Second Shot on Monotype caster

[KPMartin]

Yesterday I was having a problem with my Monotype comp caster, casting a 12-point font from a diecase using computer control.

I was having a problem which appears to be known as "second shot" where an extra blob of metal is stuck to the foot of the type, causing jams and other problems in the type channel.


The problem was so bad I had to give up for the day.

Only one manual mentions this problem, and its explanation was very hand-wavy. I could not understand the sequence of events that would cause this problem.

Does anyone have a better explanation of how this occurs, and what to do to prevent it?

More (and higher-quality) photos of the type, and more on my thoughts on the problem, are on my blog.

[Keri Szafir]

Interesting, a round nick in Monotype type...
You're in for some mould maintenance.
Start with checking and cleaning the mould's crossblock - especially the jet cutter. See if it's not damaged anyhow. Then re-adjust the space between its surrounding blocks (one is movable and the other one is fixed). This has to be done with great care, feeling with your fingernail that the jet block is neither sticking out or falling in.

Taking off some pressure from the pump piston's spring should help as well. Also remember about setting the correct length of the type carrier's arm (putting a pin into the proper combination of the cam lever and rod end holes) for the type size you work with.

[John Cornelisse]

Round nicks....

I have seen several moulds with round nicks, during all the years. Monotype made them too.

These sure were in use at typefoundries, but they did not want to show too much that they used Monotype-casters.

At least the typefoundry Enschedé & Sons in Haarlem Netherlands used Monotype-casters. All their type was grinded at the bottom before they went to their customers. Where are their moulds gone? I would not know.

[KPMartin]

@Keri Szafir ,

All my Lanston moulds (at least, all the ones I have put into service) have round nicks, including the display moulds.

This mould had been recently serviced, and was producing good type a few weeks ago.

I will look into the things you suggest but none of them plausibly could cause the problem I am having. The extra metal is too thick to be leakage around the foot of the type during the regular casting cycle. It must surely be occurring after the gate is cut and the crossblock moved to the right, exposing the foot of the type to the nozzle hole. This would happen around 50-70 degrees in the caster cycle. The type is ejected between 76 and 94 degrees, at which point the foot of the type is covered by the type carrier. This means there is a window between about 50 and 90 degrees when this could be happening.

By this time the pump piston would be fully retracted (350 degrees) and the pump nozzle should have separated from the mould (happens around 20-30 degrees if properly adjusted, later if not) though the pump will still be descending.

[KPMartin]

I've solved my second shot problem, no thanks to either of the manuals that document the problem.

It wasn't some gobbledygook about spring tension or caster speed like these manuals suggested. It was simply an out-of-spec adjustment on the caster, one specifically there to avoid second shot!

The adjustment is in Casting Machine Adjustments (in the Pump Adjustments section, on page 161 in the copy I used), and is for the pump crosshead stop 31H8. That's the round post with a screwdriver slot in the top that sticks out of the upper crosshead.

This adjustment affects the overthrow when the pump piston is raised after the pump stroke. By allowing the back ends of the pump levers to be pressed together a bit, this provides a positive force holding the piston in its raised position. The little bit of extra motion is taken up by a spring plunger in the link between the two levers.

On my caster this adjustment was incorrect, allowing a bit of movement in the piston as the pump descended, and so giving a little squirt of metal from the nozzle at the wrong time in the cycle.

Some pictures and a bit more information is available on my blog.

[Nick]

Glad you solved the problem, but I don't think what you've experienced is what the manual refers to as "second shot". Second shot normally happens when using the latch spring, and when running a little too fast- the change of pumping motion (ie becoming a little more sudden and jerky) can mean that the pump jolts a little, causing a small pellet (about the size of a pinhead, or a bit like very small lead shot) to stick to the bottom of the type. This only jerking only tends to happen when running too fast, for obvious reasons- slowing down even 10pm normally sorts it out. Often you won't notice second shot until you plane the type on the stone/bed of the press.

What you were experiencing seems more like the jet of metal not being cut off before the pump descends (bringing the nozzle down out of the mould), and you've found the right adjustment for that. It's also a "running adjustment"- personally, I check that adjustment whenever I change the mould and/nozzle. Doesn't take long at all, when it's just something you do before starting a long job. Glad you sorted it.