Knipex Cobolt disappointment
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Joined: March 21, 2017
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Knipex Cobolt disappointment
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Posted on Sat Mar 25, 2017 9:49 am
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I bought Knipex CoBolt 7101200 for cutting stainless steel and expected that I would get a nice cut rings. Not perfect as saw cut, but nice. I read that it's the best cutter ever, and also, the pics in this article: http://www.mailleartisans.org/articles/articledisplay.php?oldkey=8002 show that the cut made by Knipex is very good. But in fact, the result I have with my Knipex Cobolt, is very disappointing. The wire I used was 1mm stainless. I think the cut is just awful. The photos are below. Why so? Maybe I want too much? Is it a normal cut for this tool?




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Posted on Sat Mar 25, 2017 10:49 am
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Yes, I think you were expecting too much, or expecting something different. A Knipex is a boltcutter. A boltie works by wedging metal apart until the tension imposed on the metal exceeds its yield strength, and pops the metal apart. Consequently the cut ends are always going to look like this: ><.

And they're among the most durable hand powered cutters available anywhere.

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Posted on Sat Mar 25, 2017 12:16 pm
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LxStudio, the article describes a Score-and-Break method using the Knipex boltcutter. It looks like you cut the rings all the way.



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Posted on Sat Mar 25, 2017 1:10 pm || Last edited by Pfeiffer on Sat Mar 25, 2017 1:32 pm; edited 1 time in total
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I definitely agree, learn the score-and-break method, rather than cutting all the way through. It will come out much better.

For score-and-break, just nick the ring on the coil enough so you can bend it at the cut (with fingers or pliers). Bend it back and forth at the nick until the metal fails. You should have a cleaner joint with just a small dent like ][ rather than full depth pinch like ><. This method works well for hard metals like stainless and titanium. Not as good as a saw cut, but much better than full snip all the way through (which looks like what you did).

Knipex really are good cutters (the best IMHO for what it does), But it's not a saw. Try some crappy cutters for comparison and see how you struggle to do what the Knipex does easily.

Ironically, Score-and-Break is probably easier to LEARN with crappy cutters, because they DON'T go all the way through. But it is much better for production quantities with a good pair of Knipex like you have.



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Posted on Sat Mar 25, 2017 1:23 pm || Last edited by Pfeiffer on Sat Mar 25, 2017 1:42 pm; edited 1 time in total
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I just looked at the tutorial you linked above, and it is excellent. Try it again you can do much better. Don't cut all the way through. Show us more pictures of your progress! Coif Smiley



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Posted on Sat Mar 25, 2017 1:37 pm
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Thank you all, guys. I'll try another method as suggested.

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Posted on Sat Mar 25, 2017 7:28 pm
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Even for >< cuts I see significant room for improvement through technique.

For instance, if you look at the cuts of the ring prominently visible second from the bottom-left corner, I note two particular issues:
1) the angle of the cut is not consistent from one to the next, causing the butted ends to form a \/ when viewing the ring from its edge (this is visible on several other cut pairs to varying degrees)
2) for the leftmost cut of that ring, the cut appear to have been shallow (the tips of the cutters coming together inside the diameter of the wire rather than just beyond it), creating the wedge on the cut's topmost side

(I apologize for my inadequate descriptions and only hope any readers are more adept at interpreting my intent than I am at conveying it)

Both of these issues can be overcome with care and, as always, practice.
Both will also affect score-and-break cutting efforts to varying degrees.

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Posted on Sun Mar 26, 2017 10:30 am
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I tried the score-and-break method, but with no good result. The cut looks really better, but at the moment of trying to pull the ring away, the coil and the rings become significantly deformed. Maybe the method works with 16swg wire, but it doesn't with 19swg (1mm).

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Posted on Sun Mar 26, 2017 1:12 pm
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Sounds like your wire is fairly soft. Works best with very hard temper wire. But you have the right idea now.
Try bending it back and forth gently until the metal weakens at the joint, rather than pulling it off forcefully.
Knipex are pretty husky cutters for 1mm wire. Perhaps try the score part with smaller cutters.
You will improve with practice. Don't give up! Show us more pictures..we like pictures. Cutters



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Posted on Sun Mar 26, 2017 1:53 pm
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You are just starting to learn about metal and its properties right now. It is very interesting to see you progressing with this. Once you understand the properties of your material, you can do a lot with it. It takes years of practice and experimenting to become a seasoned craftsperson. Stay with it.

====================

Here is your next lesson:
All metals have two kinds of deformation, called ELASTIC and PLASTIC.
Elastic bending is like a rubber band. If you stay within the elastic limit while bending, it will snap back to original shape.
However, if you force the metal beyond its elastic stage, you then get plastic (permanent) bending that does not snap back. You still get all your elastic deformation back, but the plastic part remains ( the metal is deformed).

Take a paper clip and unfold it into a stick. Hold one end and move the other end to bend it. Start off gently and you will be in the elastic zone, and the stick will always be straight when you stop pushing on it.
Now increase the force you use, a little at a time. Eventually, you will hit the plastic limit, and the stick will be permanently deformed when you let go (but you still got all your elastic deformation back).
This is a fundamental property of metals, and very useful once you understand it. (now you know how to use metal to make a spring).
The amount of plastic and elastic varies considerably between different types of metals.

(For score-and-break you need to stay within the elastic range).

===================

Tomorrow's lesson will be about work hardening and wire temper (also relevant to score-and-break). Hold on to your paper clip, we will be using it again. But practice your plastic and elastic first.

Actually, I think I may copy this out to an article if I get some time.

And change my user name to "Professor"...
(Yes, I do have a degree in engineering).



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Posted on Sun Mar 26, 2017 5:36 pm
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Pfeiffer wrote:
Sounds like your wire is fairly soft

No, it's TRL's regular stainless 1/4 hard, 125 ksi.

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Posted on Sun Mar 26, 2017 6:23 pm
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Maybe a stupid question... Is there a way to 'polish' the rings with >< cut to round them off so that the cuts become something like this: )(
Maybe with stainless steel shot in a rotary tumbler or whatever...

Just curious Smile

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Posted on Sun Mar 26, 2017 6:36 pm
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LxStudio wrote:
Pfeiffer wrote:
Sounds like your wire is fairly soft

No, it's TRL's regular stainless 1/4 hard, 125 ksi.


TRL's regular stainless is strong, and relatively hard, but it is not particularly brittle, which is the measure which matters for score-and-break cutting.

If you have some of TRL's aluminum, a bit of practice with it will provide a good example of this principle.

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Posted on Mon Mar 27, 2017 4:55 pm
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I just exploit the boltie-cut for armor links, overlapping the points of the boltie cut to eliminate gaps at the link ends -- they are butted facet-to-facet, accepting a slightly out of round link, which is just fine for armor pieces.


'The Minstrel Boy to the War is gone...'

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Posted on Mon Aug 14, 2017 6:53 pm
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score&break-method: take a piece of your wire force it under one arm's gum and the other end between the rear jaws. Is what i did. (I'm just passing by; was lookin for a good saw-cut-method and found this new but old discussion)

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