May 1, 2017 by SteelWolfKnives
Tool Spotlight – Angle Grinder
The angle grinder is the most versatile tool in your arsenal. It cuts, it grinds, it sands. It does everything except heat treat and temper your knife. Honestly, if you are on a super tight budget, an angle grinder and some bricks can suffice for all of $100. The reason that this tool is so versatile is because of the different attachments you can put on it. There are different discs for most things that you need to do in the knife making process. These include cutting discs, grinding discs, sanding discs, and buffing discs. I use a 4.5-inch grinder, as I find it to be the most useful for the majority of situations. Though you could get away with a 9-inch grinder, I feel as though most of the time it would not benefit you much more and would rather just make your arms very tired from holding it up while you cut or grind.
An angle grinder (This is similar to the one that I use) is just an axis that spins, causing the disc you have to spin. Using a cutting disc, you can cut through the steel and other hard metals. It is not usable for wood or many handle materials (like G-10), because of the cutting speed. Most angle grinders spin at around 11-13,000 rpm, which will burn any wood you try to cut and melt any plastic you try to cut. It is used 90° to the metal, so that the disc is oriented vertically (as shown here).
Because the disc is straight, it is hard to make curved cuts like you might with a band saw. Relief cuts break up the metal into smaller pieces, allowing for easier cuts. In order to cut a curve into the metal easily, you add relief cuts perpendicular to the area you are going to cut. After they are cut, you can cut each piece off of the knife, leaving only a little jagged material. Using a grinding disc can quickly clean this up to a general curve like you want. However, relief cuts are also used in straight cuts sometimes. In long cuts with the angle grinder, relief cuts are necessary to reduce friction and heat. This friction and heat add unnecessary stress to both the cutting disc and the steel. Because of the size of the disc, cutting long sections with no relief to remove parts has a lot of material rubbing against the steel (picture).
Grinding and sanding discs are similar, as they are both thick discs meant to grind off material. They are used parallel to the material (like this), and can remove metal that is hard to cut off with the cutting disc. After making the relief cuts and cutting away as much as you can, you are often left with small pieces that need to be smoothed down, like in this picture. The grinding disc is able to take care of these, quickly smoothing over surfaces that are uneven. Larger surfaces, like the flat of the knife, can be sanded through the rough grits rather quickly using a sanding (also called flap) disc. Though a belt grinder is often used for this, an angle grinder works well. It is important, however, that you do not use it for the higher grits of sanding. Though this will be discussed in a later post, the basic idea is that you do not want circular sanding marks for the grits that will be seen (usually 320 and up). Instead the marks should all go in one direction, which cannot be done with a grinder which rotates. The use of a belt grinder (which moves in one direction) or hand sanding in one direction will make much cleaner and better looking finishes on the knife.
The final most commonly used wheel for the angle grinder is the buffing wheel. Though a buffing wheel is better for this job (as it only goes in one direction as opposed to rotating across the surface), using an angle grinder can certainly still improve a piece. The reason that you can use an angle grinder for this and not for the fine sanding is because with buffing, the changes are too small to see individually with the eye most of the time. While you can still see the individual marks with the naked eye at 800 grit, this is not really possible at the equivalent of 12,000 grit. When buffing with the wheel or with the angle grinder, it is always a good idea to use a buffing compound.