I am no expert but I just finished making a new key for a pair of Handcuffs. I don't know anything about handcuffs, and I am certainly no Ian McColl but I was pretty happy with the result. I don't know how this forum works yet so below is a link to the picture.
http://bushcraftoz.com/forums/showthrea ... 1#post8589
Thanks for the comments Guys.
In answer to Lark's question;
First up I did not solder anything, I did consider it after the third thread tap made and heat treated failed, the second internal threading tool was purpose ground and failed, and the first attempt at a key was flung into a distant corner of my shop.
I was flying blind making this, without a male thread to work off, it is very difficult to work out size, pitch and thread form as you no doubt know. The pitch was easy to measure as the threads were visible through the split. The minor diameter I measured by using drill bit shanks at the end of the original keys thread past the split and wear. The major diameter was harder to measure. I could have forced the split closed in the key and measured, but I made a promise not to further damage the original key so not an option. So I made a best guess, figuring it was not as critical as the minor diameter, as I could simply cut the thread as deep as I needed to until it fitted the cuffs.
The thread form was harder to measure. Judging from the original key it was clearly not a standard form, square, acme or such, it was more rounded which could have been wear, but I reasoned that even if I got it close it should work.
I hope the following is clear enough I did not take pictures.
Ok so the nuts and bolts of it. Step by Step
1) turn the outside diameter of the key cylinder, and drill the inside to the minor diameter.
2) Select two small carbide burrs, that would closely approximate the flanks of the thread on the original key. ( have been carving for many years and have a huge range of sizes and shapes, mostly dremel type. see the rest of the thread in the link in the original post)
3) hang your Dremel and run the flexi-drive down mounting the hand piece in the toolpost of the lathe,.
4) Adjust the top slide to an angle that will allow the bur to enter the required depth, and still give clearance for the burrs shaft and importantly closely approximate the form of the original thread.
5) set the lathe up for the required TPI and lock the half nuts.
6) with the dremel running at a good speed, and plenty of lubricant/coolant turn the lathe chuck slowly by hand, thus driving the tool at the required rate into the job.
7) It took about 4 passes and two burrs to form both flanks of the thread form and reach the required depth. by the third pass it was threading on one turn, a very light cut on the 4th pass increasing the depth brought it to a good running fit with no play. (do one flank at a time and if necessary change burrs for the next. Keep in mind that if you change burs you will have to be very careful to get everything aligned again (using the top slide) to ensure the cut is made correctly on the threads flank. It is fiddly but not actually very hard.)
After that and proof that it worked it was a simple matter of decorative turning the shank to approximate the original, then hand forging the back of the bar to form the "thumb wing", profile with a file... blue up to give it the aged look...
I was tempted to Stamp it Hiatt, or put my own makers mark on it, but have left it blank. Probably would look better if I stamped something on it. Anyhow, thats how I did it. Using a dremel as a cutting tool in a lathe is quite unconventional, but essentially it turned my lathe into a mill, and cutting threads in CNC mills is nothing new, the only difference is it was very small, and I did not have to program anything.
If there is a better way of doing this I would love to hear it, I killed many hours in the first attempts, but it did not actually take very long at all with the method above. If anyone knows the correct thread form of the bolt inside the cuffs that would allow the above method to be applied to make a near perfect form. Regardless the one I have made fits and works without play and as it is rarely used, if it is kept lubricated wear should never be an issue.
