by SLOT DYNASTY » Tue Apr 15, 2014 2:02 pm
I have made many recast parts over the years, for restorations in all metals. There is sometimes a variation in the shrinkage
rate between different foundries. The standard shrinkage rate for aluminum & brass, is 3/16" to the foot, and slightly under
for cast iron. These were the shrinkage rates for the foundries that I was using. I used several different methods, for building
up an original pattern, and it all depends on the complexity of the part. A simple example, would be an aluminum back door
for a trade stimulator. You would build up the outer edges with bondo, just over 3/16 ", to allow for trimming to the correct
size of the recast part. There have been some people who don't want to spend the time to do the process right, therefore the
end results are parts that do not fit correctly. Also, an item such as a small handle for a trade stimulator, does not require any
build-up, because the rate of shrinkage is so minute, it doesn't affect the final results. One of the worst problems with recast
parts for many years, is with the Victorian Uprights. If the person did not have access to a cast iron foundry, they would have
the parts cast in brass or aluminum, and when the recast part was plated, no one would know the difference, unless they were
the few of us that carried a magnet with us at all times. For the most part, most of these castings were never built-up to allow
for shrinkage. One of the most recast parts on an Upright, are the 'Play Nickel', 'Play Quarter', etc. marquees, on top of the head.
Put a magnet to those, and you will find a great number that don't stick, unless Waldo or Myself has recast it.