# Need help on Mold making and casting please



## KCmike2013 (Jul 19, 2013)

Hello all!

I am trying to make a mold and resin casting of a 3D printed part i made and i am having trouble casting it in resin. I made a mold with the high strength kit from alumilite and then tried casting a part in resin with it using a syringe to inject the resin into the mold.

I will attach a picture of the part I'm trying to cast and of the part results i am getting. I am brand new to making molds and casting and figured you more experienced guys can give me some advice on what i should be doing haha.

any help is appreciated, thank you


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## David Leech (Dec 9, 2008)

Not an easy part to cast!
I'm not sure where the parting line is on your mold - Is it in two parts?
I would try making a 2 piece mold, such that you fill as an 'open' mold from the back, and when full of resin place the back of the mold in place, displacing any unwanted resin.
Some kind of jig, or mold keys will make sure that everything lines up correctly.
A little messy with excess resin oozing out, but that way you can see that the resin has filled the mold.
If you want to do it the way that you are, I would put a lot more vents in place to let ALL the air out as I would think that is what is causing the voids.
Keep trying different things and you will find an answer.
Cheers,
David Leech, Delta, Canada


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## Burl (Jan 2, 2008)

Here's how I designed mine:












Obviously, it requires some cleanup to get rid of the flash & vents, but it will pour with gravity only. I do put them in a pressure pot to cure.


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## Ironton (Jan 2, 2008)

I looks to me like the mold is not filling fully. You will notice that in Burl's mold there are small vent holes to allow the air to escape. these have to be located at the ends of any blind part of the mold (Burl's appear to be at the highest points.


Then you might try vibrating the mold to let any air bubbles escape (Burl uses a pressure pot for this, an alternative). Only thoughts I have.


Hope this helps.


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## KCmike2013 (Jul 19, 2013)

Thanks for the response everyone,

David leech it is a 1 piece mold that i cut open part way so i could remove the part. Its apparent from everyone's advice that i don't have enough vent holes. Burl has a really good idea by printing the part with vent holes already attached. I think i will have to try that. I think one of my problems as well is that i am trying to go for high detail with lots of intricate crevices.

I have the CAD drawing skills down pretty decent, i just now have to get better at casting parts haha.


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## Burl (Jan 2, 2008)

Intricate details should not be a problem. RTV will pick up a fingerprint, if you're not careful. Venting & sprues are a whole other topic. I've been casting for 10-15 years, and developing a mold like yours took me several tries. That's why all the tutorials for beginners start with simple one-part molds.


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## rkapuaala (Jan 3, 2008)

Hi, A syringe is not the way to go. You would be better off just pouring it straight from the mixing pot into the mold.
I have a few videos for pouring on my Youtube page. rkapuaala
They were made for my brother but should explain pouring well enough for you. If you have anyother questions message me. It takes a while and there are a million ways to do it. You have to find a routine that works well for you. My videos show what works best for me.


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## GaryR (Feb 6, 2010)

truck05 by Gary Reese, on Flickr


This was made with open back mold. As said a second mold part could be for the back after the mold cavity is filled.


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## FHPB (Feb 25, 2011)

I'll throw in another two cents about vents. Before you chuck that mold, try cutting it apart -- use an Xacto blade and make the cuts as irregular as you can, so the halves will lock together positively when you put them back together. Then with the tip of the Xacto knife, cut some thin grooves from the dead ends to the outside of the mold. I've also seen people stick 1/32 inch brass tubing into the mold like a hypo needle. That stuff is very hard to come by today, but it gives you an idea how little relief it takes to let the resin force the air out.

Are you reinforcing the casting with wire or something? I don't imagine a thin cross section of resin will take much weight.


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## Burl (Jan 2, 2008)

Vance: I initially thought the same thing about the resin not being able to take the weight. If all you want is the face detail, it could be an issue. Many times we make compromises in models (like thickness) because of un-prototypical requirements. However, after I started trying to model the inside of the truck frames, with prototypical widths, I found that resin was more than rigid enough to support the car’s weight. If you think about it, the engineers who designed the trucks already worked through many of the issues we face.

I personally have always shied away from putting reinforcement in castings because the expansion rates differ in different materials. My general approach is to glue like materials together (unless it’s a high-stress joint), and to attach unlike materials with mechanical fasteners (trying to account for movement due to expansion). This is just my personal preference though.


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