3D printed threads too tight now

[brian.founds]

I have created several parts in one file that thread together with 1-1/2" wide shafts.  They have been fitting great right off the printer until this weekend when I tried to print a new part.  The new part is way too tight even though it was created with the exact same settings as previous parts.

I had noticed that Fusion had been updated since the time of printing previous parts.  Has there been a change to the thread creation tool?

I have tried to create them with a looser fit on the internal threads but seems to make no difference.

I have searched for the same issue elsewhere with no luck.  Seems strange that all of a sudden they don't fit, after printing several other connections that worked great.

Any suggestions are appreciated.

[HughesTooling]

Yes there does seem to be a change. In the past the threads created by Fusion where incorrect so maybe they've fixed them, I'll see if I can find the posts about the problems in the past. Don't have time to check if the new form is correct at the moment. Now although fixing the thread form is good for people like me creating threads using a lathe or thread grinding it's not good news for 3d printing, well unless you have a professional level 2d printer.

Here's an example. Old thread on the left new form on the right. The form on the right looks correct but will be a tighter fit. I've attached the design, as long as you don't edit the thread in the first component it will not update to the new form.

Mark

[HughesTooling · Accepted solution]

Here's a workaround that might help.

You can select the faces of the thread and offset to create clearance also in the past I've used a 2d scale to increase the diameter. File's attached.

Mark

[brian.founds]

Thanks so much for your insight and suggestions!  I will try your solutions.

[drroysteiner]

Thanks, looks very helpful, shame they fixed it, for 3d printing it was working brilliantly

[brian.founds]

Offsetting the face of the threads, as Mark suggests, does seem to help a lot.  Still not as nice as before, but I think incorporating his second suggestion of increasing diameter may get it there.

[iabisaac]

I thought I would post my solution to this problem.  I can now create male and female parts with the exact thread gap and round sharp angles for better 3d printed durability with minimal steps.

[autodesk2]

I know this thread is old, but I found an alternate technique based on this article from March 2023.
https://www.autodesk.com/support/technical/article/caas/sfdcarticles/sfdcarticles/Custom-Threads-in-...

This article shows where the thread definitions files are, and provides instructions on how to copy and modify the thread parameters to provide a looser fit.

I copied the ANSI Universal Screw thread library file, and renamed it per the instructions to 3DThread.  Then, in the copied file, I found the thread I was using (in this case 3/18-16), and for the 1B inner thread, I increased the Major Diameter from 0.375 to 0.385.
Now, 3DThread shows up in the list of available thread types, and selecting the modified 3/8-16 gives me a usable fit between screw and nut in my 3D test prints. 

And, with this method, it works for every instance of a thread in the design, and you no longer have to apply the offsets to every screw and nut.

[darinhouston]

This is the real object I'm copying and the modeled and printed one.  

I measure the top one (real one) with calipers at exactly a 5mm pitch (rainbird popup extension for sprinkler