Cutting Dyneema & Spectra

This is just a quick thought for all those people who have tried to cut this stuff with a knife or a set of cutters. Whatever you use it seems to be very hard to cut. Even an apparently sharp knife often leaves a ratty end after you have sawed away at it. A hot knife slices right through it but the result is pretty ordinary and the material doesn't really melt in the way that something like nylon does.

In frustration the other day I reached over and picked up a big Japanese Deba. For those unfamiliar with a Deba it is the Japanese knife used for filleting fish. It looks nothing like a western filleting knife: instead it's heavy - the blade is often 3-5mm thick, sharpened only on one side and very broad. Like most Japanese knives the steel is harder than western knives and it is sharpened at a finer angle. Having said that, Deba traditionally have softer steel than most other Japanese knives in order to avoid chips when hitting small fish bones.

The Deba in question

The Deba I use is a modified Deba - the steel is slightly stainless rather than simple high carbon and it has a western style handle. Nevertheless it takes a seriously wicked edge with a few swipes on a water stone. This knife is so sharp that it's not until you see the blood that you realise you have cut yourself. It is the sharpest knife in the house and I have several other very sharp Japanese knives.

Back to the Dyneema. The stuff I wanted to cut was both heat set and "normal". I put it on a board and the Deba just glided through it. I was pretty stunned. I had expected that it might help a bit, but this was a revelation...it just sliced straight through the material, no deformation, no ratty ends, it just did it.

The problem is that you don't want to be carrying around 420g of knife with an 18cm blade and 32cm in overall length - that's nearly a pound of knife and over a foot long in the old measurements.

I think there are options however, a Ko Deba is a smaller version of this knife and it comes with blade lengths of around 8 or 9 cm - so half the length of mine. An example is here.

This might become an essential rigging tool. However you'll also need to learn how to sharpen a single sided blade and you'll need some decent sharpening stones.

Perhaps a good starting point for understanding this knife is to go to Watanabe Blade and have a look at some. It's also worth having a look around that site at other knives. Please be aware that Watanabe San says he's very busy at the moment! Just for reference Watanabe's small deba have a blade thickness of 3.2mm whilst my large Deba has a blade thickness of 5mm.

Two final things to be aware of: most Japanese traditional knives are high carbon steel and therefore they will rust easily unless cared for - camellia oil is your friend! The other point is that the steel is hard and therefore more brittle than the knives you may be used to. If you maltreat these knives they will chip and it is a sad thing to see. Some of the knives have a soft iron back forged to a hard steel cutting edge. These are stronger knives but the cutting edge is still hard and therefore prone to chipping if maltreated. I'm not sure they will take being hit repeatedly with a marlin spike or mallet!