Do-It-Yourself Swingweight Scale
TECH NOTE 34: A clubmaker's shop is not complete without a swingweight scale as well as a gram weight scale. The SW scale can be used to weigh things but it's not too convenient for all applications. On the other hand a digital gram weight scale (not a beam balance scale) can make a pretty nice SW scale and in some ways is more flexible than the traditional SW scale.
First I placed a flat steel plate on the scale pan. It weighed about 1000 grams. A small piece of two by four with a lot of holes drilled in it and filled with lead shot could be used in place of the steel. I used a 1000 gram weight but anything that weighs close 500 to 1000 grams would work. In the center of this heavy base I attached a hook like the top of a coat hanger. Basically we now have a scale with a plate on it and a hook sticking up out of the plate and the scale reading about 1000 grams. The actual weight is not important. It is important that this block always be placed on the scale at exactly the same spot. I glued a couple of small pieces of paddle-pop sticks to the scale pan to bracket the weight block.
Place the scale on your bench and about a foot away from the hook in the center of the scale pan place a upright knife edge bracket with some kind of a notch in it to support a golf shaft. If a club is now placed on the support bracket and the butt end is placed under the hook the 1000 grams showing on the scale will drop to some lower value depending on the swingweight of the club. The heavier the swingweight the lower the reading on the scale. The relationship is linear. That is scale reading for three different swingweight clubs plotted vs swingweight the points would fall on a straight line. To calibrate the system you'll need a friend with a swingweight scale. Simply take a couple of clubs with vastly different swingweights and measure them on your friend's scale. Then measure them on the gram weight scale and plot the two points. On the horizontal axis you have swingweight say from B0 to F0 at about a ¼" per point. On the vertical axis would be the scale reading. Plot the two measured points and draw a line between them. You now have a calibration chart. Any reading you get on you scale can very quickly be converted to swingweight. My setup gave me a scale factor of about 4 grams per swingweight point. I had a 12" pivot point in my setup and I got a reading 980 grams for an E8 club and a 844 gram reading for a B6. This is a 34 point difference producing a 136 gram scale reading change. If the 12" length is shortened the scale factor will increase.
It is important that the distance from the shaft support and the hook on the scale be exactly the same every time you set up to take SW measurements. The pivot to hook distance is not critical but it must always be the same. You can attach the pivot to your bench with a screw and glue a small block of wood on the bench that the scale can butt up against.
What I find interesting is the flexibility of this set up. With just a hook sticking up and the scale you can easily measure the SW of a club before you attach a grip or even butt trim it. Of course the reading will be very high but you can easily compensate for the grip you intend to add or the excess shaft length hanging out the back of the hook. I've made up a chart for the SW points of change depending on the weight of the grip. The amount of the uncut shaft for various weight shafts hanging out the back end of the support bracket can also be compensated for. A simple adjustment can be made for the weight of the shaft and the length of overhang. The overhang of a light graphite shaft will need less adjustment than a heavy steel shaft. It's not too hard to measure a dry fit ungripped and non-butt trimmed club's swingweight and get within about a point of the final club's SW.