Spring Sag

snippy

snippy

Joined
Apr 1, 2014
Messages
868
To get to the point: Does leaving the backspring in the stressed position "soften" the spring?

I have read posts both pro and con. But maybe, like an old car "sagging" on it's springs, slip joint springs can sag?

Eric
 
I'm starting an experiment. I have a nailbreaker scout knife and I have filed the tang corners and still a 9 out of 10 on 3 of the 5 blades. WD40'd, blown, oiled, worked, sworn at.

I have set the springs for maximum flex and put it away. I will pull it out each year on the 4th of July with an update.

Eric
 
You might want to check it monthly, if not weekly. If both blades on each spring is in the half open position, you stand a good chance of breaking the spring. Also, some here leave a knife half open (one blade at a time if there is more than one blade on the spring) to lighten the pull, for only a few days to a week with good results.
I don 't know what knife you have, but I would hate to see it get a busted back.
 
afishhunter said:
You might want to check it monthly, if not weekly. If both blades on each spring is in the half open position, you stand a good chance of breaking the spring. Also, some here leave a knife half open (one blade at a time if there is more than one blade on the spring) to lighten the pull, for only a few days to a week with good results.
I don 't know what knife you have, but I would hate to see it get a busted back.
Click to expand...

Sounds like the five blade Camillus with the Phillips screwdriver. Yeah, check weekly.
 
Good guess. It's a cheapie knock off - Marbles.

If the springs break it will give me a better excuse to throw it into the recycle bin.

So, you guys think it will work? I'll check weekly for a while and report back if it seems to help.

Thanks for the input.

Eric
 
I have a GEC 73 single-blade that is beyond belief in the spring dept. N.B. I favour heavy sprung knives but this....

I left it open at the most acute angle for around three months and can witness no improvement, so in my experience this thing of leaving a knife open to tame the spring is an old wive's tale. However, stressing springs that bear more than one blade certainly could result in the spring's fracture. Repeated use, over years that is, of opening and closing a knife must take some of the pull out of a spring - especially on one that's tame in the first place. But sagging springs? Doubt it.
 
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I have the Marbles camp/utility knife, it is a GREAT knife, equal to the Camillus original. No gaps, shaving sharp out of the box., good walk and talk, nothing I would consider a "nail breaker" on any of the blades, maybe a 6 to 7 pull, in my estimation.
Rather than destroy it, why not sell it or gift it instead?
 
snippy said:
To get to the point: Does leaving the backspring in the stressed position "soften" the spring?

I have read posts both pro and con. But maybe, like an old car "sagging" on it's springs, slip joint springs can sag?

Eric
Click to expand...

If a spring is properly tempered and the knife is properly designed so that the spring is not over-stressed, the spring should not "soften" if the knife is left open.

If the above conditions are met, the spring will be within its elastic response zone when the blade is in the partially opened position. Within that zone it will completely return to its original shape. Springs eventually fail due to fatigue, which is repeated stretching and returning to shape many thousands of times.

I borrowed this picture from Wiki. It depicts coil springs, but the graph applies to straight springs as well.
HookesLawForSpring-English_zps1tpsaa9z.png


If the spring is properly tempered and stressed, the response will be on junction of the linear red line and the dotted line. It will be completely elastic and will not soften. If the spring is not tempered properly, or the knife is designed such that opening the knife deforms the spring too much, the spring will be outside that linear response and it can be permanently deformed.

https://en.wikipedia.org/wiki/Hooke's_law
 
As Frank said, the metal itself doesn't soften by keeping the blades open but the springs can deform. I have a Victorinox Cadet with springs that deformed after about 30 minutes of displaying the knife with all the blades open so that I could take some photos for the BF Exchange. It's now unusable and I'll send the knife in for repair one of these days.

I mention it as an example because it happened rather quickly. It might not happen right away but it's not really something you're likely to catch by checking on it. And the amount they'll deform isn't really controlled. It might help or it might make a new problem.

What worked well for me on one nail breaker was using militec-1. It didn't soften the springs but it did reduce friction a LOT more than regular oil and that made it a bit more manageable. YMMV

Also, I vaguely remember an old post... probably more than 3 years ago... where someone sanded some of the metal down while the knife was still intact. I don't recall exactly what they did. Maybe it would come up in a search.
 
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Correct, as Knarfeng said. If the spring is not properly heat treated it will fail very quickly. That's when you still have RA, but that's also what happens when someone thinks to lighten the pull by overtempering...all you get it's "sagging", because you narrow the proportional range of stress-strain.
When a spring it's stiff the only correct thing to do it's grinding it thinner in the flexing portion.
 
supratentorial said:
As Frank said, the metal itself doesn't soften by keeping the blades open but the springs can deform.
Click to expand...

Perhaps I did not word my post correctly. The force required to move the spring does not lessen, IF the spring is properly tempered and the deformation is within the linear response area. That is intended to mean that the metal does not soften, nor does the force needed to move it change.
 
I've left a Queen Mountain Man lockback in a half-open position for the last two weeks, in an effort to make the lock easier to disengage. It's actually working quite well. I used to have to use both thumbs to disengage the lock. I'm down to using one thumb now. It's still tough to disengage, but it's getting there.
 
If it's working well it is because of something wrong with the steel HT. Either (or both):
1) there is retained austenite and that structure is soft and will contribute to take a new set
2) The temper has been drawn too high and the yeld point (Knarfeng graph) is too low; exceeding it out of the proportional range leads to permanent deformation.

The problem is, when exceding the yeld point, your spring will continue to loose its shape eventually loosing the necessary preload to have a nice action.
 
knarfeng said:
Perhaps I did not word my post correctly. The force required to move the spring does not lessen, IF the spring is properly tempered and the deformation is within the linear response area. That is intended to mean that the metal does not soften, nor does the force needed to move it change.
Click to expand...

Sorry for mangling it, Frank. :o This is definitely not my field of expertise.

supratentorial said:
...Also, I vaguely remember an old post... probably more than 3 years ago... where someone sanded some of the metal down while the knife was still intact. I don't recall exactly what they did. Maybe it would come up in a search.
Click to expand...

stezann said:
...When a spring it's stiff the only correct thing to do it's grinding it thinner in the flexing portion.
Click to expand...

That may have been what was done in the prior discussion.
 
What Frank said is true. I have never had a spring's tension ease up or loosen the walk and talk over time, from leaving the blades open in this way over time. Now grinding, that's a whole other kettle of fish.
 
Grinding the spring once the knife is riveted is a tough one.
Depending on the expertise, probably the best is to take it apart. Another option is to take a burr/mill/wheel...and operate in between the scales, but depending on the knife dimensions this could be impossible without touching the tang, the walk or the center pin area (you could have a very small web there if the blade has some belly), and of course the liners.
 
Yes as our esteemed moderator said. I have one of Le Sabots' nailbreakers shown below with a just about polar opposite Nortwoods Norfolk, i left the Le Garonnais at about two thirds open for a couple of weeks with no improvement, i am thinking about getting a sheath and using it as a fixed blade. ( no seriously i have put it in the "Not likely to be used again" ) coffee can.

7CAppB9l.jpg
 
Same results here on a Northwoods Forest Jack. Three weeks left open in the 2/3 position. Not a change at all. It was still about a 9 on the nail breaker scale. I ended up trading it away. :(
 
Odd, I have a GEC 15 that certainly has gotten a bit softer on the pull over the couple months I have had it. I actually had it jump the half-stop position when I was closing it a couple days ago. I had left the knife in half-stop position overnight for maybe 3 or 4 days combined. Never in the 2/3 or 1/3 position though.
 
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