Long Thin knives and blade play

chevyrulez1

chevyrulez1

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I have several traditional knives with longer blades (3” or longer) and a slim profile blade. I am referring to a Case copperhead wharncliffe, or a doctors knife for example. Think longer and skinny
Several of the knives that I own with this profile have developed side to side blade play relatively quickly.
I am assuming it is due to a combination of less material contacting the frame at the tang and the longer blade means more leverage on the sideways force applied to the blade while cutting and such.
I have longer blades with a beefier tang construction that don’t seem to do this, and I have shorter blades with a smaller tang construction (like a medium stockman) that don’t seem to do this either.
Has anyone else had similar experiences? I am just wondering if certain patterns are more susceptible to this and if that is something that should be considered when choosing what knife to use or carry for certain purposes.
 
I’ve not had any experience with long skinny blades knives like you describe. About the most I’ve got is with the 54 trapper and 75 stockman. Some careful peening and then sanding/polishing would fix the lose ones though.
 
I have 3 long skinny knives, shatt and morgan and case 5" toothpicks and a 5" sausage knife. None have developed any play.
 
My 2013 Blade Forums knife developed blade play after a short time of use. After receiving it I tried it out peeling thin bark off a limb and then during normal use the pivot popped loose in the bolster. I returned it to GEC and for repair. It was repaired and then after more normal use the pivot pin popped again.
I felt the thin blade was too long overall for the amount of bolster material used causing too much leverage applied to the pin. The liners, the bolsters and pin are made of nickel silver which may have contributed to weakness in the joint. My knife may have been the exception due a possible flaw in manufacture.
 
chevyrulez1 said:
I am assuming it is due to a combination of less material contacting the frame at the tang and the longer blade means more leverage on the sideways force applied to the blade while cutting and such.
Click to expand...
Theoretically, I think you’d be on the right track- the bottom line is that slip joints, assuming similar construction, become less robust as the blade length increases.
1) more leverage against the pivot.
2) less mechanical advantage at the joint (due to reduced blade thickness) to resist bending (and sheer stress in the pin)
3) angular deflection has a greater arc length- wobble would be more pronounced.
4) reduced surface area contact between the pin outer diameter and tang hole inner diameter (exacerbating the impact of holes which are drilled overly large).

It’s something I’ve noticed on a Case slimline trapper. My theory is that it becomes very difficult to compensate for the stresses on larger knives and I believe that, much like there’s a practical limit to how small a computer chip can be, there’s a limit to how practical a large slip joint can be with a thin blade.

All that said- use that knife as you want to and just tighten it back up as it gets loose.
 
The only long thin bladed knife I have used a lot is an opinel slim 12, that is as solid as when new.
Slipjoints may behave differently
 
calm said:
The only long thin bladed knife I have used a lot is an opinel slim 12, that is as solid as when new.
Slipjoints may behave differently
Click to expand...
I assume you use it with the Virobloc engaged, yes? That adds and extra anchor point to the joint- pulling the blade up and giving it three points of contact at the ferrule, the lock and the pin.

You’ll likely notice, as I have, that releasing the virobloc will result in some wobble. Using it without the virobloc I believe will exacerbate the issue further as the wood in the joint can become compressed.
 
CASE Slimline - which are long and slim, no play at all. Canal St. single Trapper, lots developed, pity as it's a pretty knife. Custom Laguiole, lot of it, maker fixed it promptly.

I suspect ANY spring knife is susceptible to play if the assembly and pins are not satisfactory in the first place, for instance, very broad blades could be candidates too. None of my GECs have shown it though and that's how it ought to be.
 
meako said:
Do any of the several pertain to a particular brand? I just checked my 2 gec Makos ...the skinniest I own...both tight and good.
Click to expand...
I cannot say it is a particular brand, interestingly enough one is a Kershaw Chill which isn't even a slipjoint. I find myself constantly having to readjust the pivot screw on that one even after putting locktite on the screw. I guess that is why I started thinking long and skinny was a common theme among them, but it may be coincidence.
Once a slipjoint develops blade play I usually put the bolster in a vise and tighten it back up, so it is not really a show stopper but I guess I was thinking about blade construction and what I use it for. If I have to do some heavy duty cutting I guess I should reach for a more robust knife.
 
I don't think it's due to long skinny blades, I have a short stubby custom made slipjoint that developed play,was fixed by the maker with washers, developed play again, I fixed it with a hammer. It buggered up the bolster but it hasn't ever developed play again.
 
Squeezing the bolsters will only fix it a short time. Peening the pin will flare it more and then just polish out the marks starting with about 320 and going up.
 
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