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jonnor

Scissors using 18 mm snap-off blade

by jonnor Jan 16, 2015
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Just some quick thoughts...

Dangerous thing :-P

(Assuming the blades lay flat which is just a guess) the blades should be twisted by +/- 7 degrees (mine are 0.5mm thick and the sharpened edge is 2mm wide) so the sharp edges are so close as possible to each other.

(Same assumption than before) for thin and medium thick paper they could work fine installing the blades the other way around, I mean: the cutting edge is the non-sharpened one.

Testing shearing with the non-sharpened edge definetely worth some testing! Only problem I see is that then the sharp edge is digging into the knife handle instead, which might tear/break down the plastic very fast.

It is not so obvious from the picture, but the design has a ridge at the front, which prevents the blades from being exposed when closed. But yes, dangerous when open due to blades being so insanely sharp.

I'm very intrigued by this design and the project in general. I'm guessing that the handle end needs to be lengthened to increase the leverage for cutting, I will try to edit the design a little and report back. I'm also guessing that adding a slight wedge to the interior hinge area could boost the sheering mesh a little. Nice work.

Note that right now the main problem in function is the material being cut separating the blades from eachother (as can happen with some conventional scissors too).

The separation of the blades comes from these blades having a dual bevel. As Aubenc suggested, you might get a more efficient cut if you angle the blades along their long axis.

Scissors usually have opposing single bevel blades, so that the cutting edges meet up exactly along the friction point. Dual bevel blades (such as snap off utility blades) will have a gap between the cutting edges, which will cause this separation. scissors don't have to be very sharp, because they put a lot of pressure at one precise point at any given time. Using dual bevel blades in the same orientation splits that pressure in half across the two points.

I think you've got a great idea working here, and I'm excited to see where it goes.

Yeah, more leverage might be useful. The ergonomy of the handle can also be improved for sure. Very interested in mods that improve the shearing, let us know what you come up with!