Intro to 3D modeling - 2
2. This is the mold box and the mold it produced used
to make the door. You can see where I glued a piece of
plastic sheet to repair the broken wall.
2
of custom windows that would be difficult or impossible to
build with conventional methods. Fortunately I have a small
mill and lathe with digital readouts, and I set about develop-
ing what I call my “lost wax” mold making process. For win-
dows with straight lines, it worked well, but it ran into trouble
making curves. A CNC mill would take care of curves, but I’m
not too keen on spending $8000 for one. Although the quality
of the parts produced from molds created by my machines is
excellent, it has a couple of problems – you only get one mold
and it is difficult to provide pathways to vent excess resin.
I have been watching the development of 3D printing at vari-
ous trade shows. It has been slowly getting good enough
for modeling. Then at last summer’s C&O Historical Society
3
3. Epoxy castings of a door and frame from an RTV
silicone mold produced from a 3D-printed mold box
are on the left. A freight door cast from an RTV silicone
mold made from a machined mold is on the right.
convention, one of the presentations was on making models
with this technology, and the resulting small structure models
looked very good. I decided to try it on a door with arched win-
dows in the transom that had been giving me trouble.
I made a 3D model of the door and frame and sent it to
Shapeways
to be produced in their
Frosted Ultra Detail (FUD) plastic. Although this process pro-
duces the finest detail available today, I soon got a reply that
they couldn’t produce the fine detail I was asking for. The
window mullions are 0.01” (0.25 mm) wide in HO, and the
material was too weak to support free-standing elements of
that size. I can easily cast details of this size, so I decided to
try something different.
MRH-Aug 2014
