topic Problem creating an NPT type nut thread in Fusion Design, Validate & Document Forum

Problem creating an NPT type nut thread

RogerInHawaii — Thu, 19 Oct 2023 21:08:30 GMT

I'm trying to create a threaded nut where the thread type is NPT. If I try to use the Thread tool, it does not have NPT as a selection option. I came across a YouTube video where it shows how to create an NPT thread using the HOLE tool. But that's not working either. Here's what I did:

I created a nut-shaped body.

I then brought up the HOLE tool dialog and made the necessary selections, NPT, 1/2 inch, etc.:

Hitting OK, seemed to create the nut just fine. At least it LOOKED fine:

Looks pretty good, doesn't it? But just to be sure I used the Section Analysis tool, and it shows that no threads were actually created! It LOOKS like there are thread from the overall image, but the section analysis shows that it's just a straight-through hole, no threads.

So how do I get it to actually create the threads?

And why doesn't the Thread Tool itself provide NPT type threads?

Re: Problem creating an NPT type nut thread

jhackney1972 — Thu, 19 Oct 2023 21:27:52 GMT

NPT internal threads are not included in Fusion 360. The easiest method to mode them is to download a threaded nipple, with the desired NPT thread and use the Combine command to create the NPT tapped hole you need. Model is attached. If you cannot figure out the timeline, let me know.

Re: Problem creating an NPT type nut thread

MRWakefield — Fri, 20 Oct 2023 18:24:04 GMT

That's known as a 'cosmetic thread' and is a common method of giving a thread-like look without the computational overhead of actually modelling it. This is usually sufficient in real-world manufacturing as the hole and/or thread is usually specified on the drawing that you give the manufacturer and doesn't require it to be modelled. If you're going to 3D print your part however you'll want it actually modelled. Unfortunately as @jhackney1972 alluded to, modelled tapered threads have not been implemented as yet in F360.

Again, as @jhackney1972 mentioned you could use something with an external NPT thread and use it as a 'tool' to form the hole in your nut. Alternatively, if you don't need it to seal you can use an NPS or NPSM* thread in your hole. These will mate with an NPT but won't seal on the thread. Unfortunately F360 doesn't come with NPS or NPSM thread files. If you search the forum I think you'll find one has been posted before. If not I have one you can have but off the top of my head I'm not sure how complete it is.

EDIT: What size are you looking for?

*EDIT #2: I've since found out that there's also an NPSC thread as well. This will also mate with an NPT external threaded part and can provide a seal if conditions are right and pressure is relatively low.

Re: Problem creating an NPT type nut thread

jhackney1972 — Thu, 19 Oct 2023 22:03:50 GMT

His dialog box, in his post show 1/2-14 NPT but maybe it best for him to confirm.

Re: Problem creating an NPT type nut thread

MRWakefield — Thu, 19 Oct 2023 22:07:01 GMT

Thanks @jhackney1972 , yes I did notice that but wasn't sure whether that was just an example or whether it's actually the size he's after. As you say; we'll see if he comes back with the info.

Re: Problem creating an NPT type nut thread

RogerInHawaii — Sun, 22 Oct 2023 00:49:49 GMT

I had searched around for the proper thread designation that is typically (in the U.S.) used for bathroom shower heads and what I found (via ChatGPT and other online sources) was just 1/2 NPT. I'm assuming the 14 is perhaps a threads-per-inch designation, but nothing I came across indicated anything other than just 1/2 NPT.

So, yes, what I tried in Fusion for the Hole Tool, was 1/2-14 NPT simply because that's the only "Designation" option it provides.

I just now also asked ChatGPT if there is an ANSI Unified Screw Thread that corresponds to 1/2-14 NPT and it suggested ANSI Unified Screw 1/2-14 NPSM. Since that CAN be modelled in Fusion I'm giving it a try.

I really do need this modelled in Fusion because I'm 3D printing the object for testing for a prototype product and don't have access to actual machining tools.

So, fingers crossed.

Re: Problem creating an NPT type nut thread

Warmingup1953 — Sun, 22 Oct 2023 02:08:19 GMT

Hi there did you download and review the file that John Hackney created? ( See above)

Re: Problem creating an NPT type nut thread

MRWakefield — Sun, 22 Oct 2023 12:14:21 GMT

Unfortunately although ChatGPT and other similar AI can be useful they often throw out wrong information. There is no such thread as a "Unified Screw 1/2-14 NPSM". They are two different things. Fusion does have Unified threads but it doesn't have NPSM (see my previous reply). Pipe threads are described differently to other 'normal' threads. the 1/2 in a pipe thread designation refers to the bore size of the pipe and not the OD. If you try to use 1/2-14 UNS you'll find the diameter is way too small (0.5" rather than 0.818" of an NPSM). As I said before the NPSM will fit your 1/2-14NPT but won't form a seal so you'll probably need to seal it with some PTFE tape. I've attached an NPSM thread file for you.

Re: Problem creating an NPT type nut thread

RogerInHawaii — Tue, 24 Oct 2023 22:02:33 GMT

@jhackney1972 THANK YOU. And thank you to every one who replied with helpful info.

I did indeed download the file you provided. I had to slightly modify the body of the bolt, shrinking it by about 7.5% in the X and Y dimensions (keeping the length dimension) in order to compensate for the precision (or, lack thereof) of my 3D printer. I also created a nut version (threads on the inside) from your file and increased the size by about 7.5%, again in the X and Y dimensions. I now have a bolt and a nut that fits pretty well with each other and on the actual shower head objects.

This was the first hurdle I had to get past in order to continue on with the development of the prototype product that I'm working on.

So, thank you for the solution you provided.

It's still frustrating that Fusion 360 provides tools for modeling certain threads but only provides tools (via the Hole Tool) for Cosmetic images of others, including the NPT one that I needed. I looked on the Fusion forums and it seems this has been a concern for quite a few years, with no progress on adding any other thread types.