Threading dial help

[fatal-exception]

Ok, so my new lathe didn't come with a threading dial, and the manufacturer says that they don't make one for my lathe. So the next option is to make one.

The question I have is how many teeth should be on the dial? My leadscrew is a 1-5 ACME screw. Basically, what should the gear ratio be for a threading dial?

Any help would be appreciated.


Thanks,
Paul

[Geof]

Make it a multiple of 5?

All the dial does is tell you when the leadscrew has got back to the same point at every revolution of the screw. If you had an odd or fractional multiple of 5 for the teeth it would eventually return to the same relationship but not every revolution.

I think this makes sense.

[fatal-exception]

Ok, so I'm trying to think if this will work or not.

Would the following statement be true?

"As long as you always close the half nuts on the same dial reading that you started with, you will be starting the thread at the same spot, regardless of the pitch of thread you are trying to cut."

I can't seem to get my head around this.

Paul

[Geof]

Originally Posted by fatal-exception ..."As long as you always close the half nuts on the same dial reading that you started with, you will be starting the thread at the same spot, regardless of the pitch of thread you are trying to cut." I can't seem to get my head around this. Paul

You need a flexible head.

In the context of what I wrote earlier I think it would not be true if your threading dial had a gear that was not a multiple of 5.

You can rephrase what you wrote as:

"As long as you always close the half nuts at the same point in rotation of the leadscrew you will be starting the thread at the same spot, regardless of the pitch of thread you are trying to cut."

With the qualification that the saddle would have to be in exactly the same position.

The important thing is the relationship between the threading tool and the leadscrew; a chasing dial allows you to repeat it regardless of where your saddle is.

IF your gear is not a multiple of 5 then the leadscrew is not always at the same location every time the dial repeats a reading (I think).

I hope I am bending your head out of shape; I know I am bending my own and it is much older and less flexible.

[handlewanker]

Hi Fatal, why don't you do it the easy way and leave the halfnuts engaged all the time and just reverse the spindle at the end of the cut.

I have an old Colchester Bantam from 1920 abouts, and it never had a threading dial, but I found that it was just as quick to reverse at the end of the cut, this way you never have the problem of inadvertantly dropping into the wrong leadscrew position.

I do a lot of Metric threading on an Imperial leadscrew, and you can't open the halfnuts at the end of the cut doing Metric threads.

I did a test on another lathe with opening the half nuts and also doing it by reversing the chuck at the end of cut, and it took a little longer opening the halfnuts and waiting for the dial to line up.

You could of course chalk a line on the chuck and headstock, and another on the leadscrew and it's bearing support at the chuck end, and when the lines on each line up, you drop the half nuts in, simple but logical, but only works for IMPERIAL on an imperial leadscrew.
Ian.

[juergenwt]

Here is one I made for a Weiler Lathe with a 6mm lead screw.
The gear has 30 teeth - takes care of 95% of all metric threads. When I have some extra time I will make a 28 and a 32 tooth gear to be interchangeable and that should cover all.
The knurled nut on top of the dial is a lock nut for the dial.

[handlewanker]

The problem is that Metric threads are described as being pitch of the thread , that is the pitch of a metric screw is defined as .75mm or .5 mm etc, whereas Imperial is usually and mostly TPI, (threads per inch) orientated.

You can still define Imperial as a pitch, but the formular for calculating is a bit different.

For instance, 8 TPI is actualy .125" pitch, but not many people would understand that or be able to measure it that way, seeing as how the thread pitch indicators are all marked in TPI.

BTW, my old lathe doesn't have a reverse mechanism, but for one off threads I fit a handle on a stub mandrel in the spindle end, and at the end of the thread cut stop the lathe and wind it back by hand, it works just as well, and one day I'll be fitting a 3 phase motor with a VFD to the lathe, and that has reverse.
Ian.

[fatal-exception]

3 phase with vfd is definately the way to go.

Busy bee hasn't got back to me about the tread dial. I don't really care anymore. Like handlewanker says, I just cut and then pull out and reverse. It works well. I've read that single phase motors shouldn't be started and stopped this often, but I'll deal with that problem when it arrises.

CNC'ing the lathe will happen pretty soon.

Has anyone found a small indexable threading tool holer that will do both internal and external threads using different inserts and tool holder orientations?

[handlewanker]

Hi Fatal, in the mean time stopping and starting with single phase is a problem due, as most know, that the start windings get hot and can burn out, but as you're going to CNC soon it shouldn't be an issue.

I installed the electric clutch (12 volt) from a car's scrap aircon. compressor to my lathe, and this allows the motor to run continuously, but I get to stop and start as many times as I want, and the clutch will handle 4000 rpm + and about......well quite a few horse power.
Ian.