Who Needs A Thread Chasing Dial?

[brino]

It is possible to do a multistart without a thread dial. Just turn your compound 180 and dial in half the pitch. thats on a double lead..................... I really dont know how you could cut a triple lead any other way.

If turning between centres using a faceplate and lathe dog, then another method to cut double-start threads is to move the lathe dog to be driven by the faceplate slot 180 deg. away from the one used for the first thread. So for triple start you could use a faceplate with three slots each 120 deg. apart.

For the electrically minded that would be like adjusting the phase of a signal by adding a constant offset......

-brino

 

[kingmt01]

darkzero, It is possible to do a multistart without a thread dial. Just turn your compound 180 and dial in half the pitch. thats on a double lead. i have done a bunch of double leads and i use the thread dial to "split" the thread. even on an even pitch. I cut a triple lead a couple of times and used the compound to advance the next thread. I really dont know how you could cut a triple lead any other way. If i am missing something please let me know.

While I've never cut a double start thread my refining would be this.
My lathe has a D1-5 chuck & has 6 lugs that aligne it. So I'd assume I can get 1, 2, 3, or 6 start positions by rotating my chuck on the spindle.

 

[rustwa]

As has been said before, my threaded spindle makes reversing the motor a bad option. Threading with a thread dial is quick and incredibly uncomplicated once a person has cut a few screws. That said, because I use my thread dial, when given a choice I will chose an even pitched thread. This speeds things up a bit and gives me one less thing to think about. Just wait for the next line to come around. Otherwise I will find myself holding up 1 finger or 2 fingers on my left hand to aid in remembering if I started on an odd or even line.

 

[RJSakowski]

If turning between centres using a faceplate and lathe dog, then another method to cut double-start threads is to move the lathe dog to be driven by the faceplate slot 180 deg. away from the one used for the first thread. So for triple start you could use a faceplate with three slots each 120 deg. apart.

For the electrically minded that would be like adjusting the phase of a signal by adding a constant offset......

-brino

Brino, the assumption here is that faceplate slots are exactly 180 degrees apart. Faceplate were never intended to be used as indexing plates. The some of the faceplates that I have used have as-cast slots. In any event, I would want to verify that the slots are accurately spaced before using them for indexing. A better approach would be to disengage the half nuts and manually rotate the spindle 1/2 turn and re-engage the half nuts. If you are slightly off in your rotation, the half nuts usually have enough play in them that they will home in. If they don't, a slight rocking of the spindle while re-engaging the half nuts shoould do the trick.

 

[Idaho Jim]

This is an interesting thread about threading. I'm trying to remember the lathes I've run enough to even consider the threading capabilities. I'm thinking of six or eight, in general, and one that I actually logged a lot of hours on. I don't think any of them lacked a threading dial. These were all industrial machines of the engine lathe tribe. (Of course, this does not count specialty pieces like hydraulic tracers, Swiss screw machines & etc.) I guess my point is: I'd be moving pretty slowly until I figured out/got comfortable doing without it.

On the matter of reversing to stop, that's SOP on the old LeBlond I've put most of my time in on. It only offered to present the chuck to me once. I threw the power back on, let it coast to a stop and then performed the obligatory laundry check.

Jim

 

[Mad Monty]

A DRO can't track the position of the bed leadscrew used for threading as a thread dial does.

I had the same question, and alas, still do. Here's how I'm seeing it: The DRO tells you where your point will hit within its accuracy limit (mine is a tenth, .0001"). It even accounts for backlash and slop in the gears that a mechanical thread dial can't. So at, say 48 tpi, I can set my point down with in .5% of one thread (.0001"/.02"). Am I missing something?

 

[Tony Wells]

The DRO reports only the linear position of each axis. The gearing in the headstock, and hence the rotational position of the chuck, is not correlated.

In the world of CNC, rotary encoders are employed to do that, on lathes and milling machines with rotary axes.

 

[RJSakowski]

Yes, it is true that if the thread you want to cut is a FACTOR of the lead screw thread, you can engage at any point, such as if you have a 4 thread lead screw (common on most mid size industrial lathes) you can cut 2, 4, 8, 16, 32, etc thread pitches. If you want to cut an even number of threads, any pitch, you close the half nuts on any line, numbered or not; if you want to cut an odd number of threads, you must close on either a numbered line or un numbered line, not either one. If it is a half thread, close on opposite lines on the dial, quarter threads, close on one line or number ONLY. The lines on the dial indicate inch distances of carriage travel, so if you can stop the spindle rotation quickly enough, and open the half nuts and move the carriage back even inch distances then reclose them and start the spindle for the next cut, you can get away without the dial, but having said that, in my opinion every lathe should have a thread dial, period!

Your advice doesn't work for all lead screws. The Grizzly G0602 lead screw has 12 tpi and 12 divisions on the thread dial. Here is their section on use of the thread dial.Here are some excerpts from the Grizzly G0602 manual regarding use of the thread dial. "9, 12, 18, 24, 36, 48, 72 TPI. For these threading TPI 's, use any of the lines on the thread dial." ......"91⁄2, 111⁄2 ,131⁄2 Fractional TPI. For threading these TPI s, use the numbered lines.1 or 7 on the thread dial."......"All Other TPI. For all other TPI 's, use numbered lines 1 or 7 or non-numbered lines 4 or 10 on the thread dial."

 

[ronboult]

Hi Franko
It is my understanding that if your lathe has a lead screw clutch and it is used to stop the feed while threading, ie clutch slipps, then the relationship between spindle and lead screw position is upset. How would you reset this relationship to make a second cut? Almost impossible.

Now that you have ordered a 1228 (sieg SC10) a more important Q is have you checked to see if it has an imperial or metric lead screw? Sieg lathes can be obtained with either! Both my Siegs have metric. Makes a big difference depending on what standard threads you mainly cut.
Ron

 

[Franko]

Ron, I think the idea of using the clutch to stop has been already declared stupid.
The lead screw is NCH pitch 3/4” / 8 TPI.