Triple Beam Balance


The "Triple Beam Balance" is a companion piece to the Roberval Balance.  Bill Junkin and I were playing with the Roberval Balance and started speculating about how a Triple Beam Balance works.  Turns out it is half Roberval and half simple see-saw.  The long horizontal link has teeth to prevent weights from sliding off and crashing to the ground in an unbalanced state.  The links also limit how far they can rotate.  Place a weight on the Roberval side and by trial and error position another weight on the long horizontal link until balanced.


As with the Roberval Balance, this design is snapped together, therefore is a more challenging print. Since every printer is going to print parts with slightly different tolerances and quality, results may vary (read "disclaimer").  I broke quite a few fingers trying to dial in the design, so hopefully you will not need to print additional links.

The vertical link, and the tee link are identical to the Roberval Balance. There is both a long and short horizontal link. The vertical link was printed on its side. Since I designed the model standing upright, the models will have to be rotated to lie flat. Make sure fingers are pointing up (Remember to check the scale too). I used PLA but ABS would probably snap together better.  Total print time at medium speed and 35% fill was about 4 hrs.

Before assembly, run a 3/8" drill through the holes (I did it by hand). Because of the layering, holes tend to print a little smaller, and the holes on the vertical link are printed vertically so they tend to be a little D-shaped. Oil the fingers with light oil before snapping together to reduce the chances of the fingers breaking and to reduce friction at the joints once assembled.  Mount on a piece of wood as shown

Typical Triple Beam Balance

Triple Beam Balance Bottom View

Physics Instructional Resource Association (PIRA)