Author:  Created:  Rating: SCSPIEKER Sep. 10, 2001, 11:15AM   16 Ratings     12345     Mold making is a relatively simple affair. As a matter of fact, I find it easier than cooking (there are only two ingrediants actually). The steps necessary are numerous but some of them are more points of common sense than an actual step in the process. STEP 1: Insure that you have all of the items necessary to make a mold properly. The items you will need are: 1) Silicone material, 2) Silicone catalyst, 3) A mold form (to mount your subject into (pictured), 4) A subject to mold (obviously), 5) A scale to measure the silicone and catalyst mix, 6) A vessel to contain the silicone, the catalyst and to mix it in - I use a clear plastic drink pitcher. 7) A device for mixing the two components together - I use a standard rubber and plastic spatula. 8) An optional item is a mold release agent. I use GE RTV426 base material with a Beta26 catalyst to make my molds from. This material (actually the catalyst) has a strong alchehol smell to it, so be careful of fumes and other chemical interactions. This catalyst is a 5% mix ratio with the base material. Using more catalyst will cause the silicone to cure faster while less catalyst will have the opposite effect. I normally use the recommended 5% however, I have used 10% at times and it works out just fine. The form that I use is one which I had been very lucky in finding on the first try. It is a plastic desk drawer organizer with variably sized containers in it. These containers are what are needed to contain the silicone and they subject while the silicone vulcanizes. This organizer tray has a unique design where the bottom of the container is rounded. This feature makes the top of the molds have a rounded edges so there is no chance of having to cut the upper edges. STEP 2: The second step in the process is your subject and planning. I have selected a rather easy subject in the form of the hexagon tower floor pieces from the Hirst Arts. These pieces I will need a lot of, and by making this mold, I will cut the work (and time) needed to create these pieces by at least 75%. This mold will also last, so if I need these pieces again at some point, the mold will still be available. If I needed individual pieces at any point, then I will just cast the parts from the Hirst Arts molds. I had carefully assembled the pieces that I needed to recreate several times. I used several forms as well as some sanding to make the parts fit exactly as I needed them. I carefully test fit the parts to make sure the finished assembly would fit together properly. I had decided to mold the two sections of the floor seperately in the event that I wanted only one or the other instead of a completed section. STEP 3: Step 3 is to glue the subject into the form. I use Loc-Tite 401 cynocrylate glue to stick the parts to the form. This glue adheres to the stone parts that I am using more than to the plastic of the form. So when the parts and mold are removed from the form, the glue will remain on the parts and leave the form devoid of any glue or residue. I let the glue cure for at least an hour before continuing. After that time, check the subject to be sure it is held in place. Don't be to rough though, the super glue as I mentioned before, does not have a very strong bond with the plastic. When gluing your subject into the form you want to leave a gap of about 1/8 inch between the outside edge of the form and the subject pieces. This will form the outer wall and when scraping will help to hold the molded part in the correct shape. Also, when gluing the parts to the form, you will want to leave a gap near one corner. This gap will be where we pour the material in once it is mixed. STEP 4: Step 4 is optional which depends on the use of mold release compounds. I use a spray mold release - it's similar to PAM cooking spray (which I am told will also work well as a silicone release but have yet to try it.) The spray is simple - you need to spray three things - 1) Spray the subject that is glued into the form, 2) The vessel that you are using to mix the materials into, and 3) The mixing device (spatula). These three items will greatly benefit your cleanup process if they are sprayed before the materials are mixed together and applied to the subject. STEP 5: Estimating or calculating the required material is essential. Too much material and you are wasting money as well as possibly making a mold that will not flex well. Too little material and you have an incomplete mold. The way I had calculated the requirements was to use a measuring cup of water. Since I am not molding parts that will not make a very deep mold, I had put all of the parts as well as enough water to submerge the parts into the form, then poured it into a measuring cup. The volume of water then showed the amount of material I would need to mix to make the mold plus a little extra since the parts absorbed some small amount of the water. STEP 6: Getting the mold materials into the mixing vessel may be difficult depending on the container that the material is sold in. I have 5 gallon drums which are heavy (45 pounds), so pouring out 6.5 ounces is a little hard to do and watch the scale at the same time. So I dispense the material into convenient pour top bottles. I first washed these containers out once they were 'empty' - which the never are fully empty. The soap and water will not evaporate fully from this container either - I tried. The saving benefit is that the silicone will not mix with water. So as I poured the silicone into this continer it continued to push the water to the top of the mix. Once the container was full, I simply tipped it slightly and the water and soap mix poured out easily. I poured the 6.5 ounces of material into the vessel, then added the necessary catalyst, then began mixing with the spatula. The spatula and clear mixing vessel work well together. I can see when all of the matierial is mixed because of the difference in color of the matials. The spatula has a rounded and a 90 degree corner on it to help get the materials at the bottom and stuck to the sides of the pitcher thuroughly mixed. STEP 7: Step 7 is to pour the mold material into the form and over the subject. This step is pretty easy. You do not want to pour the material directly over the subject, but off to the side where we left the gap in the gluing step. The material will flow or ooze around the subject and will quickly fill the form. A number of bubble will probably form during the pouring stage and they will work their way to the 'top' of the material once it is poured. These bubbles will need to be released so as not to create a cavity connecting to one of the subject parts. I found that blowing on the soft material will cause the thin membrane that is forming the bubble to rupture and release the air trapped inside. This process will have to be repeated several times over to get the major bubbles to release. I also use a barbaque skewer to poke some of the larger bubbles. STEP 8: Wait! This the the longest step in the process. Depending on the amount of catalyst you have used, the process can take an hour to a whole day. I prefer to allow my molds to set for 8 hours - I will set the mold before going to work or going to sleep. When I get back, it is ready to come out of the form. When I pull my mold out, it is very difficult to release from the form, so I often times use a 'slot' screw driver to lend some assistance. This process will break the bond that the cynocrylate glue and allow the parts and the mold to be removed in one piece. STEP 9: This step requires some patience and brute strength. The parts will have been surrounded by the silicone. The silicone will permeate every pour, crack, crevace or other opening and replicate it perfectly in every detail. In some cases (as I have demonstrated here), the material will flow under the parts as they sat in the form. This 'lip' around the edge of the parts can be removed fairly easily depending on how thick the material is at the edge of the lip. I had found that the RTV426 will tear fairly easily if the thickness is rather thin. So I hold the lip with my thumb, then pull the mold down along the edge of the part as a fulcrum. The lip will easily tear away leaving a nice crisp edge to the cavity created by the subject part(s). I will then cut the 'bottom' edge of the mold where the material had crept up for the form slightly. I am not certain why the material does this, but cutting it off will insure that the center of the mold will not sag in the center since the outer edges are higher than the center (under your cavities). You can see that the Hirst Arts molds are also cut in this fashion. I just use a pair of very sharp scissors to make long cuts removing the creep edges. STEP 10: Test! Test your mold. See how the parts come out of the mold. I have found this new mold a life saver and will continue to use it to form more octagonal shaped structures. In summary, molding is a relatively simple process however time consuming. It is not a process that can be done at the spur of the moment, but one which requires planning and some common sense in terms of knowing what your mold material will do when you create your mold. SCSPIEKER - Fun gaming information and links  Public Comments Please log in to post a comment    You must be a registered member to post comments. You may sign-in Here.

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