Dreaded spring ping of doom.....

Looking back, I had a Puma Prospector in the early 70’s that broke a spring. I think I’ve only had three total, two from the same maker and the Puma. I have an 80’s (?) vintage pearl Queen that decided to disassemble itself, one of these days….
 
Will Power said:
Horrible surprise. Don't want that happening to mine as I understand they're no longer made? Unlike you, I don't have the skill to fashion a new spring either. My one has, I recall, a stainless backspring but carbon blade.
Click to expand...

You are correct on both counts, the spring is stainless & yes they are no longer available, I picked mine up in Albacete (Spain) a couple of years ago when I saw it in a shop display knowing they were thin on the ground.

Jack Black said:
A couple of years later, I was about to ship this Richards British Army Clasp Knife, from 1944, off to Charlie [IMG alt="waynorth"]https://www.bladeforums.com/data/avatars/s/149/149064.jpg?1492197516[/IMG] waynorth , when the spring pinged :(
Click to expand...

Yes, been there done that. A 1944 clasp knife with one broken spring I made into a single blade, including polishing the spring in a hope to avoid any "stress risers" or points where cracks could propagate.

8nLKEpL.jpg

Full story here.

Broken Clasp knife transformation.

I picked up this old (1944) Richards clasp knife from a flea market a year or so ago for next to nothing as it was in such bad shape. Worn & dirty with a broken blade spring. I toyed with the idea of making something from it for a while but felt it was wrong to destroy something with...
www.bladeforums.com www.bladeforums.com

Ernie1980 said:
Never a good sound to hear! Please show pictures of the repair, most of us don’t have the skill to fix this ourselves.
Click to expand...

Yes I will post progress here. Stay tuned. ;)
 
I'mSoSharp said:
Yes, been there done that. A 1944 clasp knife with one broken spring I made into a single blade, including polishing the spring in a hope to avoid any "stress risers" or points where cracks could propagate.

8nLKEpL.jpg

Full story here.

Broken Clasp knife transformation.

I picked up this old (1944) Richards clasp knife from a flea market a year or so ago for next to nothing as it was in such bad shape. Worn & dirty with a broken blade spring. I toyed with the idea of making something from it for a while but felt it was wrong to destroy something with...
www.bladeforums.com www.bladeforums.com



Yes I will post progress here. Stay tuned. ;)
Click to expand...
Hey, thanks for the link, I had completely forgotten about that! :eek: I have the memory of a goldfish these days I'm afraid :( :thumbsup:
 
1635509810628~2.jpg

At the top is the old spring C.A glued together, below is where I'm at with the new one.
Cut out of carbon steel sheet (2mm O1 Precision Ground Flat Stock) with a thin cutting disc in an angle grinder (grindette). Now I'm carefully slimming it down with a small bench grinder, more needs to be removed but soon I'll start trial fitting it & removing tiny amounts at a time & then refitting again & so on.
The reason to keep trying it for fit rather than just copying the old spring is that I won't be able to get it absolutely identical by hand, a tiny fraction out on the holes or anything else can make a huge difference to how it works so it's better (for me) to alter it very slowly by regular trial fitting.
Also I can change the shape & get the pull more or less how I like it before heat treatment, which due to being away from my workshop & doing this on my balcony! :oops: means it's going to be an old fashioned style heat treat & temper..........
 
I'mSoSharp said:
View attachment 1669815

At the top is the old spring C.A glued together, below is where I'm at with the new one.
Cut out of carbon steel sheet (2mm O1 Precision Ground Flat Stock) with a thin cutting disc in an angle grinder (grindette). Now I'm carefully slimming it down with a small bench grinder, more needs to be removed but soon I'll start trial fitting it & removing tiny amounts at a time & then refitting again & so on.
The reason to keep trying it for fit rather than just copying the old spring is that I won't be able to get it absolutely identical by hand, a tiny fraction out on the holes or anything else can make a huge difference to how it works so it's better (for me) to alter it very slowly by regular trial fitting.
Also I can change the shape & get the pull more or less how I like it before heat treatment, which due to being away from my workshop & doing this on my balcony! :oops: means it's going to be an old fashioned style heat treat & temper..........
Click to expand...
I am very interested to see how the heat-treat and temper goes for you. Doing this with around-the-shop tools can be tricky and I have not yet tried it myself. It seems to me the temper is really the hard part (no pun intended).

I have tried to hand-lap tempered springs to correct thickness before and wow, what a pain that is!
 
Rhinofly said:
I am very interested to see how the heat-treat and temper goes for you. Doing this with around-the-shop tools can be tricky and I have not yet tried it myself. It seems to me the temper is really the hard part (no pun intended).

I have tried to hand-lap tempered springs to correct thickness before and wow, what a pain that is!
Click to expand...

Just as a general question, are heat treating a back spring even necessary?

From the perspective of very basic steel characteristics (from structural steels), as long as the steel doesn't reach the yield stress (by how much it has to deflect), the steel will deform and spring back indefinitely. Given that the back springs aren't the typical 'coiled up' springs, there isn't a lot of residual stress from the fabrication that needs to be relieved.
 
euroken said:
Just as a general question, are heat treating a back spring even necessary?

From the perspective of very basic steel characteristics (from structural steels), as long as the steel doesn't reach the yield stress (by how much it has to deflect), the steel will deform and spring back indefinitely. Given that the back springs aren't the typical 'coiled up' springs, there isn't a lot of residual stress from the fabrication that needs to be relieved.
Click to expand...
I honestly am no expert at steel properties. However, I do know that un-heat-treated steels will more easily plastically deform, and not return to place after bending. I have seen, for example, fillet knives with failed or poor heat treats do exactly this. It may be this reason why steel is heat treated and tempered to achieve spring-like behavior (not just for hardness). An untreated backspring will likely see its spring coefficient noticeably decrease over time with repeated bending. Again, this is just speculation on my part.

Lol...I probably should have just said, I don't know. :)
 
Lol, thank you R Rhinofly !

Any information is good information in my books. Much appreciated.

I did look up on the popular search engine and it does say the hardened blade will wear out the spring over time so I can see heat treating the portion of the spring that comes in contact with the blade.

As you can tell, I'm no metallurgist lol
 
euroken said:
Just as a general question, are heat treating a back spring even necessary?

From the perspective of very basic steel characteristics (from structural steels), as long as the steel doesn't reach the yield stress (by how much it has to deflect), the steel will deform and spring back indefinitely. Given that the back springs aren't the typical 'coiled up' springs, there isn't a lot of residual stress from the fabrication that needs to be relieved.
Click to expand...
Also speculating, but I think the extra hardness & wear resistance afforded by heat treat is important for the sake of the bearing surfaces (spring end vs. blade tang). Especially in simpler carbon steels, which won't have many hard carbides to lend for wear resistance, if any at all. I'd think an unhardened spring end would wear and/or plasticly deform much too quickly against the hardened tang of the blade. I've noticed, in simple carbon steel folders, that the spring ends and/or blade tangs tend to wear more than with knives made with stainless steel springs & blades, which are more wear resistant than simple carbon steel, thanks to the chromium in the stainless components. So, the hardening afforded by heat treat in the simple carbon steel springs & blades is the only thing lending any extra wear resistance, for the most part.

I'm also inclined to believe the tempering after heat treat is what will make the spring more durable & repeatable over the long run, regarding long-term effects of flexing on the steel.
 
euroken said:
as a general question, are heat treating a back spring even necessary?
Click to expand...
Yes.
euroken said:
the hardened blade will wear out the spring over time
Click to expand...
This...
Obsessed with Edges said:
an unhardened spring end would wear and/or plasticly deform much too quickly against the hardened tang
Click to expand...
& this.
Obsessed with Edges said:
tempering after heat treat is what will make the spring more durable & repeatable over the long run
Click to expand...

Yes, tempering is essential after quenching as the steel is fully hard & near glass brittle, the hardness is reduced usually by "baking" in an oven at a set temp for a particular hardness.

The original spring might have been too hard hence it snapping, also to my mind it isn't a great shape with a lot of stress on the thinnest point. I don't know if my logic is correct but when I make a knife from scratch I like the spring as long as possible with a fairly uniform "bendy" section to reduce stress, again just my opinion & by no means scientific.

I'll be "running the colours" (Google it) to temper it which might upset some viewers 😄
 
Last edited:
Nice job on the repair so far! I'm not surprised that spring broke judging from the length, width and thickness. Must have had a serious pull on it. If you use a propane torch to temper you'll want an even blue colour. Temper it twice for good measure and sand off the blue between tempers.
 
A bit of time has passed while I was getting on with other stuff but back on this now, the spring has been oil quenched to harden it then tempered by watching the colours as a guide to temperature, not the greatest method but should be fine in this case. Bit of a poor image (apologies) but this is it ready to rivet back up in the knife, it will get a bit slimmer after fitted as the spine will be ground to follow the shape of the knife.


iv0JFBM.jpg
 
Peregrin said:
You really don't want to experience the "ping of doom". There was a happy ending though. I returned it to the maker in Japan and had it back as good as new in 14 days. Talk about excellent service! It was 10 years old too, and there was no charge for the repair!
Click to expand...
Figured I'd add this. Sometimes it turns out OK!
Mr. Ohta makes a fine knife, and his response to my problem was just amazing.
 
I'mSoSharp said:
A bit of time has passed while I was getting on with other stuff but back on this now, the spring has been oil quenched to harden it then tempered by watching the colours as a guide to temperature, not the greatest method but should be fine in this case. Bit of a poor image (apologies) but this is it ready to rivet back up in the knife, it will get a bit slimmer after fitted as the spine will be ground to follow the shape of the knife.


iv0JFBM.jpg
Click to expand...
Well done :) :thumbsup:
Peregrin said:
Figured I'd add this. Sometimes it turns out OK!
Mr. Ohta makes a fine knife, and his response to my problem was just amazing.
Click to expand...
That's great to hear Gary :) :thumbsup:
 
You must log in or register to reply here.
Back
Top