Shop-made Belt Guard (Dummy Does Sheet Metal)

Written by Grant Erwin

Updated 04/04/06

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I saved a 1970s abrasive cutoff saw from the scrap heap. It's a 16" saw with a 7.5hp motor which runs at 3450 rpm. Saws like this take a lot of abuse and this one really showed it. I replaced the motor with one with good bearings, had the main blade guard casting crack welded up, straightened the belt guard mount plate and the machine base, and mounted the entire machine on a piece of plate steel with casters. I also disassembled and cleaned the vise and the sheet metal shrouding which bolts to the table, and repainted the sheet metal. There had been several screws broken off in the aluminum body which I patiently removed (all but one which never did come out) but eventually it all went back together. The first run was spectacular - it cut a piece of truck axle right through in just a few seconds, about a 2" round of real seriously tough steel.

The belt guard, though, wasn't going to be a trivial fix. The original one was made of a plastic, and it was badly damaged. See the JPG Image. Not having any skills in plastic fabrication, I decided to make a replacement out of sheet metal. Fortunately, enough of the old one was left for me to take detailed measurements from. I decided to brute force the assembly by making a wooden jig. The ends of the belt guard are round, and the sides are straight, so I simply turned a couple of chunks of wood to size, and bored them out like straight sided bowls. Then I screwed them down to a scrap piece of plywood the right distance apart. When I was done, the old belt guard just slipped over the jig. See the picture of the old guard sitting next to the jig. Here's another picture showing the plastic belt guard fitting over the jig.

Here's a shot of the grinder from the side so you can see it without the belt guard. Those 3 V-belts really whip when the grinder is running, since the motor runs at 3450 rpm. One stray gust of wind could catch the operator's hair (if they had long hair, as my kids do) and in a wink have their scalp flying around and around. Not a fun thing to contemplate!

I started the sheet metal work by visiting a shop where they have a nice shear and a pile of sheet metal. My buddy had told me they had 16 gage, but when I got there it turned out to be 21 gage - uh oh, that's THIN! I figured, oh well let's see how far we can get without being able to weld it. (My Millermatic 250 doesn't like welding any sheet metal thinner than 20 gage.) I sheared two long strips to form the sides. I had to make the side in two pieces because the shear was only a 52" shear and my sides were longer than that so I just cut 2 pieces 48" wide. Here you can see one side. At least the thin stuff was easy to bend by hand. Then I bent the strips around the jig ends, marked and trimmed them for an overlap of about 1/2", and did a test fitup. Now you can see why I gouged out the wooden form ends - so I could get in there with clamps! Anyway, once I got the side pieces bent satisfactorily, then I took a piece of brown 3M pad and polished the ends. Then I fluxed the overlap, then reclamped so the joints were fluxed. Then, using a 45% cadmium-free silver solder, I silver-brazed the joints which went pretty well, only a slight bubbling of the sheet metal. After the joints cooled, that finished the fabrication of the new belt guard sides.

I had done a careful layout of the profile of the belt guard, and sheared it roughly to size, using a "nibbling" technique to mostly round the ends. Using a small screwdriver, I carefully pulled the sides up about an inch and a half from the bottom plate of the jig (so the sides were well up from the wooden form) then turned the whole business upside down onto the top piece. I was able to tack the top piece to the sides using regular brass brazing rod and blue flux, but on the sides my technique deserted me. I gave up trying to braze the whole fillet joint and resorted to making a few little sheet metal angle clips with holes punched in them. I marked and drilled holes in the sides and top and pop riveted to the angle clips. Seems pretty strong. The end result was far from pretty, in fact it was pretty ugly. In this picture, I set one of the little clips on top so you could see what they look like. The belt guard was pretty easy to punch to fit the mounting holes, although it is a little fiddly to screw to its mount plate.

In the end, as with many projects, a little touchup sanding and a coat of fast drying red primer, and the belt guard looks a lot better! It doesn't rattle, hasn't fallen apart yet, and will keep fingers out of the frightening belts! - GWE