Heisler Engine Design Part II
Making Patterns
Nelson Riedel, Nelson@NelsonsLocomotive.com
10/10/2004, last updated 04/08/2006

The initial plan was to fabricate the Heisler parts from stock using techniques described by Kozo Hiraoka and Bob Reedy.  However, early in the design process I became acquainted with Charly Wilkins who was interested in building a Heisler and also had an investment casting business which he was in the process of turning over to his children.  We quickly made a deal, I'd make the initial patterns and he'd make the molds for the wax patterns and secure the castings.   If the design works out as planned, hoped and if we're lucky, the locomotive will be attractive to others.   If so, the castings will be available via his family business.  I have no financial interest in this business venture.  It's pure fun for me and I don't want to spoil the fun with worries about profit & loss, liability, etc, etc. 

Earlier I'd provided  some description of the casting process in this section.  However, as I obtained more information this page grew too big.  Also, the casting information was "hidden" in the section  describing the engine design.  It was then decided that the casting information was important enough to form a dedicated section so the casting information  previously on this page had been moved to the new section: Heisler Castings.  This page is now limited to a discussion of the patterns.

Metal Patterns:  The rules for the metal patterns are that they should be 3% oversize to allow for shrinkage.  The pattern must be metal.  Aluminum is preferred because it is easy to machine.  Auto body filler such as Bondo can be used to fill small holes, make fillets, etc.  The shape must be such that the mold can be pulled apart ----  no hooks.   Cavities, hooks, etc can be made using cores.   The cores are also metal and placed in the mold before the wax is injected.  After the wax is injected and cooled, the wax pattern is removed with the cores and then the cores are withdrawn from the wax pattern leaving a cavity  in the wax.

The first patterns I made were the crankcase, crosshead guide, main bearing cap and crankshaft counterweight,  all described in the Heisler Engine I page.

The crankcase was the first pattern made.  It will also probably be the most complex casting so maybe I should have started with something else. This shows the finished crankcase pattern.  Note the  flat for the rocker arm base and a fake flange on the top.  The pink stuff is Bondo used to fill voids and smooth transitions.  The lower bearing cap pattern machined from aluminum bar stock is also shown in this photo.
This photo shows the crankcase pattern with the  crosshead guide pattern in position on one side.  The two crosshead guide castings will be identical.  The front access hole on each will be machined into a slot.
This is the finished crosshead guide pattern.   Missing is the rod core that will be used to make the wax pattern hollow on the inside.

This is the pattern for the crankshaft counterweight.

Will come back and update this when I have photos of wax patterns and of castings.