Author Topic: Would this solve the screw problem?  (Read 3051 times)

Offline CNO53

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Would this solve the screw problem?
« on: August 03, 2007, 11:57:55 PM »
I'm not an engineer, but I do have a question...

We're having to tighten our "RIGHT HAND" grip screws after every 50 rounds. The screws tighten by turning clock wise. When the gun is fired the recoil is to the rear or counter clockwise, thus loosening the screws.
If the "RIGHT HAND" grip screws were reversed threaded so they tighten counter clockwise, would they not tighten themselves when the gun is fired, (same as the left hand grip screws)  
Just curious...
« Last Edit: August 04, 2007, 01:31:31 AM by CNO53 »

  Perception...Reality...?

Offline Richard S

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A refRe: Would this solve the screw problem?
« Reply #1 on: August 10, 2007, 08:49:59 PM »
Now that's an interesting concept. Reverse (counter) threaded screws might indeed be less likely to work loose on the right grip panel. But then I'm no engineer either.

All right, you engineering types out there -- what's the answer?
(1963-1967) "GO ARMY!"

Offline sslater

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Re: Would this solve the screw problem?
« Reply #2 on: August 30, 2007, 10:38:39 PM »
Well, I'm a retired mechanical engineer.  My work experience was primarily with engine components.
A little background on fasteners:
The main objective with fasteners is to assure the bolt or screw (or stud / nut) is stretched enough to always provide a positive clamping load on whatever it is holding together.  
We talk about "torquing" fasteners to a particular value.  That's just a convenient (although indirect) way of specifying how much to stretch the bolt.  The idea is to stay in the elastic deformation range of the fastener.  That means there is a linear relationship between torque and bolt elongation.  You can tighten, loosen, tighten, loosen, etc. the bolt and it will always feel the same.  You've all probably tightened a bolt too far and found the wrench starts to turn easier without the joint getting any tighter.  That means the bolt has been stretched into the plastic deformation range - or you stripped the threads  >:(.   Modern engines with aluminum blocks and heads have gone to special single-use bolts that are stretched into the plastic range, but that's very specialized.
Fasteners that have to contend with rotation, like flywheel bolts, lug nuts, conn rod bolts, often have special features like castellated nuts and cotter pins (wheel bearing retainers) or place head bolts (flywheels) that deform to lock against the part.  

With our pups, I suspect the issue is a combination of differing rates of expansion between the aluminum frame, steel screws, and composite (C.F. or G10) grips - combined with the sharp rotational impulse when firing a round.

There are lots of things working against those little bitty screws in that application.  They're short; they're much stiffer than the frame or grips; they're short; you can't stretch them enough to assure there is always positive clamping load; they're short.

Without getting real scientific, the most practical solution is to apply a thread locking compound like Loctite blue, or if you're cheap like me, a dab of the wife's nail polish.

Sorry for the long (unsatisfactory) explanation, but fasteners live a very complicated life and I didn't even scratch the surface.    

Steve

Offline Richard S

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Re: Would this solve the screw problem?
« Reply #3 on: August 31, 2007, 07:42:24 AM »
Steve:

I've worked with enough expert witesses in my life to recognize a knowledgeable summary of a technical matter when I read it.  Thank you for posting that information.  
(1963-1967) "GO ARMY!"

Offline jarcher

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Re: Would this solve the screw problem?
« Reply #4 on: September 22, 2007, 04:29:36 PM »
So Steve, did you say the problem is that they're short?

Offline tracker

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Re: Would this solve the screw problem?
« Reply #5 on: September 22, 2007, 10:40:12 PM »
Or, as I think Little Richard used to say, on a non-scientific
basis, "It may be tight but that's all right; if it don't fit, don't
force it."