Threads that work

[SimonPlatten]

I've created a container using a cylinder with a thread on it, from the container with modelled thread I created a cap by creating another cylinder that goes on the end and subtracted the body of the first cylinder from the cap, keeping the object I am subtracting.

I then 3D printed both parts, however they do not screw together fully.  Have I done something wrong ?

I would share the model, however I'm not sure how to ?

[Edit]. With filing I've managed to get both parts to screw together.

[etfrench · Accepted solution]

Yes, you are doing it wrong😁 (fdm)3d printers usually don't print threads to their defined tolerances.  Offsetting the thread faces by a small amount will make them fit together better.  Fusion 360 also doesn't create the proper chamfer on the end of a thread.  You cannot add the chamfer before making the thread and the thread cannot be Modeled before adding the chamfer.  Create the thread with Modeled unchecked, create the chamfer, then edit the thread to Modeled.

[SimonPlatten]

Thank you, certainly worth a go...is there any tutorial or video on how to do this, I've filed the prints and now they screw together much better than before.

[etfrench]

Just select each face on the thread (there are four) and use the Offset Face command.  Chamfer technique is in my first post.

[SimonPlatten]

Ok, is there any guide on the chamfer size to use according to the thread size ?

[etfrench]

Start with the difference between the major and minor diameters, but a little more won't hurt.  

[MRWakefield]

Just a little heads-up... You're better off selecting just three of the faces for offsetting: crest, root and one flank. If you select crest, root and both flanks you'll find that the thread form becomes distorted. The crest flat will get narrower and the root flat will get wider. Obviously the more you offset, the greater the distortion.

[g-andresen · Accepted solution]

Hi,

This is the way for chamfer and thread offset.
You have to determine the value for the offset in trials.
I've had good experience with an offset of -0.1mm for PLA/PETG/ASA for M20.

günther

[SimonPlatten]

Thank you