Article by: Fred Hoekstra
Last month I was talking about knives and made a start on talking about sharpening knives.
I want to stress again that a knife should never be sharpened on the back side because you tend to cut into the hoof rather than taking a slice off.
If you use a bench grinder with either a linishing belt or a rubber disc, you will need to be careful not to overheat the knife. If the knife goes blue while you are sharpening it the steel will soften because it cools down too slowly. Having a knife with a soft steel blade will go blunt very quickly so you ruin the knife when you do that. Have a cup of water next to your grinder and dip the knife in the water on a regular basis. You can’t over-cool it but it is easy to overheat. When the blade of the knife is sharp, and you can see that there is a burr along the full length of the blade, you can sharpen the hook. This can be done on the outside or on the inside if you have a rubber disc.
We use a rubber disc with a grove in the side about 5mm from the edge. This groove is there especially for the hook of the knife. Because this disc is made of rubber it is important to have the disc rotating away from the operator. You can achieve this by just turning the grinder around so that the start button is at the back. If you don’t do that you will damage your knife, your disc and very possibly yourself. Once the hook has been sharpened you can take the burr off. We use a cotton disc on our bench grinder for that. Burn some paste into the cotton disc as it is rotating. Just hold the paste against the disc as it spins around. Without the paste the disc is too smooth and it will take a long time to polish the burr of the knife.
So every now and again when the cotton disc doesn’t perform very well you just burn some more paste into the disc. The cotton disc is another reason why you have to have the disc rotating away from yourself.
If you have followed this procedure properly you will have a knife that is sharp enough to shave yourself with, however a safer way to test it out would be by trying to cut a normal piece of paper by holding it up mid-air with one hand and cutting it with the knife in your other hand. The knife should be sharp enough to slice through the paper by itself – just about! Most people don’t have a bench grinder with the right discs on it and we would be happy to discuss the various options available to you.
There are sharpening pens on the market. They may get your knife reasonably sharp but it will never do as good a job as a bench grinder. However it can be handy to use a sharpening pen while you are trimming to get the dents out of the edge of the knife if you hit a stone. Using the backside of another knife is very effective for this as well.
One more thing I would like to mention concerns the use of double-edged knives. If you use the proper technique you should be able to trim a cow with one knife. The problem with double-edged knives is that you end up with quite a wide blade which makes it hard to steer your way out of the hoof when you are going too deep, and it is for this reason that I would not recommend them.