Author Topic: SEM's ... ??  (Read 5233 times)

Offline Bluechip

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SEM's ... ??
« on: July 12, 2010, 11:50:21 AM »
Hi Troops ..

I know what they are, ie. machine screws with captive washer(s).

Used them for donkey's years ... but ... never thought about them much, until earlier today one of the nauseating spotty erks young folk I know asked me what a screw with captive washer was called.

I said they are SEM's ...

What does that mean ??? from n.s.e ..

I don't know    :scratch:   , a trawl around produced all sorts of stuff, ie. Scanning Electron Microscope etc.

Anyone any ideas ?? Apart from taking Laundry Personnel Hostage ...  :lol:

Dave BC

 
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Offline Brass_Machine

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Re: SEM's ... ??
« Reply #1 on: July 12, 2010, 12:17:28 PM »
Hmmm...

Seems the origin of the name is a but confused:

Quote
SEMS
    A screw and washer assembly. A screw or bolt which has a captive washer. The washer is frequently loose on the plain shank of the fastener, the shank diameter being equal to the effective diameter of the thread; the thread being rolled from this diameter. The origin of the word is a frequent question. In the 1930's E. C. Crowther was a representative for a company that sold both shakeproof washers and screws. He came up with the idea of placing the washer on the screw before it was thread rolled. The major diameter of the screw being larger than the washer hole prevents it from coming off. The Illinois Tool Works made machines that produced these patented pre-asSEMbled washers and screws. The s at the end of SEMs is thought to have been subsequently picked up because they are not usually purchased individually. In spite of the original patents and trademarks the word SEMS is generally recognised as a generic term applicable to screw and washer assemblies.

Eric
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Offline Bluechip

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Re: SEM's ... ??
« Reply #2 on: July 12, 2010, 02:10:39 PM »
Thanks Eric   :thumbup:

Where did you get that? I spent about half an hour looking, came up with all manner of irrelevant stuff, but missed that one.  :scratch:

Seems a good account, I'll leave it at that ... life's too short etc..

I suppose it's a comment on my lack of imagination, I've used the things for half a century, it's never occured to me to ponder what the origin was ?

Dave BC

« Last Edit: July 12, 2010, 02:13:40 PM by Bluechip »
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Offline Brass_Machine

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Re: SEM's ... ??
« Reply #3 on: July 12, 2010, 02:47:03 PM »
David,

Got it from HERE.

Eric
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Offline snub

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Re: SEM's ... ??
« Reply #4 on: July 13, 2010, 09:27:38 PM »
The question of how they get those washers on over the threads has been bothering me for 40 years. So they put the washer on, then form the threads. Oy, that never occurred to me. I learn something new every day!

Offline dsquire

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Re: SEM's ... ??
« Reply #5 on: July 13, 2010, 09:43:31 PM »
Snub

Me too. No wonder I have had so much trouble trying to take a washer off when I needed one for another screw.  :lol: :lol: :lol:

Cheers  :beer:

Don
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Offline Lew_Merrick_PE

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Re: SEM's ... ??
« Reply #6 on: July 14, 2010, 01:36:37 AM »
Yeah, way back when (1983-ish), I was designing an experiment modules for the STS (aka "Space Shuttle" -- STS = Space Transportation System, the correct name).  As this is something disassembled and reassembled in orbit, all the screws that can be removed must be attached to the unit and have all their washers attached as their coming free and floating about is poor form.  There were five such removable screws in the module, so getting a "run" of SEM's was a non-starter.

What I did was to turn the body of the (socket head cap) screws to a couple of thou below the minor diameter of the thread (about 1.5X the thickness of the washer in length), make a custom washer with an "ear" on it (which was drilled to accept a 1/16" wire cable attachment) with the ID drilled and tapped to match the screw thread.  Once threaded onto the screw, a prick-punch damaged the threads in the washer to prevent it from backing out.  Not a bad solution when you only need a couple of non-standard SEM's.

Offline andyf

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Re: SEM's ... ??
« Reply #7 on: July 14, 2010, 07:14:00 AM »
David,

Got it from HERE.

Eric

When is a SEM not a SEM?
When it's a KEP, according to Eric's link.

I had never heard either expression before now.

Andy
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Offline Bluechip

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Re: SEM's ... ??
« Reply #8 on: July 14, 2010, 07:56:22 AM »
I'd never heard of KEP's either. New one for me too!

Another gem on Eric's link were CLEVELOC nuts ..

I once had some, chucked 'em out, thought there were damaged ..  :bang:  :bang:

Ah!, the follies of youth .. and Owd Codgers ....   :D

Dave BC

I have a few modest talents. Knowing what I'm doing isn't one of them.