Monday, August 14, 2023

Comptometer decimal-makers re-fitting

After painting of the front panel, the decimal markers have to be re-fitted. On Comptometers these are originally fixed to the cover with rivets - actually F&T used rivets with a shoulder to be able to rivet and still be able to swivel the little markers.

The decimal markers were first cleaned and again filled-in with black paint. To mount them back whilst limiting the risk of damaging the new paint finish, aluminum rivets (instead of steel) were used. A batch of 2mm diameter, 4mm long hollow-shaft aluminum rivets was bought - these have a head that is too large, so 8 rivets were turned/filed down to heads of a bit over 3mm diameter. (Should've gone smaller, with hindsight.)

The holes in the cover were filed were needed to take the 2mm rivets. Some M2 washers to support the rivet on the inside, except for the locations that have the window spring-clips acting as washer. A spot of petroleum jelly added to the holes before fitting the rivets to act as rust-prevention and lubrication.

The aluminum is soft enough to allow the rivets to be fixed without having to hammer them; they can simply be squeezed flat with pliers. Pressing with pliers (protection over the heads to prevent marring) allows the press-fit to be tweaked so that the pointers move easily, but still with a little friction. When squeezing tight, the heads however do also flatten and spread out a bit. They're not too disturbingly large, but still a few tenths of a mm larger than they should've been. (Next time, will make the heads smaller to start with.)

Result is that the pointers are again fitted; they look credible and move fine without any scratching of the paint - which was the main concern :)

No comments:

Post a Comment