I've heard that it's a bad thing to open two blades on the same spring at the same time- that it can break the spring. My question is- why? Aren't springs supposed to be... well, springy? Does opening both blades at the same time really bend the spring that much?
I've opened both blades on a single spring a couple times before (before I knew any better) and the knives seem fine. Is this mostly a problem with older knives, or all stainless ones or something? You see SAKs with multiple blades open all the time, but I can't recall ever hearing about a SAK spring breaking.
I have the same question in my mind. I have a stockman here in front of me now with the spey and sheepsfoot on the same spring. With the knife closed, the spring is flush with the back of the knife. When I open the spey blade, the spring is flush with the back of the knife. If I then open the sheepsfoot, the spring is flush with the back of the knife. I guess I don't understand why this stresses the spring anymore than only having one open at a time, since there is no more deflection when the knife has one blade, both blades or neither blade open. Admittedly, the only time I would want to do this is to clean the knife to get the gunk and dirt out of it. Point is that I need to do that occasionally.
My thoughts are that for a spring to break, there must have been a defect in the spring itself or of simple fatigue failure of the spring. After all these springs have a hole drilled in the center which is at a high stress location and is a discontinuity in the geometry, both of which cause stress concentrations. A rough grind on the inside of the spring could be a crack initiator in a particular spring.
So, I don't see how opening one blade and then the other would have any significant effect on the knife, in fact it seems to me that the knife springs would see as much or more stress as the knife is fixtured for assembly.
Now, I will admit that people that have three arms/hands might be able to stress the backspring by opening both blades simultaneously. This is something that I have not been able to do myself without a vice. And I have found no reason to do so as yet.
So, if you have problems with a spring, you have a situation where there is a fatique failure (you've used the knife for many years and the spring broke due to many cycles) or the knife was overstressed in use (extreme cutting pressure brought to bear) or a manufacturing or design issue exists with the particular knife you have.
Alright, you guys that make these knives, let me know what is wrong with my thinking.
Ed
