Time to mkae a new mini

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inonickname
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Thu Jun 04, 2009 4:32 am

Well there's been an influx of well..kind of normal miniature cannons lately. So to show that I am the boss (did you doubt it?) I've decided to make a new mini.

It's a hybrid (which I shall consider my first, seen as the last was well...crap) machine from a solid piece of 35mm, high-carbon, case hardened steel. There is a 10mm hole drilled directly through (chamber).

Then the end 10mm on each side is tapped with a 20-1.5 metric thread (D+T teacher is ordering in a bottoming die for me, yay). So the chamber works out to be 10x20mm.

Mix will be 20x until I find a better way to pressurize the chamber.

All that's left to do is tap the ends with a bottoming die, cut threads in the plugs and make up something to sleeve my 2mm barrel with (anyone for thinwall aluminum holding 3k psi?).

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The stock before being cut, in front of plans

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Omg is this stuff rated? DWV nazi me please.

Note pics were before starting to cut threads.

Btw, ignition will just be a tiny spark gap. If for any reason that would fail (it won't) I'll use steel wool ignition. Fill will be through a 1/8" NPT stainless schrader when I get one.

Any thoughts? - before anyone asks, the burst disk will be forced between the threaded plug and a flat face near the chamber- hence the bottomed threads.
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USGF
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Thu Jun 04, 2009 6:22 am

inonickname wrote: SNIP machine from a solid piece of 35mm, high-carbon, case hardened steel. There is a 10mm hole drilled directly through (chamber). SNIP
Inonickname, exactly what kind of steel is it? We find a length of chrome moly etc and go nuts thinking of all the cool things we can (and do) make with it. I think you are down under, they have a different numbering and naming scheme.... USGF
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inonickname
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Thu Jun 04, 2009 6:30 am

USGF wrote:
inonickname wrote: SNIP machine from a solid piece of 35mm, high-carbon, case hardened steel. There is a 10mm hole drilled directly through (chamber). SNIP
Inonickname, exactly what kind of steel is it? We find a length of chrome moly etc and go nuts thinking of all the cool things we can (and do) make with it. I think you are down under, they have a different numbering and naming scheme.... USGF
Unsure of the exact grade, it's last service was as a car axle, and there's 12.5mm of steel in any direction from the combustion so I'm not concerned.

It will of course be tested thoroughly in my blast chamber.

(the grade is takes 10 minutes to cut through with a drop saw)
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USGF
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Thu Jun 04, 2009 1:45 pm

Car axle is great stuff. Usually somthing like 1040 or 1045. Not a chrome moly. This is heat treatable stuff so if you struggle with tapping, you might consider annealing. I'm sure you noticed but the area close to the chopsaw cut is already annealed.

USGF
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drac
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Thu Jun 04, 2009 4:32 pm

Good luck with getting fuel calculations for that thing right. You'd be better off making a Gen II hybrid. Plenty of searching will help you understand the topic. However, I do like the machined chamber. It's different. And good.
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inonickname
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Thu Jun 04, 2009 6:13 pm

USGF wrote:Car axle is great stuff. Usually somthing like 1040 or 1045. Not a chrome moly. This is heat treatable stuff so if you struggle with tapping, you might consider annealing. I'm sure you noticed but the area close to the chopsaw cut is already annealed.

USGF
It's already case hardened, which is why the outside comes up to a polish without even buffing. The area near the cut was blue (burnt iron).

The fuel will be easy, for 20x mapp I'm basically filling the whole chamber.
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Thu Jun 04, 2009 6:14 pm

drac wrote:Good luck with getting fuel calculations for that thing right. You'd be better off making a Gen II hybrid. Plenty of searching will help you understand the topic. However, I do like the machined chamber. It's different. And good.
IIRC correctly Nova's "bruiser" used a conventional fueling system, and it was about as small as this...
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inonickname
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Thu Jun 04, 2009 6:25 pm

I just checked, and this will be a LOT smaller.

Chamber volume is about 2.5ml, filled with a syringe from mapp, butane or propane. If I want to go much over 20x (need something else than shock pump for fuel) then I'll have to rig up a pressurized fueling system.

Any ideas to pressure test past a measly few k psi?

By the way- I don't have metalwork this afternoon, and I'm away next week, so next update will be ages.
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Thu Jun 04, 2009 6:48 pm

inonickname wrote:
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Omg is this stuff rated? DWV nazi me please.
Um OK.. :shock: What using case hardened stuff! Don't you know that is brittle. It may explode on you. :shock: You need something that can take the shock. Stuff they use for Impact Wrench sockets would be much better. :D


How did I do. Are you happy now. :D
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inonickname
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Fri Jun 05, 2009 7:00 am

Well, around 7.5mm is non hardened, and around 5mm is (on either side). So that gives me the best of both I guess.

I can't see it failing..
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