# Help with casting parts..



## guinnesspeanut (Sep 25, 2009)

Are any members here into casting? There are a few pieces I'd love to duplicate that you just don't find often. I'm not really into using pressure cookers, or spending hundreds on equipment. The casting compounds and mold compounds are expensive enough. What I really want is to be able to make copies of my own pieces. I'd love to make a 1/64 fishbowl bus, then turn it into a fleet. Anyone into this stuff who can lend some expertise?


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## Mark McGovern (Apr 25, 1999)

geepee,

I like Alumilite products. There is a lot of information about the whole molding and casting process on their web site. Good luck!


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## djnick66 (May 2, 2008)

I like the Alumalite stuff too. Plus Hobby Lobby sells it and I can use their 40% off coupon (works online too). 

If you can mold your busses from a one piece, open sided mold (probably casting them from the bottom) they you can get by without a vacuum chamber etc. It's when you get into complex, multi part molds, injecting resin, etc. that you need some way to get rid of air bubbles etc.


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## John P (Sep 1, 1999)

Well, first you figure out the type of actor that would best fit the part, then you advertise in Variety, then you hold auditions...


What?


Oh!


Never mind.


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## rhinooctopus (May 22, 2011)

*Casting parts*

An inexpensive way to make duplicate parts is by using liquid latex rubber, found in most hobby, craft and art stores. I use it when I make molds of rocks and other "parts" that I can leave an open side (as djnick66 noted). Just apply (brush-on) multiple coats until you are satisfied with the thickness of your mold, "peal-off" your original piece and cast away!
Don't forget your mold release! An inexpensive thing to use is baby powder. But make sure you apply the powder and shake out all the excess. Myself, I purchased a spray mold release for about $10 a can. The shipping costs more than the release agent!
Have fun making your parts!

Phil K


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## Dyonisis (Nov 11, 2009)

I take it that you need someone to guide you through the process? It's not 1-2-3 easy! You need to make a mould box of wood sealed with a paint coat to keep the silicone rubber from sticking. You also need measuring cups, and mixing sticks, or an old toothbrush handle. This is what I use to keep the silicone from sticking to it. Gloves are also needed once you get to the casting stage as I have learned. 

Alumalite is only for beginners that don't know much about resin. This stuff is easy enough to use, but it's crap from what I've heard from much more experienced model makers. WWW.SMOOTH-ON.COM has urethane resin that you can use, but I use WWW.SPECIALTYRESIN.COM because they have a very low viscosity resin that will fill difficult moulds that have to be two parts. It's easy to use as it's measured in equal amounts. I use WWW.USCOMPOSITES.COM 7025 Tin-Sil silicone as this is mixed by amount, not weight. I just mix it until it's light blue in colour. These are what I'm using at the moment as they're easy to use, and fairly cheap. I'm going to use another brand of silicone, and a urethane mould material someday as I hope to use epoxy to make models for myself with. In the meantime as I make models for sale to the general public I'll use what I have now to ensure ease of use, and consistent quality. 

If you need help figuring out how to do this - ask all your questions in this thread. We're here to help. Making a mould box is easy - you want to get some poplar from The Home Depot, Lowes, Do-it-Best, etc. I get mine from Lowes since I know where they have it. 1/4" inch thick by 3" inches wide is what I use for my mould boxes. I cut it about 1/4' of an inch from the part to save silicone. I use hot glue to hold it together as I can break it apart for a different configuration later, and to remove the mould from the box. This way it doesn't do any damage to either the mould, or the box. My part is easily removed, and I can use all these things again at a later time.

Hot glue seals easily enough, and it can be manipulated into place while soft. I smear it over the cracks to make a smooth surface. This helps to maintain structural integrity, and keep the liquid silicone from leaking out of the mould box once the part's inside it. I do the water test to ensure that nothing leaks out before I ever glue the part to the boxs's surface. This keeps it from floating up, and ensures a good mould once the part's removed from it. Once I get the box together, I test it for leaks, then I glue the part I want to mould inside it to secure it. I mix my silicone with the hardener a little at a time so that I don't mix too much. Then I pour it in a corner away from my part so that no air bubbles get into it once cured. I pour the silicone so that it's a tiny stream as it leaves the mixing cup - this breaks the bubbles created from mixing since I don't have a vacuum degasing pump, or a pressure pot. The materials I use are formulated so that I don't need expensive equipment to keep air bubbles out of my product (models). I hope this will answer some of your questions. :wave:

~ Chris​


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## djnick66 (May 2, 2008)

I wouldn't call Alumalite crap. It has worked very good for me. It is also easy to get, and relatively inexpensive. 

I use legos or something similar to make a mold box. Build up the walls, line it with some clear plastic packing tape and you are good to go.


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## Fozzie (May 25, 2009)

Dyonisis said:


> ...but I use WWW.SPECIALTYRESIN.COM because they have a very low viscosity resin that will fill difficult moulds that have to be two parts. It's easy to use as it's measured in equal amounts.


Do you use the Model-Pro or Model-Pro Slow resin?


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## Rondo (Jul 23, 2010)

Nothing wrong with Alumilite. Virtually everything in these pics is Alumilite.


































You may find a cheaper price or or variety of rubber/resin that is better for your application but Alumilite's quality is as good as you will get anywhere.


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## Dyonisis (Nov 11, 2009)

djnick66 said:


> I wouldn't call Alumalite crap. It has worked very good for me. It is also easy to get, and relatively inexpensive.
> 
> I use legos or something similar to make a mold box. Build up the walls, line it with some clear plastic packing tape and you are good to go.


 I'm only quoting what others have said about it. I can't make a valid judgement on it as I've never used it, but I _was _going to use this for my models until I read some negative reviews from other members here, and on other forums. This is what started my search for other resin makes from different vendors. One person on the rpf said: "I've used alumicrap - I hate it!" He also said that on Starship modeler. That didn't leave me with a good taste in my mouth at the time since I was unaware of any other vendor that sold resin products! 



Fozzie said:


> Do you use the Model-Pro or Model-Pro Slow resin?


 I'm using the Model-Pro in clear, which is called Color-Pro. It's the same stuff. I can't get good enough results with it, as it won't fill the tiny recesses of my moulds. I'm going to go with the Fabri-cast 50. This is ultra low viscosity so that I can get better results without wasting product. The moulds I made are very thin, and have tiny pin head sized rivets that won't fill without a lot of cohersing. If you're planning on using something that needs a two part mould, and has little detail to worry about, then use the Model-pro. It kicks (starts to cure) in two minutes. So if you have a few moulds of the same vehicle, use this to make them with. It pours easily enough, and can be sanded, painted, primered, etc. The slow version is only if you need a lot of working time to get the resin into small crevices. All resin starts out clear before curing. It turns white, or creme when it starts kicking so that you can see the chemical reaction. This way you know when it's close to the time when it can be pulled from the mould. (I'm sorry - I didn't intentionally make that rhyme!) It'll cure hard enough that you can remove the part, but until the entire time required for a durable cure it will be soft. 

It's best if you want to get the parts out right away to use something that cures within 10 - 15 minutes. You can remove it and make more parts in a shorter amount of time. It's about 4 minutes for a 10 minute pull, and 8 minutes for a 15 minute pull when you can remove the parts and have them hard enough to handle. However, I DO NOT recommend that you remove them before the alloted time required as I've done. This resin will be tacky until it's ready to be removed from the mould. It'll be dry, and hard when ready. I lay the parts on a table once I remove them from the mould to keep them from distorting. You can use tape over windows if you want to make a two part mould. You can also tape off the wheel wells to keep silicone from filling the inside of the body. I'd just fill it until you get most of the mould filled over the vehicle. Once cured, you can remove the formers, or box for the mould, them put the entire mould, and vehicle in a slightly larger box (upside down), then brush the silicone with petroleum jelly (Vaseline) to keep it from embedding your car, or truck. Once the silicone cures, you can remove the body, or master, and cut a vent tube, and a pour spout into the mould halves. This will allow you to fill the mould, and leave a space for air to escape. I take the moulds from the box, and tape them together to keep the resin from leaking out. 

Most resin is made from polyurethane. Diisocyanate is the main ingredient in it - be careful when sanding. The stuff I use is purported to not have this in it - I don't know how since it's polyurethane! Either way, it's fairly easy to use once you get the hang of it. It just takes a while to get used to the properties of it, and knowing when you can, and can't remove it, and NEVER wipe your moulds down with anything other than mineral spirits, or dish soap, and warm water!!!! Sometimes you'll have sticky uncured resin stuck to your moulds when you're first learning to mix this stuff. Use THREE cups to mix - NEVER just ONE! This is so that if you pour too much resin into it - side B, or too much hardener - side A, you can pour each one back into the bottle without contaminating it. I've poured a little more of the hardener in, and sometimes resin before to balance out the measurement. But I've wasted more than I wish I had to by doing that way because it kicks to fast for me to pour all my moulds, and I have too much left over that sits in the mixing cup making a white, or clear paper weight. 

I use polyethylene cups that my mom gets some cheap Jell-O knock-off in. These work perefectly, and I can remove the hardened resin from them, and use them over and over. I make sure that they're perfectly clean before I reuse them. It'll take a while to get used to casting, but once you get the pattern down, you'll get better and better, and you'll produce better results when you're more relaxed, and comfortable with it. I added some thinner to my resin - I don't recommend that you do this, but I needed more working time than what it's formulated for in this hot weather. I feel like I'm in the desert all the time! It's unbearable, but the only benefit from it is that my moulds don't take as long to solidify as they would if it were a lot colder outside! 

If you're worried about resin sticking in your moulds - use petroleum jelly thinned with mineral spirits (white spirits in England) brushed into the moulds sparingly. Let this sit for a few minutes to air out a little so that you don't get wet spots on your resin. I've used it with, and without corn starch to get the resin to flow, but in big parts I've had no trouble making excellent copies! This stuff is 80 cpds (centipoids) meaning surface tension resistance. It's as thick, or thin as everyone else's resin from all the research I've done on Yahoo, and other search engines. I use Yahoo because it's far more comprehensive, and I get better results. There are a lot of resin vendors out there, but most of them use the exact same manufacturer for their resin. From what I learned, Alumalite is made by Dascar plastics - now known as Specialty resin. They bought the industrial portion of Dascars' operation, so now as Specialty resin they only make the modeling resin and nothing else. This is what I've heard from the owner of Specialty resin. They changed their name now that they don't have the heavy plastics division of their company. 



Rondo said:


> Nothing wrong with Alumilite.
> 
> You may find a cheaper price or or variety of rubber/resin that is better for your application but Alumilite's quality is as good as you will get anywhere.


 You got very good results with that despite it being so small! I've been having trouble getting resin to flow into all the tiny recesses, and details in my moulds, but I'm going to a lower viscosity so that I can get more pulls successfully without wasting a lot of resin. Most companies sell 80 cpds viscosity, even Smooth-on. This makes it more difficult for me to get the results I need without going to a single vendor that specializes in resins only. This is why I use Specialy resin - they have more variety of resins than what I've been able to find anywhere else. Otherwise, this would work for most of the projects that I'd cast in resin. 

~ Chris​


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## Mark McGovern (Apr 25, 1999)

Dyonisis said:


> ...One person on the rpf said: "I've used alumicrap - I hate it!" He also said that on Starship modeler. That didn't leave me with a good taste in my mouth at the time since I was unaware of any other vendor that sold resin products!


Therein lies the danger of listening to only one opinion. Alumilite was recommended to me by Ron Gross, who used it in building his 1/48 scale _Jupiter II_ that became the basis for the Polar Lights kit. Alumilite's products have performed just fine for me, and I am by no means an expert resin caster. I've heard good things about Smooth-On's products as well, but have had no reason to switch manufacturers yet.




Dyonisis said:


> ...I've been having trouble getting resin to flow into all the tiny recesses, and details in my moulds...


Alumilite's viscosity is darn close to water and warming Part A before mixing makes it even runnier.




djnick66 said:


> ...Build up the walls, line it with some clear plastic packing tape and you are good to go.


Thanks for the tip, deej! I've been pushing modeling clay against the outside walls of my Legos mold boxes. Effective, but cleaning the clay off the plastic is time consuming.


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## guinnesspeanut (Sep 25, 2009)

I like a lot of what you said. I have no opinion on any products at this point. The pieces I need to recreate will be sides, front, rear, top, wheel well fenders, lights extending out from the body, axles, undercarraige, etc. I'm pretty sure most or all of them can be 2 part molds. I've experimented a bit with wax, just to see if my 2 part molds are air tight. I used a modeling clay that hardens in water. Cutting out the first half so the flash ends up where you want it to is the hardest part. I didn't have mold release, so I tried WD40 and silicone. Worked for the most part. As far as pouring goes, to eliminate bubbles, wouldn't it be better to have the mold open so you can pour directly on to the surfaces of both halves? Then close it up and fill? If you look carefully at older model kits, you see a lot more relief holes for the parts on the sprues. Years ago, I bought a cheap vac pump for bleeding brakes. Couldn't a clear hose be hooked up to it to 'pull' out the bubbles? And, one last question for now.. Let's say you cast a part that has a few bubble defects. Can you put a few drops of resin into the mold, approximately where the bubbles are, then press the defective piece into the drops to repair it? Seems to me, trying to repair a piece with a few leftover drops is better than tossing it.


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## guinnesspeanut (Sep 25, 2009)

Are there any hardeners you can add to it? If I could get it a bit harder than styrene, it might be worth pursuing. I had a few cars made by Auburn rubber.. Some were like rubberband consistency, or balled up rubber cement from elementary school craft class. Others were harder. I've also seen some resin HO slotcar bodies that were pretty flexible. A rubber body might be a good idea for little ones just getting into the hobby.. It'd sure save a lot of time, not having to search for the bumpers that flew off, and then the extra time to glue them back on.. If you've played with any hardeners, or 'tweeked' the 2 part formula so it comes out firmer, please let me know. And thank you.


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## Y3a (Jan 18, 2001)

I used Alumilite to make many many HO scale model buildings. I also use ACE products as I like their molding compounds better than Alumilite. The 2 part casting stuff is GREAT! I use a toothpick to get any bubble out of the stuff before it sets. Sets in 3 minutes, and I used to make 5-6 copies of the subject a day. Usually HO scale houses, coal hoppers n such.


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## djnick66 (May 2, 2008)

Properly mixed resin is NOT flexible. It isnt good for slot car bodies because it is hard and brittle and will shatter easily.


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## guinnesspeanut (Sep 25, 2009)

First, what scale are these? Alot of those details look like you'd need 2 or even 3 part molds. The best way to make the bus is 1 side at a time, for me anyway. I've done wood carving and there's nothing worse than screwing up the piece after you put a few hours into it. This bus is the smallest thing I've ever tried, aside from premade models. Things like axles will be copied from existing models. Why recreate perfection? Still, I can't see casting the rear axle in a 1 piece mold. I'd be wrecking the mold every time I pulled the cast part out. Picture the side of a 50's bus, with the corrugated shiny steel(or aluminum). You look down and see latches to get at the luggage, you look up and see formed steel surrounding the windows. The total thickness for the sides of my bus is about 1/8 inch. If I use an open sided mold for the sides, I'd want about 1/32 inch thicker so I could sand them flat. Every last resin I've looked into says you need some kind of very expensive equipment for best results. I can hook up a brake bleeder vacuum to make sure the resin gets into all the tight spots. When I see resin going into the clear hose, I know it's all the way in..


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## Rondo (Jul 23, 2010)

Using vacuum and pressure are a big expense and add some complication but do make it easier to get perfect castings. From the start of my casting, I have used a cheap nylon bristle craft paint brush for every pour. I use the brush to mix the resin which it does very thoroughly and after pouring the resin into the mold, I will "scrunch" the pour side of the mold to open it up (if necessary) and use the brush to agitate and dislodge any air bubbles. 

At this point, I will then put the mold under pressure to crush any remaining bubbles but if you have designed your mold well, you really shouldn't have much in the way of bubbles even without pressure. The brushes run about 10 cents each which is a trifling amount considering the importance of our work. 

Personally, I almost never use a 2 piece mold. Instead, I would pour something like your bus side standing up on edge in a 1 piece mold. The cavity would look like a trench in the mold. You could pour the part right side up or upside down depending on details which might give an advantage one way or the other. I would build a "sprue" onto the master part, attached by the smallest practical points. You can actually pour the rubber solid around the part/sprue and then carefully cut the mold open to get the master out. Parts poured from this mold will have a very thin film of resin where the knife cuts are. Easy to clean up, along with the small sprue attachment points.

That's just my approach and others get great results with other methods. The thing I like about a 1 piece trench mold are that it won't leak resin out like a 2 piece mold can. You can scrunch the mold open and work the bubbles out with a brush and the resin really can't go anywhere. And unlike an open face mold, you get a part that is almost fully finished on all sides.

Wish I had a better picture of some parts "on the sprue" to show better what I mean but here is an ok shot which may give you an idea. The sprue on most parts was Evergreen plastic. On many flat panels, I glued the backside of the part to very thin styrene sheet, then built the sprue onto the sheet as well. The thin sheet allowed the mold to open up much like a knife cut would, with very little parts cleanup.










Part 2 is probably closest to what I've described. The sprue is at the top (1/4" square Evergreen) with a flat panel of thin stryrene surrounding the actual part. Of course, all of the styrene which was part of the master is now resin.


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## guinnesspeanut (Sep 25, 2009)

Have you or anyone else here ever made an HO slotcar chassis? I'm also looking for XLerator parts, and it just hit me, maybe someone could make them for me.. I'm ready to buy my first batch, as soon as I decide on which product, but I doubt I'm ready to make high heat/stress parts. The original XLerators had a plastic top plate w/plastic gears(except for the one mounted to the arm). I'm sure some or all of the gears were used on other Aurora/Tyco cars.. I have a few old MM chassis, but that's about it. Are you or anyone else interested?


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## Rondo (Jul 23, 2010)

Usually, I like to say that anything that can be injection molded can be cast in resin, as well as some shapes that would be impractical to injection mold.

I don't know how complex your chassis is though so there could be some sticky points. Any small diameter deep hole is tough (like an axle hole perhaps). In that case, I'd probably make the casting with a locating dimple and drill the hole after. Properly mixed, polyurethane resin is pretty tough but probably more brittle than nylon. Pretty sure that gears would not be as durable either. There may be varieties of resin that approach nylon's toughness though.

Post a pic of the chassis if you can.


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## Dyonisis (Nov 11, 2009)

djnick66 said:


> Properly mixed resin is NOT flexible. It isnt good for slot car bodies because it is hard and brittle and will shatter easily.


The stuff I use isn't brittle - it's practically bullet proof! Especially when properly mixed, I've had no breakage from brittleness. I've given parts a toss across the room (on the floor) to test the durability of the product I'm using. It passed - with flying colours! Most of the parts I've made are about 1/8th of an inch in thickness, and less. Even the smaller parts I've made are practically indestructable. I've had to take side-cuts to break some of the parts only to see what resistance they have to abuse! Polyester, and epoxy are very brittle. Especially in thin layers you need to use caution to keep them from getting damaged. I don't have that problem with polyurethane resin - what most people simply refer to as resin. 



Mark McGovern said:


> Alumilite's viscosity is darn close to water and warming Part A before mixing makes it even runnier.


Interesting. I did think of that at first, but of course what I'm using is thicker viscosity than what I need. I was afraid of doing this for fear that it would only make it thicker! Soups, and certain consumes' have the tendency to become thicker when heated, and left to cool. I thought that heating it would only make matters worse! It turns out that using other chemicals with it only do this.  


guinnesspeanut said:


> I like a lot of what you said. I have no opinion on any products at this point. The pieces I need to recreate will be sides, front, rear, top, wheel well fenders, lights extending out from the body, axles, undercarraige, etc. I'm pretty sure most or all of them can be 2 part molds. I've experimented a bit with wax, just to see if my 2 part molds are air tight. I used a modeling clay that hardens in water. Cutting out the first half so the flash ends up where you want it to is the hardest part. I didn't have mold release, so I tried WD40 and silicone. Worked for the most part. As far as pouring goes, to eliminate bubbles, wouldn't it be better to have the mold open so you can pour directly on to the surfaces of both halves? Then close it up and fill? If you look carefully at older model kits, you see a lot more relief holes for the parts on the sprues. Years ago, I bought a cheap vac pump for bleeding brakes. Couldn't a clear hose be hooked up to it to 'pull' out the bubbles? And, one last question for now.. Let's say you cast a part that has a few bubble defects. Can you put a few drops of resin into the mold, approximately where the bubbles are, then press the defective piece into the drops to repair it? Seems to me, trying to repair a piece with a few leftover drops is better than tossing it.


 I replied to your email. I'll try to answer some of the other questions you've posted here.

You need air to esape. Cutting holes in the rubber once cured with allow for this. You need a pour spout, and some vent tube for this reason. I glue vent tubes, and pour spouts onto my master in places that make it easy for me to remove the stub with a pair of side cuts. These are what some people mistakenly call "wire cutters". These have a blade on the side of each bars' head that allow it to cut. I use these to remove the stubs. Then with 220 grit sandpaper, I remove the rest, then sand with 600 grit wet-or-dry sandpaper to smooth the surface to resemble the surface texture it once had. This makes it easier to paint as well without leaving sanding marks. 

You need to make a five piece mould. One for the top of the bus. One for each end (front and back). And two for the inside of the bus's interior. Use Scotch brand, or similar tape to mask the windows to keep it from embedding your bus body. Each one of these moulds can be created with the help of clay. This makes a barrier to keep the rubber from going into other places that you don't want it to. A mould box sealed with a clear coat will help tremendously. What this does is allow for a form to keep the silicone in place allowing you to make a perfect copy of your part. When you're done with the first part of the mould, you can remove clay as you need to. Use silicone release agent over the first mould part to keep them from sticking, unless you want to make a more complete mould. This will be a little harder, or more difficult to remove the part, but it will eliminate mould, or parting lines from the mould. I'd personally only join the top with either the front, or the back of the bus to the top mould. This will have joint lines in the resin, but the tighter you make your lines with clay, the less apparant your parting lines will be on the cast part. You can always sand those away with 600 grit wet-or-dry sandpaper. I glue my sandpaper to popcicle sticks to ensure a flat, and smooth area. 

With each successive rubber mould part that you create, you remove more clay until you only have one more rubber mould piece to make. There are videos on youtube to show how to make a rubber two piece mould. These will make it easier to understand what I'm saying here. This way you can get an idea of what it means to remove each piece of clay to fill the void with silicone. You'll only need to spray the silicone itself to keep it from sticking together. If you have more questions, just ask. I'm here to help and so is everyone else here. :thumbsup:

~ Chris​


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