Dreaded spring ping of doom.....

[JB in SC]

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….

 

[I'mSoSharp]

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.

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.

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

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.

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

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

Yes I will post progress here. Stay tuned.

 

[Jack Black]

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.

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

Yes I will post progress here. Stay tuned.

Hey, thanks for the link, I had completely forgotten about that! I have the memory of a goldfish these days I'm afraid

 

[I'mSoSharp]

I have the memory of a goldfish these days I'm afraid

You & me too!

And below is what the spring looks like removed, I'll use this as a template for the new one.
As you can see there was no need to disturb the pivot pin, only drill & punch out the two smaller pins holding the spring.

 

[Jack Black]

You & me too!

And below is what the spring looks like removed, I'll use this as a template for the new one.
As you can see there was no need to disturb the pivot pin, only drill & punch out the two smaller pins holding the spring.

View attachment 1668602

It's nice that you can fix that yourself

 

[I'mSoSharp]

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! means it's going to be an old fashioned style heat treat & temper..........

 

[Rhinofly]

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! means it's going to be an old fashioned style heat treat & temper..........

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!

 

[euroken]

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!

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.

 

[Rhinofly]

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.

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.

 

[euroken]

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

 

[Obsessed with Edges]

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.

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.

 

[I'mSoSharp]

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

Yes.

the hardened blade will wear out the spring over time

This...

an unhardened spring end would wear and/or plasticly deform much too quickly against the hardened tang

& this.

tempering after heat treat is what will make the spring more durable & repeatable over the long run

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

 

[Rhidian]

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.

 

[I'mSoSharp]

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.

 

[Peregrin]

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!

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.

 

[kamagong]

You guys are causing me worry. I have both an Aitor and an Ohta, and I will be checking them both as soon as I have a free moment.

 

[Jack Black]

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.

Well done

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.

That's great to hear Gary

 

[I'mSoSharp]

And here it is riveted up with steel rivets, the original were brass. I've not let it open quite as far in the open position as it did, I prefer it this way.

 

[Will Power]

Fine workmanship

I know where to turn to if mine busts....