends. Flexing of the work can frustrate a novice to the point of abandoning the hobby. I don't recommend learning on PVC pipe, since it usually isn't round and it also isn't concentric on the ID and OD, unless you prep the pipe properly (which is also good practice). It's best to have a nut handy in order to test fit your threads, so practice with the thread pitch of the nut.

Having a SHARP tool of the correct geometry is also mandatory. Grind a piece of HSS to the correct geometry, then hone the edge to a very fine finish. DO NOT USE CARBIDE at first. LEARN to grind your own HSS tool bits. It is a skill that you will use as long as you have your lathe.

Ha. Ha. Good catch. There is no chuck involved when using collets. I understood what you were trying to say without noticing any problems with the wording.

 

[mickri]

As I said in my previous post #6 make a chuck keeper. It will prevent the chuck from unthreading when running in reverse.

 

[twooldvolvos]

As I said in my previous post #6 make a chuck keeper. It will prevent the chuck from unthreading when running in reverse.

Mickri. Good point. Being a newbie and wanting to add thread cutting to my resume, I am considering coming up with a chuck keeper and beginning my thread cutting career cutting away from the chuck or using collets. I really don't want to run my tool post into my chuck, but then who does?

 

[Ken226]

Is running the toolpost
into the chuck a common thing?

I haven't done it a single time since I bought my first lathe in 2007. Perhaps I've been lucky.

 

[mickri]

This hobby is not for the inattentive. You have to keep track of what you are doing. Threading towards the chuck is no different from turning towards the chuck. If anything threading is easier to keep from hitting the chuck because as soon as you release the half nuts the carriage stops moving. Whenever I do anything on my lathe I always do a dry run by hand looking for anything that might hit the chuck. I spin the chuck with my left hand while I move the carriage towards the chuck with my right hand. I then change my setup if I have to. The closest that I come to the chuck is when doing internal boring because you want to keep the boring bar as short as possible. I get really close sometimes. Within an 1/8" at times. I should probably turn away from the chuck when boring.

Don't let this stress you out. A little preplanning and you will be fine.

 

[Dabbler]

@twooldvolvos @SLK001 the advice that @mickri is giving is golden.

Even Joe Piecyznski will tell you to never thread away from the chuck if you have a screw on chuck. Joe is on the forum here from time to time, and I hope he chimes in on this thread.

I know that some of our best British friends have made innovative ways to 'keep' the chuck on the lathe including that neat drawbar suggested by @mickri but these devices are more in an 'intermediate to advanced' operators. Take their advice and get used to threading the normal way before trying to use the variants on your threaded spindle.

As a matter of safety and protection for your lathe, the cuts you take for threading should be in the order of .004-.005, so you can slack off the drive belt in case the 'bad thing' happens.. I won't prevent all damage, but it will take care of the worst of it, especially at 150 RPM.