Who else cringes when they see all the blades on a knife open at the same time?

I was always under the impression that as long as a spring was used within its elastic limits, any time spent with the spring at any position within those elastic limits would not hurt a properly designed one.

I guess this means that in some cases, having the springs bend on both ends at once causes the spring to be bent past its limit?

I've never had anything happen to my knives from opening multiple blades at once, but admittedly, I don't really have a reason to do such things outside of the occasional photo. At any rate, it certainly isn't going to bother me, or change my habits in the least bit.
 
In classical physics, a spring can be seen as a device that stores potential energy, specifically elastic potential energy, by straining the bonds between the atoms of an elastic material.

As long as they are not stretched or compressed beyond their elastic limit, most springs obey Hooke's law, which states that the force with which the spring pushes back is linearly proportional to the distance from its equilibrium length:

For deformations beyond the elastic limit, atomic bonds get broken or rearranged, and a spring may snap, buckle, or permanently deform.

A knife spring is a Cantilever spring – a spring which is fixed only at one end. A diving board is another common example of a cantilever spring.

As long as a spring is used within design limits concerning elastic limits and operating temperatures, the atomic bond of a properly designed and heat treated spring cannot be realigned, causing excess relaxation.

Shuttin' up now Boss.

Edit: For weak snap or no snap, don't forget to consider poorly maintained and badly worn tangs, sometimes caused by improper tang heat treat.
 
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Shuttin' up now Boss.

Edit: For weak snap or no snap, don't forget to consider poorly maintained and badly worn tangs, sometimes caused by improper tang heat treat.
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Thanks for the technical explanation, I never really considered tang wear before due to poor maintenance or improper heat treat but what you said makes a lot of sense. :thumbup:
 


Here's one from Sheffield museum, been like that a while ;)
 
Jack Black said:


Here's one from Sheffield museum, been like that a while ;)
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AAAAHHHHHH!!!!

homer_the_scream.jpg
 
jwren said:
I cringe, but more because I'm thinking about fingers getting in the way/getting cut when opening or closing (or snapping shut :eek: ) all the blades at once.....
Never really thought of the stress on the springs, but that's a good point....
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Bingo. That's most of what worries me, when I see it. I've mentioned it before, but I managed to neatly clip a 1/4" oval of skin from the tip of each of my index and middle fingers, when attempting to extract a 5-blade Case sowbelly from it's display tin (pic below w/all blades open; brace yourself). Three blades were partially open at the time, maybe 1/3 or so, and two of those were at opposite ends of one spring. The spring was tensioned to the extreme, and the small clip blade snapped shut on my fingertips as it cleared the molded recess in the tin.


David
 
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I displayed a Lil' Cuttin' Horse sow belly Boker in the open and partially open position for a solid ten years and the knife is still a bear trap. No weakening that I can discern
 
T. Erdelyi said:
That sure is a purty Sowbelly, (ya know when I say like that I kinda expect to hear "duelin' banjos" playin' in the background somewhere. ;))
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Thanks. Appropriately enough to the topic, I seem to get that same uneasy, nervous feeling viewing that pic, as I'd expect to feel if I did hear Duelin' Banjos while alone in the woods. Just seems like something BAD is about to happen... :eek:


David
 
It wont hurt the springs of a good knife to have all the blades open. We used to display hundreds of slip joints this way in our knife store many years ago.
 
> I was opening the blades on this Ulster Boy Scout knife to take some pics of it and the backspring snapped in two.

Really, Really sorry for your loss.

When you opened the blades at each end of the same spring, did you open the blades to half stops, that place the spring flush with the frame? Or was the spring being held cocked above the frame, at both ends, when it broke?

> The only time there is extreme stress on a spring is when you got a blade on each end and you tweak both ends of the spring at once.

Is the problem with springs breaking, specific to making both ends of the same spring sit above the frame at the same time?

imho, If the blades are open all the way, or to half stops, there is no more tension on the spring than when the blades are closed.

> like Mr Bose

Great Video! Thanks

"you wanna let them down easy, the jar will crack the handle material, and you don't wanna slam them open"

Mr. Bose is opening his blades to either the full open, or the half stop position. He is not opening any of the blades part way and leaving the spring sticking up above the frame.

And he is definitely not leaving both ends of a single spring cocked above the frame.

Given the number of Jack Knife photos Ive seen posted here, with the primary at half stop, and the pen cocking its spring above the frame, I don't see a rash of broken single blade springs. I agree the concern is primarily for springs with blades at both ends, that are not open to a half stop, and instead raise both spring ends above the frame at the same time.

fwiw, yesterday I left my Pemberton half cocked, with the spring sitting above the frame, for several hours. I was trying to reduce the pull strength. I don't think it made any difference. otoh, since Im home all day recovering quickly from hernia repair, all the oiling, and the 300+ open and close cycles I did with the blade, has made the blade walk much smoother :-)

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jon_slider said:
When you opened the blades at each end of the same spring, did you open the blades to half stops, that place the spring flush with the frame? Or was the spring being held cocked above the frame, at both ends, when it broke?
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I already had the bottle opener opened at about a 45 degree angle and when I went to open the can opener the spring snapped. The knife does not have half stops.

Nice summary. I agree with everything you wrote. The risk only presents itself when both ends of the same spring are stressed at the same time. This is exactly what happened with my Ulster.
 
Great thread, very informative. I had never even thought about this before. Glad I read this before I inadvertently ruined a knife.
 
Railsplitter said:
I have a bunch of knife pics with all the blades opened. They were taken before I learned my lesson.

I was opening the blades on this Ulster Boy Scout knife to take some pics of it and the backspring snapped in two. You can't see it in the photo but the backspring is toast. If this would have happened to almost any other knife I probably wouldn't have been so disappointed. The knife belonged to a very dear friend of the family who passed away in 2011 at the age of 98. It holds more sentimental value than any other knife I own or have ever owned.

I was going to carry it but not now. It sits in its own display case instead. A lesson learned the hard way.

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I have one just like that, that was my Papaw's. And like yours, it had a broken spring. I wound up having it repaired, and occasionally carry it.
 
Campbellclanman said:
Jack - that beauty od a multi bladed knife-is that Stan Shaws work?
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It is Duncan, made in 1997. Here's another Stan Shaw (bottom) from the same museum, this time from 1987, and a knife from Joseph Rodgers & Sons from 1840.

 
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