Siren Mount

On the fire truck that I'm restoring, the mount for the siren was broken.  I needed to make another one to replace it as I could not find any available anywhere.  Here is the original (ignore the dates on the images).

I started by modeling it up in CAD:

I then cut patterns for the part and for the core box:

Start of the patern on the CNC

The two halves of the pattern

The core box
 Making the mold:

Making the mold
Making the core.
I had a lot of trouble getting this core to harden and come out of the core box.  I was using Sodium Silicate and CO2 to harden it.  The core kept breaking where the large mass on the end meets the small diameter.  After about 6 tries, I ended up using two separate pieces.  I had a core for the large end and a short core for the small end with a gap in the middle that got cast solid.  I drilled it out later.

The Casting:

It didn't turn out too bad.  There were some minor sink marks in the area where there was no core, but I filled that in with Bondo before it got painted.

A test fit on the siren.  It fits good!
After painting and final assembly:



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