[Elecraft] Tightening screws

[Dauer, Edward]

I can see the point of this for mass or machine-made production, but for a 
home-built kit there’s a simpler idea.  If the instruction is not to 
overtighten – as for the screws holding plastic bezels in place – I use a 
screwdriver with a smaller diameter handle. If the screw needs to be 
ferociously fastened, then a larger diameter handle.  The relative mechanical 
advantage could be calculated but probably not the actual torque – that’s a 
function of muscle exertion and I don’t know how to calibrate that.  When the 
instruction says “Do Not Overtighten” I just reach for a smaller tool.

Ted, KN1CBR
--

Message: 25
Date: Sun, 29 Oct 2017 08:34:04 -0500
From: Clay Autery 
To: elecraft@mailman.qth.net
Subject: Re: [Elecraft] PA Transistors Maintenance in K2
Message-ID: 
Content-Type: text/plain; charset=utf-8; format=flowed

It is possible that an explicit torque has never been calculated.? It is 
not a particularly hard thing to do however.

I do not have a K2, so I can't do it, but here's the idea:

1) Fastener size/type, material, thread spec: (e.g. 4-40 x ___ pan head, 
phillips, zinc coated, non-rated steel
2) What does fastener anchor in?? (e.g. aluminum heat sink, what alloy 
aluminum, thickness of threaded area.
3) Thread spec... not JUST the #4, 40 tpi, but the rating for thread 
engagement.
4) Check the specs for the RF transistor package, et al.? Docs 
may/should have a max torque spec for the package maybe... package 
material, etc.
5) # of fasteners... usually 1 maybe 2.
 


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[Elecraft] Tightening screws (WAS: Prospective K3 Owner)

[Ron D'Eau Claire]

The K3 manual emphasis over and over to avoid over tightening screws.
Corresponding with many builders, it seems clear that they don't realize
that parts screwed together are actually held together by a stretched
spring attached to them. When a screw is threaded into a nut, the inclined
plane of the threads pulls the nut and screw together until they meet, then
further turning literally stretches the screw lengthwise. 

On large parts (like a building or bridge) designers provide torque values
that must be used to insure just the right amount of stretch for the most
secure assembly.  

On small parts, like the Elecraft rigs, the actual torque isn't real
critical but, within the broad range permissible, using the right torque is
still important. 

Don't just twist as hard as you can. 

Always consider the materials you are fastening.  

Once the surfaces mate and you feel the torque needed to turn further
increase quickly, only a small amount of additional torque is wanted to
set the spring action, depending upon the material involved. Forcing the
screw beyond that point only puts unnecessary strain on it and the parts
you're fastening. 

Use a little too much torque and the screw shaft breaks because you
stretched it too far or you destroy the inclined plane (strip the threads).
If you're fastening a not-so-strong material like plastic or pc boards, you
can damage the plastic or board by crushing the material.  

The bottom line is that when it comes to tightening screws, more torque is
definitely not better. It's often far worse than not enough. 

Ron AC7AC 

 

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