I have no experience with actual CAD drawings and CNC machines so please forgive me if this is a really stupid question...

Anyway I have a part which I have 3D printed and it contains some internal screw thread for an ISO metric screw. I modelled the threading myself so it will get 3D printed which took some trial and error. Now since I need it in high quality metal I want to CNC it. But I am wondering whether I have to let the screw thread stay in my model or indicate somehow this is actually ISO metric screw thread of this spec? Since I imagine there is special machinery/settings to make the threading.

Any help is appreciated

  • 2
    $\begingroup$ Is your threaded hole thru or blind? If it is blind, you should have a hole a little deeper than the threads to allow clearance for the threading tools and for chips if the threads are to be cut $\endgroup$
    – GisMofx
    May 8, 2018 at 1:36
  • 1
    $\begingroup$ a bit aside but you may have been better off to 3d print holes, and tap the threads. $\endgroup$
    – agentp
    May 8, 2018 at 15:28

2 Answers 2


Most CAD software has the facility to automatically generate screw threads in a model. Often this will be represented on the model as a texture to reduce the complexity of the model but the file will contain the specification for the thread.

Ideally for machining you want to specify the tread rather than modeling it because, as you surmise the process for machining a thread is typically different to machining some arbitrary shape.

If all else fails the best thing to do is probably just mark have the holes and specify the treads with annotation.


It’s not a hard no, but do not model threads. They certainly look a lot prettier, but they are mostly unnecessary. They can consume more memory and require more stress on the computer to render them. This is a big factor with larger models with many parts.

Anyway, as @Chris Johns stated, simply indicate the standard thread on the drawing. The machine shop should do the rest.

Furthermore, if you have specific requirement, you could specify the way the threads are to be manufactured(cut or formed)


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