OT: Another word (injection moulding this time)

A variety of things, I should imagine, often preceded by any number of four-letter words.
Reply to
Tim Wescott
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I need another word. Injection moulded plastic parts are sometimes held
together by a small plastic tab, which from a certain angle looks like a
barbed fish hook. Push the two parts together and the barb bends to one
side, then drops into a recess, holding the parts together. But you
can't usually open it again. It's a bit like a night latch without a
handle. I have in my mind something like "snap tab", but that might be
because they're always snapping off. Anyone know what this part is called?
Many thanks,
Chris
Reply to
Christopher Tidy
That's known as a "Whinley Catch", named after the inventor John Whinley...who I hope is rotting in hell with the bastard that invented the circlip.
Reply to
Buerste
Good guess! Some guys I know that design such infernal things call them "snaps", or sometimes "snap features". Some of these designs are positively ingenious.
Reply to
Don Foreman
IME, the most descriptive term is probably "cantilever snap beam", but "snap hook" or just "snap" are probably used more often. There are other kinds of snap joints (annular, for example).
Best regards, Spehro Pefhany
Reply to
Spehro Pefhany
There has to be a story or 3 behind that clear and precise comment.
Gunner
I am the Sword of my Family and the Shield of my Nation. If sent, I will crush everything you have built, burn everything you love, and kill every one of you. (Hebrew quote)
Reply to
Gunner Asch
I detect a teensy bit of acid there, too. Me, I love the circlip but hope that Whinley is, indeed, rotting in hell with the sole task of taking his invention apart _without_ tools, 24/7/365.
Whinley likely taught the inventor of the nylon auto door panel retainer his trade. Those break half the time even WITH the tool.
-- Some people are like Slinkies ... not really good for anything, but you can't help smiling when you see one tumble down the stairs.
Reply to
Larry Jaques
They are called snap closures, and the first person to invent them flew off on a broomstick cackling when they were finished. I have defeated some after locating their position by drilling a small hole over the barb, and depressing it with a pick tool. These rely on the flexibility of new plastic, but after the material ages and becomes stiff/brittle, these closures often won't flex to pop back apart, or more likely break. JR Dweller in the cellar
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Reply to
JR North
How so? I would interpret that as a snap-on cap, as on a Sharpie felt pen, rather than a feature on a cover or whatever. Usually "closure" in the plastics business refers to things like bottle caps, which may snap, slide or screw on.
Some plastics get brittle because the plasticizers are volatile, so it's a matter of temperature exposure and time. Stuff in a car, for example, gets pretty hot during the summer, so it tends to get brittle fairly fast even though the car may just be parked most of the time.
The main problem is that for the dimensions to be resonable you have to design the snap hook beam to be bent to a fair fraction of the yield point during assembly. Often the designer saves some tooling and parts cost by omitting stops (which ideally would act so that they can't easily be overstressed). And the plastics may not be molded under optimal conditions (overheated or regrind material is more brittle) and may age or be affected by chemicals (solvents especially) or other environmental conditions to become more brittle.
Best regards, Spehro Pefhany
Reply to
Spehro Pefhany
Hmmm, it does look sorta rude from one angle!
Chris
Reply to
Christopher Tidy
That sounds like a good term. Easy to understand. Thanks.
Interesting that you mention them relying on the flexibility of the plastic. I'm guessing a lot of these closures are made from ABS. Any idea how long it takes to stiffen?
Chris
Reply to
Christopher Tidy
Point taken. I had forgotten about that definition of "closure". I was hoping for a less technical term than "cantilever snap beam" because although it's very descriptive, you need to be an engineer to understand it. I thought there might be something simpler?
I've seen one of these beams with a stop before, but only once I think. Of course, it doesn't usually matter during assembly. It's when you try and dismantle the product that you risk overstressing the beam. I did it with a CD writer case a few months ago.
Thanks for the thoughts.
Chris
Reply to
Christopher Tidy

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