An E-Z 1. Need two bumps to create plastic stop 1

[remotecontrol333]

I shouldn't even be allowed write a thank you note, but here I am trying to explain a design problem. Here goes...

I have a 2-part polypropylene enclosure which is a cap for a water container. The top and bottom are press fit together, percussively, to form one piece. Each piece has a lip which, when pressed together during assembly, allows the upper piece to slide along/rotate around the lower lip. Sort of like 2 round rails. Because there is no pitch to the lips, when the upper part is rotated, the is no translation. The parts simply rotate along the axis. OK, so far?

I need to incorporate a locking mechanism, so when the cap is "closed", the cap won't leak. I have tried designing 2 bumps -- one on top, one on lower part -- which pass over each other, but don't know how high the bumps, nor shape should be with respect to securely closing the cap, and future wearing down of the parts.

Certainly you engineering experts know of a more technical term than bump, but it describes what I need.

Additionally, I tried using a simple cylindrical protrusion on the top part, and a cup for it to fit into on the bottom. But, I don't see the need for the cup. Seems to me, if one bump passes over the other bump, it'll "click", or drop into a closed position.

picture at

http://home.usamedia.tv/taumas/images/cap.jpg

Thanks.

 

[CorBlimeyLimey]

Take a close look at some Tupperware containers.

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Helpful SW websites faq559-520​

How to find answers ... faq559-1091​

 

[Airmack]

If I understand you correctly, you are wanting to know about annular snap-fit joints. There was a great article in the January '05 issue of Machine Design.

http://www.machinedesign.com/ASP/viewSelectedArticle.asp?strArticleId=57767&strSite=MDSite

 

[remotecontrol333]

Airmack, that's exactly what I needed. Now it doesn't matter the size of the enclosure. Problem solved. Thanks a million!