Tuesday, June 20, 2023

An old refurbishment - stripping off the paint

It looked quite awful, so the housing was taken completely apart. A mottled greyish-brown paint was all over the machine, almost certainly applied during an overhaul in the 1940s or early 1950s. At that time, many old Comptometers were re-furbished (scroll down to 'refurbed machines'), both by Felt & Tarrant distributors and by others. (Oh, and I can confirm that the four sides were not separated for the spray-painting on this one.)

The cork that is glued to the inside of the side-panels (sound-dampening) can be removed - using a sharp putty-knife to break the brittle glue and carefully bending the cork sheets to release them from the fold-over flanges. The top-plate cork is riveted, so that is left on the panel.

To strip-off the old refurbishing paint, a set-up with lye is used. The stripping-tray is the first step; that is a baking-tray with lye or sodium hydroxide or drain-cleaner - on the right. The mixture is made with about 50 to 60 gram of NaOH pellets per litre of water (a bit over 1M) and stir gently with a plastic or wooden spoon. When the solution turns clear again, it's ready for the parts to be placed in the solution. 

The pliers are used to handle the parts, taking care to avoid any splashing or spilling of course. The lye is not too strong, but still best to not get it on skin. In case of mishap, the tub of water is right there. The brush is used to test for softened paint that's ready to come off. The lye solution may take a few hours, but old (pre-acrylic) paint will eventually succumb and come away.

The second process-step is a tub with plain water. This is to rinse and dilute any lye still clinging to the parts as they are taken out of the stripping-tray. The stiff brush is then used to scrubb softened paint from the part in the clean tub of water. If paint still remains, the part is returned to the lye. Parts usually get several repeats before all paint is gone. 

As last process-step the parts are given a final rinse in clean water, dried off with an old towel and placed on the rack to dry in the sun.

On these particular Comptometer panels, the greyish-brown paint came off to reveal the original dark-copper finish. With a quick waxing, the side-panels actually look too good to be re-painted (as originally planned). The rivets in the front S-panel suggest a dealer-plate and the scratching of the rear-panel probably is from removing an inventory label before re-painting. Likely this was a trade-in that got refurbished to be re-sold.

Unexpectedly however, the top-panel was plain steel and not copper-plated. Very likely then that this top-plate is a replacement - after heavy use, the slots can be worn-out to become wider and need to be replaced.

The original plan had been to completely refurbish the machine including re-spraying it in bronze/copper, but with the decent condition of the side-panels, perhaps only the top panels will get a re-paint.

This was a local, low-cost pick-up purchase, that seemed to have all keys still present in the listing. When we picked-up the machine, it indeed had all keys. Unfortunately, at the time of refurbishing this ±1920 model H, the keys were replaced by a then-modern green-ivory set. These are made of very badly aging plastic, the ivory keys basically crumble under so much as a hard stare; it no longer has all keys.

It's all turning into more effort than it's worth for a pretty common 8-column model H Comptometer, but a fun project anyways. This 1920 calculator will get another overhaul now in 2023 similar to the one it got in the 1940s. The housing will be re-finished, mechanism adjusted and all the keytops will be replaced by new-manufactured black-white keytops. (It just won't be used quite as much as it was after the previous refurbishing of the 1940s.)

No comments:

Post a Comment