[MFchief]

Hi All,

So I've wanted to thread mill pipe threads for a while now, and I decided to try it with Fusion 360. Fusion does not directly support pipe threads but googling around showed some folks that say they made it work. I also knew that fusion doesn't have a thread mill in it's tool library, but after watching John on NYCCNC, I knew that you just set it up as a flat end mill of the appropriate diameter for the cutter. I wanted to use a single point thread mill, because my reading seems to say to do it with a multi-tooth cutter, you need to buy dedicated NPT mills of the appropriate pitch.

So I modeled an internal thread by doing an extrude cut of a 1/4" NPT thread by setting the large diameter from a chart that I found at the Maryland Metrics website, and cutting at the taper for NPT threads (1.7899 degrees), to get the tapered hole to thread. The part I have trouble figuring out is what you would call the "minor diameter" on a standard straight thread. My approach was to take "depth of thread" number from the same chart and use that and add the "max truncation" number from that chart and set it as "Stock to leave" when I set up the boring operation in fusion. I then did the threading passes at the proper diameters setup when I modeled the tapered hole.

This worked and I was able to get acceptable threads on my test pieces, but it was "fiddly" and I had to adjust by a couple of thou to get what made me happy.

So the point of all this is, there must be a better way to do this, so I'm hoping someone can set me straight.

If anyone is interested the chart is here: https://mdmetric.com/tech/thddat19.htm


Terry

[GLCarlson]

Try the Advent2008 code generator. There's a youtube:
Single Point Threadmilling Tutorial - YouTube

you'll probably have to hand correct a few things (safety block, offsets, maybe more). I haven't tried it yet with PP. Works fine on Mach3. And it's got every thread known to man in it. Downloads so there's a local copy.

[SCzEngrgGroup]

Make the hole in the model the correct OD and taper for the finished thread. Then if you set "Stock to Leave" to 0.000, the thread should come out exactly as you want, assuming your tool definitions are correct. With thread-milling, you pretty much always have to do a test cut or two to exactly dial in the fit.

Regards,
Ray L.

[MFchief]

Thanks guys for the advise, I had seen the video for the Advent software before, but it's been a while and I was looking at it in terms of straight threads, I'll go back and take another look.

Ray, I'm not sure I understand your advise correctly. Currently I am setting the OD of the hole to the finished diameter of the largest thread, then setting the stock to leave number to what I want the minor diameter to be, then boring the hole. But when I use the threading tool, the stock to leave is set to 0.00. Is this what you mean?

Thanks again
Terry

[SCzEngrgGroup]

Keep in mind, there are 50 different ways to do this....

What I find most straight-forward, is to make the hole in the model the major diameter of the thread. That way, if you set Stock To Leave to 0, you should end up with exactly the right thread diameter, without having to figure out how much to add to the minor diameter to get what you want. You only have to set up how many passes to cut. If the final thread is not quite right, just chance Stock to Leave a few thou to compensate. It works correctly for straight or tapered threads. For tapered threads, just put a properly tapered hole in the model (using the "draft" feature of the Extrude), and HSMXpress will take care of the rest.

Regards,
Ray L.

[MFchief]

Thanks Ray, I'm going to experiment some more.
Terry