OD Threading Lathe

Likely me being confused, but is parameter 3 the start / total diameter of the piece or the radius?
Or put another way, would the example in the screen shot make a 3/4 - 16 od thread or a 3/8 - 16 od thread.
Looking at the G76 code it seems to be the radius, or the difference between the drive line and the thread peak, where the thread peak is expressed as a radius.( I think )

I have yet to thread anything successfully, found this and thought it would be a great tool to get me started, and want to make sure I understand.

BTW, I thought putting the G76 image in with this might be helpful, but the more I look the less sure I am, it seems like you would need an explanation as to how the parameters get mapped, and it might get too busy. Something like this but cleaned up.



At any rate, John, thanks a ton for putting these up, and Dewey, you are some kind of crazy geek / artist hybrid thanks for the code, and I love your woodworking.

Pete

re-worked the image a bit, and I'm hopefully understanding better, put it with the th_od.ngc file and it should appear in the tab when opened.



Pete

It's automagic, once the tab exists, you just put the image (same name with .png) in the same directory. There's one option as to it's location, but I don't think I needed to mess with it.

Pete

BigJohnT wrote:

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

File Attachment:

File Name: th_od.ngc
File Size:1 KB

John

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

Steve

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