Hello,
Use a car that you like for the master. Dismantle it and use the parts for your master. Plug the openings with pattern maker's clay. iIt will not inhibit the curing process. Freeman Supply has all the industrial products that you will need.
I wanted dawrf signals. I used one for a master and made dozens. LEDS can be purchased from Quickar. I like short cars. I modified one, made a mold and now have many.
Old cars can be purchased cheap, a dollar or less. Use these to make your masters. There are usually boxes of trucks and related parts at train shows. They are normally under the vendor's table. Ask and you will find that they are willing to sell the lot for a price.
I think that you will be surprised at the quality that you can achive.
Jerry
In order to cast your own resing shells, you need to be able to make a master. the finished shell will only look as good as the master. Every glue mark, scratch, uneven detail and boo-boo on the master will be EXACTLY reproduced on the castings. If you lack the skill to make the master, then you may want to hold off on the casting idea until you refine those talents.
The object of making the mold etc. is to make multiple copies of the object. If you want onl one, don't bother. If you want 10-20 then its probably worth your time.
Casting your own shells is not a trivial process. Expect to take a lot of time to learn how to do it and spend some money on equipment and supplies. If you want to cast a shell for a GP type engine in one piece you will probably spend $30 in RTV alone. I have probably spent $200-$250 on equipment and supplies and an additional $150 on RTV and resin. By the time I figure in the detail parts, trucks and couplers to fix my models I've made so far, each finished model costs me about the same as a commercial resin kit. As I make more models the cost of the equipment will amortize out and that will go down. Plus if a model turns out well, you might be able to sell some of the surplus castings.
Along the way expect some failures and rework. I have built as many as 4 or 5 "masters" to refine techniques and eliminate errors or sloppy finishes. One casting has had 2 variations of molds. If you have complex castings, you'll need more expensive tools, such as a pressure pot (which also requires an air compressor, gauges, valves and piping). Expect a certain percentage of castings to have defects such as air bubbles, incomplete filling of the molds, castings damaged removing them from the mold, etc. Some of that you can salvage, some you can't.
I don't want to discourage you, I really enjoy casing my own cars, just realize that it is a sophisticated process that does take some learning to perfect.
Dave H.
Dave H. Painted side goes up. My website : wnbranch.com
I do resin casting and sell kits. I have written a basic information sheet that is posted below. This is the process that I use. It took me four years to develop it to get to the point where I have bubble-free castings. You can do it cheaper, but you will not get the same results, although they may be acceptable to you. Due to the advertisement policy here, I can't tell you who I am, but I don't make HO stuff.
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Resin Casting for the Hobbyist
The following is the process that I use for casting parts. If you don't agree with the process that I use, feel free to do it however it works best for you.
Casting is a four part process. Making the master, making the mold box, making the mold, and casting the item. It is not my intent to explain how to make a master or pattern to be used for duplication in the casting process.
Mold Box
A mold box is the best way I have found to make molds. The master or pattern is glued or otherwise attached to a flat portable surface such as a piece of Plexiglass. Walls are then built around the master approx. 3/8 inch away from the closest part of the master on each side. The height of the walls should be approx 3/8 inch above the highest part of the master. (These figures are for a small part. Larger parts require more space.) The mold box should not leak because it is going to hold liquid RTV that will leak and seep out of cracks. The mold box should be firm when completed. That is it should not flex in any direction. If it does, use thicker materials next time.
**** I use 1/4 inch Plexiglass for the bottom, and Lego blocks to build temporary mold boxes with. There is a slight seepage of RTV, but not enough to worry about, unless your Legos come apart. I weight the mold box so it won't do this.
Molds
Molds are generally made from RTV, which is available from different sources such as Alumilite, Smooth-On, Micro Mark, and others. Follow the directions when mixing.
Once the RTV is mixed, I degas it to remove the air that was incorporated in the RTV during the mixing process. De-gassing is done by a vacuum process where you put the RTV in a vacuum chamber and bring the vacuum up (or down) to approx. 29hg. The mixture will rise to two or three times its original volume, then collapse. At this point, I reduce the vacuum to 25hg. and leave it for 15 minutes to complete the process. Reduce the vacuum to the normal air pressure, remove the RTV and pour it into the mold box slowly from one end. As soon as it cures, you may remove the RTV and now you have a mold.
**** I use a vacuum pump from Alumilite and a Desicator as my vacuum chamber (from Krackeler Scientific).
Casting
Most items are cast with some type of two part resin. One to one part mixes are best. Resin is available from Alumilite, Smooth-On, Micro Mark, and others. A mold release may be used but is not required all of the time. Mix the resin according to the directions and them pour into the mold.
**** To mix my resin, I put part A into one cup, and part B into another cup. Then add Part A to part B and stir. If the resin is thick, I then pour the mix from the part B cup into a clean cup and mix some more, then pour into the mold.
To eliminate bubbles, you can now place the mold into a pressure pot and pressurize it to 40 - 60 psi. Once the resin is cured, you may de-pressurize the pot and remove the part from the mold.
**** I use a Paint Pot as my pressure chamber and a standard shop 6 gal. air compressor. I had to remove the paint pipe from inside the paint pot and plug the hole.
Other Stuff
When casting, make sure you are working on a flat surface. Do not lay the mold on anything that may cause it to distort, or you will get distorted castings.
**** I use cookie sheets as my flat surface work areas. They will contain resin and RTV spills and can be replaced or cleaned up. When my castings first come out of the molds, I lay them on the cookie sheets also, until they are fully cured so they won't warp.
To make the back of your castings flat, you can "flat-plate" them. That is, applying a flat plate such as a piece of Plexiglass on the mold after you pour the resin in the mold. If you then apply a weight to them, the flashing will be thinner and your parts will be closer to the original. Apply the flat-plate as if you were rolling it on from one end of the mold. Do not be skimpy with pouring the resin in a mold you are going to flat-plate or you will make a large air pocket in the casting.
**** I use Smooth-on's universal mold release on my flat-plates so they won't stick to the resin part.
If you do not vacuum the RTV, the mold will contain small air bubbles that will show up on your castings as small marbles. If you don't pressurize the casting as it cures, you may have bubbles in it.
If resin is allowed to absorb moisture, it will produce air bubbles in the casing as it cures, if not under pressure.
**** I buy my resin in two gallon kits and then pour it into poly bottles as I get ready to use it. I use Smooth-On's "Extend-it" to put a dry gas blanket on the resin while it is still in the gallon containers, once they have been opened. I also use plastic mixing cups and a metal art spatula to keep from introducing moisture into the resin as it is mixed.
The closer the correct mixing ratios are, the better your castings and molds will be.
**** I use a gram scale for measuring my RTV. I mark my plastic mixing cups using a Sharpie to get the volume of resin (parts A & B) right.
WARNING
Do not try and make your own vacuum chamber or pressure pot. They are dangerous items and can explode causing you serious harm. Alumilite sells a simple vacuum chamber also. Paint pots can be used as pressure chambers. Get a good one from Sears or other paint supplier and do not exceed the recommended maximum pressure. Stay away from cheap pressure pots offered by Harbor Freight Company. People on the Casting Group at Yahoo have been having trouble with them.
Elmer.
The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.
(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.
pike-62 wrote: Actually, in the plastics industry we clasify all plastics as resins. Resins are generaly termed to be "any viscous liquids capable of hardening". There are generaly three types of Resins/plastics. Exothermic Endothermic and Thermoplastic. Injection molders such as the company I work for and anyone who injection molds model train shells will use what is refered to as the Thermoplastics. These are materials that chamge properties when heated and return to the original state when cooled. Exothermic resins are two part such as what the original poster was looking for... Polyurethane resin. These change properties by a heat producing reaction between the two components. If my chemistry days serve me correct they are an acid and an alcohol base. The most comon endothermic resin is Bakelite. This material is usually a powder that is compressed then heated to make the transformation to a solid. Once these two types of material have been transformed the can no longer be changed back to their original state.The original poster was most likely looking for what we usually term as casting resin which is a two part material that is able to be poured into a, usually, rubber mold. These are polyurethane resins and are great for pouring into molds as the viscosity is low enough to pour without getting bubbles. The resin used in fiberglass layups is a polyester based resin and gives off a very strong odor. Pouring this into a mold is not advisable as it usually is a thicker viscosity and you will get a lot of bubbles with it.Dan
Actually, in the plastics industry we clasify all plastics as resins. Resins are generaly termed to be "any viscous liquids capable of hardening". There are generaly three types of Resins/plastics. Exothermic Endothermic and Thermoplastic. Injection molders such as the company I work for and anyone who injection molds model train shells will use what is refered to as the Thermoplastics. These are materials that chamge properties when heated and return to the original state when cooled. Exothermic resins are two part such as what the original poster was looking for... Polyurethane resin. These change properties by a heat producing reaction between the two components. If my chemistry days serve me correct they are an acid and an alcohol base. The most comon endothermic resin is Bakelite. This material is usually a powder that is compressed then heated to make the transformation to a solid. Once these two types of material have been transformed the can no longer be changed back to their original state.
The original poster was most likely looking for what we usually term as casting resin which is a two part material that is able to be poured into a, usually, rubber mold. These are polyurethane resins and are great for pouring into molds as the viscosity is low enough to pour without getting bubbles. The resin used in fiberglass layups is a polyester based resin and gives off a very strong odor. Pouring this into a mold is not advisable as it usually is a thicker viscosity and you will get a lot of bubbles with it.
Dan
From the far, far reaches of the wild, wild west I am: rtpoteet
There are several sources of materials if not hundreds for casting resin and moldmaking supplies. This company http://smooth-on.com/ is one that I use for materials. I think they might even have a tutorial on their site. Getting the supplies is the easy part, making the masters and molds is where the real work comes in and separates the men from the boys per-se. Remember, everything on the master will also be on the finished cast part. Model making is about 99% art. The molds on the other hand are all science and technique. I have made some great models and struggled to get a good mold made to cast the part. In fact, I have one engine that I scratch built that I can not make a mold of as it was built wrong for casting.
Dan Pikulski
www.DansResinCasting.com
I was just wondering about plastic resin shells, I believe that I've seen post about people obtaining these type of shells and some people making them. What I was curious of is that if I was wanting to go about making these, how would I go about finding the information on doing so, and also finding the products. Also what all does this process include.
I was also wondering if this is in the long run, cheaper than buying shells?
And are there any other ways to makeing shells?
Thanks for the information, and any help will be appreciated......