Repairing a Frank B stiletto

J

Joopie

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Jul 10, 2021
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I have some leaf spring material from knifekits.com that needs some shaping in order for the new spring to fit. How should I go about heating and bending this spring to avoid messing up the temper or metallurgy?
 
It's at https://www.knifekits.com/vcom/leaf-spring-material-070-length-p-1080.html. The spring material is .160" wide x .070 thick and:

Our leaf spring material is made from the steel recommended by the world's top custom automatic knife makers and is composed from carbon stainless steel, heat treated to the government specifications for springs, at 40-45 rc. Our springs are not 301 or 302 work hardened stainless steel. You can have comfort in knowing that our spring stock will not get weaker over time like work hardened spring stock will!
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I plan to use it to replace a broken kicker spring in a Frank B stiletto. The idea is to cut off the broken stump of the kicker spring on the back spring and cut a notch near the bottom to receive the new spring.
 
I bought some of the same stuff to use in a scale release auto I was making. I found it to be very poor quality. It does not hold its shape.
 
I'm betting you'll need to heat treat it, if You're going to do any kind of bending etc.
 
When I make springs for Italian autos, I start with 1/8" 1095 (usually.) I cut the spring to approximate length, eyeball the thickness and taper. Bend properly to shape. Clean. Heat treat to cherry red throughout the spring, quench in room temperature canola oil. I then clean the spring to bright steel and temper with a small, soft torch flame to just past blue and let it air cool.

You will have to grind the inside of your backspring down considerably, and either slot it or dovetail it at the rear of the knife. If you use a slot, it should also have a slight dovetail to prevent the spring from coming out.

While you may do it successfully, this repair usually requires some experience.
 
Bill DeShivs said:
When I make springs for Italian autos, I start with 1/8" 1095 (usually.) I cut the spring to approximate length, eyeball the thickness and taper. Bend properly to shape. Clean. Heat treat to cherry red throughout the spring, quench in room temperature canola oil. I then clean the spring to bright steel and temper with a small, soft torch flame to just past blue and let it air cool.

You will have to grind the inside of your backspring down considerably, and either slot it or dovetail it at the rear of the knife. If you use a slot, it should also have a slight dovetail to prevent the spring from coming out.

While you may do it successfully, this repair usually requires some experience.
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Thanks. I've done similar fittings in non-knife tinkering without heat treating. As I waited for a response, I was thinking that 1/8" square rod would be ideal. Thanks for cluing me in on the alloy and heat treatment. Is it okay to use filtered used peanut fry oil for quenching?

So far, I've successfully removed the middle and bottom pins so I can extract the back spring. There was only a tiny bit of scratching on one of the bottom bolsters -- these can be easily buffed and polished prior to reassembly. I've also prepared a means of reassembly using screws instead of pins so any future spring breakage will not take too much time to fix. I made lots of drawing and documentation, but have not yet cut anything other than the two pins I mentioned. At this point I can reassemble using pins or screws.
 
After scanning in a tracing of the combined back and kicker springs and considering what was written here, I think I've come up with a design for a new kicker spring. It generally follows how old Latama knives had their kicker springs. One tricky part of this was clearance between the middle pin hole and the blade. I think that's what Bill was referring to when he said "...grind the inside of your backspring down considerably.". What I have calls for grinding the back spring within a millimeter of the middle pin hole. I'll experiment with some test strips to see what really fits in there before I grind down that part of the spring.

Here's a graphic of an intact spring with my new kicker spring laid over in red. Comments please?


11d831e1e9_shrink.jpeg
 
Looks good. I would leave a little more than 1 MM over the pin hole.
Your dovetail doesn't need to be anywhere near that large.
 
I can't seem to make a 1/8" square rod dovetail into the back spring more than 1mm and yet have the same thickness at the moving end as the original. Not a big problem as I'll be cutting mine from a 2" wide bar... Just curious how you made it work with 1/8" square rod.
 
Bill DeShivs said:
As I said, I cut my springs out of sheet.
Click to expand...
I was under the impression that it could be done with 1/8" square rod. Maybe I could make it work if I went with the approach of sticking the root of the spring into a notch, but now prefer the dovetail approach. Thanks.
 
After several pauses, false starts, and botched kicker springs, I think I have something usable. Tools used include a set of files and a Dremel (with A576 sanding guide and EZ-Lock cutoff wheels), mallet, wood scraps, and c-clamps. The sanding guide can be used as a sort of guide, but don't let the workpiece get too hot the guide will melt. Soon I hope to acquire some more precise and easy to use tools as I don't plan to stop my knife tinkering after finishing this repair.

c73ffc5dc9_shrink.jpeg


I started with a practice kicker spring to get a feel of things and figure out how to lay out the dovetail socket in the back spring. I made that socket by pressing a large triangular file against the backspring and filing down 2mm. Then I pressed the file against each side of the notch and finished the corners with a small triangular file. After several tries with making a kicker spring, I settled on this approach:
Cut a 7mm wide strip. File a 60 degree bevel on one end. Apply blue (or sharpie ink) and scribe a line about 5mm from the bottom as seen in this picture. Lay the strip on the backspring with the bevel in the rightmost corner. Mark a point about 5mm left of the leftmost corner. Cut a little notch with the Dremel to make the mark more visible. Cut the strip just above the scribed line just past the marked point. Cut at the notch down to meet the horizontal cut. Press a triangular file against the other side of the "flag" to form the other side of the kicker's dovetail. At this point, the dovetail is too tall and too wide to fit. So file the bottom until the dovetail laid in its socket diagonally until the inner side of the backspring meets the moving part of the kicker. Then file down the beveled end on the right until the width is right. As the correct width approaches, do one stroke, test fit, and repeat.

I got to the point where the dovetail went in with some resistance, so I laid it between two pieces of softwood and tapped. It was in but still rocked around and I can see light through the mated pieces as I can't get things perfectly square with the tools I have at my disposal. I think I can work around this by putting some divots in the kicker with an automatic punch to stake it firmly in place.

Next up is bending the kicker to the correct shape, trimming to correct length, and shaping the tip. The metal is soft enough to do the bending cold. However, I'll do some tests on scraps and botched kickers to see if it matters. Then it's on to heat treating, which I will also test on scraps before doing it to the kicker you see here.

Please comment.
 
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