Abrasive Metal Cutting Chop Saw Basics

Last Revised: Jube 17, 2014


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Introduction

Some years ago I participated in building six of the Original ABANA Gade-Marx Treadle Hammers.
Bob Walsh (Walsh Forge & Foundry, Pepin Wi.) parcelled the construction out to several of us. My job was to buy and cut all the steel, some 1500 pounds of mild steel, ranging from 5/8" round to 4" X 6" X 1/2" wall tubing, to 1" X 4" plate and many sizes in between. Guild of Metalsmiths member Gary Crowther (knowing better than I how much work was ahead) graciously offered to loan me his 3 horsepower Royobi 14" wheel chop saw to make the job easier. I hadn't used one before and I learned a lot about chop saws as I cut enough steel to wear out 3 wheels over two mid winter week ends. The experts out there in reader-land probably won't find much new information in this "how-I-used-a-chop-saw-for-the-first-time" article, so only the novices like me need read further.

The chop saw, or cut-off saw, as some people call it looks like a Skill Saw held captive above a vise. The idea is that you clamp a piece of steel in the vise and then draw the saw down and through the workpiece to cut it off. The main difference between a chop saw and a skill saw is that the chop saw uses a large diameter, skinny abrasive wheel instead of a toothed blade.

Pete's discoveries:

The chop saw seems to work best when the wheel is taking a short bite into the material. If you are going to cut a 1" x 3" bar, you'll want to stand the bar on edge, so the saw is only cutting thru the 1" dimension. If you are cutting a 1/2" by 3" bar, the same holds true. If you lay that 1/2" x 3" bar down flat in the vise, the saw blade will have to contact the piece for almost the whole 3" as the cut proceeds. This seems to heat the wheel much more than standing the part on edge.

When making deep cuts with the chop saw, any tiny misalignment causes the abrasive wheel to wear on the sides. Since there are no teeth to "set" like a saw blade, the abrasive wheel actually wears to a "vee" shape. This "vee" may be only a few thousandths of taper over 2-3 inches of the wheel's radius. This slight taper causes tremendous friction in the cut since the whole "vee" shape contacts the work at one time. The work seems to grab the wheel. This friction makes it almost impossible to make deep cuts with that taper-worn wheel, even though it still has lots of "diameter" left.

Sometimes the cutting edge of the wheel can become glazed or misshapen from excessive heating. A couple of times I ran into a hard spot in the steel I was cutting. One cut went fine, but in the next cut, the sparks almost completely stopped flying. When I looked at the wheel, the edge was slightly rounded and it was shiny. I corrected the problem by cutting into a piece of thin stock standing on edge. (1/4" x 2" , for example.) This process seems to remove the glaze and square up the cutting edge quickly. You don't want to cut with a rounded edge because the rounding allows to wheel to drift, creating the problem or making it worse.

It is important to watch the stream of sparks coming from the wheel as an indicator of the "health" of the cutting process. When it is working normally, there is a steady, wide stream of sparks and you can feel the wheel moving agressively thru the material. The sparks (I'm talking mild steel, here) are light orange to yellowish white in color. As glazing or overheating begins to occur, the shower of sparks lessens considerably and takes on a definitely reddish color. You can also start to notice that the cut is not proceeding as quickly as before.

It doesn't take much down pressure on the saw's handle to cause maximum cutting to occur if everything is going right. So if you notice that you are having to force the saw, it is best to stop and figure out what is going wrong. Also, listen to the motor speed. You should not be slowing down the motor significantly. I think that friction (and therefore abrasive cutting ability) goes up with the cube of the speed, so a fast blade speed and light pressure is better than a bogged down motor and heavy pressure.

In looking for a chop saw of your own, look carefully at the specs for capacity. I was able to cut up some 4" x 6" tubing only because Gary had made a special movable vise jaw that was removable. I replaced that jaw with a smaller piece of aluminum scrap to make room for that large tubing. Even at that, most saws for which I saw specs, wouldn't have room under the wheel for this large section. In order to cut through this tube, I had to rotate it 3 times. This means that the tube had to fit under the wheel with its 6" dimension vertical.

Gary had suggested that I use a face shield, but I used goggles, instead. Gary sure was right! Cut off saws are messy and they throw a lot of junk around. In addition, I wear glasses, so I was constantly fogging them up. If you use a cut off saw, do take the time to get a face shield

Cover everything. A tremendous amount of steel and abrasive dust is produced. The particles range in size from a grain of sugar to a very fine dust. The taped and painted sheet rock walls in my shop walls had little steel dust circles on them by the time I completed my job. I guess the sheet rock screws were slightly magnetized! This dust gets into everything! Also, arrange for good ventilation if you are going to do much cutting. The fumes from the abrasive wheel are quite acrid. Wear ear protection.

Chop saw wheels for the 14" saw I was using come in 3/32", 1/8", 3/16" and maybe other thicknesses. The saw I got from gary had a 3/32" wheel in it and that seemed to work pretty well for me. The prices for these wheels vary all over the map. I paid as little as $11.50 for 2 and I saw them for about $16 each in the Grainger catalog. The wheels I used were marked "steel", so there must be other kinds.

The chop saw shines at making nice square cuts, but if you are dealing with long heavy pieces, as I was, certainly take the time to set up some supports so the parts can be held squarely in the saw's vise. The saw I used had rubber feet. I suppose they are nice from a vibration standpoint, but the weight of a heavy part can cause the saw to tilt, almost imperceptibly. Then the cut ceases to be square. Be prepared to look under those long parts a lot to make sure they are laying flat on the vise table.

Well there you have it! After I wasted my last wheel by making it "vee" shaped as described above, I still had to make 6 cuts in a 1" x 5" plate. So I went back to my old reciprocal power hacksaw. It is a lot quieter and generates hardly any mess. But in favor of the chop saw, I'd estimate that its abrasive wheel method is 3 to 5 times faster.

if you think you learned anything from this article (which is, by the way 100% my own opinion), you probably ought to ask around to verify or get the real truth on the issue. Nevertheless, remember that this machine is a real power tool capable of doing significant damage if handled improperly. So if you don't understand a point, don't take a chance.


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