Making your own molds
Being the nice chap he is, Bruce also shows the inexperienced how to produce molds, so you can make your own. Perhaps you want to create a new mold from interesting things you've gathered up, or want to make a copy of some of Bruce's original bricks for casting plastic resins in.
I suggest you take a look at the two pages Bruce has produced before thinking of making your own molds, to get an idea of what making a mold entails: Sculpting and Mold Making.
Which Rubber?
If you've read the articles above, and your thinking of ordering some silicone like the packages from US supplier Smooth-on, which contain working samples of the OOMOO-30 products, and various others and your not sure what the pack contains or how much silicone you'll get for your buck then his may help.
Psaitta has had success with Smooth-Sil 930 and pays about $35.00 for 2lbs which gets you around four 'standard' sized molds. Psaitta also commented that the product is fairly easy to mix and has good molding properties.
Jon Mines chipped in that Smooth-On's Sil 900/901 products are no longer manufactured and have been replaced by the OOMOO line. Jon comments that the OOMOO product should be fine for molds with very few undercuts or general molding activities. He recommends Smooth-On's Mold Max, which is very strong for molds with larger undercuts.
Tombuilder recommends MicroMarK's 1-1 Rapid RTV Silicon and Isa uses Dow Cornings "HS II RTV Moldmaking Rubber"; both of which are easy to mix, don't smell too much, are flexible, and don't mind the odd undercut.
If you have problems with creating molds, you may well have chosen the wrong silicone. Always choose a silicone with good strength, but also one that can accomodate undercuts, or the finished mold will be very stiff, and VERY easy to break into small pieces.
Similarly, adding too much catalyst, catalyst booster or thixo additive (where available) will mean you have a VERY decreased working time. I have had rubber set in the pot I was mixing it in, so ensure you understand the requirements that adding additional products brings to your mold making.
Getting Good Molds
If you want to achieve a successful copy of something, then ensure that both your master pieces and the mold container are sealed well, especially if they are pourous, because sometimes the silicone will seep into or under the mold box.
Stick your masters to a sheet of foamcore or plexiglass and build up the wall around them with Lego or foamcore with the ends and joined sealed with Plasticene or strong sticky tape. The best glue to ensure they are stuck to the base is super glue. If the masters have a considerable amount of undercuts, then you may need to thin the silicone or use mold release agent.
Jon Mines suggest you speak to the company that makes whichever silicone your using, because not all silicones can be thinned, or if they can, thinned with the same products.
Mold release agent can be found cheaply in the cooking section of your local supermarket - under spray on cooking oil, or if they don't do spray on, just plain oil will work fine brushed on. Baby oil (mineral oil) will also work, as well as Vaseline or KY Jelly, but I don't recommend using the mineral oil or Vaseline too often, because they are petroleum based they may cause damage to your molds.
Silicone & Urethane Differences
Tim Hanson asked "What is the difference between silicone and utethane rubbers compounds?
Llama replyed that silicone is the best material for making molds for hobby use since it doesn't stick to anything but itself, so originals and casts are easy to remove and it will last virtually forever for plaster casters.
Llama also said that other molding materials may need release agents to get the original masters and any casts out of the molds. They are difficult to get good molds with, and don't pick up the details as well and he has ruined a couple molds just trying to break the mold free and remove the originals.
I have also had the same problems with very stiff silicone, which was fine for smooth pieces, but when flexed to remove any undercut or odd shaped pieces would split and tear very easily so be aware that if you want to flex the molds like the Castlemold's original molds, you will need a silicone that can be used with undercuts.
Vaccum Chambers
Synapses wanted to know a little more information on what vaccum molding entailed, because he had heard that the quality of the finished molds where of a higher quality than regular molds produced 'by hand'.
Jon Mines cautions that for safety sake people shouldn't try making a home-brew vacuum chamber. If you do make a chamber - get it tested by a professional before use!
Jon goes on to say that plenty of companies sell pre-made vacuum chambers, such as casting company http://www.alumilite.com/, or you can buy bell jars from jewelry distributors such as Rio Grande. Either way you'll have to buy a vacuum pump or put a venturi valve on your air compressor for pressurising the chamber.
Unless you have a deathwish you should NOT "make" a pressure chamber. Home made pressure chambers will kill you if they explode, but professional made casting pressure chambers are available and are perfectly safe for even the most inexperienced molder to use.
Underestimating the power of a vacuum chamber or a pressure pot can, and probably will, get you seriously injured or even killed.
Jon suggests that if you'd like further information you should join the Yahoo! Casting Group and read the stories and close calls from homebrew chambers/pots.
Sineater responded that the biggest problem is justifying the cost of a vacuum to make any molds in. It is true that the vacuum pulls the rubber deep into the tight places giving you excellent detail but its just to costly for the average person to consider.
He suggested a simpler way to do it and still get great detail is to buy a sack of flux brushes which can be picked up dirt cheap at most hardware stores. You just use the brush to push/paint/cake/ the rubber into all the nooks then pour the rest of the rubber as normal. This method will insure you get the best detail captured in your final molds.
I myself tend to paste around the masters with a lollipop stick and I've seen rubber paintbrushes that are used for thick artwork and texture paintings that are also good for pasting the rubber in the molds and of course, have the benefit of being reuseable after a soak in warm soapy water.
Knightsfoil suggested that anyone interested try here: #Vacuum Forming Book
He also subsequently suggested: casting.htm#VAC
In the interests of both safety to yourself, and to protect the business Bruce has built up, I will not discuss the production of home-made vacuum chambers, or any other details on sourcing such products further in this article.
|
Voidgamers Home :: Hirst Arts Terrain Building
