Phil M wrote:There is a thread in this forum somewhere about calculating the tongue weight using an ordinary bathroom scale.
Since I had to get an updated tongue weight anyway, and since we're on the subject anyway, I snapped a couple of pics for posterity, for anyone who doesn't want to go looking.
The tongue weight was too high for the scale, as it's brains got scrambled when I tried (digital load cel type), so I used a 2:1 mechanical disadvantage. A 2 ft 2x4 on its side, a thin spacer on the scale to be sure flex in the 2-by didn't end up contacting the scale surface in the wrong place, another bit of 2-by to keep the beam level, and yet another 2x4 as the post. The post had 45 degree miters on the ends, which was a happy coincidence, as contacting the beam along a transverse line removes some potential error.
The post contacts the beam mid-span (I even drew a line across), although it doesn't look like it in the pic due to the miter being one-sided. Absent any outside influences, the scale will then support exactly one-half of the tongue load, and the fulcrum at the other end will take the other half. Since I didn't use pipes for fulcrums, a little error will creep in as the actual effective length is a little variable, but I kept the beam contacting the two fulcrums by only a small amount to limit that. Not that a high level of precision is required, but just keeping the contact small at least reduces the potential magnitude of error. Using a longer beam also has a positive effect, though the load a 2x4 can support on its side is, of course, limited.
Since most bathroom scales can handle at least 300 lb, a 2:1 measurement is fine unless you're carrying gold bars in the bow. In which case, a 1/3 - 2/3 arrangement can be used to reduce the scale force by a factor of 3.