What do back springs do in a slip-joint knife?

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FireDragon76

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Jan 21, 2016
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What exactly does the back spring do?

I am a bit clueless about traditional folders. I had a Swiss Army knife as a kid in Scouts but otherwise I've had more modern lockback knives, generally.
 
It holds the blade in place by applying pressure to flat spots on the tang. This keeps the blade from swinging free when open or opening in your pocket.
Heres a pic I found on the internet showing what it does

3XC73c3h.jpg
 
black mamba said:
Yes, the firmer the spring, the more snappy the closing.
Click to expand...

I have an Imperial Schrade Sodbuster that has very stiff backspring (requiring a firmer grip to open), and it does snap shut hard if you let it free fall. On the other hand, I also have a Schrade Old Timer 120T, a small pocket knife with a 2 inch blade, and the backspring is alot lighter.

Do backsprings wear in over time, or will a firm backspring always remain firm?
 
The metal at the juncture of the spring and blade can wear over time, especially sans lubricant, and thus the snap becomes softer. I am not sure about springs losing their 'springiness;' there are metallurgically inclined folk here that could answer that. Meanwhile, slip joint knives only have one kind of spring, so it is redundant to call them backsprings. Kind of like 'ink pen,' or 'pin number.' I like to roll my eyes a bit in a superior anal manner here. By the way, I like your knives.
 
FireDragon76 said:
I have an Imperial Schrade Sodbuster that has very stiff backspring (requiring a firmer grip to open), and it does snap shut hard if you let it free fall. On the other hand, I also have a Schrade Old Timer 120T, a small pocket knife with a 2 inch blade, and the backspring is alot lighter.

Do backsprings wear in over time, or will a firm backspring always remain firm?
Click to expand...

With years and years of use, it might lose a little tension. But, generally, stiff ones will stay stiff. And light ones stay light. It is possible to take it apart and remove some metal, effectively lessening the tension, but it usually requires some skill. If it’s the initial pull, some folks have had luck using a dremel or skinny diamond file and altering the shape of the corner of the tang (called the run-up I believe). But I think you have to know exactly what the issue is to know what’s needed.

I’ve now typed every single thing I know about tight springs in a slip joint so I can’t help another bit lol.
 
The back spring's only job is to keep the blade from flopping partly open or shut by gravity.

A stiff spring does not make a slipjoint "safer" or "lock the blade open". Quite the contrary. You are more likely to "get bit" fighting with your knife to open it, than you are with one that has a pull you don't have to fight, that opens smoothly.
Especially when your hands are cold and/or wet.

Personally, I don't carry or use a knife with a pull much over a "6", and much prefer a lighter pull. In my opinion, the pull on a Buck 301 is just about "perfect", somewhere between a "3" and "4" on average.
I know many others disagree on my assessment of the 301's pull, and wish it was a little stiffer.
I'm not sure why, the blades don't flop partly open or closed.
 
afishhunter said:
The back spring's only job is to keep the blade from flopping partly open or shut by gravity.

A stiff spring does not make a slipjoint "safer" or "lock the blade open". Quite the contrary. You are more likely to "get bit" fighting with your knife to open it, than you are with one that has a pull you don't have to fight, that opens smoothly.
Especially when your hands are cold and/or wet.

Personally, I don't carry or use a knife with a pull much over a "6", and much prefer a lighter pull. In my opinion, the pull on a Buck 301 is just about "perfect", somewhere between a "3" and "4" on average.
I know many others disagree on my assessment of the 301's pull, and wish it was a little stiffer.
I'm not sure why, the blades don't flop partly open or closed.
Click to expand...
I understand what you're saying about the dangers of fighting to open a knife. It is an opportunity to slip and cut yourself. If you are using proper technique, you are using the knife to cut things (rather than stabbing) which will put force on the blade in the direction of keeping it open.
On the other hand, sometimes when I'm whittling or using the tip of the blade to bore a small hole in something, or otherwise using the knife "improperly", I appreciate a stronger spring.
For me, an ideal configuration is a blade that's easy to open and harder to close. This is more a matter of tang shape than actual spring tension. As SVTFreak SVTFreak said, a blade with a square tang can sometimes be adjusted somewhat. It has two corners that move the spring: one when opening and one to close.


tongueriver said:
The metal at the juncture of the spring and blade can wear over time, especially sans lubricant, and thus the snap becomes softer. I am not sure about springs losing their 'springiness;' there are metallurgically inclined folk here that could answer that. Meanwhile, slip joint knives only have one kind of spring, so it is redundant to call them backsprings. Kind of like 'ink pen,' or 'pin number.' I like to roll my eyes a bit in a superior anal manner here. By the way, I like your knives.
Click to expand...
Not to get too off topic, but...there are some areas of the country where the words "pin" and "pen" are pronounced the same way, and "ink pen" is used for clarity. When I first moved to Texas, a classmate asked to borrow a pin. I asked, "A straight pin or a safety pin?" and she answered, "No, an ink pin." :D
 
r8shell said:
Not to get too off topic, but...there are some areas of the country where the words "pin" and "pen" are pronounced the same way, and "ink pen" is used for clarity. When I first moved to Texas, a classmate asked to borrow a pin. I asked, "A straight pin or a safety pin?" and she answered, "No, an ink pin." :D
Click to expand...

There's another way to pronounce it?? :confused:
You swerved, I followed. Maybe the mods wont mind a little cross over the white line:p
 
This topic came up in a thread some time ago and I posted these two pics, a before and after, if you will.

The first shows a normal tang with two sharpish corners, which would be stiff to open and close.
OWsde7P.jpg


This second pic shows a modification of rounding one corner to make the opening pull both lighter and smoother. Doing this to a finished knife would probably make the backspring "sink" in the closed position.
hwaGeCg.jpg
 
......yes, spot-on black mamba black mamba

It's not just the backspring that has an effect, it's also very much the heel - or tang - of the blade......the part that works in concert with the backspring.

The corners or rounded end of the tang should never really raise the backspring beyond the spine (liners) by more than 1mm. Anything beyond that, with a less than perfect backspring, may possibly see a snap/break occur.....from what I've gathered talking to some custom slippie makers

I have one folder where the corners are asymmetrical - it's easy to open to half-stop, much harder to open to fully open - this is good for some folk as they like a strong backspring. The maker of this particular folder is good at tempering, so I think it will be ok because the half~open raises the backspring to over 2mm.

Then again, who's to say what's wrong or right ;)

Below, simple diagram showing difference between the half-stop tang with square end versus the no half-stop with rounded end.

Personally, I'm quite happy with no half-stop and a light spring of say 4~5 pull.........if I think I 'need' more, then I'm not using a slippie correctly imho.........switch to locker or fixed..!


Screen Shot 2020-02-16 at 15.16.18.png
 
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..and, just to be persnickety, even if the tang has worn down to the point of not moving the spring at all, it most likely would not just "flop open". There still would be friction holding it. At that point, it would have become a sort of friction folder.
You guys have some really great diagrams and mock-ups to show how a slip joint works... I'm going to get my ink-pen and write some of it down....:D
 
hornetguy said:
..and, just to be persnickety, even if the tang has worn down to the point of not moving the spring at all, it most likely would not just "flop open". There still would be friction holding it. At that point, it would have become a sort of friction folder.
You guys have some really great diagrams and mock-ups to show how a slip joint works... I'm going to get my ink-pen and write some of it down....:D
Click to expand...
This is true I have a little Utica souvenir pen knife that must have had a soft tang. The corners are completely worn away on the main but it doesn't fall open,acts just like a friction folder. Surprisingly it has fairly full blades,I wonder if it was someone's desk knife and they opened and closed it allot just to fidget with it. Also the secondary works with halfstops just fine. A pic cause we like'm lol
kfR0EqH.jpg
 
hornetguy said:
..and, just to be persnickety, even if the tang has worn down to the point of not moving the spring at all, it most likely would not just "flop open". There still would be friction holding it. At that point, it would have become a sort of friction folder. :D
Click to expand...
True. I have an old Schrade Walden that has that problem because previous owners did not lube it.
I still don't carry it though.
 
Personally I'm not a fan of file worked springs. Back when I was working and making springs I learned that any marks on a spring, even a small scratch, can be a place of weakness, and the most obvious failure point. The better the finished surface of the spring before heat treat, the better the spring. Cutting a spring after heat treat is a bad idea. Flat springs should always be polished along their flex line.
 
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