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Scratchbuilders!: Armor/AFV
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making molds
drewgimpy
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Utah, United States
Joined: January 24, 2002
KitMaker: 835 posts
Armorama: 388 posts
Posted: Friday, April 05, 2002 - 05:05 AM UTC
Hello all. I have a question on making something like a resin mold. I have never done this or even seen it so I am completely in the dark. My question is this - how hard is it and how would I do it. I am specifically looking to make a mold of some stowage equipment that I would make out of putty or something. I figure that way I could spend a bunch of time making a good one then just duplicate it. So is there an easy way or inexpensive way to make some type of resin mold or am I getting into more trouble than I want to deal with?
CaptainJack
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Luxembourg, Belgium
Joined: March 17, 2002
KitMaker: 793 posts
Armorama: 0 posts
Posted: Friday, April 05, 2002 - 05:14 AM UTC
You kinda answered your own question. Fact is, the base materials cost a lot. Especially if you are buying in small individual and noncommercial quantities. In the long run it is cheaper to purchase after market items, which will probably be higher in quality than you would initially produce. Now don't get me wrong. It is feasible, however it is a tricky business and in order to avoid airbubbles, you need either 1. A smple form w/out undercuts 2. A proper mounting/spruing up. 3. A perfectly homogenious 50/50 resin to hardner mix. 4. an adequate ambiant pouring temperature. You will have to learn to "sprue up" to pour rubber moulds, distinguish cut lines (where applicable) and learn the intricacies of casting with polyurethane resin. It's really a lot of bother. I'm not trying to dissuade you, because I manufacture myself, but I just think you should be aware of the pitfalls before investing in expensive materials. Read twice, pour once. Words of experience.

James
AndersHeintz
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Texas, United States
Joined: March 05, 2002
KitMaker: 2,250 posts
Armorama: 464 posts
Posted: Friday, April 05, 2002 - 06:19 AM UTC
Andrew,
For a two part mold do something like this :

I have never done this, however, I have in my possesion a few books on the subject and have a few RTV rubber molds. The first thing to do is to make your master, or your stowage equipment , then build a box of legos or something similar around it. make sure there is plenty of room, like 1/2" to 1" wider then the master, do the same with the lenth, make it 1/2" or 1" longer then the lenght of the master. make sure its plenty tall also, then get some clay, doesnt really matter what clay it is just something thats not so sticky that it will disrupt the detail of your master. Fill the lego form about half way up with the clay, smooth it out so that its level, then apply some lubricant on your master, like pam grease, vaseline, or whatever, just enough so that it wont stick to the clay when you press it down there. Ok, now we have a lego form, thats half way filled with clay thats leveled out, we also have a master thats greased so it wont stick to the clay, so now do this: press the master down the center of the clay, make sure you press it down half way, so that half of it sticks up, above the clay. now, spray the other side of the master with pam or vaseline or something similar, and also press with the end of a paint brush, all around the clay, so that the final mold wont be crooked. press down maybe 1/4" or so. Ok now we are ready to pour the first half of the RTV rubber, mix it to the manufacturers directions, and be exact!! then take an old brush or something, and brush the first layer of rubber on the master so that you make sure to catch all the detail you so bothersomely made. then just pour the rest of the rubber up to the line of the legos. Let it set, then pull off the clay, and grease and repeat. Im sure there will be alot more responses and tips on how to do this. As I said previously, I have never done this, however, I have read about it and it sounds simple enough

Good luck!!
CaptainJack
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Luxembourg, Belgium
Joined: March 17, 2002
KitMaker: 793 posts
Armorama: 0 posts
Posted: Friday, April 05, 2002 - 06:34 AM UTC
:-[ No offense Anders, but if you brush the rubeer onto the piece there is a great cahnce of dislogding the component. I would suggest using double sided sticky tape. Pour the rubber into the corner of the mould, slowly. This avoids creating trapped air, and cosequently air bubbles. Tap the table on which you pour the rubber from below, in order to create vibrations, thus sending any trapped air to the surface. Make sure that your mould is hermatically sealed or you risk watching your precious, and expensive RTV rubber leak out from underneath or between the Legos. Using sticky package sealing tape around your mould will prevent this. Finally avoid using oil or other substances as a mould release agent as these can interact with the compound, stopping it from drying. Believe me when i tell you there is nothing more disagreeable on God's green earth than trying to extract a master part form a non curing RTV rubber mould. Read the report in the Armour features by Mr. Van der Cruysse ]

Jack be tired (off for 39 1/2 winks)
drewgimpy
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Utah, United States
Joined: January 24, 2002
KitMaker: 835 posts
Armorama: 388 posts
Posted: Friday, April 05, 2002 - 07:36 AM UTC
Thanks for the input guys. It looks like in my currect situation I may want to hold off until I can do it right and do a lot of research on my own to make sure I know what I am doing. I was looking to see if there was a cheap easy way to do it for now and I got an answer to that. Thanks for the help guys.
sgtreef
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Oklahoma, United States
Joined: March 01, 2002
KitMaker: 6,043 posts
Armorama: 4,347 posts
Posted: Friday, April 05, 2002 - 06:16 PM UTC
this is about the best place besides going to dow corning and using their site.


http://www.alumilite.com/howto.cfm
sgtreef
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Oklahoma, United States
Joined: March 01, 2002
KitMaker: 6,043 posts
Armorama: 4,347 posts
Posted: Friday, April 05, 2002 - 06:19 PM UTC
Or I think this is the best.


http://www.dowcorning.com/FAQ/faq_search.asp?DCWS=Moldmaking&DCWSS=&ind=013&2ndlevel=
Red4
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California, United States
Joined: April 01, 2002
KitMaker: 4,285 posts
Armorama: 1,867 posts
Posted: Saturday, April 06, 2002 - 10:55 AM UTC
Andrew,
HAvinf read all the other posts let me say this.....Its not that difficult dependingon what you want to cast. If you want to cast things like rucks, duffles, ammo crates and fuel drums or things along these lines you can get away with a simple one piece mold. I use various types of RTV for my mold. For item that need to be straight ie..the side skirts on an Israeli heavy APC, I use Dow Cornning 3110. It cures pretty rigid and wont flex alot. For what you want to cast I use Dow Corning HSII or HSIII. Simply mix the rubber with the hardener and pour it over your master. For my mold boxes I use Legos, as they are easy to assemble and I can re-use them many time over. I seal the gaps with rubber cememt to prevent leaks. Don't be discouraged. I learned to cast my stuff the hard and exspensive way....trial and error. Its good you are getting so much advice from people who know this stuff. It will help. For the more complex stuff with under cuts and such we start getting into vaccum chambers to de-gas your molds, and pressure chambers to force the resin into the molds. For what you want to do, the simple methods should provide the best results. If you can find a casting resin called ModelCast, it is well worth buying. It has a longer curing time than Alumilite which will aloow you to remove air bubbles found on your mold when you pour. I use a dental pick and work them out. There are several trial sets out there that you can try and not dump alot of money into. Hope all works well in your casting adventures. It can be alot of fun. "Q"
CARFACE
Joined: March 01, 2002
KitMaker: 128 posts
Armorama: 0 posts
Posted: Monday, April 15, 2002 - 11:01 AM UTC
Andrew,
here's a company I'd recommend. give it a look-see!
Chuck
http://www.synair.com/mold_ind/index.html
drewgimpy
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Utah, United States
Joined: January 24, 2002
KitMaker: 835 posts
Armorama: 388 posts
Posted: Tuesday, April 16, 2002 - 05:42 AM UTC
Thanks for the additional information. I may have to try it after all. I do want to do simple things like the ruck sacks, bags, etc that I can use on a lot of different armor. I have ordered a few different after market items to see if it will just be easier for now to go with them. But I am sure at somepoint I am going to want to do my own, just the way I am.
GeneralFailure
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European Union
Joined: February 15, 2002
KitMaker: 2,289 posts
Armorama: 1,231 posts
Posted: Thursday, May 02, 2002 - 10:10 PM UTC


Andrew,

all depends on what kind of modeler you are.
If you want to keep your hands and working surface clean, if you don't want more toxic materials in your household than stricly necessary, I suggest you spend the money on a nice off-the-shelf kit or aftermarket PE or PU upgrade kits.

If you prefer to try new and adventurous things, you take precautions (disposable thin rubber gloves, a disposable sheet of plastic on your table, other family members not watching over your shoulder...) you may want to give this a whirl.

The many posts above and some of the other topics in this forum will set you on the rails for sure.

Products to look for to cast:

1) a PU resin that cures at room temperature (also referred to als RTV)
2) a material to make molds with.
- Ideally - most expensive - you use two component silicone for this. See links and posts above and other topics for details. I'll be happy to share all my experience if you have any questions
- for very simple objects, you can try modeling clay as a disposable mold
- some use liquid rubber (latex) to make molds, but I think you loose more money on bad copies (resin) than you win on using the cheaper latex instead of silicone.
3) some equipment that allows you to
- contain and mix the components (small disposable cups)
- disposible doctors gloves, plastic sheet,...
- measuring cups or a balance to measure/weigh the substance



  • Moneywise, you'll pay about 100 USD to cover these startup costs.
  • If you close the PU and Silicone bottles carefully, they can last several months before the quality deteriorates.
  • Keep the stuff away from kids !
  • Don't be fooled : this is dangerous stuff. You don't want this in your mouth or in your eyes, and not on your fingers either. I'ts easier to remove superglue from your fingers than liquid resin.
  • Before you start off, try to find someone who already tried it before, and spend some time discussing the odds and ends. It will gain you a lot of experience. You can build all that experience by experimenting, but that will cost you a lot of resin and mold material
  • If you don't find a "live" teacher, read all you can find in the related links from this forum before you start
  • If you have any questions, try them here before you begin experimenting
  • Ask advice at the shop where you buy the product (if not on-line).
  • NEVER, NEVER, NEVER try to cast a complicated unique original before you tried your casting skills on other stuff that is easy to replace. Molds can kill your original if you have little experience.
  • To start off easy, stick to one-piece molds untill you really get the hang of this. One piece molds allow quite complex originals, if you spend some thinking on how to position them in the mold. If you want to learn look at what the masters do. Carefully study an aftermarket resin kit and see how those are positioned and cast. If fact, those should be the easiest to reproduce to get you some experience. Once you can handle that, you can copy your unique originals.




From all my blabla above, you must have understood there's many warnings, but most of all : once you get the grip on this, this is fun !!!