Cooking up a little something...

Harness the power of precision mixtures of pressurized flammable vapor. Safety first! These are advanced potato guns - not for the beginner.
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Moonbogg
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Fri May 10, 2019 10:56 pm

This is a build log update.
Hard at work tonight. Assembly going well. I had to turn an egg-shaped pipe to be semi-round with nothing but sand paper. Guess how hard that was. My next project is to buy a lathe and mill for the garage. That will take a while though, lol.

EDIT: File attachments not working. Hmm...
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Sanded, buffed and cleaned.  All ready to assemble.
Sanded, buffed and cleaned. All ready to assemble.
What a mess.
What a mess.
Now that's just sick AF!
Now that's just sick AF!
The plastic looks good on the barrel insert.  That barrel insert came out real nice and fits great.
The plastic looks good on the barrel insert. That barrel insert came out real nice and fits great.
Cannon building:  An Olympic sport
Cannon building: An Olympic sport
Up next: Hydro testing.  That gauge goes up to 600psi.  I'm only going to 450psi though.  I fully expect the end caps to shear off at the bolts and me cry for the following 12 hours.  Stay tuned.
Up next: Hydro testing. That gauge goes up to 600psi. I'm only going to 450psi though. I fully expect the end caps to shear off at the bolts and me cry for the following 12 hours. Stay tuned.
Cannon taking the piss.
Cannon taking the piss.
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mrfoo
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Sat May 11, 2019 2:12 am

A lathe is a really good purchase. Bear in mind that you can do limited (by size, and / or depth of cut) milling on a lathe using a vertical slide.

I would personally recommend, for the same money, getting a second-hand "old iron" machine rather than brand new chinesium. Whilst an older machine may require a certain amount of TLC to get it back into 100% working state (they rapidly become a project in their own right), capacity and capabilities are liable to be significantly better, rigidity and build quality almost certainly will be. I've never seen a new chinese machine that didn't require a full strip down and clean just to remove the grinding dust that comes with a low price, deburring of all sharp edges, and a very careful alignment and adjustment to get any sort of accuracy - this latter may require re-scraping the bearing surfaces and gibs of the machine. On the other hand, you need to not be in a hurry to buy - the right machine at the right price may take months or years to crop up - and it's a good idea to have someone who knows what they're talking about to come and inspect before purchase.

Machine tools become a money hole in their own right. Cutting tools, metrology tools, tool sharpening equipment, collets, chucks and other workholding equipment, toolholding equipment, consumables such as cutting fluid and oil, and even boxes and cabinets to hold all the miscellaneous crap mentioned above, it all adds up.

As far as cutting tools go, I would strongly recommend going for HSS over carbide inserts. Cheaper, more versatile (you can make and sharpen your own tools for a particular purpose), and you simply don't need the increased throughput that carbide gives you in a home shop environment. Unless you're machining stuff that's harder than HSS (bearing races, for example), and then you need stuff that's harder than carbide anyway - CBN inserts, etc.
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Moonbogg
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Sat May 11, 2019 2:46 am

It's not finished, but I had to do a preliminary photo shoot. It's looking pretty good...

Nylocks won't work for the tie rods and the breach o-rings are way too tight, so they have to be replaced with softer X shaped o-rings. Lots of work to do, but getting closer!
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mrfoo
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Sat May 11, 2019 4:04 am

That looks frickin' awesome.
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jackssmirkingrevenge
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Sat May 11, 2019 4:53 am

Moonbogg wrote:It's looking pretty good...
That's an understatement if I've ever heard one, looking great! Now let's hope she performs as well as she looks like she should :D
hectmarr wrote:You have to make many weapons, because this field is long and short life
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Moonbogg
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Sat May 11, 2019 11:42 am

Thanks guys. Hey, what kind of valve could I use to release the 450psi water pressure after testing? A little ball valve? I'm thinking a needle valve. Also, if the thing passes the test, I could just cut the line with a hack saw...
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mrfoo
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Sat May 11, 2019 12:49 pm

Any kind of valve, or, as you say, just cut the line. Static hydraulic testing is done specifically for pressure vessels because you're dealing with [very nearly] incompressible fluids - failure is non-explosive. As soon as you've opened the vessel, there's no pressure left. If you do it with a compressible fluid like air, or if there is air in the system, however, failure is dramatic, to say the least.
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Moonbogg
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Sat May 11, 2019 7:43 pm

It passed hydro! I had to pump like crazy once it got past around 250psi because that needle valve was starting to leak. I kept going with my heart racing until it hit 400 and I kept going until 450psi was cleared. It only sat there for a few seconds and I went back to try to hold it longer, but I ran out of grease. It passed without as much as a leak. Not even the spark plug leaked and it only has a little teflon tape on it. Looking good!
Now I get finally put hydro behind me and get to finishing it.

I included a pic of my super sophisticated hydro testing facility. Take special note of the blender pitcher near by that was used to fill the chamber with water. Also, cleaning up all that grease was an absolute train wreck. What a titanic pain in the ass that was.
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hectmarr
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Mon May 13, 2019 10:20 am

It looks excellent! I die to see shoot that thing :bounce:
Ideas don't make holes, guns do!
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Moonbogg
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Sun May 19, 2019 1:27 pm

I've been super busy studying, but I took a minute to test the piston with air. Good news is the pilot area and chamber both appear to seal and hold pressure. When I release pilot air, the chamber air dumps out, so the valve works. The pilot area sat at 50psi for several minutes and didn't appear to drop. I only plan on using it around 20psi.
The uncertain news is that with a pilot pressure of 20psi, that should result in an opening pressure of around 135psi, but air starts to escape past the piston sealing face at around 50psi. My hope is that the volume of leakage is small enough to not wreck performance since combustion takes place so quickly that it may not matter much. I know some pneumatic cannons have air leaks and they work fine because the leak is small enough to not matter.
Of course test firing will tell but I'm curious as to your thoughts on this.

EDIT: LOL first sign of semi-success ahaha. I did a pneumatic shot at 60psi and launched a stuffed toy lion across the house. I was like to my wife "Hey babe, watch this" ppffFFOOOMP! as it flies and hits the wall, lol! I have myself a SICK t-shirt launcher right here. It works perfectly as a pneumatic toy launcher.
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jackssmirkingrevenge
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Mon May 20, 2019 4:09 am

Moonbogg wrote:"Hey babe, watch this"
This is the married equivalent of "hold my beer!" :D

Looking forward to seeing this thing spark.
hectmarr wrote:You have to make many weapons, because this field is long and short life
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Moonbogg
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Mon May 20, 2019 10:33 am

jackssmirkingrevenge wrote: Looking forward to seeing this thing spark.
It's almost ready for testing. Regarding that, can you think of a quiet way to test a 3X hybrid in the garage?
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Labtecpower
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Mon May 20, 2019 11:42 am

According to several sources a cat shoved over the muzzle makes a good muffler, but to avoid the mess and other issues that may or may not arise, I would fire into a box filled with wet rags (so you dont start a fire while you muffle the noise)
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Moonbogg
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Mon May 20, 2019 12:23 pm

That sounds like it could work! (not the cat part)
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jackssmirkingrevenge
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Mon May 20, 2019 2:43 pm

Do you have a stack of old tires?

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hectmarr wrote:You have to make many weapons, because this field is long and short life
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