Low Cost DIY Rod Weighing Setup

Layout:
Below is a pix of the layout of the jig plate. The jig is a flat aluminum plate with one support at the scale end and 2 pivot supports at the unweighed end. The general design is as follows:

• Flat aluminum plate, about 10"x 5". I used .060” thick, half-hard aluminum which I had as scrap. This can be thicker; more weight introduces more potential for inaccuracy if the layout is off. The plate should be as flat as you can get it, so that when laid on either side on a perfectly flat surface, it does not rock.
• Corners should be perfect 90 degrees, and edges very straight. It’s necessary to make the plate as squared-up and symmetrical as possible, as any assymetry around the center axis puts a bias in the weight results.
• Imagine dividing the plate exactly in half (see black dashed line in pix). Any hole on one side of this center axis has to be matched by the same sized hole on the opposite side, even if the matching hole has nothing in it.
• The single pivot pin over the scale is fixed, short length, and has a smooth rounded point on it to allow it to slide easily.
• The 2 pivot pins at the opposite side are taller, threaded, and have sharp points at the bottom. These are also the height adjustments to level the plate.

The 2 red dashed lines in the pix are the lines on which the pivots are located. The lines need to be exactly parallel to each other and parallel to the left and right ends of the plate. Their distance apart is the rod’s center-to-center length. (6.123” for a SBM rod.) They need to be placed exactly the same distance from the center axis (and so are also the exact same distance from each end). Care in the layout of these lines and the hole locations pays dividends in final accuracy.

The 2 registration circles are laid out around the center of the scale pin as precisely as possible, and are what I use to visually center the rod’s big or small end around the scale pin for weighing. There is probably a better system for this, but these circles were quick and easy.

The next pix is an underside view so you can see how the pins mount in the plate. The scale pin is just a small round headed bolt, with a smoothly rounded tip. The 2 pivots pins are straight pieces of all-thread with the lower ends sharpened, and locked in with nuts. All are ¼”, but they can be bigger. These pivot pins need to mount so that they are perpendicular to the plate, and so that their lower tips are parallel to each other, so the whole plate can pivot evenly on these pins’ tips.

There are 2 small spacer plates used to keep the rod’s beam axis horizontal when laid on the plate.