HEMI 49
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I would sharpen it and then close it as it should be closed... Blade rap is caused by the blade over traveling and whacking the spring when it slams closed...... I'm sure you know that....
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I would sharpen it and then close it as it should be closed... Blade rap is caused by the blade over traveling and whacking the spring when it slams closed...... I'm sure you know that....
In my experience once I've sharpened out the damage it usually does not reappear. Even if I let the blade snap shut
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Yeah, I don’t mean to start the whole “proper closing” technique debate, but man that sucks. I have to gingerly let the main blade of my SAK because it smashes up the tip... oh well. With enough use eventually it will go away.
Jiki
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I'm sure.
btb01
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I think the shape of that pattern makes it more likely to suffer from a little blade rap, unfortunately. I would’ve noticed.
It’s one of those things that can drive you crazy, but it happens; sharpen it out and close that one softer from now on. Or put a small piece of leather down in the well where the blade was hitting (this is my preferred fix for blade rap, because you don’t have to over-sharpen the blade to keep it from hitting or from repeated hits, and you don’t have to think about how you close the knife.)
HEMI 49
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If slamming the blade closed is your thing there are knives that close against a pin that prevents overtravel.... Mike at CK sells that "cough, cough" brand.... I have 2-3 myself...
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A.G. Russel is another one that uses stop pins. He liked a full broad blade in his slipjoint designs so the stop pins came as a necessity, I think.
To contribute further to the discussion, blade rap bugs the crud out of me too and I would surely notice. Two patterns that come to mind where I've experienced it are the #43 and the #85. The #43 was a soft closer and I wouldn't have thought that it would snap closed with enough force to create the ding but it did nonetheless. My #85 is a much snappier knife and I have to be very mindful of how I close it, hence why I do not carry it much - old habits die hard and all.
It's not that I slam my knives closed with prejudice, snapping them open and closed is a perfectly natural method of opening and closing a knife with a backspring. Less than 1% of my slipjoints experience this issue when opening and closing so it becomes rather notable when it does occur and I have to be mindful of it.
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Pàdruig
the interesting thing is that the back spring is also what decelerates the blade at the end of its travel, so a weaker spring might work against you there. This may imply that spring strength doesn’t indicate likelihood of blade rap.It’s a spring/mass/damper system, where the dampening is a material property of a given metal spring. The kick slaps into the spring which slows the blade as it travels past the point of rest. The moment of inertia of the blade about the pivot gets greater as more mass hangs out at the end. This moment of inertia is what the spring has to counter through deflection, which is what we think of as over travel. I would not be surprised that long spear blades succumb to blade rap more often as they have the most mass at the end opposite the pivot. (Editing because I’m obsessed with accuracy: most mass at the end with respect to knife blades of similar mass but smaller moment of inertia due to geometry.)
(Additional edit for clarification: take a knife that has blade rap and skeletonize the blade. the reduction in rotating mass should eliminate the over travel.)
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Jiki
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By design, the spring pin is literally outside the well.
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Which means, I take it that the 92s do not and can not have blade rap.
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No blade rap on either of my 92's. There is also an ample amount of available room between the edge and the spring's pin hump.
But - the kicks on both of mine are at full height, making them protrude at least 1/32" beyond the edge. I've noticed on some knives, the kick will be filed or ground down a bit at some point during assembly. So perhaps if the kick gets adjusted to be a bit shorter, then the knife may need to be sharpened a bit.
But - the kicks on both of mine are at full height, making them protrude at least 1/32" beyond the edge. I've noticed on some knives, the kick will be filed or ground down a bit at some point during assembly. So perhaps if the kick gets adjusted to be a bit shorter, then the knife may need to be sharpened a bit.
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See my original post, #17560.
I see the damage to the edge and the location where the edge has rapped on the back spring, so your statement that it cannot have blade rap is false. I have not filed the kick on this knife, merely put a fine edge on it. Now if you look into the blade well you’ll see a rise on the back spring where the spring pin goes and that’s precisely where it’s striking.
the fact is that ANY knife can have blade rap if the geometry is in bad combination. As an example, go ahead and file the kick on your #92, Mayonardo. You could file that sucker until the blade rests on the back spring for the ultimate edge-crunching rap.
anyone have a good guess at stamping tolerances? Uncertainty on blade weight? Spring constant variation? A distribution of primary grind accuracy? Or likely the killer- the accuracy of the final set of the blade height, by a person grinding the kick who’s probably eyeballing it? I had a 92 show up at my house with a proud tip, so I figure it’s at least possible they can bury it too far.
It’s an excellent knife, well designed, but mine happens to exhibit blade rap and I suspect it’s due to knife-to-knife variation. If this was a more common occurrence it would be considered a flawed design by most.
Sorry if that comes off strong- rough day in the office and seeing the dinged edge of my beloved 92 didn’t help much.
draggat
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I've noticed that the 65 & 43 are among the worst offenders regarding blade rap. Spear, clip, doesn't matter, they are long blades. It does make sense that softer springs would make it worse. Some knives like the 73 and the first run of 78's have gator snaps and no blade rap. I generally don't let knives slam shut but occasionally the blade slips. It's annoying but I don't let it ruin my day it'll sharpen out.
HEMI 49
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I think it would be interesting to test deflection forces on a sampling of springs to determine uniformity of strength....
Consider a 1/2 truck and a 3/4 ton truck... If I drop 1000lbs into the bed from 6 feet high the 1/2 ton is going to deflect and bounce further than dropping the same weight into the 3/4 ton .... So if one knife has a weaker spring than another the same comparison could happen... Thus blade rap could occur... So some money $bucks$ member needs to buy 10 identical knives and pull the springs out and have the physical properties inspected by a NDI laboratory....
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your point about blade length is well founded. Approximating a blade as a rectangle and trying to move it at a point on its base, the equation for its moment of inertia is I=(b*h^3)/3.
Here “b” is the width of the blade from spine to edge, and “h” is the length. If we change the width we see a linearly proportional change in the moment of inertia. If we change the length we see that the effect is to the 3rd power! Remember that the moment of inertia is what you fight to get the blade rotating (obviously plus some spring force) and it’s what the spring fights to bring it to a halt when it closes.
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precisely! And consider the variation from pattern to pattern; now blade shape (namely length) for even blades of the same mass is analogous to dropping different loads in different trucks!
I like this idea. I could try to prove it with math, but an actual test would be best. Good thinking, Hemi
HEMI 49
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We just need to find someone with deep pockets to fund the experiment!!
HEMI 49
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We just need to find someone with deep pockets to fund the experiment!!