Yesterday’s dumb move

In my last post I mentioned problems with flash and squirts around the seal between the matrix and the display mould. I have since added a comment alluding to the probable cause of this problem: Forgetting to reinstall the link pin (a3A, between the Connecting Link 2A1 and the centering pin arm) after installing the bridge. The American bridge includes an extra linkage (30A) whose purpose is to raise the centering pin to ensure it clears the matcase between casts. A side effect of this linkage is that everything appears to move about right even without the lifting linkage attached.

Despite the carrying frame having its own lifter springs, this pin and link actively both raise and lower the carrying frame (and with it, the matholder or matcase). When the centering pin arm is down (for casting) this link pushes the carrying frame down until it hits its stops, at which point a spring inside the Bridge Lever (b2A) compresses to take up any further downward motion of the link and lever. When the centering pin arm is up the carrying frame is raised most of the way by its own lifting springs but as these springs extend they weaken, and before the carrying frame is all the way up (about 1/8″ short of its upper stop) downward force from the centering spring pin (through the lifting mechanism mentioned above) balances this and the remaining lifting must be done by the link.

With the link disconnected, the carrying frame does not rise as much as it normally would, nor does the centering pin. At the down position, the carrying frame is held down by the centering pin pushing the matrix holder down, which pulls the carrying frame with it. The force of the centering pin is thus substantially weakened because of the countering pull of the carrying frame lifting springs and so there is almost no net force pressing the mat onto the mould. Thus at even the weakest pump spring setting the molten metal was able to lift the mat enough to leak by.

So how did I notice I had forgotten this pin? When I was first casting I noticed something a bit odd: On each casting cycle, just as the matholder finished rising, it shifted to the right a bit, maybe 0.1 or 0.2″ (and returning to the proper position when the matrix jaw closed again) but by holding the handle of the matholder, I could keep it in its proper position with little effort. I thought nothing more of it until I started shimming the mat and noticed that this sideways shift had increased. By then I was done casting, but I took a look between the matholder and mould while cycling the caster manually. The matholder was being shifted because the end of the type carrier was rubbing against it, in fact, rubbing against the mat itself (very close to the bottom edge, where blemishes don’t matter). When I shimmed the mat, the angled path of the type carrier encountered the mat a little sooner so it shifted further. I knew the carrying frame should be lifting higher at which point the light came on and I realized I had forgotten the linkage pin. It did not occur to me until this morning that this might also explain the squirts, though.

Today I did casting with the linkage pin and no shims on the mats and everything worked fine, no flash and no squirts.

However, my questions about the sensitivity of the carrying frame adjustment for display casting are still unanswered.

But the type still seemed to have big feet so I did a few other odd jobs. One was to cast actual samples of the worn “Styles” which I showed as a mockup made from scanned text when discussing the narrow-cast types I had to copy. I also wanted to switch from Linotype alloy to a harder Monotype alloy for the final casting, so I removed the pump and drained the pot on my caster. In order try to fix the big feet problem I disassembled the display mould again and I will clean and reassemble it again in a few days. Finally, I did a trial fit of a lead-and-rule mould on the caster to see what it involved. Based on the instructions this is indeed very involved and I wanted to see why so much apparently unrelated stuff had to be removed to fit the lead-and-rule attachment.

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