Help designing small snap-fit

[improd07]

We have a consumer product which needs a removable tip and we would like advice on the feasibility of a plastic snap-fit. The item is small and would require a "tubular" exterior shape (like the barrel of a pen). The outside diameter of the tubular snap-fit would only be .25 inch (by approx 1" long). First of all if it's feasible, what would be a guestimated pull-force limit for that size snap fit?

 

[MikeHalloran]

Full circular snap fits in that size range require impossible tolerances and still result in unacceptable forces and short life.

Segmented ring details get expensive fast, and are fragile.

So you have to cheat.

Your molder probably already has a favorite detail for this sort of thing. Most of them comprise some sort of 'bump' of simple geometry that deforms the mating cylindrical part, or its own substrate, or both, into a bilobular, trilobular or quadrilateral shape. So instead of expanding a circle uniformly, you deform it into an ellipse, or a hypocycloid or something like that.

Work with him; have him build a simplified aluminum tool at your expense to help him work out the exact details needed for your part.






Mike Halloran
Pembroke Pines, FL, USA

 

[Pud]

Here is one of tons of stuff on Google:

http://www.dsm.com/nl_NL/downloads/dep/snapfit_design.pdf

Page 6 onwards, to save you doing too much work...

H

http://www.tynevalleyplastics.co.uk

 

[improd07]

Thank you for the insights both Mike and Pud.
Mike, do you consult outside the forum?

 

[MikeHalloran]

I'll be home in a day or two.
I'm in the book.


Mike Halloran
Pembroke Pines, FL, USA