How to repair shears?

[sharp_edge]

I have a pair of Kershaw Taskmaster shears, which worked great for a few years until it no longer cut. It appears the problem is the two blades are not tightly mating each other when cutting. Tightening the pivot screw does not help; sharpening would not solve the problem either. I shipped it to Kershaw warranty for repair and also noted them that if it is un-repairable, they can just dispose it (that would save me $7). The shears was returned a couple of weeks later, noting it was honed. Unfortunately, the problem remains unfixed. See the video below (taken right after it came back from kershaw warranty).

Does anyone know how to repair it?

[media]

https://imgur.com/CHg4pWh

 

[000Robert]

Take it apart and see if you have some burrs on the inside of the two sides. Maybe a burr or two is making a gap? I'm just guessing here. Instead of the video, just some photos would be nice.

 

[sharp_edge]

This is the best shot I could take. One or both blades seem to be warped as you can see the gap in between them. Laying each on a flat surface however does not show any gap (maybe the gap is very small?)

 

[rpttrsn]

Did you send this video to Kershaw with what you have done and how they cut (don't) when returned?

 

[Obsessed with Edges]

The 'warp' in most scissors / shears is supposed to be there, and the gap seen with the blades closed is not abnormal. That warp is normally what ensures tight, flush, consistent contact between the two edges at the point of contact, if they're bowed and tensioned against one another. This is why scissors aren't supposed to be sharpened or flattened on the inside contacting faces. That'll ruin them, if it's done.

If it's not cutting well, it might be that the pivot nut/rivet itself has loosened or distorted slightly (lengthened, bent) over time. Even if sharpened and properly 'bowed', if the pivot isn't snug enough to keep the blades tensioned against one another at the point of contact, it'll impede cutting.

 

[sharp_edge]

Did you send this video to Kershaw with what you have done and how they cut (don't) when returned?

I sent the video to kershaw warranty a few days ago (again it was taken right after I received it from the warranty trip). I have not received any response. Frankly I've lost my confidence with their being able to fix it, as the issue is exactly the same as when it was sent in for warranty.

The shears served me well for a few years so even if I throw it away I will still feel my money well spent. I just wonder if there is any easy fix that can be done by me.

 

[sharp_edge]

The 'warp' in most scissors / shears is supposed to be there, and the gap seen with the blades closed is not abnormal. That warp is normally what ensures tight, flush, consistent contact between the two edges at the point of contact, if they're bowed and tensioned against one another. This is why scissors aren't supposed to be sharpened or flattened on the inside contacting faces. That'll ruin them, if it's done.

If it's not cutting well, it might be that the pivot nut/rivet itself has loosened or distorted slightly (lengthened, bent) over time. Even if sharpened and properly 'bowed', if the pivot isn't snug enough to keep the blades tensioned against one another at the point of contact, it'll impede cutting.

Thanks for your explanation. I'll check another cheaper pair that I have to see how different They are at different positions. I think you are right that from the beginning position of cutting, the two blades are not tightly contact each other.

 

[Obsessed with Edges]

Thanks for your explanation. I'll check another cheaper pair that I have to see how different They are at different positions. I think you are right that from the beginning position of cutting, the two blades are not tightly contact each other.

I've noticed with inexpensive scissors, over time, that the loosening of the pivot seems to be a common issue. If you can see or feel any movement or 'slop' in the fit, laterally, when the shears are opened up, that might be hinting at a problem there. If you can tighten the pivot nut a bit, I'd at least try that. Some scissors' pivots are just riveted together, and those aren't tightenable, obviously. But with a threaded fastener and nut at the pivot, it might leave some room for adjustment.

 

[FortyTwoBlades]

Correct tension in scissors (the "ride") can be easily checked for by opening the blades into a "+" position and allow the pivoting blade to fall closed under its own weight. It should close 2/3 of the way on its own. Similarly, open the blades and look at them top-down as you close them slowly. You should see the contact point move from the heel to the toe of the blades. Also, check the interior faces of the shears to ensure they haven't become deformed in such a way that it's preventing a proper shearing action from occurring at the edge. I've sometimes seen an interior bevel introduced from plastic deformation from someone cutting things they shouldn't have with them.

 

[sharp_edge]

Correct tension in scissors (the "ride") can be easily checked for by opening the blades into a "+" position and allow the pivoting blade to fall closed under its own weight. It should close 2/3 of the way on its own. Similarly, open the blades and look at them top-down as you close them slowly. You should see the contact point move from the heel to the toe of the blades. Also, check the interior faces of the shears to ensure they haven't become deformed in such a way that it's preventing a proper shearing action from occurring at the edge. I've sometimes seen an interior bevel introduced from plastic deformation from someone cutting things they shouldn't have with them.

Great suggestion! I did exactly what's told here and boy aren't you right - there is no contacting point until the tips of the two blades meet, with the pivot tightened. If I loosen the pivot a bit and use two hands to twist the two blades while closing them, I can cut some paper.

I am guessing that with years of use, the edges of the two blades where they meet have been worn to the point that they no longer contact normally. If so, the only way to fix the problem is to grind the flat side of each entire blade (including the pivot area). Obsessed with Edges said the flat side of the edge should not be sharpened, which makes perfect sense. I don't recall I ever sharpened that side although I may have knocked the burrs off from that side when sharpening the other side. Each blade is a chisel grind and hence sharpened that way.

Anyway, this will be too much work for me to do and I don't have the right tool to grind. I cannot guarantee to do it 100% accurate if free-hand grinding the blade on some diamond plate. Time for the good folks on BladeForums to recommend a good pair of shears. Appreciate it.

 

[FortyTwoBlades]

As far as a good pair of shears goes, it's a matter of what you want them to do! I'm rather partial to my own Humboldt Utility Shears for most tasks but your needs may be different than mine.

You may be able to repair your current set if you have access to a slow speed wet grinder. Disassembling the shears and hollow-grinding the backside to restore a crisp mating surface could help. Even if you mess them up they'd be no functionally worse than they are now!

 

[Sharp Steel]

I watched this video recently and you could give it a shot on your shears. He has the same type of explanation on how scissors function, as mentioned earlier in this thread.

 

[catspa]

Some scissors' pivots are just riveted together, and those aren't tightenable, obviously.

Sure they are, by a method that’s easy to overtighten them.

Set them on your anvil, with the flatter of the two rivet ends down. Strike the rivet LIGHTLY with a hammer, then check the action. Strike it again if it needs it, as many times as it needs it.

The temptation (for me, anyway) is to give it a good hard swat, to try and tighten it up with 1 or 2 hits. The problem with that is that if you get it too tight, it’s a real hassle getting it loose again. Sneak up on the proper tightness with many light blows, and avoid that problem, is my advice.

The old boy who taught me to tighten farrier tongs this way used to insert a pop can shim, about 4 thousandths. That’s probably too loose for small scissors.

Parker

 

[Obsessed with Edges]

Sure they are, by a method that’s easy to overtighten them.

Set them on your anvil, with the flatter of the two rivet ends down. Strike the rivet LIGHTLY with a hammer, then check the action. Strike it again if it needs it, as many times as it needs it.

The temptation (for me, anyway) is to give it a good hard swat, to try and tighten it up with 1 or 2 hits. The problem with that is that if you get it too tight, it’s a real hassle getting it loose again. Sneak up on the proper tightness with many light blows, and avoid that problem, is my advice.

The old boy who taught me to tighten farrier tongs this way used to insert a pop can shim, about 4 thousandths. That’s probably too loose for small scissors.

Parker

That occurred to me as an afterthought, as well. With the hardened stainless rivets used on most of them, it did give me pause as to how tricky it could be, to snug them up with hammer blows.

The shim suggestion is good too. I think at least some manufacturers of folding traditional knives do the same, when pinning the pivots. Pretty sure Case does that, in fact. I think it was shown in a 'How It's Made' video featuring their process.

 

[catspa]

The cheap imported Fiskars etc. probably aren’t worth the effort, their blades get bent and sprung too easy. But there are some quality old shears and scissors out there, tightened up they might have another 50 years of work left in them.

Parker

 

[jiggyfly16]

The cheap imported Fiskars etc. probably aren’t worth the effort, their blades get bent and sprung too easy. But there are some quality old shears and scissors out there, tightened up they might have another 50 years of work left in them.

Parker

Absolutely, Hit up a local swap meet, or yard sales and you can find some great vintage shears for dirt cheap.

 

[Obsessed with Edges]

The cheaper scissors like Fiskars, etc. can be good for practice sharpening. I have an unbranded pair of inexpensive ones that my Dad was ready to toss out years ago, after he purchased a new pair. He'd used those for awhile to open plastic packaging & such, and they started to get difficult & painful in his aging & arthritic hands. I rescued and resharpened that pair, and they really didn't need anything beyond that. Just needed some crisping up at the apex of each of the two sides' bevels. I experimented with diamond hones (DMT Dia-Fold, for example), as well as simple oilstones of SiC or AlOx - any one of which would've done the job, just sliding the stone along the upper bevel of each blade. That pair now cuts as if new and I use it all the time now, with a still unused, brand new pair of Fiskars in my desk drawer. Even with the cheap stuff, it's fun & satisfying to bring new life back into them.

 

[Guy McVer]

It appears the problem is the two blades are not tightly mating each other when cutting. Tightening the pivot screw does not help; sharpening would not solve the problem either.

The shears served me well for a few years so even if I throw it away I will still feel my money well spent. I just wonder if there is any easy fix that can be done by me.

from the beginning position of cutting, the two blades are not tightly contact each other.

I have tried this with some limited success: after examining both blades thoroughly, select one blade and put it in a bench vise and carefully bend it inwards towards the direction of the other blade. Sometimes this works. It will improve the cutting performance, but obviously it will not perfectly restore the original geometry, and it's a pretty clumsy and imprecise method. You may need to do it several times before it is bent enough. You might over-bend it, or you might bend it in the wrong place or wrong way. You might even break the scissors. I've broken two pairs this way. But if you've tried everything else and you're just going to throw the scissors away, it's worth trying.

Best case scenario is that you will restore some but never all of the original cutting performance. It will cut some things just fine without issues but it will still struggle in some ways that a new pair wouldn't have issues with.

Obviously never do this unless you are at the point where the scissors would be thrown out anyway. Never risk damaging something that you're not willing or able to afford losing.

I've noticed with inexpensive scissors, over time, that the loosening of the pivot seems to be a common issue. If you can see or feel any movement or 'slop' in the fit, laterally, when the shears are opened up, that might be hinting at a problem there. If you can tighten the pivot nut a bit, I'd at least try that. Some scissors' pivots are just riveted together, and those aren't tightenable, obviously.

It is possible to tighten riveted pivots by squeezing them in a bench vise, but there is a danger of over-tightening and ruining the tool. There may also be a risk of bending the pivot so that it's not straight. Once you do either of these things it would be pretty much impossible to fix at that point without replacing the pivot.

Also, check the interior faces of the shears to ensure they haven't become deformed in such a way that it's preventing a proper shearing action from occurring at the edge. I've sometimes seen an interior bevel introduced from plastic deformation from someone cutting things they shouldn't have with them.

I've gotten a hold of some used scissors where you can see that people have indented the contact edge so badly that it would be impossible to completely fix, because you would have to remove so much of the edge that it would compromise the geometry. It makes me wonder what the hell they were trying to cut that they were able to chew up the scissors up so badly. Maybe thick wire or something...

 

[catspa]

I bet a guy could make a pair of hardwood “vise dies” with the desired curve plus about 3% springback allowance. Would probably work well on the thin stamped scissors, little trickier on the drop forged ones. But faced with enough sprung scissors, it could be worth it.

Parker

 

[garry3]

Any one else give the shears a light stoning at the pivet when they sharpen?