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Post by burlrice on Jan 28, 2017 18:05:41 GMT -5
I am looking for input/advice on a project I am working on. I am early in the design phase (this is for a large scale boxcar), and my goal is to try to make the body as a single piece. I want the finished casting to look something like this:  I’ve had success with rotational casting in the past. However, this project will have a few undercuts, and some small surface details (rivets) that I am concerned will trap bubbles if I go the roto-cast route. I want the casting to have 5 finished sides. If I pour one side at a time, I think I can tease out any trapped bubbles with a toothpick before the resin kicks.  I realize the mold will have to have a few cuts to get the casting out. I also realize sagging could be a problem with the mold, and I have a few ideas on how to solve that. Here is where I’m getting into uncharted waters: 1) Will there be any problems with delamination? 2) Will shrinkage cause the casting to be out-of-square? Any input from anyone who has done anything similar would be greatly appreciated. |
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Post by Brian on Jan 29, 2017 12:34:32 GMT -5
G scale...am I right? Might be casting a HO scale Silver Streak Caboose platform for one of the rail roaders from the local hobby shop myself. Do you have a master/buck of the car you are wanting to cast or is this a scratch build? If you have a master/buck I would cast this the same way that I cast an automotive car body...one piece....verses trying to get five pieces to fit up and align. With a 2 piece mold, you will have better control of the thickness of the body verses trying to get 5 pieces to have uniform thickness......I know that you have to have some weight in those cars to pull right, but you may end up having the weight where you don't want it....like in the roof or a high point on one of the sides. Here is Bob Hayes Fotki site where he explains how he does the BIG 1/8th scale molds and pours....http://public.fotki.com/molderone/ Bob has helped me A LOT and taught me even more....he has also contributed to the Alumilite site as well......here is a video from from the main Alumilite website youtu.be/fYatp46SNP0 Check out some of the other videos that Alumilite offers...they may be of help to you as well. As far as the 2 questions you asked, if done correctly as per the instructions, you should have no issues...it's when some one skips over a portion of the instruction or doesn't take the time to fully read the instructions and understand them that there becomes issues. |
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Post by burlrice on Jan 30, 2017 7:08:28 GMT -5
Thanks for the links.
I had considered a two part mold, but there are a couple issues I couldn’t think my way out of:
1) This is too big to pressure cast, so I need access to the inside of the mold tease out bubbles on the surface of the casting. I also don’t know if I could get all the resin in the mold before it kicks.
2) So far, every how-to I’ve found on large two part molds are items similar to what you have suggested – automobile bodies. They don’t have under cuts, and the core pops out easily because of the sloping design. I need the inside of my casting to have square corners. I can’t see an easy way to remove a core of RTV of that size.
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Post by mike on Jan 30, 2017 9:12:00 GMT -5
If you are worried about demolding the core ... perhaps make a rigid plug that will fit in the core so you can remove it, then collapse the center core to remove it more easily.
Hope that makes sense.
Mike
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Post by burlrice on Jan 31, 2017 6:02:57 GMT -5
Mike: got any examples you could show me?
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Post by mike on Jan 31, 2017 7:10:02 GMT -5
Not sure. I will look later this morning to see if I can find anything that would be similar. Will also ask our engineer to see if he has worked on anything that would give you the visual.
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