3D Printing Threads (Cosmetic/Virtual Threads vs Real 3D Threads)

There is a lot of confusion regarding 3D printing threads when it comes to the translation of CAD data to a physical prototype. This is largely because CAD vendors have introduced some shortcuts to make it easier for engineers and designers to add “virtual” or “cosmetic” threads to the designs without manually drawing the actual threads. They did this for two reasons that I’m aware of:

Drawing physical threads into a CAD model is time consuming, and
Drawing physical threads into a CAD model make the file much larger and takes up more computer resources when you start getting lots of files placed into an assembly

What the CAD software allows you to do is to call out threads on a cylindrical feature with just a few clicks. When you create a 2D drawing, it will recognize the “virtual” thread and place a thread call out in the appropriate location for your design. The trouble it, the threads are not actually there in the CAD file. The CAD file just has a smooth hole or a cylindrical shaft with no actual threads.

Below I have drawn out a sample 3/4 NPT coupler. One side I have drawn with virtual/cosmetic threads, and the other side I have cut the actual threads into the CAD model.

STEP 1, Draw a cylinder:

STEP 2, Insert Cosmetic/Virtual Threads:

STEP 3, Physical Model the Actual Threads:

Do you see how one side is smooth and one side has actual threads? The 3D print will turn out like what is actually in the 3D CAD file, so this smooth side will look smooth, not threaded. Just because there is a note on a PDF drawing that says there are threads does not magically make the threads actually there.

It take a little extra work if you want to succeed with 3D printing threads in your prototype.

Feel free to download our SolidWorks 2017 sample file illustrating 3D printing threads.

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