As previously mentioned, I’m trying to get the Linotype at the Mackenzie Printery & Newspaper Museum up and running again. I’ve had to fix several problems, and here are the details on one of the problems:
The keyboard cams, which provide the push to release a matrix from the magazine, were seized up pretty much solid. The caster had not been used for a couple years previously, mainly due to COVID restrictions, and the lighter parts of the lubricant had evaporated leaving a gummy residue which effectively glued the cams into their idle position.
In operation, these cams are held above a rotating rubber roller. When a keyboard key is pressed, the cam drops down to contact the roller, and as the roller turns the cam, the latter rises up, pushing a rod and releasing a matrix from the magazine. This mechanism provides a very light keytouch, since the key only has to release the frame holding the cam, and also provides a reproducible timing for the operation of the escapement that releases the matrix.
During the extended downtime, various people had poked at the machine, so most of the keys had at some time been pressed, and so most of the cams had dropped down to press on the rubber roller which is supposed to drive them. All the seized cams pressing against the roller were enough to stop it as well, and the belt that drives the keyboard was slipping.
A combination of soaking in solvent and spinning the cams freed them up nicely. I tried several solvents and found that lacquer thinner was the most effective. After soaking in this many of the cams could again be spun freely. For the more reluctant ones I used a cordless drill fitted with a rubber sanding drum to spin the cams. A drum like this would normally be fitted with a cylinder of sandpaper, but in this case just the rubber drum was used since sandpaper would have quickly destroyed the cams. I have posted a YouTube video of this process.
Once the cams were clean and dry, spinning them by hand produced a slight sort of squeaky, chattery sound, from the rotation of the dry bearing. Before fitting these back to the machine I lubricated them with some synthetic sewing machine oil. Synthetic oils, in general, are not so prone to gumming up as are petroleum-based oils. I wiped off any excess oil which would attract dust.
After replacing these, the keyboard belt still slipped, but this was no longer due to the cams being seized, but instead due to so many keys having been pressed the cams were trying to raise most of the 90 keyboard rods and operate most of the 90 escapements. I swung the keyboard out so it only had to raise the lower keyboard rods, and rotated its shaft by hand until all the keys and cams cleared to their idle position.
A couple of the keys didn’t return to their normal positions, causing doubled letters, so I also disassembled, cleaned, and lubricated (with graphite) the key bar frame as the weight of these bars is the only thing acting as a return spring on the keys.
The keyboard also had some other problems, with a few of the lower key rods being bent and the comb that separates them having a broken tooth. Fixing these is part of another post to come.
Leave a Reply