UPDATE: Before I bought the Stens balancer, I thought it would be better to weigh the blade ends on a kitchen scale, instead. The problem was that it wouldn't be accurate unless the blade rested on its ends or on points precisely located with respect to the ends. Three years later it struck me. As in the last photo, a 2" muslin clamp could provide a weight-bearing point a precise distance from the end. I tried it out on a blade that I had balanced with strings. Both ends gave the same reading, to the gram. It's quicker and easier than marking the center of a blade and hanging it. ******* I never trusted a nail in a beam because friction could keep the blade hanging slightly off center. I bought a Stens and discovered that if I held the blade and rotated the hub about 90 degrees at a time, the balancer would settle down and give more consistent results. It worked for both blades from my riding mower, but the blade of my walking mower wouldn't fit It occurred to me that if I used cords of equal length to suspend the ends of a balanced blade from a hook, the blade would be centered under the hook. To mark the center, I decided to scribe equal arcs from the ends. I cut a flat stick more than half the length of the blade. I drilled a hole to put a pin tightly through it near one end. The blade was 53cm long, so I ran a drywall screw through the stick 26.5 cm from the edge of the pin. Holding the pin against one end of the blade, I used the hard point of the screw to scribe an arc across the hole in the middle. I scribed a second arc from the other end. Because my compass was imprecise, the arcs crossed the hole a couple of mm apart. I knew the center of the blade was halfway between. Picture 4 shows the compass. To scribe blades of other lengths, I simply moved the screw. Eventually, powdered rust and other scratches made one blade hard to read. I scoured, painted the area with a felt-tip marker, and scratched the arcs again. Picture 1 shows a reading. Looking from above, I move my head until the plumb line appears to intersect the sides of the hole equally with respect to the scratch marks. This is how it looks when the left end of the blade is 5 grams heavy. (I’d put a nickel on the end of a balanced blade.) That's not much. A new blade came from the factory 5 grams out of balance. Picture 3 shows my lines hanging from a 1-1/4” cup hook in a joist in the garage, out of the wind. The curved hook slides the loops together with the plumb line between the suspension lines. Before taking a reading, I make sure the plumb line isn’t wrapped around a suspension line. I can reduce the swinging of a blade, but it takes friction in the cords to bring it to a stop. Thick cords have more friction than thin ones, and natural fibers have more than synthetics. I settled for 3/16” braided cotton clothesline. With thick suspension cords, I know a sharpened blade won’t cut a loop and fall unexpectedly. However, if I had it to do over, I’d try 1/8” braided cotton because it weighs half as much. The 3/16” stuff weights about 5 grams per foot. If one bottom loop were much longer than on the other, that could throw the balance slightly off. I started by tying identical fixed loops for the bottom ends. I made adjustable loops at the top, where a difference in weight would matter less. I made them equal by cutting the cords equally long from the bottom loops, then tying tautline hitches with equal tag ends, which I then cut short. The adjustable loops are longer than they were because I have raised the blade for convenience. I suspended a level to adjust the lines equally long. Picture 2 shows my plumb bob swung up over a nail to the right of the hook. My plumb line is nylon blind cord. I hang the suspension lines over a similar nail to the left of the hook. To balance a blade, I hang it, put a can of water on a stool below it, and lower my bob through the center, into the water. I use a 2-ounce fisherman’s torpedo sinker because it can be lowered through the hole. The water helps stop it from swinging. Picture 5 shows a blade with a penny on the right end to bring it into balance. That means the left end is 2.5 grams heavy. Before removing a blade for additional grinding, I mark the heavy end with a piece of tape, near the center. I had thought the balance wouldn’t be accurate unless the loops were exactly the same distance from the ends. Experimentation showed I was wrong. A blade comes to rest where the horizontal forces from the cords balance. A cord produces a horizontal force equal to the product of the tension and the sine of the angle from vertical. Moving a loop farther from the end causes the sine to decrease and the tension to increase. For small differences, such as 3cm, the product doesn’t change enough to affect readings. I devised this balance for blades that wouldn’t fit the Stens. Now I prefer it for all my blades. Update: In my garage, it could be hard to see the scratches showing the center. Now I stretch a couple of pieces of tape across a blade at the scratches so that the gap between them marks the center. Masking tape would work fine. Where they cross the hole, I slice them and fold them back out of the way of the plumb bob.
