[BIGBLOCK1965]

This was posted on another forum, and I thought some folks over here might have some ideas on how to do it.

I am in the market for a lathe.

Something I need to do frequently is to clean up threads on large fasteners. These are usually old motorcycle axles. This is easy to with a manual lathe that has a fixed relationship between the tool and the spindle. How would you do this on a CNC lathe that only controls the speed of the spindle, not the absolute position?

[MichaelHenry]

Sounds like a job for an adjustable die or a die head. Geometric makes the latter, though there are other brands. What size threads do you need to chase? Using a die head for 1-1/2x8 threads will need a serious lathe.

[tmarks11]

I would say that a cnc lathe would be the wrong tool for that job.

[BIGBLOCK1965]

I would say that a cnc lathe would be the wrong tool for that job.

Yes, a manual lathe would be a better choice, but he wants a CNC lathe and wonders if he could still do the occasional thread chasing.

[BIGBLOCK1965]

Sounds like a job for an adjustable die or a die head. Geometric makes the latter, though there are other brands. What size threads do you need to chase? Using a die head for 1-1/2x8 threads will need a serious lathe.

I doubt that any motorcycle uses anything like 1-1/2 x 8 threads, but yes, that would require a very large manual lathe. A smaller CNC lathe could do the job by programming a lot of lighter cuts.

[300sniper]

Should be simple by adjusting your z start point.

[tmarks11]

Should be simple by adjusting your z start point.

except that you would also have to specific that angular position of the spindle, or you will pick up the thread in the wrong spot. Tormach doesn't accurately measure the angular position of their spindle, so picking up a thread like that wouldn't work.

You could always mount a die on the cross-slide, but that seems like a good way to break something.

[300sniper]

except that you would also have to specific that angular position of the spindle, or you will pick up the thread in the wrong spot. Tormach doesn't accurately measure the angular position of their spindle, so picking up a thread like that wouldn't work.

You could always mount a die on the cross-slide, but that seems like a good way to break something.

So if you run a threading cycle with an X just above your part, starting at z.1 and watch it, and notice you are about .010' ahead of where you need to be, then you try it again changing only your starting point to z.11, it will not track .010" behind the first attempt?

[tmarks11]

You can probably do it with some practice, but it would be very cumbersome, and I suspect you would wipe out quite a few parts for everyone you got right.

Definitely easier on a manual lathe to pick up the thread.

But (depending on the size of the part), cleaning up a damaged thread is easiest by hand with a die.

[BIGBLOCK1965]

Assuming the guy only has a CNC lathe to work with, and the part is an odd size or very large, for which there would not be dies available, here is how I would approach it. My machine uses mach 3 with a single spindle sensor.

1. Make a wire pointer to the somewhere on lathe spindle and turn the spindle slowly by hand until you see the sensor red light come on and mark the spindle at the pointer. This will give you a reference point where you know the sensor is sending the signal to Mach 3.
2. Put your axle in the chuck and bring the spindle around to the pointer mark. Then move your threading tool into the threads where they are in good shape and run it all the way to the bottom of the thread. This should put your Z axis at the start point of the thread and your spindle at the start point of rotation.
3. Back the X axis out to clear the threads and them move the Z axis back a multiple of the thread pitch. EX- If you were cleaning up 13 TPI threads, your pitch is 0.0769 , so you would move your Z axis back a multiple of that number until it cleared the end of the axle- maybe 0.769 or 1.538 etc.
4. Now your rotational point is set and your Z axis start point is at the thread start. You can set your threading wizard for 13 TPI and whatever the diameter is. I would set the infeed angle to zero, because you are just plunging in to clean up damaged threads. Now, when you start your pass, the Z axis will not start moving until Mach 3 receives the signal from the sensor which is at the appropriate rotational position and Z axis will travel at the proper feed rate to cut the 13 TPI, so it should follow the existing threads and clean up any damaged areas.

[MichaelHenry]

I doubt that any motorcycle uses anything like 1-1/2 x 8 threads, but yes, that would require a very large manual lathe. A smaller CNC lathe could do the job by programming a lot of lighter cuts.

Just an example to qualify my comment since you didn't specify any sort of thread spec and you did mention large fasteners.

[Eldon_Joh]

buy a thread file. combined with the lathe, you should have the thread cleaned up by the time you can get the tool bit aligned.

[adamvs]

+1 on the thread file .. it's a repair, right? 1-1/2-8 would be easy enuf for the SlantPRO. Just take a few more passes, another, what? 10 seconds.

[LeeWay]

You could probably rig up a floating tap head with a die. It would take the path of least resistance I think and chase the threads already there.
It depends on how bad they are, but chasing threads require nowhere near the torque that cutting new threads with a die would.
Then there is a reason most guys with a cnc lathe also have a manual.
My manual doesn't run, but for that, I have two cnc lathes.

Just a thought. You could mount a single point cutter in a floating tap head and that might be all that you need. It would pull itself into the thread. Might take a bit of practice, but I bet you could get it done.

[300sniper]

You can do it easy enough with a Fanuc and Haas has built in cycles for thread repair I believe. I'd find it hard to believe that you couldn't do it with a Tormach.

Save the thread files for repairing that alternator bolt on you '87 Honda Civic. On a restoration type project, do it right.

[tmarks11]

Definitely no "built in cycle for thread repair". But than it is 1/6th the cost of a [new] Haas.

[300sniper]

Definitely no "built in cycle for thread repair". But than it is 1/6th the cost of a [new] Haas.

Fanuc does not have a thread repair cycle (at least not my control) but it's pretty easy to do.