Plastic Lip and Groove Mechanism Makes No Sense 1

[U Offor]

Hello all,

I am trying to understand the mechanism of a lip and groove locking system and how it allows two plastic bodies to stay together in order to make a protective box in which a cellphone will be placed. I am not fully sure on the material yet but I plan to use acrylic, but if anyone has any material suggestions (cheap/easier to manufacture/strong to survive a fall from 8ft), I'm all ears.

To me, it doesn't make sense how the lip and groove system is usually designed (the left picture shows the typical lip-groove cross section). How is that supposed to hold together?? Just a little frustrated haha.

What makes sense is the cross section in the right picture, if you use an interference fit. That actually looks like it will hold. I can't think of any fit that would allow the left picture to hold together. Is there an angle between the lip and the groove? Because if I recall, these usually don't have any angles between them, just clearances, which makes it more confusing.


Thanks for any explanations,

Uche (Mike)

 

[MikeHalloran]

The lip/groove details shown are appropriate for solvent bonding, which is permanent.
You might look into snap fits, but they can be difficult to close or open by hand.

Acrylic is not super impact resistant.
Polycarbonate is impact resistant, but has other issues.

Some commercial cases for protecting whatever you might want to put in them, use a gasketed lip/groove rim, and mechanical toggles to actually hold the case together.

Go examine the cases for sale at LL Bean or Bass Pro Shops.



Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

Have you looked at any commercial products that work as you describe ?

I have not. yet. But I suspect for a "lip and groove" to be at all self locking there is an additional, subtle feature. Maybe a slight dovetail shape, and a gentle curve in the long dimension to provide some "snap".