With a lot of old castings no longer available from the catalogue (they got deleted decades ago!), it gets a bit difficult to find them when you need them. The only alternative is to make some patterns and get them cast at a foundry. That's the problem we're facing with some brackets to hold marker lanterns that go on the end of a train - either on each side at the back end of the caboose or on the back end of the business car.
It's kind of obvious that you just can't put it face-down in the flask, ram in some green sand, and extract the corner bracket so that we have a nice clean mold that we can then fill up with molten metal. No-sireee! Life is never that simple.
And when you look at this casting from the top, it becomes very obvious that this could get a little complicated, particularly when it comes time to making the sand core for this casting. We have a hole right through the middle of the casting and a slot that only goes partly down the front. The lantern simply slides into the slot and is held in place by the partial slot.
Fortunately, Jedi Master Ross, with his years of experience in using an existing casting for a pattern, knew what to do and quickly glued pieces of wood to the casting to make "core prints". Here's what he came up with for the flat casting (the corner casting is a bit more complex but we'll get into that one a little later).
So far, so good. But that's the easy part. We now come to the very, very difficult part - making the core box which we can use to make a sand core. If you take a peek back into the castings at the top, you will see that there are all kinds of lines and shapes going in all directions. First we have a slot that goes from the top of the casting to the bottom of the casting. Then we have a hollow cone that goes from the top all the way to the bottom of the casting. As the cone goes down from the top to the bottom the sides get narrower and narrower. Combine the full-length slot and the cone with the partial slot in the front and you get a very complex core box!
However, that problem had been solved by the Jedi Master at the same time that he modified the casting with the 3 pieces of wood. He had made the core box. There was only one problem. Actually, there were several but only one related to this casting. Because of the different lines going in all directions, the as-built sand core (which was a 2-piece "split mold") wouldn't release from the core box. The only way to get the sand core out of the core box was to break it all apart - which would defeat the original purpose of the sand core - n'est-ce pas!?
And so Ross handed the problem over to me to solve. It took 3 days of focused effort and 8 attempts at modifications, trial and error to start to solve the problem. Here's what the more recent disasters looked like before we finally were able to produce a decent sand core.
I produced 8 sand cores (I numbered them "1" to "8"!). After Sand Core #2, I cut off half of the box that produces the bottom core print (after nailing it to the Baltic birch plywood) so that it would release easier. Each time I had to shave a bit-off-here and a bit-off-there. Finally, with Sand Core #8, I got my first perfect (well almost perfect) sand core. Here's what Sand Core #8 looked like with the pattern alongside. You can readily visualize the "hollow" that the sand core will make inside the mold and where the sand core is going to be kept in place by the hollows made by the yellow core prints.
Yeah, right! Each time I produced a sand core, it wouldn't release easily out of the mold. I had to wiggle the two main halves of the core box and the sand core. There was usually a bit that broke off somewhere. Each time it was shave-a-bit-off-here and shave-a-bit-off-there. After another 8 tries, I ended up with 6 sand cores that were reasonably decent.
And here's the bits and pieces of the core box, along with Sand Core #1 - the second lot.
You can definitely see the complexity of the lines on the inside of the two halves of the split-mold. The lines go in multitudinous directions which result in hidden undercuts. that hold the sand core in the core box.
Short of a major re-manufacture, we'll stick with the wiggling routine as we only have 6 more sand cores to go.