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hi all, this is my first casting project, so any feedback is appreciated! i'm interested in casting a beer bottle shape for a game called polish horseshoes*. a quick search online shows that a typical (US) 330 mL bottle is about 225 mm tall, 58 mm diameter at the base, and weighs around 237 g. while i'm not too particular about the precise shape or reproduction of details, i would like to get the weight fairly close. still working out the details, but after a bit of reading i think this is a good way to proceed: - make a solid silicon mould around an empty bottle, probably with a dowel to plug the mouth. cut the mould down the middle to allow removal of the bottle.
- put the mould back together (i assume these will need to be housed in a wooden form). the hole from where the dowel stuck out will allow for filling.
- weigh out proper mixture of polyurethane resin (say, 100 g total) with aluminum trihydroxide filler (the rest, 137 g), and possibly some coloring. pour this mixture into the mould and continuously roll it around.
i have a few concerns though, before i take the plunge and buy materials: - is polyurethane resin going to be strong enough? since all the materials will drive the cost to around £5 per bottle, it'd be a shame if they just shatter on the first hit. the mixture will be less dense than glass, and therefore the bottle will have thicker walls, so my intuition tells me it might be alright. however, i havent worked with this stuff much, so my intuition may just stink in this case.
- is silicon the best way to go with this? it seems that one of the big advantages to silicon is very good feature reproduction. since there are no real features to reproduce, this isnt a big issue for me. i'd probably need 2 kg to have enough for a bottle (assuming i need 20 mm or so at the thinnest parts of the mould).
- the whole rolling bit might be a pain. i'd have to make a rig for it (or else turn it myself for an hour!) and then i'd be worried that the neck would be very thin or nonexistent. one idea is to plug the top and then i can roll + tilt to cover all sides a bit more evenly. the other option would be to fabricate a core, but then that has to be very precise if i want to hit the weight tolerance. that would also require gluing two halves together, which maybe isnt so bad.
anyway, hoping to get started on this very soon, but thought i'd throw it out for any suggestions from veterans before i take the plunge. thanks in advance for your help! -p *the goal of the game is to knock an empty beer bottle off of a pole with a frisbee. i had a place in boston that was already littered with broken glass, but now that i've moved i need to find something a little more park friendly (ie, doesnt occasionally explode into hundreds of tiny sharp fragments). there's not a ton of info about this game that i've found online, so i can post more elaborate rules for any who are curious!
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Hi looks like a cool project you have there. You could indeed work with a silicone mould just like you said. there are FOUR ways I would do that1.Siliconethere are 2 ways to work with silicone: - You pour silicone all around the part like you said - You build up some thickness by brushing the silicone on your part. you could make a fixture attached into the bottle neck so that your bottle is floating and you can get everything brushed in silicone. Once you have build op lets say 1cm you put your "silconed bottle" into a box and pour some 2K polyurethane (like isolation foam)around the silicone bottle. this will give the silicone some stiffnes instead of being flexible when the bottle is removed. Once the PU hardened you cut the Foam into 2mouldparts and remove silicone from the PU. You then cut a fine line through te silicone over the lenght of the bottle and remove the bottle. when you put back the silicone into the two halves of PU foam you have a strong mould with silicone on the inside. why that much effort? you use less silicone (quit expensive) silicone is selfreleasing so you don't need to apply any releasagent. 2. Fiberglass 2-part mouldAnother way to do your project is making a 2part mould with fiberglas. if you want to make the bottle just put the mould together pour resin in it and turn it around. Once cured remove the fiberglas mouldpart and you have your part you willl have to use mouldrelease here. 3. Silicone brushed mould with fiberglass shell.Its a combination of the 2 ways above. -Brush Silicone (let it cure) -Apply fiberglass shell around silicone instead of using PU foam(2-part mould) 4. Using hard mould to make 2 halves and glue them together.
Here's a 2part video tutorial I made on how to make an open Silicone mould and casting parts with fast cast PUThe advantage here it only takes 10min to harden so it's possible to rotate the mould yourself |
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you could cast the bottle in epoxy and tint it and fill the inside with expanding foam. that could keep all the parts in one place.??? i think you need to make a few bottles and see what can stand up to the abuse. smooth on has stage props and materials that might be of help. to break a bottle i think it has to either have brute force applied or a lesser force and lots of vibration. the foam would add slight weight and stop the vibration and the foam will resist the brute force breaking it. i must say... i shot a beer bottle with a shotgun.... muzzle about 3 inches from the bottle......... all it did was leave scuff marks on the glass. i also have seen bottles break easier when no cap was in place on the bottle. must have something to so with the vibration/osciollation to the point of breakage. how to make a bottle
CarbonFiberCreations
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the link shows how to make a bottle for a stage prop to break, you just substitute a different resin for your bottle that is stronger.
CarbonFiberCreations
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Thats cool how they solved the problem of a core trapped inside the resin by leaving the bottom open... Makes me think of something I did before... Here is a link to my website with something similar they did (It is in dutch but you should be able to understand by just looking at the pictures  ) |
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Hi,
You will need a release agent between glass and some silicone products. Remember that glass and silicone are almost the same thing, as they are both derived from Silica (Silicon Dioxide).
Think about how a fish tank is made and you can clearly see how well silicone sticks to glass...
Kev.
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thanks for the excellent advice and links! things got delayed for a bit due to work, but i'm hoping to work on it this week. to start off, i'm going to go with brasco's idea and simply fill a bottle with expanding foam. i found some thats quite light (~0.03 g/cc), so the overall weight wont increase substantially. this is the cheapest and easiest thing to try so i think it makes sense to see if that solves the problem. if not, then i'll step up to more sophisticated methods. brasco, i think you're right about vibration being an issue. i'm suprised a bottle could withstand a shotgun blast, but we usually only break them after many repeated hits. perhaps the material is being weakened by cycling to the point that it can be shattered by a solid frisbee hit. unfortunately, might be a while before i get a decent chance to test it out. gotta wait for the nicer weather to really see how well it works. will keep you posted. -p
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matthieutje65 (26/01/2013)
Thats cool how they solved the problem of a core trapped inside the resin by leaving the bottom open... Makes me think of something I did before... Here is a link to my website with something similar they did (It is in dutch but you should be able to understand by just looking at the pictures ) http://matthieulibeert.webs.com/alessifrietsnijder.htmOne extra remark... they tell you to buy a release agent for glass?! not sure but I dont think Silicone will bond to glass?! Just a thing to make you buy some more stuff I think... nice....i checked out your link. very cool indeed. for some parts of some some languages i can muddle my way thru. Slavic languages not so much LOL
CarbonFiberCreations
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