[Elecraft] OT - Screw & Bolt Torque

[Bob McGraw K4TAX]

Here is one reliable source for screw torque.

http://www.mgtd.ca/screw%20torque.htm

Now, to get the proper torque tools and use them.

73

Bob, K4TAX



On 10/29/2017 8:34 AM, Clay Autery wrote:
> 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.
>
> There are tables that specify general torque specs for fasteners, 
> threads in various materials, etc.... The idea is to take the lowest 
> max value from the list.  This becomes the MAX NTE.
> Then, use some analysis and judgement in what forces are to be 
> imparted to the joint....  static tension, sheer, axial, radial, 
> vibration, et al...
> Then in this instance consider the qualities of the mating 
> surfaces....  are the flat?  What is the run out?  Are they smooth? To 
> what grit spec are they smooth?  There's a difference between flat and 
> smooth.
> What is the interface material being used?  Thermal pad? Insulating?  
> Non-insulating? Initial thickness? Read the spec sheet for the thermal 
> pad/compound.
>
> I suspect here that the RF package has an insulating thermal pad 
> between it and the heatsink...  It was probably spec'd to keep the RF 
> package within its operating envelope under 90% of expected operating 
> conditions... knowing Elecraft, probably even a higher spec, and maybe 
> a little extra to cover the "cheater".
>
> Thermal pads and MANY top quality thermal compounds REQUIRE a curing 
> period.  If the package is held with a tension spring/fastener, there 
> is usually no requirement/need to re-torque.
>
> IF it is JUST a screw and maybe a locknut, you NEED TO RETORQUE after 
> a given number of thermal cycles....  The thermal interface material 
> flows under heat and cools when not in use.  Eventually it reaches an 
> equilibrium.
> You torque the fastener JUST enough to hold the junction static at 
> this point.  I'm a freak, I would use a thermally conducting thread 
> locking/anti-seize compound (I made one).
> I NEVER torque unlubricated fasteners.... ESPECIALLY steel to aluminum 
> interfaces.
>
> The final torque for this application is likely in the relatively low 
> inch-pound range.... just guessing.  I have 2 inch-pound wrenches... 
> 0-15, and 0-70.  Most people don't....
>
> Key... do NOT over-torque.  Consider the lever length and force 
> applied...
>
> 73,
> Clay, KY5G
>
>
> On 10/29/2017 8:03 AM, David Woolley wrote:
>> As far as I can tell, no torque settings are given for any of the 
>> fasteners, wouldn't it be an idea to provide those, for people who do 
>> have suitable tools.  Generally there are just warnings not to 
>> over-tighten.
>>
>> On 28/10/17 20:24, Mel Farrer wrote:
>>>   If the people at Elecraft have done their job and mounted the 
>>> transistor properly with the correct torque on the mounting hardware 
>>> procedure, no additional maintainance is required.
>>
>> -- 
>> David Woolley
>> K2 06123
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