[Elecraft] OT - Screw & Bolt Torque

Tox scott.small at gmail.com
Sun Oct 29 17:25:53 EDT 2017


Perhaps a bit big for electronics work, but I’ve become a big fan of the
Borka adjustable torque wrench for mounting optics.

On Sunday, October 29, 2017, Bob McGraw K4TAX <rmcgraw at blomand.net> wrote:

> 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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>
>
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-- 
Scott Small


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