Key Construction Ideas
The joining of the main spring in a bug

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, one of the trickiest things I've found with making bug keys is fitting the spring steel to
the main arm, I tend to use rivets rather than brazing which is messy and will affect the steel spring,
My methods are Amateur but practical, and born out of hours of trial and error, anything you don't
understand , ask and I'll do my best to answer.
As mentioned above I'm struggling with another fun project, the Patent 457 one part of the construction
as in most bugs is the mainspring here below I have already cut and riveted one end of the mainspring
to the arm and about to connect the other, the following is  how  I do it :)



Before any key construction you do need some sort of mearsuring device, I use a digital micrometer, they
are really cheap on Ebay just a few $ and can measure in Metric or imperial, also they can scribe easily
as the pointers are quite sharp, they are excellent tools. here you can see I am measuring the width of the
arm ready to mark it out.







Having marked the centre line I'm now about to slot the arm ready to take the steel spring, now here
you can see the slotting blade in the jaws of a lathe, usually this would be in a milling machine, the
reason I slot cut in a lathe is because it is very difficult to get a fine cut to run straight, it tends to veer
off one way or the other and is difficult to correct. so I use the lathe table screw to "Steer" it, the picture
below is "Starting" the cut by advancing the work and rotating the  chuck back and forth by hand, this
starts the cut in the right place, as soon as the cut is a mm or so deep then the lathe can be
started and the cut advanced under power




Here below you can see the cut being "Steered" my hand is on the bed travel my other hand (out of sight)
is slowly advancing the work, if the cut starts to veer one way I offset it by moving travel in the opposite
direction, these are very fine adjustments, the lathe is over 100 years old, no Hi-tech in my workshop :)



Here is the cut slowly progressing down the center mark


And here is the end of the arm slotted into the spring to see how it fits, the spring doesn't have to fit exactly
I use the same slot cutter for a few different spring gauges, as the act of forming the rivets will close any fine
gap I've found, if the slot is to tight a fit it becomes difficult to work so a loose fit is an advantage at this stage.



Now comes the marking of where the rivets will go, by using the mic mark the end of the slot, measure the width
and devide by two and scribe a line, and then simply decide on two suitable points along the line where the rivets
will go, provided there is enough space at either end of the slot the position is not critical unless you are following a
plan of some sort,



Having scribed where the rivets will go its time to centre punch the marks, this is standard workshop practice,
centre punching stops the drill bit wandering out of position, you notice I have placed a bit of scrap steel spring
in the slot, this is to stop the slot closing up when I hit the punch, obvious I know but we are in the basics here.
and I'm pitching this at beginner level, apologies to the pros (Rich:)



And below I'm drilling the rivet holes, I'm going to use 1/16" brass rivets, cheap as chips from model
engineering sites, I don't bother to clamp the work for fine holes, they can tend to wander even being
centre punched, so I can steer if needed, this comes with experiance, a beginner would probably be
better with the work clamped in the vice



Now after drilling there will be burrs in the slot, these are best removed with a piece of scrap steel spring
tapped gently into the slot.



Now the time has come to fit the rivets, they will almost certainly be slightly over size, so you can clear
the holes by running the drill bit up and down the holes a few times putting very slight pressure left
and right, not to much or you will snap the bit, here again experiance counts :() and after clear the slot
of any burrs.



And below are the two rivets sitting in the holes, they MUST be a push fit, if they stick and you can't get
them out gently tap them out with a suitable punch, care needed as they will bend and be useless.



OK now the tricky bit punching the holes, start off by placing the work on a hard surface, here I'm using the
flat part of a vice but the best way is across partly opened jaws with the work positioned each side, that way
if you hit the punch to hard it won't be damaged, again experiance counts, line everything up makesure the
work is pushed right into the spring and hit the punch smartly, making the first hole in the spring




Now carefully pull out the punch and remove the spring from the slot, you may need to lever it gently side to side to
get it out, again almost certainly it will be undersize, carefully ream out the hole slightly using a pointed file or similar
until a rivet is a push fit, remove any burrs or it won't go easily into the arm slot





Now, gently push the spring into the slot and gently tap the rivet into the first hole as below, now the
critical bit, line up the two parts of the arm exactly, if you get it wrong the arm will point up or down when assembled
when everything is right punch the second hole, this way the two holes in the arm will line up exactly with the holes in
the spring. you can see me doing this over the part opened jaws of the vice





And finally push or very gently tap the rivets in place, if you look carefully I have pointed the rivts slightly
this helps them locate easier, you can use the punch to line things up before inserting the rivets.
Don't cut the rivets or form them until the last possible moment as you may need to remove them later
for something like further work or plating or similar, if you need to remove them cut them ready to form
but then gently tap them flush and tap them out with the punch over the open vice jaws
If you have done it all correctly you will have a first class join of the spring to the arm when you finally
form the rivets, I tend to form the rivets by resting the heads on a hard surface and gently tapping the
unformed ends until they are fairly flat, easy with brass, you can of course used a correct rivet head former
but hardly worth it with tiny brass rivets like these, variations include riveting a round arm where you have
to cut a flat on the arm and so on, but the basic idea is the same, if this sort of thing helps I could describe
other difficult jobs like making the contact spring etc.
anything not clear drop me an email
from Ron g3yuh...