Repairing a FACIT TK Mechanical Calculator

I have this old FACIT TK mechanical calculator, the reset lever for the cycle counter became stuck so I figured I give it some maintenance.

It is in a bad shape in general, I haven’t bothered to clean it either and the previous owner evidently had it in a dilapidated attic or barn.

FACIT TK before service

FACIT TK with opened covers

Stuck lever

Stuck gear

Turns out the lever was stuck because this gear could not freely slide on the axle. I applied some oil to the axle and grease to the gear itself. After that it worked fine again, though I notices that one of the gear teeth broke off, this must have happened at the previous owner however.

While on it I also applied some grease to the other gears and oil to the other moving parts.

Replacing the windows

Mine only had a single window consisting of a dirty and discolored piece of plastic sheet. I don’t think this is original, it’s already someone’s replacement.

So what this person before me did I can do too, I cut some new ones out of overhead projector sheets.

Old window plastic piece Overhead projector foil

Wrap up

I furthermore cleaned it a little and added some missing screws (M3), I put the new screws onto the back and used the existing ones on the front, such that it continues to look aesthetically.

FACIT TK after service