This is an additional test of "crush ribs" which I learned about from this video from this video :

See also :

https://www.prusaprinters.org/prints/43586-test-print-crush-ribs-version-01

Short version :

A general solution to the problem of getting one printed part to fit firmly into another while allowing for small discrepancies in print accuracy.

Longer version :

Although I have flagged this as a re-mix of my Version 01, it is actually a completely new design to test the concept at a smaller scale.

This print illustrates the basic design feature of a cylindrical shape that needs to fit firmly into a round hole. The ideal design for this is a "press fit" - the cylinder is just slightly large than the hole so that it fits tightly into the hole and is held in by friction. The problem with this design is that getting the precise fit is usually a matter of trial and error. Further, what works for one make of filament and printer may not work with a different filament or printer.

In this print, I have provided a cylinder piece and and a piece with multiple holes. My hole pieces used a 0.3mm rib height with a symmetrical pattern of four ribs; the cylinder diameter is 8mm. Hole pieces were created with the following drafts and results :

Bottom row, through holes (left to right) :

• 1/2° draft = tight fit, very difficult to remove
• 1° draft = good firm fit, difficult to remove
• 2° draft = loose "wiggly" fit, easy to remove

Top row, all 1/2° draft, various depths (left to right):

• 7mm depth, tight fit, broke trying to remove
• 6mm depth, tight fit, removed with difficulty
• 4mm depth, tight fit, removed with difficulty

The prints provided here serve these purposes :

• introduce the concept of crush ribs
• show how crush ribs work in practice
• develop a conceptual model for testing the method
• develop 3D CAD methods

The last one is only indirectly related to 3D printing, but is important for me at least if I am going to be able to apply this method more generally.

OnShape 3D CAD files for this :

https://cad.onshape.com/documents/b4493acd7fc8145bc0e7f9e7/w/567793688a7f5ef5584f3b04/e/25e93a0018f17576c3d09a97

Print instructions

Print in PLA with the 3mf file provided.