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This Instructable will teach you how to cast an aluminum slingshot capable of great power and suprising accuracy. The actual casting method used is "lost foam casting", in which foam is carved into the final design and buried in sand. Metal is poured into the foam, vaporising it and filling the mold cavity to make the final object. The basic slingshot design is Joerg Sprave's Rambone slingshot, although I did not use any templates in the creation of this slingshot.

I decided to do this one day when I had seen a video on making a lost foam aluminum slingshot. I had tried greensand casting (https://www.instructables.com/id/Cast-an-Aluminum-B...) and lost wax casting (https://www.instructables.com/id/Cast-a-Metal-Ring/), so I decided that I should try this last common method of casting in order to more fully master the subject. I also got hooked on slingshots after seeing Joerg Sprave's videos on YouTube.

Enough talking, let's get slingshotting (yes, that is an actual word)!

Step 1: Acquire Foam

First off, get some foam. I believe polystyrene foam (aka Styrofoam) works best for this, so try to get some. It should be very common - I heard that furniture stores might even give you some for free. I started with some oddly-shaped box inserts made of Styrofoam and began to butcher them with a large kitchen knife (pic 2). Once these were cut into nicer flat sheets (pic 3), I glued them (woodglue) together to make a thicker block (with an extra-thick part for the handle) and compressed (using iron railroad spikes) them to get rid of any space in between the seams (pics 4 and 5). Basically, you need a block of Styrofoam; you may already have yours in the right shape.

<p>It seems like aluminum can be cast into just about anything. I've seen many different projects where they have used aluminum to create just about anything. In this case you made a sling shot. Did you mold the aluminum into the shape yourself? http://www.sincomachine.com/sincomachine/product.aspx?id=38</p>
<p>cool project dude</p>
<p>This looks a lot like JoergSprave's Ram-bone slingshot, only it's aluminium.</p><p>You could probably double the bands(w/ Theraband Gold, one of the strongest type) w/out breaking the slingshot, and use steel bearings. With those additions, it could probably even destroy solid concrete.</p>
Yeah, I modeled it after his. Thanks for the tip about the bands! I think I must have banded the slingshot wrong, because they broke after a few days of shooting. I will definitely try the TBG! I like the prospect of demolishing concrete!
i did not have a foundry at the time so I couldnt melt aluminum but I was able to melt zinc so I used it. its 1 lb and 14 oz so its heavy but I like it
Wow, that slingshot is absolutely gorgeous! I bet it feels awesome to heft it in your hand! Well done!
thank you
do you watch youtube videos of &quot;joergspreve&quot; and &quot;the art of weapons&quot; ? :D<br>very cool instructable :)<br>
Thank you! And yes, I frequently watch both channels. They do some pretty crazy stuff. :)
I am inspired! I have seen a few crucible/casting type projects online and really want to try it out! Have you ever watched King of Random? he intends to release a video very soon about an aluminum can ...forge? is that the correct term? I dont know... anyway. please consider instructables for your squirrel meat and hides!
<p>I am pleased to have inspired the love of metal casting in you! I do follow the King of Random quite eagerly - he does some really cool stuff! I look forward to seeing his new video. Also, I will certainly make an Instrctable about doing something with squirrels bagged with a slingshot (once the weather warms up!). I imagine there are some tasty squirrel recipes... :)</p>
<p>Styrofoam cups disolved in a little acetone goes to a rubbery ball ,pieces of which can be torn off and pushed into any hole you want plugged like roofing iron. It sets hard as and no more leaks</p>
Wow, thanks for the great information! I will be sure to remember this helpful tip for my next lost foam casting.
<p>Cool instructable ! </p><p>This should people get over their fear of flaming metal. </p>
Thanks! And flaming/molten metal is quite awesome to watch, indeed.
it is primal...like bacon (American smoked bacon), or peeing off a tall structure.... UHOH Santa will be all over me for that one!<br><br>Attention, bacon and flaming metal... Sanity has left the building!<br><br>pick a holiday and enjoy!
<p>PopsicleGhoul</p><p>First, I and 8 generations before me have all resided here in the USA, into colonial america, not the UK.</p><p>Second, the propulsion of a projectile from your catapult defines it as such. A catapult, uses a arbal&egrave;te mechanism like a spear-gun. Yes, a slingshot means exactly that and yes that is what is. It relies on centrifugal force to launch the projectile.</p><p>It may seem a small issue to refer to an object or process by an incorrect term, but it does diminish credibility.</p><p>As with any major or minor technical issue, communicating or accurately describing methods, materials and systems are the key to replication. Whether or not Gran-Paw made you, what he called a slingshot it is in fact a CATAPULT. USA or UK it is the same.</p>
<p>So... I don't mean to start any ongoing exchange here, but I believe that my use of the term &quot;slingshot&quot; is correct. If you Google image search &quot;slingshot,&quot; you will find pictures of the same type device I made. While the term &quot;catapult&quot; is also correct, it is most commonly used in the UK (I verified this on a few forums). A Google image search for &quot;catapult&quot; primarily returns pictures of the medieval siege weapon. Thus, I could have used either term and I would be correct. Additionally, King David used a &quot;sling,&quot; which relies on spinning, rather than a &quot;slingshot/catapult,&quot; which relies on elastic stretching force. I hope this helps with any confusion or misunderstanding.</p>
Btw your casting will be most reliable if you minimize the handle to yoke voids. They could result in a dangerous failure.
<p>Yeah, this was my first lost foam casting. Hopefully my next one will be improved from experience.</p>
My mis-statement<br>This catapult uses a arbal&egrave;te mechanism like a spear-gun. A<br>catapult can use a number of mechanisms/ methods to store energy. Look into punkin chunkin.
<p>Great ible!</p><p>I used a similar process back when I was in art school in the last century. </p><p>We used a sand that had some clay mixed in, so if you squeezed some it would hold its shape when you released it. We also used masking tape to cover the foam, and this made for a smooth surface (with a slight wrinkle from the tape surface). You could also tape a piece of paper onto the foam for larger flat areas. The surfaces that resulted were very smooth with no voids. One last tip, we made the sprue out of foam as well. Two more thoughts: You can get large flat panels of white foam at Home Depot and similar stores in the insulation section and I think you could also use a hot wire cutter on the foam to make it easier to carve.</p><p>BTW Be careful about the fumes from lost foam casting. My teachers told us it contained cyanide, so make sure you are in a well ventilated area.</p>
Thank you! Also, thank you very much for your deeply insightful comments and suggestions. I am excited to try them out on my next lost foam casting project! They should be helpful!
Feel free to ask any questions that you may have about the process. <br><br>We also used another unconventional process borrowed from the automotive industry. It is a variation on traditional lost wax casting. First you then make your piece and sprue out of brown micro-crystalline wax, find a cardboard box that is at least 5 inches bigger than your piece (on each side) and mix up regular construction sand with some liquidy epoxy until it is thoroughly coated and put about 4 inches of the coated sand in the bottom of the box. <br>Coat your wax piece with a paint like substance we called a zircon wash (which did such a great job of holding detail you could see fingerprints in the wax on the final piece) and carefully pack the coated wax in the box with the remaining epoxy sand. After a couple of hours the epoxy is cured and you pop the box in a preheated 300&deg; oven big enough to hold your box and over the next couple of hours the wax melts through the zircon wash into the sand. While the wax is melting out you heat up your metal (I used this process with both aluminum and bronze). When you are ready put one of those ceramic funnels over your sprue and pour the metal into the cavity. The beauty of this technique is that after pouring the metal the epoxy in the sand starts to break down, and by the time the metal is cool the epoxy is so degraded the sand breaks off in big chunks with a few whacks with a hammer. There is very little cleanup on the finished piece, and the quality was as good as plaster investment casting.
<p>When using molten aluminium the slightest bit of moisture can cause extreme explosions so be very careful. when Molten aluminium covers water the water explodes followed by another explosion when the aluminium is in the air and can cause massive damage. I worked in the Aluminium smelting industry for 17 years and we had to be very careful with moisture around it</p>
Ahhh yes... very good point! I believe I mentioned this somewhere in a comment, but I have had a few &quot;exciting&quot; experiences with those explosions. You see, molten aluminum on concrete causes extremely violent and forceful explosions of both liquid and solid metal at ~1200F. While fun to watch (at a distance), this is definitely something to be avoided! Metal casters should always make sure their tools aren't wet and should also put all scooped-off dross on a metal surface to avoid explosions. Thanks for the input!
<p>Thanks</p>
Good info on simple Al casting. BUT <br>The etymology of this mis-used term &quot;slingshot&quot;, can be debated but king David of biblical fame did not have access to any old inner tubes for his catapult. Citing wikipedia as a legitimate source for info is a joke, Google - wikipedia unreliable info. Anyone can pontificate on any wiki subject but verification is not reliable. Are american Indians from India. Wrong is wrong irrespective of tradition or vintage.
<p>Ahh yes - good point. It seems there is a fair bit of confusion on naming Internet-wide. King David in the Bible used a sling, which is spun around the head. The term slingshot is commonly used to refer to what I made in the US. Catapult, I believe, is more common in the UK. However, the word catapult can also refer to the Roman siege weapon thar uses a flinging arm. I hope that helps. :)</p>
This frame is not a &quot;slingshot&quot; which is an entirely mechanism this is a catapult
<p>Au contraire:</p><p><a href="http://en.wikipedia.org/wiki/Slingshot" rel="nofollow">http://en.wikipedia.org/wiki/Slingshot</a></p><p><a href="http://en.wikipedia.org/wiki/Catapult" rel="nofollow">http://en.wikipedia.org/wiki/Catapult</a></p><p></p>
<p>What?</p>
<p>in the US it IS a sling shot, in UK and Europe it is catapult, kinda like foot ball and soccer. But I do agree with you, but most people in the US would not picture this as a catapult, that is reserveved for a Roman catapult or Bucking Ass. </p>
<p>Nice Instructable. Personally I'd do some strength testing, if it fails due to a casting defect it won't be pretty. For the surface you could try and use solder to fill the gaps. </p><p>I'm also planning on making a wooden Slingshot (one day...), I like the design &quot;doberman knives&quot; makes on his YT channel. In one of his older vid's he shows how he makes them.</p>
Thank you! I'll have to check out the video you referenced... I bet stained wood and Theraband gold would look pretty nice. Also, regarding the strength testing, it is a very good idea - even just trying to bend the arms by hand is helpful in making sure that the slingshot is structurally sound.
Look for the older how to off the high end slingshot. It's a laminated piece with hardwood, micarta and felt. The video is in 5parts and from last year(2013)
<p>Thanks for the instructable! The slingshot looks amazing. Wish you shot something that explodes in your video :p</p>
Yeah, totally! I hope to buy some of those little caps for toy guns and take out all the powder to make explosive ammunition. I'll have to post a video to this Instructable when that happens! :)<br><br>I also wonder if the shock of hitting a hard surface would detonate dynamite...
cool instructable! Would you say water displacement in a graduated cylinder would be the easiest way to measure the volume of aluminum you need?
Thank you! The graduated cylinder would work well, although for the sprue to fill with metal and supply the shrinkage, you should have extra aluminum melted. I just filled my crucible full and then poured what fit. The extra molten aluminum in the crucible can be made into ingots for later. Good luck!

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