Thread Dial Indicator engagement

[Vogavt]

I've been successfully threading for some time now, but have a general question. I use the numbers given for the indicator based upon which tpi I want to cut. I've noticed that some threads say engage at any, some threads use 1,3 5 or 7 and some say use 1 or 5.

I see that any thread can use "1". There seems to be a pattern with the number 8.

For example, starting at 12 tpi and adding 8, each time you add 8, the indicator says to use 1, 3, 5 or 7 (12, 20, 28, 36 & 44).

Starting at 16 and adding 8, each time you add 8, the indicator says to use any number (16, 24, 32 & 40).

Starting at 14 and adding 4, each time you add 4, the indicator says to use 1, 5 (14, 18, 22, 26 & 38). I suspect that if you need to cut a 30 or 34tpi it would use the 1 or the 5 as well.

I note that 13 and 19 use only the "1" to make the cut.

I'm using the GearsVB6 software that Paul Bussieres to come up with some gear combinations that reveal threads that can be cut on the mini-lathe although not listed in the manual.

However, one thing I noticed is the software is missing which thread dial number to use. I've already sent him an email but he has yet to respond. Hopefully he will soon, but until then I'm trying to wrap my mortal mind around the relationship of the lead screw pitch and the thread dial indicator.

So here's the question: What's going on, i.e., can someone explain in mathematical terms, or otherwise, why a leadscrew with 16tpi would use odd numbers to get an even number tpi?

Thanks in advance,
Vogavt

[hoss2006]

Don't get bogged down with details.
If you use the same number everytime you will be ensured to get it right everytime.
I use 1 for odd threads and 2 for evens.
When you've used as many different lathes as I have, you learn to keep it as simple as possible to make life easier.
Hoss

[Vogavt]

Is it really that simple? Seems like they would not have given such detail in the manual. I'm sure you're right, but boy they can send a newbie into a tailspin quickly. I've been doing it for a while and like I said, just been mindlessly following the chart. Only started getting bogged down when I began to think.

Reminds of a true story I heard once in college. There was a very successful farmer who sent his son to college to get his degree. The son continued in school until he earned his PHD in Agriculture. One of his professors asked him what he was going to do with it now that he'd gotten to that point. To his amazement the young man he was going back to the farm. When the professor asked why he would do such a thing, the young man simply replied "You know it gets pretty boring driving a big tractor around at 3 a.m., but now I've got a lot of things to think about".

Sometimes I get to thinking to deep on stuff myself. As they say the Devil is in the details. Just wanted to understand things more clearly.

Thanks,
Vogavt