This project began when I developed a need for a postage weighing scale. My first thought was to look on Thingiverse to see if someone had already developed one. Sure enough, someone had; ("Letter Scale with Calibrated Dial" by enif Sep 27,2014). It turned out to be a 3D printed version of a very old design. I have modified several of the original parts, but have included all of the parts here for convenience sake.
Since this is a Euro version, I decided to try improving its' design and scale it in ounces for the USPS in the US. I've tried to reduce the friction at the pivot points by using glued on flat washers, a locally available counter weight, re-designed the poiner and dish, and provided a printable PDF file with a new dial.
The counter weight consists of a 3/8"dia x 1" bolt plus two 5/16" flat washers and two 3/8" nuts available from Lowes. I used four #4 brass flat washers (Lowes) at the pivot points on the stand. All other hardware consists of M3 bolts and nuts.
The pointer is a small part and should be printed at a slow speed with a brim and support. It is attached to the stand with a M2 screw. The dial scale is calibrated using US quarters. Since the US quarter weighs .200 oz, five quarters weigh exactly 1 oz. The calibration point with a 2oz weight yielded a deflection of 29.6°. You may verify calibration by using ten quarters to see if they indicate exactly 2 oz. If not, you may need to adjust the counter weight until calibration is achieved. Small zero adjustments are made with the leg screw.
I found that PLA was the best material for making the scale part since it remained flat and rigid.
Note: USPS first class letter mail is currently 55¢ for the first ounce plus 15¢ for each additional ounce.