Topic: Grinders, an overview

ArtMetal
Bramblebush

Posted by Chris Ray on August 25, 1997 at 09:43:17:

The most familiar grinder that many artisans use is what is known as a body grinder. This unit is a small disk grinder with an abrasive wheel generally around 4 1/2" or so. This is often used to perform all around work such as grinding down welds or seams, grinding the material with the leading edge of the disk. Then the unit is sometimes used to finish up the rough grinding by applying the face of the disk to the work. For best control this tool should be used with two hands but because it is small and lightweight, one handed operations when called for are possible.

I find this particular grinder and it's general application to be fairly ineffective for anything other than rough finishing, unless one considers other options with this tool. For instance after rough ginding, the disk may then be replaced with a layered wheel disk, the most effective that I know is called a tiger disk. This special type of sanding disk can clean up rough areas as well as doing a magnicent job of blending uneven areas together.

Using a standard rubber backed flat sanding disk is another option that could be used and this kind of disk is fine for leveling off rough areas and to surface sand a work.

If only one tool may be had, then this is the most common tool of choice. Often some folks get to be so skilled using this single tool that it can become as much a brush in the hands of a skilled person as for a painter. However, I still consider it a limited tool for large works.

If one can afford it, other finishing tools may be added to the inventory, and often the next tool obtained by some is a die grinder. This tool is an in line rotary tool with a small cone or other shaped stone gripped by a collet. It is very useful for grinding a radius around the weld zone, blending the welds from one piece of metal to the other. This tool is also fine for using in areas that are inaccessible with a disk grinder, or for smoothing the interior of pierced openings.

In addition to various shaped stones used with a die grinder, there are carbide bits available as well. These are very effective for stock removal and there are a greater variety of shapes for specialized work and this makes this tool extremely useful. However there is one thing to keep in mind. A carbide bit shaves the metal rather than grinding it and those very sharp slivvers flying in your face can be very dangerous even while wearing goggles. Be careful and make sure that things like your eyebrows and the front of your hair or cap are thoroughly dusted off before removing your goggles or face mask. In spite of all your precautions, you can still have an errant sliver fall into your eye and they are sharp enough to do serious damage.

A disk sander is sometimes considered an auxillary tool and may not have enough importance to include in your inventory because it only does one kind of thing. If you can afford it then it is recommended. These tools turn at a slower rpm than a disk grinder and is really more suitable for finish work, although the grinders are often used instead, mainly because it is convenient but not necessarily an efficient way to do the work. A sander that turns slower will prolong the life of a sanding disk, and is designed specifically for this type of work.

My favorite tool is a larger right angle grinder normally used as a heavy duty disk grinder. However I can find nothing better for all around work than to replace that disk with what is known as a cup grinder. This cup is a grinding stone that has a taper towards the top and may range in size from about 5" to 6" dia. more or less. It's performance far exceeds the capability of either sanders or disk grinders for both rough grinding and then for surfacing or flat grinding afterward. This is a tool or more pointedly a particular stone that is perhaps not understood by many. It is easy to handle, even though it adds weight to the grinder head but that is an advantage not otherwise. I use this tool as a kind of planer and can level a flat surface with ease which is not quite true when using a disk grinder. This type of grinder requires two hands to use, unlike a small body grinder. One important thing to remember though if you are interested in using a cup grinder. The rpm rating of the grinder is an important factor and should NOT exceed the rated rpm recommendations of the stone. They are not very common but a mid sized angle grinder rated at around 5000 rpm is recommended. The 15 pound heavy duty grinders are usually rated at the slower rpm but the excess weight of that kind of tool is impractical. Try to find one that weighs about half of that with the appropriate rpm.

Finally there is the rotary grinder which is an inline straight grinder that has a round grinding wheel attached to the end. This stone is used on edge only and is primarily used for fast removal of stock. Sometimes a flexible shaft with a rotary stone attached to the end is used instead but it lacks the weight of a dedicated grinder for steady control. If a lot of rough grinding of welds or casting seams is the order of the day then this type of tool deserves a good look.

Finally those small Dremel rotary tools, although they look flimsey and are made of plastic are surprisingly effective and strong little grinders for fine or detail work. They are a bargain and can be a long lasting tool if cared for.

Chris Ray

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