another wacky idea to fix switches on Racal/Dana frequency counters

[slburris]

Like many of you, I have some Racal/Dana 1992 and 1998
frequency counters with those stupid switches that deteriorate
and finally stop working. 

Since exact replacements aren't available, repairs involve replacing
with modern switches and deciding how to attach the key caps.
The original key caps expect the switch to have a plus sign shaped end,
but modern switches have circular ends. I've seen three solutions to that problem.

1) Have your own replacement key caps made.

2) Machine a metal fixture of some sort with a plus shaped cutout, heat
that fixture and melt down the switch top to form a plus sign.  Alternatively,
somehow use a dremel tool to cut the switch top!

3) Cut the innards out of the original key caps and epoxy them on to the
replacement switches.

#3 seems most straightforward, but I really hate to modify the keycaps if I don't have to.

So I was thinking of a different approach.  Purchase some shorter switches, such as the
Panasonic EVQ-21507K.  Create an adapter widget which fits over the round end of
the switch but presents a plus sign shape on the other end.  3D print the adapters.
Epoxy the adapter to the switches.  Now the switches have the proper mating surface
for the original keycaps!  Of course I have nearly zero experience generating the design
of such an adapter, although I've launched Google Sketchup sometime in the past :-)
Nor do I have a 3D printer, but I've had stuff made at shapeways.com

Looking for thoughts along the line of:

--- That's a stupid idea. 

     Suck it up, modify your original keycaps, and stop complaining

--- That's a brilliant idea

     Go make this adapter, post pics and let us know how it goes
     (Or if someone else makes something like this and offers some adapters
     for sale, that's good too!)

Scott

[slburris]

So here's what I'm thinking, a little adapter to fit over the shaft of the replacement switch, presenting the appropriate interface for the existing keycaps.  Now to get this printed on a 3D printer and try it out!

[slburris]

The original faulty switch is on the top, the new switch (without the adapter) is on the bottom.

[lowimpedance]

Actually that sounds like a good idea, certainly worth a try.
Maybe if you want to you could post up the STL file of the adapter ,in case anyone with a 3d printer was interested to have a go.

What about using super glue instead of epoxy.
Anyway interested in any results you may have. (updated pic's  )

[edpalmer42]

The plus sign is a perfect shape for an extrusion.  Anyone know a company that would have such a thing as an off-the-shelf item (i.e. no setup charges)?  A quick Google search didn't turn up any companies with decent online catalogues.  They were all 'contact us' sort of thing.

Glue the extrusion into a tube that slips over the new switch actuator or just glue the three pieces together.

Should be cheaper than having each adapter 3D printed.

Ed

[slburris]

Here is my best results, a couple tries ago.  The body is too long and the plus size is too thick to mate correctly with the keycap.



Attached is the STL of my latest design. I'm having trouble getting the features on this to print cleanly, using a Makerbot Replicator 5G.  I'm not sure if I'm asking too much of the printer, or if it's having issues, or if I need to tweak some settings. 

I might have to go to shapeways to get it printed correctly.  Unfortunately, it's almost $2 to print one, and there's no quantity discount apparently.  But I haven't given up on the Makerbot yet.

Anyway, feel free to play with the STL if you're trying to repair your own Racal Dana 1992, etc.

Scott

[slburris]

Trying a different tack on this since I still can't get the plus sign to print with enough resolution for the keycap.  So I made an adapter with an integrated key, like this.



I got the dimensions a little wrong, but here it is integrated on the replacement switch.



This works well enough that I may just print out this integrated version until I can solve the resolution problem.

[dr_dan]

The plus sign is a perfect shape for an extrusion.  Anyone know a company that would have such a thing as an off-the-shelf item (i.e. no setup charges)?

I don't know the required dimensions for the adaptor, but the plus-sign part looks just like a Lego cross axle...

Dan

[babysitter]

Clean up that 3d-print (file/acetone vapour) to something that is close to what you want and use it as a mother for a silicone mold. Just make dozens of the little molds. Go for epoxy resin for hard buttons, or polyester stuff for soft buttons. Do some qc and sell it to all the suffering owners !

[psykok]

Hi,

Let me share my solution.

The goal was to made new switches by reusing the with part of the old ones.
I bought some standard switches by Farnell with 11mm height.
remove the white part from the genuine switches


After that I had to cut a little bit the base of this part otherwise it will not fit the new switches and will  fit the front panel.
The solution is pretty easy, clue the white part on the top of the new switches


The new switches are a bit higher as the original one but it fit good in the front panel and work pretty well



Regards,

Alex

[slburris]

Attached is the STL file of the adapter with integrated keycap.

[slburris]

Here a comparison between the new and old switches, using the latest integrated keycap



Scott

[LaurenceW]

Can I suggest another possible approach? I should start out by saying that I don't yet have a Racal counter, but am thinking of buying one, and am assuming I will have to find a solution to the collapsed switch problem!

The very specific bit which has failed as the silicone/rubber button and integral carbon/conductive pad. If you could just prise the white plastic tops off without disturbing the black base and solder connections (seems very doable), then replace the rubber element, then replace the white shaft - bingo! 

Now, the rubber bit strikes me as exactly the same idea as used for keyboard switches in some of the (ironically) cheaper PC keyboards. Might be a bit of a lottery finding the right one - something with a membrane key "mat" might do the trick. You need to trim the round part from the sheet, but it might work. Of course, most of the common keys will have been hammered in any used old PC keyboard, but the Function keys will no doubt have led a much easier life.

Just a thought?