Strength of pull on slipjoints

[dks]

This was done quickly, just to see how strong the springs of some slipjoints were and how hard it is to open them.

A strong spring keeps the blade safely open but also makes it hard to open it, so most times the strength of the spring will be a compromise between ease of opening and safety when open. (Yes, I am aware of locking folders, but I do not expect a slipjoint to fold on me during normal use).

The assumption here is that the force needed to start the blade moving, so as to close the knife, would be similar to or at the least proportional to the one needed to open the slipjoint. I am aware that it is possible to make the knife pivot area in such a shape that it is easily to open, whilst being hard to close.
Ideally I would have tested the force needed to open a knife but it was nearly impossible to attach the weighing scales to the blade without damaging the blade.

Boring bit: 

To make this experiment fair I tried to pull the blade from right at the edge of its nail nick away from the pivot area, thus providing the maximum torque at the pivot that could be provided with a nail (with some blades because of their curvature that was difficult). I also tried to keep the pulling force at right angles to the blade, thus utilising it as fully as possible in turning the knife.

No I did not repeat it 10 times for each blade to get an average. 

I, however, did all the pulling myself thus keeping that factor constant.

A picture was taken just as the blade begun to move.
Note that when the blade actually begins to move the force required to keep it moving becomes less, though for this experiment this was not considered.

Also my scales show mass in kg, since they are designed to be used to measure mass, by the effect gravity has on it (F=mg). I will not go into detail, as to the relation of mass and force (Newtons) so lets use the good approximation that 1 kg on my scales is an indication of 10 Newtons of force.

End of boring bit. 

All knives used were in new or very good condition.

Here are the pictures with the reading shown on the scales.

Case Large Sodbuster:



91 mm Vic, large blade



and small blade..



84mm Vic (Recruit) large blade



and small blade..



Another Recruit with noticeably harder pull.



An 84mm Wenger (Cigar) with a very light (possibly too light) pull. note that the actual number was about 0.40kg, as the picture was taken as the scales begun to slip a bit.



Northfield Trapper main blade



and secondary blade



Rough rider Scout knife




Rough Rider trapper, main blade



and secondary blade



Buck Canoe large blade



and small blade



Camillus USA 77



Case xx peanut main blade



and secondary blade




Nail Nick (or opening hole) placement and effect on the pull:





So, the further away from the pivot the nail nick is the easier it will be to open the blade, whilst still maintaining exactly the same safety when open!

[nuphoria]

Rather good idea, although I suppose the weakest (furthest from pivot) point of any slippie is the relevant safety measure here.

[dks]

...the weakest (furthest from pivot) point of any slippie is the relevant safety measure here.

Exactly, when the knife is already open.

When you are trying to open the knife, however, the further away from the pivot the nail nick (or hole cough!! cough!! spyderco) the easier it will be to open, but still makers place the nail nicks close to the pivot sometimes for no apparent reason e.g.   LM style CS !)

[AimlessWanderer]

Nice one dks  It's a fair indicator of how secure blades are open, but I take Nuphy's point that at the furthest point would show that better. I'm not sure how accurate this is against opening resistance though due the the angles at which they try to move the springs in each direction? Did they feel similar by hand at the points where you tested them?

As an aside, I've been meaning to do a thread for a while on why locks aren't needed (to stir up a bit of good chinwag), but never seem to get round to doing the necessary pics 

[dks]

Just clarifying that the idea was to get an indication of how hard it is to actually open the knife, by seeing how hard it was to close it from near the nail nick.

I did not examine how hard it would have been to close the knife, so I did not take measurement pulling the knife from the edge of the blade. It would not have been difficult to do, but I did not set out to examine knife safety. Maybe next time. 

As I wrote: "The assumption here is that the force needed to start the blade moving, so as to close the knife, would be similar to or at the least proportional to the one needed to open the slipjoint. ....Ideally I would have tested the force needed to open a knife but it was nearly impossible to attach the weighing scales to the blade without damaging the blade."

People are encouraged to make their own tests taking measurements as the knife is opened from the nail nick (I tried,it is hard to pull from the nail nick without potentially damaging the knife), or measuring the force needed to close the knife i.e. safety.  
The equipment needed for the latter test is pretty basic; the hardest bit being taking an action shot!

However that was never my intention, nor do I claim, or had the time to, perform a full 100% accurate double blind peer reviewed test.

See it as a review (like any review you see here or elsewhere) based on my opinion and observations, like all other reviews I have posted here.

50ft-trad, the opening and closing of each knife did "feel" similar with respect to the force needed, though I expect them to be proportional rather than equal (that is, a knife that is hard to close, from the nail nick, should also be hard to open, from the nail nick, and vice versa)

So the northfield "felt" the hardest to open and close and the Wenger was the easiest, though it still did not feel unsafe.

[Ashley]

I've never seen any knife with a tough of a pull as GEC! :

Sent from my Ash forum mobile

[dks]

I've never seen any knife with a tough of a pull as GEC! :

Sent from my Ash forum mobile

The only other similar pull I have experienced was in one of the tools, I think the can opener, of Rough rider scout knives (I have too, they are exactly the same). Actually they are a bit worst than the Northfield; I damaged my, manly, nails on them...

[Sazabi]

I've never seen any knife with a tough of a pull as GEC! :

Sent from my Ash forum mobile

The only other similar pull I have experienced was in one of the tools, I think the can opener, of Rough rider scout knives (I have too, they are exactly the same). Actually they are a bit worst than the Northfield; I damaged my, manly, nails on them...

They are a bitch to open.   I had to handle half a dozen Scouts at SMKW before I found one that I could open without a knife pick. @_@

[dks]

They are a bitch to open.   I had to handle half a dozen Scouts at SMKW before I found one that I could open without a knife pick. @_@

It is a beautifull knife, though the flat screwdriver is a bit too polished.

The funny thing is that, technically, they are aimed at children. How the heck are 9 year olds supposed to open them?

[Sazabi]

They are a bitch to open.   I had to handle half a dozen Scouts at SMKW before I found one that I could open without a knife pick. @_@

It is a beautifull knife, though the flat screwdriver is a bit too polished.

The funny thing is that, technically, they are aimed at children. How the heck are 9 year olds supposed to open them?

I don't know. 

[Mike]

I have an old Camillus Electricians knife, the screwdriver/wire stripper blade is a real nail buster and the blade itself is pretty stout. Next in line is my Camillus made Remington 9501 jumbo stockman, it has near-nail buster pulls. Bear in mind, these are pretty old knives.

The weakest are my Buck stockmans 301 and 303. But, they are quit usable for their intended purposes.

In between my Camillus and Buck knives are my Vic SAK's. Vic just has it down for so many things and pull is one of them.

Personally, I like the pull to be stout as long as it doesn't snap my thumbnail!

Mike

Mike

[AimlessWanderer]

By far the worst I've ever experience is a BAK (British Army Knife). The can opener on those takes so much effort, I don't think it would be much harder to try and open the can with your teeth 

[Sazabi]

By far the worst I've ever experience is a BAK (British Army Knife). The can opener on those takes so much effort, I don't think it would be much harder to try and open the can with your teeth 

To be fair, have you oiled the pivot?  I have a Sheffield-made, civilian, non-marlin-spike version and both blades are quite easy to open, though not floppy or lazy in the slightest.

[AimlessWanderer]

By far the worst I've ever experience is a BAK (British Army Knife). The can opener on those takes so much effort, I don't think it would be much harder to try and open the can with your teeth 

To be fair, have you oiled the pivot?  I have a Sheffield-made, civilian, non-marlin-spike version and both blades are quite easy to open, though not floppy or lazy in the slightest.

Oh yeah, that element's fine. It's purely the weight of the backspring. Once youve got it past the sheepsfoot blade so you can pinch it fore and aft it's a lot better - it's just rather challenging to get it to that point

[dks]

and talking about the Rough Rider Scout knife:

(I have reversed the scales so that I would be able to attach them to the opening pin. To be accurate remove 0.06g from the reading; the weight of the scales).

[dks]

(... remove 0.06g 0.06kg from the reading...).