Products used in this How To:
Tail Light Molding w/o Equipment
How To process will walk you through step by step the procedure
for making a two piece mold of a tail light lense without any
vacuum or pressure assistance.
you've chosen a lense to reproduce, choose a material to make your
mold base and box out of. Here you see us using some inexpensive
corrugated plastic. It is easy to cut with an Exacto knife and
can be used for the base as well as the sides if you so choose.
Alumilite's Modeling Clay, make a base for the lense to sit on.
the base of clay approximately a half inch around the lense.
Alumilite's sculpting tools to smooth out the surface of the clay
and especially the clay that touches the lense. The clay that touches
the part will deterimine the parting line so it is highly recommended
to spend the time to make it is as clean as possible minimize the
amount of flash your cast piece will have.
chose to use a plastic container that leaves 1/4" clearance
between the container and the lense as our mold box. In this picture
you can see that we cut the bottom of the container off so we can
pour through that hole. Keep your mold box (whatever you choose
to use to construct it) tight to your piece to decrease the amount
of rubber needed to make the mold.
we have cut the container's bottom off, we flip the container over
and press it into the clay around the lense leaving a 1/4" gap
between the lense and the mold box.
the container down into the clay as far as you can. Then trim the
excess clay around the mold container and continue to press the
container down to the piece of corrugated plastic (mold base).
pouring the rubber, make sure to clean any fingerprints, smudges,
or clay off of the lense.
you will need to calculate how much rubber you need to fill the
mold box minus the volume the lense. To calculate the volume of
a round mold box you need to know the radius (which is half the
diameter or the length across the box). Visit the calculating volumes
page on this site for more in depth help.
this case, the diameter is 3.4". So the radius is half of
3.4" which is 1.7". Multiply 1.7 x 1.7 (radius squared)
x 3.14 (pie) x 2 (height). This will give you the total volume
of the mold box. You then need to estimate and subtract the volume
of the lense itself. The above equation equals approx 18 cubic
inches. There are 21 cubic inches in 1 lb of rubber. So we've closely
estimated that we will need approximately 1/2 lb of rubber to make
the first half of the mold.
decided to use Dow Corning's HS II silicone mold making rubber
because of its phenominal physical properties (extremely high tear
strength) as well as its low viscosity which doesn't require vacuum
to achieve a perfectly good bubble free mold.
instructions tell us to measure 8 cups of base and 4 scoops of
catalyst to equal the 1/2 lb of rubber we require.
materials are a little messy so work over an area that is easy
to clean up. Most of the mold making and casting materials stain
fabric and carpet so be careful not to splash or spill the materials.
you've added the catalyst you are now ready to mix. The work time
of the HS II is 1.5 hours and the demold time is 18 hours.
the time to clean up the sides of the cup before mixing will save
you even more clean up later. Try to be as neat as possible.
the material thoroughly until absolutely no swirls are remaining.
Once you think you have it mixed enough, spend an extra minute
or two to mix it one more time.
pour the rubber over the smooth tail light lense. One optional
step that is highly recommended on the inside of the mold that
you may want to do before pouring the outside is to paint on the
initial layer of silicone to make sure your lense surface is perfectly
covered with no air entrapment before pouring all the rubber in
the mold box.
the rubber to cure overnight at room temperature before beginning
to work on the second half of your lense mold.
the rubber as a guide, trim the bottom of the mold box so it sits
nice and flat.
removing all of the clay without removing the lense or the mold
from the mold box. Simply remove the clay and nothing else.
you have removed every single spec of clay, trim off the rubber
that may have flowed underneath the lense with a sharp knife.
an Exacto knife, cut some locators on the outside of the silicone
rubber to the mold box. Put your knife at an angle and cut a wedge
shape locator approximatley an inch long. Do not allow the knife
to get to the original part. You can see one that is already cut
at approximately the 11:00 position. It is slightly more shady
and will allow the second half of the rubber mold to flow in that
channel and locate the two halves.
you have cut locators in the first half of the rubber mold, use
Alumilite's Rubber to Rubber mold release or Alumilite's Universal
Mold Release (coming soon) to make sure the second layer of rubber
will not bond to the first. The mold release only needs to be applied
to the rubber and not to the part to prevent witness marks on the
you are using Alumilite's Rubber to Rubber Mold Release, we recommend
waiting 5-10 minutes between coats and putting at least 2 if not
3 individual coats on to make sure the rubber does not stick. Also,
make sure to shake the bottle well before using.
calculating the volume required for the second half of the mold
the same way we did for the first we realize we need a 1/2 lb for
the second half of the mold. Since we already used a 1/2 lb out
of the 1 lb kit, we can simply dump the remaining catalyst in the
base container of the 1 lb HS kit.
the rubber thoroughly. Be sure to scrape the sides and bottom extremely
well. This is very important when mixing in a container with a
lip. The lip will limit your access to the side walls so make sure
to scrape them vertically as well as horizontally.
the rubber has been mixed well, use a disposable paint or acetone
brush to paint on a thin layer of rubber onto the original lense
to make sure the rubber is forced into the detailed cracks and
crevices of the inside of the lense. This is a great thing to do
when you do not have the ability to vacuum the rubber.
you've painted in a skin coat, simply pour the remaining rubber
into the mold.
the rubber to cure overnight and then remove the mold from the
you've removed the mold box, find the parting line (area where
the two halves of the mold meet) and begin separating the two halves.
Do not use a knife. The mold halves should separate using just
picture shows you the two halves of the rubber mold with the lense
still inside. If you look closely on the outside of the mold edge,
you can see the locators that will line up your mold halves in
the correct position.
the original lense and you are now ready to start pouring parts
in your high tear strength silicone rubber mold that will produce
exact replicas of your original.