OD Threading Lathe

Oh Cool! I love automagic.

John

BigJohnT wrote:

This is the subroutine I use for OD Threading on the lathe.

Attachment th_od.ngc not found

John

Just looking at altering this to do metric threads as per your tapping subroutine. 99% of threads outside the USA are metric

Steve

Take a look at the tapping one. It is already a metric/inch choice and might give you some ideas.

John

I have a question about parameter #6 (Thread depth)

I have been making test threads in 1/4-20 size. My chart says these have a major diameter of .250 and a minor diameter of 0.1887. Looking at the pictures on the prior page, it seems to me like parameter would be 1/2 of the difference between the major and minor, so I tried .031 (rounding off), which of course wasn't nearly deep enough. So, I tried again, using the full difference (.0613) plus .002" for Kentucky windage.

That didn't work either, so I jacked it up to .085", and my nut went right on. Checking with a mic, the unthreaded portion of the shaft was .250, and the threaded portion was .246, so the .085 thread depth was pretty close.

Anyway, I am trying to figure out how to get this "right," meaning that I can produce a standard thread size more or less right on the first shot. I can see a few possible sources for error in this:

1. I'm setting the hread depth wrong and/or mis-understanding it
2. My tool table offset is inaccurate
3. I touched off incorrectly
4. Need more spring passes (that won't take .015" off though... not on a 7x10 mini)

I am assuming that I could sit down and experimentally determine values that produce desired results for the common threads I use, but I want to make sure I've wrung the other problem possibilities out first. And I want to know what param 6 is supposed to be :huh:

It's complicated.
I have not done many threads, and like you I always seem to have to keep at it for about 3x the expected depth.

I think one issue is the tip radius of the cutting tool. How does the standard define the depth and how are you touching off. I think that the disparity might be there. (or part of it)

I see that I had a preamble in that one that sets it to diameter mode. Could that be your problem?

I would remove that first line completely and use the ngcgui std.ngc file to set up your machine so it will be consistent. In fact I'm going to change mine before I forget. If one of the subroutines needs a special setting be sure to set it back at the end of the subroutine.

John