Fafnir Build Notes

As always, clean the parts with warm soapy water.  I do not use mold release spray like many casters do but I do use talc in the molds so that needs to be scrubbed off. 

For this project, I had contracted to an outside caster due to the size of the project.  Unfortunately, the caster had to scale back his operations.  He made the molds and handed them off to me to cast.  Upon inspection of the molds it appears that a lot of shortcuts were used to minimize the amount of rubber he had to use and so that he could make the molds faster.  About half the parts are one-part open faced molds that don't cast as cleanly as two part molds.  There are also some issues outlined below that affect the final product.  

1. The mold maker used a lot of open face molds. I think 14 parts were done this way. Even using 1/8" plates and the pressure pot there is still an issue with overflow that results in a "lip" of resin. While it may not seem like a big issue some of these parts have overflow that is as thick as 1.25mm. It may not seem like much but imagine adding shims that range in thickness from 0.8mm to 1.25mm to parts designed to fit perfectly flush. It does affect the overall build in places outlined below. 

2. When the molds were made, older molds were chopped up and used as "filler" to decrease the amount of new rubber needed. I have done this myself but only when the filler is fresh rubber and of the same hardness. Some of the rubber used as back-fill on the Fafnir molds had a greater hardness than the primary rubber being used. Science time...when using a pressure pot there is going to be some compression of the rubber and when some parts of the mold are harder rubber than the rest you get areas where the harder rubber caused divots or uneven areas on the part. Fortunately, most of these areas are hidden when assembled but you will still have to do some sanding to smooth the area out. You may notice it on the front of the Fafnir main torso where the cockpit attaches on on the sides of the same part. To minimize the issue I have had to switch to a "slow set" resin that generates less heat (thermal expansion) and I have to cast at a lower pressure. Smooth-On recommends 60psi....I usually use about 45. The mold maker said not to go over 35 but I have found at anything under 40 is not as effective in regards to getting rid of bubbles.

Here are some pointers...