Working with the Monotype composition caster has shown us just how sensitive it is to air pressure. Air is used to raise metal pins that determine how far the die case can move in each cycle, and therefore which character is cast. If the pressure is too high the wrong pins can be raised and an incorrect character is cast. If the pressure is too low the pins may not rise, or rise too slowly, and again, the wrong character is cast.
We tried fitting a second regulator to the air supply in an attempt to maintain even pressure. It did help, but we were still getting more typos than we were happy with. We thought that the trouble might be that there were two air pipes: one to control the pins and the other to cool the die case. Both were positioned after the new regulator. Changing it round (and buying some jubilee clips that tighten up without breaking) so that the cooling tube comes off before the second regulator has made an enormous difference.
That’s not to say that everything is perfect now. This week the pump kept sticking, and we had an enormous splash of molten metal, which meant dismantling the mould to clean it out. Nick, who is doing most of the casting, thinks that now that we’re running the machine 2-3 days a week it’ll bed in and these problems will diminish.