[enderw88]

I am in the market for a lathe. The Mill Turn is very interesting for the usual reasons.

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?

[BlackICE1]

I don't know of an easy way to sync up the thread.

I have done it once by using a Casio camera set to high speed mode. I started the X off too big and ran a thread pass with the right parameters. Looking at the video I changed the starting Z a little to match up the cutter to the existing threads. As the sync got closer I reduced the X to more the cutter closer repeating the process until the starting Z is right and the X is small enough to cut. To clean the thread probably would have to do at least two separate G32 passes one for the left and another for the right size of the threads. I assume you just want to clean up rusted or slightly deformed threads.

Another way that might work would be to do a complete multi-pass thread cycle G76 by trying to sync up the tip of the cutter to the right side peak of the major diameter of the thread.

[BIGBLOCK1965]

I am in the market for a lathe. The Mill Turn is very interesting for the usual reasons.

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?

I would assume that you are not buying the Mill Turn just for this specific job, because you could probably buy the various dies or thread chasers to cover almost all the axles around for a few hundred dollars. Using a tap or die to chase damaged threads is far easier than setting up in a lathe. I keep a set of the most common ones around, both left and right hand threads for use on trailing arms, tie rod ends etc. However, if you had a Mill Turn and came across an odd ball thread such as a whitworth for which it would be hard to find a die, you could probably chase the thread under CNC.
I have never done it, but here is how I would approach it.

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.

[enderw88]

Thank you. It certainly wouldn't be its primary purpose. The procedure you came up with isn't far off the manual lathe procedure


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[n1tr0]

If you want to clean up threads on a CNC lathe you'll need one that has a proper spindle encoder as a bare minimum (200+ pulses/rev, preferably a quadrature encoder). I'd recommend a machine with a controller running UCCNC or something that's similarly setup for doing threading. The single index counter on the Mill-Turn is not sufficient for any sort of precise positioning, nor is Mach3 over the parallel port consistent...
You could add an encoder wheel and replace the computer and controller on the Shopmaster

[BIGBLOCK1965]

Thank you. It certainly wouldn't be its primary purpose. The procedure you came up with isn't far off the manual lathe procedure


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Make your own conclusions from this other guy, he clearly is only interested in scaring away a potential Mill Turn buyer. I can say without any doubt that the Mill Turn can cut perfect threads, and there are thousands of people out there using the Gecko drives and mach 3 software on all sorts of other machines. Here is a video from a gunsmith cutting threads, and he mentions specifically that he has been able to pick up threads as well.

[BlackICE1]

My Patriot cuts great thread easily. He asking about cleaning up existing threads. Why don't you explain an easy way of doing that? Yes you can do it but it I haven't found an easy way. It isn't a Shoptask limitation but more of how Mach3 works.

Ok removed the bs part, my phone didn't show the other post ???

[n1tr0]

BS I'm not trying to scare him away.

I think he was referring to my post which a moderator edited to remove anything negative about Shopmaster. Apparently when people ask about equipment you can't actually comment about any negative experience you've had with vendors.

[BIGBLOCK1965]

My Patriot cuts great thread easily. He asking about cleaning up existing threads. Why don't you explain an easy way of doing that? Yes you can do it but it I haven't found an easy way. It isn't a Shoptask limitation but more of how Mach3 works.

Ok removed the bs part, my phone didn't show the other post ???

Blackice,
Yes, I was referring to the other guy who threw in a bunch of name calling which the moderator removed. I explained my idea of doing it, but I don't think there is really an easy way on any CNC machine to do thread the cleanup Enderw88 was describing. No matter the program or sensor setup, you will have to manually figure out the Z start position and the rotational position of the spindle in order to create the necessary commands. Probably in the end, it takes longer to describe the process in words than it does to actually do it. I am going to do a copy/paste of his question and post it on the Tormach lathe forum and see if anyone over there has an answer.

[BlackICE1]

I made this steady rest adjuster and threaded them LH M8x1.25. I used 4 tools with out removing the stock and it was pretty easy. This is the 1st time I ever to the trouble to setup the tool table. The BXA QCTP came in handy. Much better than what came with the machine.

I am making 2 sets of roller bearing fingers for the steady rest. I need 2 sets to span the full range of the steady rest from about 1.1 to 3.5". Anything smaller than 1.1 can fit inside the spindle.

BTW I highly recommend using this threading helper with new macros for G76 to G78. They work great and are easier to use than the Wizard. You choose the threads from a menu and it generates G code to turn the stock to the correct size and thread it. Showing how many passes are used at what DOC for each pass. Also tells you what RPM you can use given the max feed rate and acceleration settings of your machine


Stephan Brunker

Project Homepage:
Mach3 Threading Helper download | SourceForge.net

[RCaffin]

I wouldn't.
I would use a manual lathe (by hand) or a die.

Cheers
Roger

[BIGBLOCK1965]

I wouldn't.
I would use a manual lathe (by hand) or a die.

Cheers
Roger

Roger,
Yes, in an ideal world you would have a machine for every type of job, but I think he is trying to find a single machine that will do a variety of jobs.

[RCaffin]

You do not use a Morris Minor to move a houseload of bricks.
Anyhow, you don't need any machine to use a die to clean up a thread on a shaft held in a vice.
Use the right tool for the job.

Cheers
Roger

[enderw88]

You are correct. The actual job is more complex than just cleaning up existing threads, but does require aligning the single point to a specific point in space relaltive to an existing machined part then running in on a specific trajectory. Cleaning up threads is the simplest way to explain it. I need to look elsewhere.


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[RCaffin]

Ah, in that case it is tricky. I try to anticipate (and avoid) such problems when programming the operations, but if it is in the nature of a repair job then that option is out.
One alternative (maybe) could be to use the A axis on a mill instead of a lathe, but only if you have such a mill and if the job would work that way. The exact details would matter. Could be difficult.

Cheers
Roger

[BIGBLOCK1965]

You do not use a Morris Minor to move a houseload of bricks.
Anyhow, you don't need any machine to use a die to clean up a thread on a shaft held in a vice.
Use the right tool for the job.

Cheers
Roger

Of course for run of the mill threads, a die is the simple solution, but who owns a LH die for the threads on a 100-4 Healey knockoff hub?

[RCaffin]

Ouch!
You don't mention what thread it is, but no matter!

OK - that problem can be handled in one way that I can think of right now:
A axis on a mill with a 60 degree V cutter. The program details are obvious.

Otherwise ... hum. Manual thread chasing with a thread chaser maybe, but they are usually for a RH thread. Small 60 degree triangular file by hand - which is getting a shade desperate. Buy a custom die for it: possible and not too $$ from the right sources. What thread?

Cheers
Roger