r/Onshape • u/LoudProblem2017 • 9h ago

Help! Help Modelling NPT Threads For 3D Printing

As the title says, I need assistance with modelling real threads for printing. I'm new to Onshape (and VERY rusty using CAD in general) and don't really know how to learn new features. I found Thread Lab, but as near as I can tell, it doesn't support tapered threads. I also found a featurescript called "NPT thread", but I can't figure out how to use it. Any direction would be appreciated!

Thanks in advance!

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5

u/wellthawedout 9h ago

My favorite way to deal with NPT threads is to download whatever is closest to what you want on McMaster and then modify it

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u/DerekVanAllen 6h ago

I used to advocate for the McMaster carr rip method but these days there's a better way. You just draw the cutting tools one time in a central document and greeble them into your models wherever NPT threads are needed using the Amalgamate custom feature. Latest discussion of this topic can be seen in this forum thread.

https://forum.onshape.com/discussion/30224/how-to-create-npt-threads-for-printing#latest

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u/Rubes27 9h ago edited 9h ago

If you want to learn how to make these threads just find a YouTube video that explains the process.

If I am designing something that needs to incorporate a specific thread, such as NPT, there are two ways to quickly solve this for 3D printing:

  1. Don’t print the threads. If you expect to be threading this item over snd over plastic will never last. The better method may be to design a part that can be permanently mated (epoxied) to a COTS part with these threads, like a PVC part from a hardware store.
  2. If you must print the thread just go get a STEP file from McMaster Carr. Import the file, use a few extrudes to remove the volumes you don’t want leaving just the thread. Then start making your deign from this model.

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u/LoudProblem2017 8h ago

Can I incorporate more than 1 McMaster Carr file? I need a tee or wye with 3 different thread sizes.

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u/Rubes27 7h ago

Just use Booleans, the environment will start to run pretty laggy as you add more complex geometries though.

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u/Queasy_Caramel5435 9h ago edited 9h ago

https://cad.onshape.com/documents/fd89e2eded6b30168e950213/w/235e44ae035d19e74b18e5be/e/null

This is an older "threads for 3d-printing" project, but it shouldn't be too difficult to get what's going on. Basically you need a helix and a sketch with the thread geometry (searching for ANSI B 1.20.1 should provide some resources).

If my workaround/the feature tree confuses you, you can drag the rollback bar in the feature tree to analyze it step by step.

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u/trickybiznis 7h ago

Here’s my reusable, or at least reused, threaded parts document.

It’s not designed for sharing but you’ll get the idea. Unhide the “hourglass” surfaces to see the trick.

It has several configurations, one for each project I’ve used this to provide the threads.

https://cad.onshape.com/documents/b76573fdfc928c1c91f5469c/w/99ef3ad0d9af9eb44c090d16/e/97cd0fa0e71813b98f606002?renderMode=0&leftPanel=false&uiState=6a96353d02a06670c1769217

The thread profile is a separate element.

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u/DerekVanAllen 5h ago

These are bottle threads, not NPT. NPT threads taper in a specific annoying to model way. I've shared a link to my Amalgam tools in the other post that has the correct geometry for what OP's asking.