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I ain't spending $130 on no vibrator that doesn't have his 'n her ends wait, wut? Quoted:
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Some bubbles get trapped, but there is little choice. Would gentle agitation -- say taping the mold to a brass tumbler, or maybe an "electric toothbrush" -- get bubbles out or just make a bigger mess? Go through your wife's underwear drawer looking for a (wink, wink) massager. Yes it works, though not as good as a vacuum, something like this is what I use. http://www.amazon.com/DENTALNY-Denture-Vibrator-Medium/dp/B00CB1ZV4Q/ref=sr_1_1?ie=UTF8&qid=1435088078&sr=8-1&keywords=dental+vibration+table&pebp=1435088104582&perid=1F0V9QDHPVB67YFSWSF6 I ain't spending $130 on no vibrator that doesn't have his 'n her ends wait, wut? I bet 90% of those get bought for "alternate" purposes, like this Sawzall Adapter |
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How much shrinkage does the Moldstar 30 give you? I'll have to defer to your expertise in plastic casting, I do mostly metals. I bet the low temp metal you are using now is too malleable and will shoot loose pretty quickly. For the guys asking about vacuums. For larger stuff like this you need an air tight chamber to hold the piece/liquid, and a pump that will pull 25-30 inch Hg. http://www.amazon.com/Gallon-Aluminum-Shatter-Vac-Kit/dp/B00JTNTPA0/ref=sr_1_3?s=industrial&ie=UTF8&qid=1435088668&sr=1-3&keywords=vacuum+pump&pebp=1435088682215&perid=040Y6C9AKACE31FCVS8D Quoted:
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Awesome. From a guy who does a lot of casting and mould making. A vacuum will up the quality of the build. Sorry I was away from the computer for a couple of days. De-gassing RTV with a vacuum makes the mould stronger and removes any bubbles that will cause surface defects on the casting. Also the 2 part plastic should be de-gassed to make it stronger, especially when reinforcements are added. The vacuum can be modified to aid in the casting as well to draw the compound into the mould for a more consistent fill. This is true with all school and most RTVs now, but I used MoldStar 30, which does not require degassing. I've been using this stuph for a long time, it's the best thing that happened to castable rubbers. Again, no degassing for it. For plastics, smoothcast 300 has really short pot life, like a minute or two. There is no time to degass it and it has viscosity of water. Some bubbles get trapped, but there is little choice. Plastics with longer pot life are probably better candidates. How much shrinkage does the Moldstar 30 give you? I'll have to defer to your expertise in plastic casting, I do mostly metals. I bet the low temp metal you are using now is too malleable and will shoot loose pretty quickly. For the guys asking about vacuums. For larger stuff like this you need an air tight chamber to hold the piece/liquid, and a pump that will pull 25-30 inch Hg. http://www.amazon.com/Gallon-Aluminum-Shatter-Vac-Kit/dp/B00JTNTPA0/ref=sr_1_3?s=industrial&ie=UTF8&qid=1435088668&sr=1-3&keywords=vacuum+pump&pebp=1435088682215&perid=040Y6C9AKACE31FCVS8D That looks a lot like a pressurized paint pot. |
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I don't know what a paint pot is but the bucket vacuums are used for stuff like the OP is doing and removing bubbles from plaster type investments. I suppose if you wanted to remove air from paint it would work well. No, I just meant in general form and appearance. 
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How much shrinkage does the Moldstar 30 give you? I'll have to defer to your expertise in plastic casting, I do mostly metals. I bet the low temp metal you are using now is too malleable and will shoot loose pretty quickly. I don't have a quantitative answer. I believe that MoldStar doesn't shrink at all. Plastic has a small shrink, so it fits tight over the buffer etc. but it's flexible. 281 actually expands when cooled so I just tried to screw in buffer tube and it feels like a little loose, but threads age good and it's holding it fine. |
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I am really, really interested in trying this with Aluminum and lost wax. Given that plastic seems to hold up ok with some reinforcement, would any kind of aluminum work? Or do I need to buy a specific alloy? I'm not sure, durability will depend on alloy, casting procedure and the whole "durability" is kind of hard to quantify. I don't know how much it's better than material X or material Y. In terms of casting, sprue, risers etc design could have a lot to do with the toughness of the finished product as would the whole procedure of casting (i.e. keeping porosity down etc) It can get pretty complicated. For Ali alloy, there are many. You should avoid virgin aluminum (extruded or pop cans) because it shrinks a lot and it's softer. I usually have a pile of scrap from Ali engine block parts to Ali wheels (not magnesium) I'll just pour some and see what happens, f-it. I'm mainly curious about shrinkage, because Ali shrinks as does wax, so I'm not sure what I get. We'll find out soon enough. I was also thinking about casting some in Zink. It's cheap and available. |
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Quoted: I'm not sure, durability will depend on alloy, casting procedure and the whole "durability" is kind of hard to quantify. I don't know how much it's better than material X or material Y. In terms of casting, sprue, risers etc design could have a lot to do with the toughness of the finished product as would the whole procedure of casting (i.e. keeping porosity down etc) It can get pretty complicated. For Ali alloy, there are many. You should avoid virgin aluminum (extruded or pop cans) because it shrinks a lot and it's softer. I usually have a pile of scrap from Ali engine block parts to Ali wheels (not magnesium) I'll just pour some and see what happens, f-it. I'm mainly curious about shrinkage, because Ali shrinks as does wax, so I'm not sure what I get. We'll find out soon enough. I was also thinking about casting some in Zink. It's cheap and available. Quoted: Quoted: I am really, really interested in trying this with Aluminum and lost wax. Given that plastic seems to hold up ok with some reinforcement, would any kind of aluminum work? Or do I need to buy a specific alloy? I'm not sure, durability will depend on alloy, casting procedure and the whole "durability" is kind of hard to quantify. I don't know how much it's better than material X or material Y. In terms of casting, sprue, risers etc design could have a lot to do with the toughness of the finished product as would the whole procedure of casting (i.e. keeping porosity down etc) It can get pretty complicated. For Ali alloy, there are many. You should avoid virgin aluminum (extruded or pop cans) because it shrinks a lot and it's softer. I usually have a pile of scrap from Ali engine block parts to Ali wheels (not magnesium) I'll just pour some and see what happens, f-it. I'm mainly curious about shrinkage, because Ali shrinks as does wax, so I'm not sure what I get. We'll find out soon enough. I was also thinking about casting some in Zink. It's cheap and available. |
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I hadn't thought about shrinkage. If nothing else, aluminum bar stock in appropriate alloys is readily available from places like onlinemetals.com. but they are crazy overpriced. I get some things from there from time to time, not aluminum. There are cheaper alternatives if you look. Old pistons are the shit. Any scrap yard would sell you plenty at rock bottom price or local dump is good place. You don't need much either. Just look at things that were cast, not extruded. Also, if desperate, go to yard sale or thrift store. |
| Boris, could you show us some pictures of the bottom of the crucible, as well as the inside, particularly the height of the magazine well sprue? I've the basic dimensions, but the bottom and inside is still a bit of a puzzle. Swinging by the Lego store this afternoon to get more bricks. |
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try potting in a way that fills the mold from the bottom, this will force the voids out as you fill it. no need to raid mom's panty drawer for a battery powered agitator or a vac chamber/pump.
Modify the mold and add a funne(1.5" metal line?)l to the side that fills a void at the bottom of the mold and as you pour it in it will fill the mold from the bottom up, this will really minimize trapped air. you'll waste a little more material because of the excess in the fill side but like you said, its re-workable. i make my own molds at work and deal with a lot of different issues, i like what you're doing, the other option is to put some sacrificial cavities around the thin spots so you can get even more voids out. sorry for the ninja edit: like the sample in the middle: 
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I had been contemplating doing something like this for some time. I also want to do FCG parts for a cutaway display model. You can cast the receiver in optically clear plastic, so no need for cut-away. The problem is that most optically clear plastics are weaker than opaque versions, but this is easy peasy. You can also cast the upper in clear plastic as well, if you want to show how things inside operate. |
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Boris, could you show us some pictures of the bottom of the crucible, as well as the inside, particularly the height of the magazine well sprue? I've the basic dimensions, but the bottom and inside is still a bit of a puzzle. Swinging by the Lego store this afternoon to get more bricks. Ok, sorry for delay, here it is. Basically it's just a box around the receiver. You need around 1/4" from all receiver surfaces, but you can make this box as tight as you want. Also, you need to suspend the receiver 1/4" from the bottom. You can do it with thing fishing line from top or like I did, 4 pins from the bottom, but it's hard to balance it on pins. The point is, you want rubber all around the receiver. The smaller the box, the less rubber you need. So it's up to you to make it as efficient as possible. The wall on my box is double (regular 2x4 bricks) 
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This is probably the best thread on arfcom currently. Can't wait to see you pop out a fully functioning alloy receiver with this! Like this? 
This is Aluminum, but you can cast it in low melt alloy too. Material is just a function of longevity. You will never make an eternal receiver, so you just pick something. Plastics are good for hundreds of rounds without any reinforcement whatsoever. It's the cheapest and easiest way by far. |
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Quoted: Like this? http://s3.postimg.org/hxooooa9f/IMG_0645.jpg This is Aluminum, but you can cast it in low melt alloy too. Material is just a function of longevity. You will never make an eternal receiver, so you just pick something. Plastics are good for hundreds of rounds without any reinforcement whatsoever. It's the cheapest and easiest way by far. Quoted: Quoted: This is probably the best thread on arfcom currently. Can't wait to see you pop out a fully functioning alloy receiver with this! Like this? http://s3.postimg.org/hxooooa9f/IMG_0645.jpg This is Aluminum, but you can cast it in low melt alloy too. Material is just a function of longevity. You will never make an eternal receiver, so you just pick something. Plastics are good for hundreds of rounds without any reinforcement whatsoever. It's the cheapest and easiest way by far.  Eta: I'll be in my bunk. |
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Like this? http://s3.postimg.org/hxooooa9f/IMG_0645.jpg This is Aluminum, but you can cast it in low melt alloy too. Material is just a function of longevity. You will never make an eternal receiver, so you just pick something. Plastics are good for hundreds of rounds without any reinforcement whatsoever. It's the cheapest and easiest way by far. Quoted:
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This is probably the best thread on arfcom currently. Can't wait to see you pop out a fully functioning alloy receiver with this! Like this? http://s3.postimg.org/hxooooa9f/IMG_0645.jpg This is Aluminum, but you can cast it in low melt alloy too. Material is just a function of longevity. You will never make an eternal receiver, so you just pick something. Plastics are good for hundreds of rounds without any reinforcement whatsoever. It's the cheapest and easiest way by far. 
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So how exactly would you cast in a reinforcement piece. I've been trying to wrap my brain around that for a while now, and I just cant seem to figure it out. I also wonder if making the mold so that it fills up from the bottom first, and has burp vents, might help eliminate more air bubbles to make it a bit stronger. |
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Quoted: Take 10-24 threaded rod, cut to length, place in vacant space in mold. Pour in casting material, when it hardens, it now has a steel 10-24 threaded rod running through it. LOL I should have clarified, how would you put a trigger pin/buffer tube re-enforcement plate/piece and be able to mold it in all at the same time. |
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LOL I should have clarified, how would you put a trigger pin/buffer tube re-enforcement plate/piece and be able to mold it in all at the same time. Quoted:
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Take 10-24 threaded rod, cut to length, place in vacant space in mold. Pour in casting material, when it hardens, it now has a steel 10-24 threaded rod running through it. LOL I should have clarified, how would you put a trigger pin/buffer tube re-enforcement plate/piece and be able to mold it in all at the same time. reinforcement are put when you are casting, not when moulding. You just put whatever you want to put into the empty space of the mold, pour in liquid plastic. So any reinforcement becomes embedded inside, it's like rebar in concrete. It's all negative. In the mold, the spaces are represented by rubber. So the "future" holes are actually rubber pegs. You just hang wire or any structure. |
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LOL I should have clarified, how would you put a trigger pin/buffer tube re-enforcement plate/piece and be able to mold it in all at the same time. Quoted:
Quoted: Take 10-24 threaded rod, cut to length, place in vacant space in mold. Pour in casting material, when it hardens, it now has a steel 10-24 threaded rod running through it. LOL I should have clarified, how would you put a trigger pin/buffer tube re-enforcement plate/piece and be able to mold it in all at the same time. The buffer tube is interesting. Someone is proposing to use a carbine or entry tube, and a rifle buffer, thus moving the threads back several inches. Another proposal is simply to use a threaded aluminum tube, and screw an end cap on it, a la M231, and just cast the aluminum tube in place. Ergo, no threads whatsoever. If we can cast something like the Cav Arms lower, we'd be golden. War Fairy's Charon can be printed in multiple pieces, so could be cast in multiple pieces, and glued together. |
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Quoted: reinforcement are put when you are casting, not when moulding. You just put whatever you want to put into the empty space of the mold, pour in liquid plastic. So any reinforcement becomes embedded inside, it's like rebar in concrete. It's all negative. In the mold, the spaces are represented by rubber. So the "future" holes are actually rubber pegs. You just hang wire or any structure. Quoted: Quoted: Quoted: Take 10-24 threaded rod, cut to length, place in vacant space in mold. Pour in casting material, when it hardens, it now has a steel 10-24 threaded rod running through it. LOL I should have clarified, how would you put a trigger pin/buffer tube re-enforcement plate/piece and be able to mold it in all at the same time. reinforcement are put when you are casting, not when moulding. You just put whatever you want to put into the empty space of the mold, pour in liquid plastic. So any reinforcement becomes embedded inside, it's like rebar in concrete. It's all negative. In the mold, the spaces are represented by rubber. So the "future" holes are actually rubber pegs. You just hang wire or any structure. Ah ok so it's basically drop in and pour, I think I can visualize that now. Thanks |
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The buffer tube is interesting. Someone is proposing to use a carbine or entry tube, and a rifle buffer, thus moving the threads back several inches. Another proposal is simply to use a threaded aluminum tube, and screw an end cap on it, a la M231, and just cast the aluminum tube in place. Ergo, no threads whatsoever. If we can cast something like the Cav Arms lower, we'd be golden. War Fairy's Charon can be printed in multiple pieces, so could be cast in multiple pieces, and glued together. Quoted:
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Quoted: Take 10-24 threaded rod, cut to length, place in vacant space in mold. Pour in casting material, when it hardens, it now has a steel 10-24 threaded rod running through it. LOL I should have clarified, how would you put a trigger pin/buffer tube re-enforcement plate/piece and be able to mold it in all at the same time. The buffer tube is interesting. Someone is proposing to use a carbine or entry tube, and a rifle buffer, thus moving the threads back several inches. Another proposal is simply to use a threaded aluminum tube, and screw an end cap on it, a la M231, and just cast the aluminum tube in place. Ergo, no threads whatsoever. If we can cast something like the Cav Arms lower, we'd be golden. War Fairy's Charon can be printed in multiple pieces, so could be cast in multiple pieces, and glued together. Boris mentioned in the OP to use clay to "smooth" things over, as well as building more mass to create a bigger pocket in your mold. With that concept, you could make any potentially weak points 2x-4x thicker than the original aluminum. Take a look a at cheap 80Polymer lower for example. Only you have the option to build it up as you see fit. Like around the receiver extension tower. Hell, leave the receiver extension attached, built it up with clay all around it. Mold an aluminum tub into your casting with the stock as part of your casting too. Mold an upper receiver with a 22 liner as the barrel insert. Cheap project for the kid's 22lr AR. |
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For the guys asking about vacuums. For larger stuff like this you need an air tight chamber to hold the piece/liquid, and a pump that will pull 25-30 inch Hg. If you could live with less vacuum, a gasoline engine typically pulls around 18-22 inches of manifold vacuum at idle. The only other thing you'd need to use your car, truck, SUV, etc. for this purpose would be a few feet of vacuum hose. |
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If you could live with less vacuum, a gasoline engine typically pulls around 18-22 inches of manifold vacuum at idle. The only other thing you'd need to use your car, truck, SUV, etc. for this purpose would be a few feet of vacuum hose. Quoted:
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For the guys asking about vacuums. For larger stuff like this you need an air tight chamber to hold the piece/liquid, and a pump that will pull 25-30 inch Hg. If you could live with less vacuum, a gasoline engine typically pulls around 18-22 inches of manifold vacuum at idle. The only other thing you'd need to use your car, truck, SUV, etc. for this purpose would be a few feet of vacuum hose. Unfortunately, pulling out air usually starts around 25 inches. Casting with a vacuum shouldn't require as much pull. |
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Impressive.
Boris, I have one question. Seeing as you close a very thin plastic to minimize bubbles and since the remaining bubbles tend to rise in the liquid plastic, do you think making the mold and casting the receiver upside down would improve the relative strength of the receiver? |
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Quoted: Impressive. Boris, I have one question. Seeing as you close a very thin plastic to minimize bubbles and since the remaining bubbles tend to rise in the liquid plastic, do you think making the mold and casting the receiver upside down would improve the relative strength of the receiver? or possibly designing the mold so it fills from the bottom to the top when you pour the resin in. I.E. having a funnel next to the molded item with burp holes for the air to escape the mold. ETA: How'd that Roto281 lower fare? |
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