Test Print - Crush Ribs - Version03

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

and

https://www.prusaprinters.org/prints/43599-test-print-crush-ribs-version02

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 :

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.

This print differs from the Version 2 print in the way that the ribs were created in CAD. In Version 1 the ribs were a half-circle in profile and had the same draft as the sides of the hole. In this Version 2 print the ribs are a half-square in profile, and are not drafted at all; this effectively makes for a bigger rib which is not tapered like the hole.

Hole pieces were created with the following drafts and results :

Bottom row, through holes (left to right) :

• 1/2° draft = does not fit
• 1° draft = very tight fit, difficult to remove
• 2° draft = tight fit, difficult to remove

Top row, all 1° 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.

Update : I added a photo showing how the cylinder broke when trying to remove it. I will address this issue in Version 04 of these tests.

OnShape 3D CAD files for this :

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

Print instructions

Print in PLA using provided 3mf file.