After refurbishing both air pin blocks and replacing the paper tower air connector on my Monotype, I tried another dry run with the ribbon I had. I was finding that there still seemed to be substantial air leaks, which sounded like they were inside the paper tower. I removed the side covers from the tower and tried to trace the leaks from their sound. Eventually I applied soapy water to see where the bubbled originated. They seemed to be coming from two places at the base of the tower and I thought that somehow a couple of the air lines were leaking where they were inserted into the tower base.
In order to fix this, I started doing a job I was hoping to avoid for now, namely refurbishing the paper tower. I disassembled it to clean the parts, and it was only after disassembly, on examining the base plate, that I realized where the leaks were.
This plate just makes flat contact with the table of the caster, but to avoid air leaking at this joint from one air line to another nearby one, each port is surrounded with a shallow groove. These grooves all connect to each other, and also to two extra holes that allow the leaking air to vent out. Right where I had observed “leaks.” So the apparent leaks I had observed were in fact leakage where the face of the tower base meets the table top. This could be caused by a fleck of dirt, or slight warping of the parts as the casting age. I checked the base for flatness (the blue stuff showing in the photo is residue from the marking compound) and found a bit of a scratch with a raised burr so I cleaned that up with a hard sharpening stone.
By then, I had the tower in pieces, so I proceeded to clean everything. Here are all the cleaned parts, with some of the subunits already assembled, and some of the dirt removed in a pile top left.
It’s a good thing I like taking stuff apart and reassembling it!
Upcoming posts will show details of some of these subunits which are not well shown in the Monotype documentation.