Errr..can't cut cardboard

G

GarageBoy

Joined
May 23, 2003
Messages
5,952
Well I was using my Frosts Mora to cut cardboard. Well, the knife keeps slipping and I nearly cut my self a few times. What's wrong? It's sharp enough to hack away cleanly at paper
 
You need to explain the symtoms of your problem in a bit more detail for us to give you a reliable answer. My problems with using a Mora to cut cardboard are that the blade is thicker and wider than what you want for cardboard and the saber grind makes matters worse. Cardboard is stiff and rigid. It is easy for a sharp edge to cut the cardboard, but it is difficult to get the rest of the blade to follow the edge. The cardboard pushes back against the blade bevel as it tries to wedge its way into the material. This wedge-resistance is more difficult with a saber grind (rather obtuse blade bevel compared to a full grind) and with thick blades. The cardboard also drags on the sides of the blade and the bevel due to friction. This effect goes up as the blade gets wider and also increases with all of the wedging forces. If you try and make a curved cut in the cardboard that is also harder with a wide blade.

A good blade design for cutting cardboard is a small pen knife blade like on a SAK or a stockman. Thicker tactical or hunting knives will give you much higher drag. A Mora knife might work well for whittling where the wood chips peel off the surface without being able to wedge or drag on the blade, but the blade will bind in thick cardboard.

To see if this is the type of problem that you are seeing, try a test. Compare the force of cutting through the middle of a piece of cardboard with the force it takes to slice off a quarter inch wide strip along the edge of a similar piece of cardboard. When you sort of whittle that quarter-inch strip off the edge the wedging and drag forces should be much lower. Next try cutting through the middle of the cardboard using a narrow, skinny pocket knife blade.
 
Cardboard is fibrous, so push-cutting will not be as effective as draw cutting. If you have a finely polished shaving edge, it may increase friction. A roughly sharpened or serrated blade might do better. Also, as mentioned, the thicker the blade, the harder it will be to continue a cut through the middle of a section.

Let us know how your experiments turn out.
 
My polished hair blasting calypso with factory edge went through like a breeze. Anyone of you guys will be @ NYCKS, I want to see if my sharp is sharp at all
 
If it really is sharp and doesnt have a hard to see rolled over wired edge, just start the cut with a slight draw motion, then continue the cut with the blade held at an angle so that it has a natural slicing motion even though you only use one part of the blade.
 
Calypso has a higher grind/thinner profile if I remember right. They are flat ground aren't they? More efficient for things like cardboard than the sabre grind of a mora. The more is like a splitting wedge when it comes to cardboard.
One thing you can try is to hold it at an angle so that instead of it going through the cardboard at 90 degrees its more like 45 degrees (side to side, not up and down)
 
Okay, then sounds like the blade shape is not as good as the caly... Also, Spydies are sharpened to a high angle in general, so maybe the caly has a thinner edge grind.. giving you much less resistance.. what angle is your Mora shapened at? Is it a bigger angle than the caly?
 
If the knife is binding in the cardboard, try cutting with the knife at a 45 degree angle to the cardboard. If you were breaking down a box, the knife should be pointing at a corner, not parallel to a side.
Clear as mud, right?
Cutting on an angle lifts one piece away from the other and the blade doesn't bind.
 
mY kaBAR D2 EXTREME FIGHTING CUTS CARDBOARD LIKE BUTTER ESP. WITH THE SERRATED PORTION, LIKE BUTTA.
 
I have been in that position before a couple of times. Trying to cut up a box with a knife that will easily shave hair, slice paper, or pass any other common edge test easily, but gives problems on boxes. In my case the cause was always the type of grind the knife had, nice sharp edge that got thicker towards the spine. The problem is most noticable as the grind becomes more and more pronounced.

I good example knife would be the Buck/Strider tanto knives. Right around the center of the knife the blade goes from a ground portion to a full thickness. This acts as a wedge and you need to use more force to get that wedge through whatever you are cutting. This will be true of any "tactical" knife due to the general use of a thicker blade. Thinner = better cutter, thicker = stronger (as in if it is abused mostly).

I try to choose an EDC knife that makes a decent compromise between stength thorugh a thicker blade, and cutting ability through a good grind. Currently that is a large TNT, and on order is a DDR 3.5" EDC.

BTW, will be at NYCKS on Friday!
 
Ebbtide has a very good suggestion. I hope that what he was describing is clear, but let me try and augment his description and explanation.

If you stab into the side of a box and hold your blade perpendicular to the surface you are in a maximum drag position. As you pull the edge through the box the cardboard will have to compress to let the blade move through the material. If you tilt the blade forwards so that the edge is parting the cardboard like the bow of a ship your cutting will get a little easier since some of the cardboard can bend down out of the path of the blade (which is easier than compressing the cardboard). However, much of the cardboard will still be getting pushed to the side and will be in compression. Ebbtide's trick is to also tip the blade sideways as you cut (such that the side of the handle gets closer to the box surface). It might seem like this should be inefficient since the blade will now slice diagonally through the cardboard and it will need to cut through a greater width of material. It is much easier however, because the edges of the cut material can now easily bend up and down out of the path of the blade. The pinching and wedging effects almost completely go away and you are left with just cutting and a little friction to provide blade drag.
 
JC, you've got it :D
GB, good name for it :D

This concept also works when you are cutting on a board, using the point of the knife. Angle the attack and the blade will separate the materials, lifting one, pushing down on the other.
Think this /
Instead of this l

Eric, that should work with that Strider too.
Give it a shot and let us know :)
 
Unless you are taking slices off of the end of the material a chisel grind will tend to make curved cuts. The bevel will push the edge towards the flat side. When you slice material off the end the thin-sliced material won't push back enough to cause a problem. If you work in the middle of the cardboard you will have trouble cutting a straight line.
 
You must log in or register to reply here.
Back
Top