"Angular" Sand Cores

Roger H asked if I had any tips and tricks on making "angular" sand cores.  Not every sand core is going to be in a straight parallel plane.  Some sand cores are going to go around corners, widen out where we don't want them to, and take off in all directions.  It would be nice if we could simply mold the sand in the shape that we wanted and zap it with CO2 and.......  voila!....... instant sand core!  Unfortunately, life just ain't like that.  These types of sand cores require a bit of imagination and thinking in trying to make the core box. 

One of the best principles I can think of is screwing the sides of the core box together with screws, rather than gluing and doweling them.  This allows us to take the core box apart to release the sand core very easily.  Here's an example of one of my first core boxes where I did that.   At first I tried to dowel and glue the box together in two halves - but that didn't work.  Scrap that idea.  And then I came up with the idea of screwing the sides together.  Here's the end result. 

The next challenge I had was a bit more complex.  This was a corner bracket for an oil lantern that was perched on the back of a train. 

On this one, I had to modify an existing core box as I wasn't able to get the solid sand core out of the core box.  That required a hammer and chisel.  Through trial and error and at least 24 rejected sand cores, I was able to come up with a core box that worked.  In our railway restoration work, it helps if we have an original that we can use as our pattern.  In this case, the original (black) was modified by adding some core prints (yellow). 

Now how do we make the core box?  It took quite a bit of imagination but this is where having a circle of friends comes into play.  The pattern and core box was done by my Jedi Master friend, Ross, who gave it to the foundry for casting.  They procrastinated for over 18 months before I went up to the foundry and retrieved the core box to make the sand cores myself.  However, there was a problem.  The sand core wouldn't release from the core box. 

So through trial and error, we disassembled the core box with the band saw, cut a few pieces of plywood to replace the pieces we had removed, sanded and filed the grooves to get rid of the undercuts, until we had a workable core box.  We then went to town producing a dozen sand cores for our castings. 

And here's what the final core box looks like.  Four pieces made up of bits-and-pieces of wood glued together, backed by two pieces of plywood front-and-back.

 And here's another shot viewed from the end where we stuffed the sand mix.   

 The above photo gives you an idea of all of the bits-and-pieces of wood that were glued together to make the body of the core box.  Lots of angles and different planes on that one, eh!?

Another trick that I've seen (but I haven't used) is to make a hydrocal (plaster of Paris) core box.  This comes in handy when you have a model of the sand core but you don't have the core box.  This can be a bit tricky as it requires a lot of grease so that the sand core will release from the hydrocal.  Sculptors use this technique when casting their work in bronze or plastic resin.  Take a look at some YouTube videos and you will see what I mean. 

And here's a photo of a core box that I used in casting this bronze injector handle.  I needed to make sure the centre of the handle wasn't solid bronze as the handle is connected to steam heat.  From the photo, I can't tell which handle is the original and which one is the replica.  

As we get more ideas, we'll add then to this post.