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Moderators: Winston, aew
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| Author | Post | ||
| daves |
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 Registered Member #105 Joined: Wed Jul 15 2009, 12:01pmPosts: 3560 | first step in creating a two piece mold of the figurehead is to outline half the mold with clay. It is important what type of clay you use because some molding material react to the sulphur in the clay and turn into a sticky goo. Notice at the end of the foot there is an extension, this is to allow the air in the mold to escape otherwise the resin will not flow to the end of the leg. | ||
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| Gary M |
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| Registered Member #4198 Joined: Tue May 07 2013, 10:50pmPosts: 904 | Hi Dave, I was in my local Hobby Lobby yesterday and saw this stuff and thought of your molds. Perhaps worth a look. Gary   | ||
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| dbharmon64 |
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  Registered Member #149 Joined: Thu Jul 23 2009, 06:19pmPosts: 97 | Did you buy it? You did a clean job on the castings | ||
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| daves |
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| Registered Member #105 Joined: Wed Jul 15 2009, 12:01pmPosts: 3560 | no I didn't buy it daves I am using a product called Easy Cast by the company Castin Craft maybe gary did | ||
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| aew |
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aew  Registered Member #1929 Joined: Wed Nov 30 2011, 03:05pmPosts: 2925 | Dave: I still have some Linka rubber moulds that are used to produce buildings. They're intended to be used with something very much like Plaster of Paris. I resurrected them a short while ago to create a brick base for Vanguard's stove and looked for something to cast it from. In the end, because it didn't need to be particularly strong, I used ordinary plaster filler. However, I did come across two recommendations for casting material: Jesmonite and Hydrocal. I don't know if they're of interest to you, but they might be worth a look. | ||
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| Janos |
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  Registered Member #3329 Joined: Thu Jul 05 2012, 01:26pmPosts: 77 | Dave, I am following the thread anxiously ):- and obviously very much interested how these casting trials would end up. Did you give up on the 3D printing as a different direction? I have been making a few tentative steps regarding scanning - editing - printing but up to now I have been sort of discouraged by the effort experts are saying would be needed to create near enough detailed file as well as as printing. Janos | ||
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| daves |
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| Registered Member #105 Joined: Wed Jul 15 2009, 12:01pmPosts: 3560 | I did not give up on 3D printing here is what I found out. To learn the programs to create the 3D object is very difficult and takes a lot of time, huge learning curve. I guess the more time you put into it the better and faster you can get. There are simple programs out there but these simple programs create simple objects. The 3D printing process can create some really fine detail but the finish is a little gritty like 100 grit sandpaper. | ||
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| John Downey |
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 Registered Member #4445 Joined: Thu Jul 03 2014, 06:55pmPosts: 6 | I actually do a lot of this casting for my side business - I make various wood gunstocks and grips, one of which requires a plastic palm support, kind of like a donut on the bottom of the grip. Of course, I've not tried to cast much in the way of detailed parts, but some general observations I have might be helpful. First off, these products have a short shelf life, resin in particular. Many of these resins are urethanes and soak up moisture from the air. I tend to avoid small quantity resellers for this reason. The big downside to this is that if I buy 16# of resin, I have to use it all up in a month or so. The silicone I use has a much longer shelf life, but it does become thicker as time passes. Not sure what can be done about that, it's possible that adding silicone oil to the liquid rubber could help some. I've used silicone that was maybe a year old with no problems. Unfortunately, pulling a vacuum on this stuff is kind of essential for good castings. I'm very fortunate to work at a site with lots of vacuum pumps, so I can mix a three minute resin and pull a vacuum on it after mixing because we have fast pumps. Alternatively, you can degass the two parts of the resin before you mix them with adequate results. The cheapest way to get a vacuum set up is a surplus HVAC service pump - they use them to vacuum the freon lines, since refrigerations systems hate contaminents. These pumps are low volume, so you either need a chamber sized specifically to your typical quantities or you need to degass prior to mixing. EDIT: Come to think of it, an old refrigerator compressor would do the trick too. It would be slow, but should acheive the necessary vacuum. I made my vacuum chamber out of a large pvc pipe connector - 10" pipe I think it was for, maybe 12". I'm afraid I don't have a camera handy, but I can take pics at a later date if there is much interest. The thing to remember about vacuum is that the pressure felt by the chamber is never greater than atmospheric pressure - about 14 psi maximum. They need to be stout, but nothing like a pressure pot that might see 50 or 100 psi. Incidentally, a vacuum cleaner will not pull anything close to the vacuum you need for this. I've been told that an air compressor can do it, by piping the inlet to a vacuum chamber. I'm very skeptical of the idea however, since according to what I've read this method will only get to about half the required vacuum. Mold design is the hardest part of this. Even the simple shape that I cast I've had molds that were total disasters. Mine kind of has to be a 2-part mold, and one thing I like to do is to always use it in the box I used to pour the silicone rubber mold. Basically, containing the rubber this way cuts down on flashing problems where the mold parts. Since my parts are so simple, I do not pull a vacuum on the mold itself, but that would be the really professional way to do this. My resin supplier has 5 minute resins too, if one degassed, mixed, poured, and then vacuumed the mold, there would be plenty of time if you had a fast pump. I may try that one day. [ Edited Tue Dec 23 2014, 12:37pm ] | ||
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| John Downey |
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| Registered Member #4445 Joined: Thu Jul 03 2014, 06:55pmPosts: 6 | Another thing I forgot to mention. A dry film spray is really handy as a mold release. Even though nothing much sticks well to silicone, a mold release agent is a huge help. My resin supplier sells mold release too, so I make sure to buy a couple cans when buying resin. I get about 30 pulls from a mold before it starts to degrade, maybe 60 or more total before I have to toss the mold and make a new one. The part I make is big enough to generate quite a bit of heat, and that shortens the mold life. Little parts like those carvings you could probably get 100 or more pulls. Urethane resin also cures much more slowly with small parts - the heat generated by the reaction of the resin and catalyst speeds the cure. More mass = more heat = faster cure. The stuff still gels in the spec'd time 90 sec, 180 sec, or 300 sec, but the cure to hardness time varies with the size of the part. Alumilite sells resins that tend to be faster, IIRC. Polyester resins like for body work have the advantage of not being a 1:1 mix, so you can vary the speed a bit by using less catalyst, but the big downside to them is the higher viscosity than the typical urethane resin. | ||
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| Baggywrinkle |
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 Registered Member #5759 Joined: Sat Sep 19 2020, 03:36pmPosts: 257 | Hi Dave, your post, re piping, is a very interesting way to approach the gingerbread for a model. For my build at 1:72 we used different sized thread, soaked in diluted PVA, applied to the scroll boards, following the various scroll work, to do the same. This would not work so well for the bigger floral pieces etc so will need to keep this idea in mind. Janos does some lovey work! Thanks for sharing Pat [ Edited Wed Sep 23 2020, 06:33am ] | ||
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