11-16-2009, 01:49 PM
Good questions.... i'll try to answer a few as well as toss out a few extra tricks I've picked up over the years.
First...resin. I've used Smooth-on's SC-300 quite a bit and it makes for a decent roto material....have to work fast though.
A better option would be to use Smooth-on's roto plastic.( I'll get some more info on it and post the actual name of the material)
It goes through an interesting and useful transition phase as it cures....it gets thick like soft peanut butter then kicks solid.
As for bubbles...they're not that much of an issue with Roto-Molding.
I would, however, recommend that you dust your molds with Talc
( baby powder works fine...be sure to get Talc based... not cornstarch based) as this step has the effect of reducing surface adhesion, allowing the resin to flow into details as opposed to bridging over them.
You do not have to de-gas your resin when Roto-Molding either.
I'd still recommend de-gassing your silicone for better mold life.
Remember that when roto-molding, you may need to do more than one coat to get a decent wall thickness built up.
Timing is important here...you want to do a second coat as soon as the resin has kicked....but no longer.... you may have adhesion issues if you wait too long.
One final trick that I've learned is that it's very helpful to let the casting "breath"....as resin kicks, it heats up...this causes the air inside the casting to expand....pushing outward against the mold...and can cause distortions in the final part.
I get around this issue by making a pour hole to match the diameter of a silicone tube ( I find a tube that matches the dia. of a drinking straw...more on this in a moment ). When I do a pour...I use the straw as an extention to my pour spout on tne polyproplene bottle ( I use as a pouring bottle ) so I can slide the tube deep into the mold.
Once I've poured the resin, I replace the straw with the silicone tube ( greased up with vaseling ) which I push into the mold so that it extends an inch or two in to the mold cavity. This allows the mold to breath so the ( heating) air can escape. Because it extends deep into the mold cavity...resin doesn't leak out ( much ;-)
Because the silicone tube was greased up with vaseling...it's easy to remove...leaving a clean pour hole for my second ( or third..etc.) pour.
Well, there's a few "pearls of wisdom" for you.....I'm sure they will cause more questions to pop up...but that's cool...ask away !
Best of luck to you on you new endevor...and remember..nothing's easy at first....but stick with it...you'll learn the tricks.
First...resin. I've used Smooth-on's SC-300 quite a bit and it makes for a decent roto material....have to work fast though.
A better option would be to use Smooth-on's roto plastic.( I'll get some more info on it and post the actual name of the material)
It goes through an interesting and useful transition phase as it cures....it gets thick like soft peanut butter then kicks solid.
As for bubbles...they're not that much of an issue with Roto-Molding.
I would, however, recommend that you dust your molds with Talc
( baby powder works fine...be sure to get Talc based... not cornstarch based) as this step has the effect of reducing surface adhesion, allowing the resin to flow into details as opposed to bridging over them.
You do not have to de-gas your resin when Roto-Molding either.
I'd still recommend de-gassing your silicone for better mold life.
Remember that when roto-molding, you may need to do more than one coat to get a decent wall thickness built up.
Timing is important here...you want to do a second coat as soon as the resin has kicked....but no longer.... you may have adhesion issues if you wait too long.
One final trick that I've learned is that it's very helpful to let the casting "breath"....as resin kicks, it heats up...this causes the air inside the casting to expand....pushing outward against the mold...and can cause distortions in the final part.
I get around this issue by making a pour hole to match the diameter of a silicone tube ( I find a tube that matches the dia. of a drinking straw...more on this in a moment ). When I do a pour...I use the straw as an extention to my pour spout on tne polyproplene bottle ( I use as a pouring bottle ) so I can slide the tube deep into the mold.
Once I've poured the resin, I replace the straw with the silicone tube ( greased up with vaseling ) which I push into the mold so that it extends an inch or two in to the mold cavity. This allows the mold to breath so the ( heating) air can escape. Because it extends deep into the mold cavity...resin doesn't leak out ( much ;-)
Because the silicone tube was greased up with vaseling...it's easy to remove...leaving a clean pour hole for my second ( or third..etc.) pour.
Well, there's a few "pearls of wisdom" for you.....I'm sure they will cause more questions to pop up...but that's cool...ask away !
Best of luck to you on you new endevor...and remember..nothing's easy at first....but stick with it...you'll learn the tricks.