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Re: impossible stud

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"John Larkin"  wrote in message 
news:jg5kdddookkqqkamj6enuq2idvkfcn6lrk@4ax.com...

On Fri, 20 Apr 2018 11:50:21 -0400, "Carl Ijames"
<carl.ijames@NOverizon.net> wrote:

>On Fri, 20 Apr 2018 07:38:42 -0700 (PDT), tabbypurr@gmail.com wrote:
>
>>On Friday, 20 April 2018 15:22:28 UTC+1, John Larkin  wrote:
>>> On Fri, 20 Apr 2018 08:41:23 +0100, Martin Brown
>>> <'''newspam'''@nezumi.demon.co.uk> wrote:
>>> >On 20/04/2018 04:51, John Larkin wrote:
>>> >> I want a lot of these:
>>> >>
>>> >> https://www.dropbox.com/s/dmj4vff7mnldrcs/Impossible_Stud.JPG?raw=1
>>> >>
>>> >> It probably doesn't exist. Maybe a Swiss screw machine company could
>>> >> make us a bucket full of these.
>>> >
>>> >Not quite what you asked for but how about getting some threaded bar 
>>> >and
>>> >turning down to the other size and using a nut to make the collar.
>>> >Or don't turn it down at all and use a larger countersunk screw.
>>> >
>>> >If you did it in copper or brass then they could be soldered in to the
>>> >daughter board and so wouldn't need to be a tight press fit.
>>>
>>> Yes, one option would be to delete the knurl and solder one end. I
>>> want the botton of the baby board to be essentially planar, but a
>>> little solder bump would probably be OK.
>>>
>>> >>
>>> >> Six of these would press into a small PCB, which could then be bolted
>>> >> onto the bottom of a bigger PCB.
>>> >
>>> >Does it really need 6 of these supports? I don't envy production 
>>> >putting
>>> >it together. Wouldn't 3 or 4 thicker ones be much easier to assemble?
>>>
>>> They are electrical connections too. I need six connections between
>>> boards. The baby board is about 0.5" on a side.
>>>
>>> https://www.dropbox.com/s/dsjwdnize4ig2gx/Impossible_App.JPG?raw=1
>>
>>I'd hate to rely on solder for a mechanical connection. I know consumer
>>stuff does it routinely, but we've all seen the reliability problems that
>>result.
>>
>>
>>NT
>
>The screw head would probably stick up too far for you if a bump of solder
>is your limit, but you could put a 0-80 x 1/4" screw through the baby board
>and tighten down a nut with a drop of blue loctite to hold it.  That takes
>the place of the knurling and pressing and machined end of your stud, then
>insert through your main board and put on six more nuts.  If these 6 screws
>are all within a 3/8" square then little height differences might be enough
>to put in some significant bending stresses, causing cracks or bad
>connections over time.  Hmm, browsing at www.mcmcaster.com there are a
>couple of head styles that are 0.032-0.037" tall, and they have brass and
>stainless steel.

I guess I could just smash the boards together with six nuts and
bolts. That's inelegant but easy. I'd have the screw heads poking out
the bottom of the baby board, so I'd have to live with that. I would
want low screw head height.

The parts on the baby board will get hot. The baby board pushes
against a silicone gap-pad that conducts heat into an aluminum
baseplate. Some of the gap-pad material is very compliant, about like
chewing gum, so would flow around the screw heads and make a decent
thermal interface. I could use thermally conductive putty, but that's
messy.

John Larkin         Highland Technology, Inc

lunatic fringe electronics
===================================================================

I thought you wanted an air gap between the boards, that's why I suggested 
two nuts (and it retains the screw and makes assembly easier).  You could 
counterbore the screw head side of the baby board to sink the screw head up 
to about half the thickness of the board, which would probably make it 
basically smooth for your gap-pad.  Or you could just put a header row of 
through-hole pins with spacers in the main board with matching holes in the 
baby board and solder the baby board down.  Assembly would be easy, R&R for 
service not so much :-).  If the two boards can touch without shorting, put 
six pads on the main board and six vias on the baby board large enough to 
get a soldering iron tip all the way through to touch the main board and 
solder the baby board down.  Like a plug weld, only with solder, and you 
don't really need to fill the via.  Remove with a heat gun to melt all six 
at once.

-- 
Regards,
Carl Ijames

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