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Chamber and welding questions

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: rp181 » Fri Aug 08, 2008 9:00 am

spudfarm, there's a point where that just becomes extra weight, i dont have anything on hand, i have to buy it.

Ive just started looking into ETC, before i was mainly researching ETG and reliable switching circuits for the multistage coilgun.

EDIT: i just looked at larger steel rods on mcmaster, and the biggest one i can afford is 2in dia. General-Purpose Low-Carbon Steel, would that bored out 1/2in be sufficent for low quantity (couple of grams?) flash powder?

looked at wikipedia:

If ever mixing flash powder, never make more than 5 grams at a time. Even experienced hobbyists should never make more than 50 grams at a given time. Producing more than 5 grams for one device is considered a federal offense in the United States and is punishable by up to 6 years in prison.

the potassium and mag. one looks most resonable to me.

anyone know the answer to the welding question?
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Unread postAuthor: Larda » Fri Aug 08, 2008 10:42 am

Ok, lets see.
Both 1117 and 1215 have high or very high sulfur content so i wouldn't recommend either of then if you are going to weld your chamber.

http://www.metalbarsinc.com/stock.htm
1117
Weldability: Due to high sulfur content, this material is not readily welded. Gas or arc welding can be used, but the joint must be preheated. To achieve equivalent strength in the weld, an alloy filler is recommended.


1215
Weldability: Due to very high sulphur content, welding is not recommended.
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Unread postAuthor: rp181 » Fri Aug 08, 2008 12:00 pm

i could always just tap it, and screw it in.
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Unread postAuthor: Larda » Fri Aug 08, 2008 4:04 pm

Or use another material?
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Unread postAuthor: DYI » Fri Aug 08, 2008 7:09 pm

EDIT: i just looked at larger steel rods on mcmaster, and the biggest one i can afford is 2in dia. General-Purpose Low-Carbon Steel, would that bored out 1/2in be sufficent for low quantity (couple of grams?) flash powder?


Using a 2" diameter bar made of 8620 alloy steel, with a 1/2" hole bored down the middle, you'd have a yield pressure of somewhere in the neighbourhood of 300 kpsi. Using the same thing made of general purpose steel, assuming the minimum yield strength of 54KSI, we get failure at around 160 kpsi.

How long of a bar do you need? Because 36" of 2" diameter 8620 steel bar is less than $90. You might want to use some sort of nickel alloy as an inside sleeve, or risk the bore gradually expanding over time.

8620 has good weldability and machinability as well as a yield strength of 100KSI, and isn't really all that expensive. Seems like a good choice to me.
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Unread postAuthor: rp181 » Fri Aug 08, 2008 10:43 pm

my budget is low, all my money will be burned on capacitors. I was only going to make the chamber 6in long

EDIT: looked at mcmaster, that plus chemicals plus accesories will be too much, ile stick to my original plan of just ETG and coilgun.
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