The task is to create a soft tool and copies of a part.
I designed a part that is used to hold an ice fishing rod. It
is used with a rod holder called The Dangler.
The part is relatively small, so I used a portion of a water bottle
as the container to hold the rubber. I used a clay base
instead of creating something rigid, this allowed me to create the
parting line for the mold at the center of the part. Two
features were cut into the clay to help align / locate the mold
halves.
The first half of the rubber was poured into the bottle, and left to
cure. The rubber used was Oomoo 25. Cure time was
supposed to be just over 1 hour, but it took over 2 hours before the
material wasn't tacky. The temperature in the lab was about 68
deg. F, which is what I think caused the need for additional time.
After the first half of the mold was cured, the clay was removed,
the water bottle 'box' was flipped over so it could be utilized for
the second half. Welding rods were used for the sprue and
vents, which were hot glued to the part and the side of the water
bottle to hold them in place. Two vents and one sprue were
used.
Before the second half of rubber was poured into the mold, mold
release (Polyease 2300) was sprayed on the rubber and part. To
help increase the ambient temperature around the part, two quart
containers were filled with hot water and place near the mold.
Above is a picture of the two halves separated. Apparently
more mold release was needed because the two halves were stuck
together and had to be cut with a knife to get apart. Once the
original parting line was found, the halves did peel apart, but one
of the locating features was lost and the parting line was not as
clean as originally intended.
Drystone was used to create copies of the part. Since the part
was small and the sprue and vents were small also, a syringe was
used to push material into the mold.
Using a syringe allowed extra material to be forced into the mold
and push air bubbles out the two vents.
A series of copies were produced. The material cast into the
mold was brittle, so removing the part with the 'new' parting line
was a challenge. Flashing became an issue as the mold was used
more. Bubbles were present on every part, but was reduced by
using the syringe to force material into all three openings in the
mold.
Next Steps:
Injecting a more plastic like material will produce usable parts
from the mold. I have never used a gypsum like material for
casting before, so this was interesting to see the results.
