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piston

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Unread postAuthor: roughboy » Sat Mar 28, 2009 2:36 pm

What other material can a piston be made out off thats strong like a hot glue but lighter then hot glue?
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Unread postAuthor: daberno123 » Sat Mar 28, 2009 2:49 pm

Epoxy?
It's definitely stronger, but I don't know about the weight.
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Unread postAuthor: jackssmirkingrevenge » Sat Mar 28, 2009 2:57 pm

daberno123 wrote:Epoxy? It's definitely stronger, but I don't know about the weight.


A solid epoxy piston would definitely be quite heavy, but as explained in my tutorial there are ways of using light materals such as foam to have a hollow core, retaining strength while reducing weight considerably.
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Unread postAuthor: psycix » Sat Mar 28, 2009 3:56 pm

Wood, pvc (hollow) or even metal.
Though you can't cast those like epoxy or hot glue.
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Unread postAuthor: john bunsenburner » Sat Mar 28, 2009 4:12 pm

Half a deo can, a clean out cap, epoxy, woad, expandable foam, machined teflon, HDPE, metal, self made plastics.

To summerize; there are many different things you could make your piston out of, be creative, use what you have around.
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Unread postAuthor: ralphd » Sat Mar 28, 2009 4:21 pm

The best thing that I found to use was furniture grade plywood. I don't have a lot of tools so I used a hole saw, slightly bigger than the guide tube, and cut several "plugs". I glued them together and put a section of all thread through it then used a drill press from work to sand it to the exact diameter I needed. I then cut the excessive length of allthread which was in the chuck of the drill press. It was amazingly light, 4.4 ounces. Just remember, I'm a newbe in pneumatics, my launcher failed to fire. I need a larger pilot valve, mine was 1/4 inch and I need at least 3/4 or 1 inch.
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Unread postAuthor: chrissilvermancs » Sat Mar 28, 2009 5:17 pm

well it depends on the size of the tee but for a 3inch tee u can use half a blue propane can be careful not to spark it even though it is empty when cutting
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Unread postAuthor: Biopyro » Sun Mar 29, 2009 4:28 am

john bunsenburner wrote:expandable foam,


Surely because this has bubbles of air inside it, when under pressure it would sink. You would have to encase it in something strong to stop the pressure crushing it or making it fit badly by shrinking?

Polymorph mouldable plastic works well for metal cannons, but is harder fro PVC because it sticks to it badly when you cast it.
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Unread postAuthor: ALIHISGREAT » Sun Mar 29, 2009 4:55 am

Biopyro wrote:
john bunsenburner wrote:expandable foam,


Surely because this has bubbles of air inside it, when under pressure it would sink. You would have to encase it in something strong to stop the pressure crushing it or making it fit badly by shrinking?

Polymorph mouldable plastic works well for metal cannons, but is harder fro PVC because it sticks to it badly when you cast it.


vaseline!




or anything really will stop it from sticking.
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Unread postAuthor: john bunsenburner » Sun Mar 29, 2009 5:11 am

The problem with gease, vasiline or any other "hard" lubricants is that it may affect the shape of the end product, for example if you have a 1mm layer of vasiline whate you are casting then your piston will have a very bad fit, so it is important that you spread a thin and equal layer of it. Personally i like using WD-40 or other oils as lubricants for my molds.

Expandable foam should really only be used if you want to fill up a hollow piston, for what ever reason, or for very low pressures(i doubt it will shrink much at pressures under 50psi). If you do want to us efoam dissolve styrofoam(the stuff used for packaging) in aceton(paint thinner), once you have a liquid with the consistancy of pancake dough(yes there is something else the consistncy, and color, can be compared with...) pour it into a mold, the aceton will evaporate and leave you with a niece piece of plastic, this should be good for pressures under 150-200psi, and is very cheep.
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Unread postAuthor: Sparkie » Wed Apr 22, 2009 4:01 am

john bunsenburner wrote:
If you do want to us efoam dissolve styrofoam(the stuff used for packaging) in aceton(paint thinner), once you have a liquid with the consistancy of pancake dough(yes there is something else the consistncy, and color, can be compared with...) pour it into a mold, the aceton will evaporate and leave you with a niece piece of plastic, this should be good for pressures under 150-200psi, and is very cheep.


Thanks for the explanation. I have looked at the other thread about using this as a piston but somehow it didn't explain how solid it can get.
I have created a copper monstrosity but I cannot work out a good piston.
I started with hardwood but it is just not fat enough to work 100% of the time.
I might try this as a short term solution so I can fire the damn thing.
Sorry for the hijack.
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