What's the secret to LK201 leaf springs?

[steven at malikoff.com]

Tony said
> On Sat, Sep 12, 2020 at 6:41 PM Adam Thornton via cctalk
> <cctalk at classiccmp.org> wrote:
>>
>> I got an LK201 recently that was a little damaged in transit.  A couple of the keycap assemblies and their corresponding leaf springs have come off.  I can see how the leaf springs fit on the little posts on the keycap assemblies, and I can see where those snap into the board, but what I don’t
see is how to get that put together and then keep it together while I turn it over and then get it in place.>>
>> Clearly there is some simple trick I am missing.  What is it?
>
> When it was made, those posts were much longer. After fitting the leaf
> springs and fitting the unit to the membrane/chassis plate, the posts
> were melted and formed over to make a large 'head' that held it all
> together (this is commonly called heat staking).
>
> My guess is that the formed over part has broken off (you might find
> some little white disks of plastic, about 1/8" diameter, rattling
> about inside the case). Alas I have never found a way to re-fix them.
> There's not enough plastic in the housing to drill it out and fit
> screws/nuts. There is no way of gluing something to the ends of the
> posts that would be strong enough,
>
> -tony
>

Perhaps using a 3D printed jig, I would set up the key post in a lathe collet and
drill a sub-millimetre hole through the axis. Then glue a sliver of carbon
fibre rod in, lastly mill some channels a few thou deep along the outside of the post
for binding with a strand of de-braided Kevlar thread to hold the end on.
A tiny drop of cyanoacrylate applied with a sharp toothpick keeps the Kevlar
in place. The end cap would be drilled with the same drill.

I've used this CF+Kevlar method for repairing a number of things where there is not
enough surface area for adhesive alone and I am sure the repairs will outlast the items
I've fixed. It takes some patience and a need to set up the job reasonably carefully.

Steve.