Key Construction Ideas
The Making of a standard contact spring

Hi I often get asked about certain areas of key construction, although making something is always
subjective and guys have their own way of doing things, there are certain tips that can make the path
easier for beginners, Making these spring contacts is fairly straightforward but does need a little practice
but the materials are fairly cheap so you can have lots of tries at it until you get it right, I shall keep it
simple and try to explain why I make my spring contacts this way, Below you can see the contact I'm
going to copy, first thing is to measure the length of the spring if you are copying an old one it is
quite difficult owing to the curve which obviously needs to be taken into account with the overall length
nothing is more irritating than to make a spring and half way through you realise it's to short !!
So I use a bit of stiff wire and mimic the shape of the original spring then straighten it out and use it
to measure the amount of spring required.


Here below you can see this being done, I use Starette precision steel strip, which can be bought on Ebay or good
model engineering  suppliers




Next you need to measure the width of the old spring  as below



Then scribe a line on the strip so you know where to cut, I use these excellent digital Micrometers for this job, they
are essential for making keys, here you can see the spring I am making is 5mm wide, the gauge of the strip in this
case is .012  Vibroplex use .01 in nearly everything,  but 012 is really as thick as you would want to go for a bug key
spring contact, unless you are using very heavy weights.



Now you can see below the spring strip being cut to size with tin snips, even this thin gauge is hard to cut so make sure you snips
are nice and sharp


As soon as the the strip is cut to size clean it up with a file or in this case a flat bed grinder to remove any burrs
as they can be as sharp as razors



Next mark on the strip where the fixing holes are to go with a felt tip pen, a fairly wide dot is required.



Next you will need to punch the holes in the strip, I have my own way of doing this which I call "Holey Brass"  This is a bit of scrap brass with a
fine slot cut into it and to which  holes of various sizes have been drilled, the spring  strip is slipped into the slot until the mark can be seen in the
correct size hole, the punch is then placed into the hole and given a sharp tap with a hammer, and the hole is punched



A quick word here about hole punches, I no longer use punches made for the job, they can be expensive and often poor quality, so I make my own
a simple idea passed to me on the engineering forum,  you simply use an HSS drill bit !!  a scrap piece of brass rod or similar has a drill bit of the size
you want drilled into it leaving a few mm sticking out and this is your punch, it works perfectly provided you don't leave to much drill shank sticking out
sometimes you have to grind a flat on the end  if they have a shamfer



Anyway now the holes have been punched time to fit the contact, just insert the contact into the hole punched for it then placing the face of the contact on a hard
surface pane the back of the contact flat



Now the tricky bit, bending the strip, I've tried all ways, using heat and templates etc, but for this job the easiest way is to use a pair of round
nose pliers, making sure the contact is pointing out grip the strip with the pliers and roll the strip around the plier just a few degrees, then take
another grip a few mm further round the bend made and repeat the process, just a few degrees and not to much force or it will snap like a carrot
(These are in fact circlip pliers but just as good)



Take you time, the less movement of the plier each time will tighten the curve,  below its at 45 degrees



And finally you arive at a nice U bend in the strip



Now you fit the contact fixing ring which is just a collar with a flat and a tapped hole through it and slide it onto your key arm and tighten up,
Easy Peasy ..........





A quick word about the gauges of bug key springs,  if you are making your own key, don't be tempted to use to fine a gauge
strip for your contact spring or it will vibrate giving "mushy" dots or to heavier gauge this will not only be hard to bend but
it will effect the speed of the key when the dwell time of the contact is adjusted, the same goes for the main spring, to heavy
a gauge means heavier weights are required, the combination of contact spring and mainspring gauges against the weight of
the arm weights can make the difference between a silky smooth key action and a rough difficult to adjust one.



N