SpudFiles

Sweet. I hope you didn't forget to roughen the pipe on the inside?

While it's curing you might look into finding new batteries for you camera. The overview picture is somewhat out of focus, did you turn on macro mode?

psycix wrote:Sweet. I hope you didn't forget to roughen the pipe on the inside?

I only did thatonce

While it's curing you might look into finding new batteries for you camera. The overview picture is somewhat out of focus, did you turn on macro mode?

Macro mode was on, but I only saw the photo on the PC after I had sealed everything up. Here, have a properly focused picture of the cartridge curing. Note the canted schrader which still doesn't protrude from the body diameter to facilitate potential future magazine storage

Wouldn't it be expensive to have 10 to 100 shrader valves in your cartridges?
You might need to look into something else... and I just got a great idea:
Push the BB onto the sealing face with a spring, and pressurize the cartridge from the barrel port, so that it acts as a check valve!

Ammo, burst disk AND filling valve in one!

psycix wrote:Wouldn't it be expensive to have 10 to 100 shrader valves in your cartridges?

Not at all

You might need to look into something else... and I just got a great idea:
Push the BB onto the sealing face with a spring, and pressurize the cartridge from the barrel port, so that it acts as a check valve!

Ammo, burst disk AND filling valve in one!

SPG beat you to it

Let's see how this goes and move from there.

edit: No go the spark is arcing externally from the schrader threads to the cartridge body, which doesn't seem to make sense because it's a shotrer distance from the edge of the schrader internally to the cartridge wall...

any chance your epoxy ran down the inside of the tube, insulating it? I'm sure the epoxy king wouldn't have made such a beginner's epoxy mistake
How do you get all that rubber crap off of your schraders, it's always looked like a bit of a pain to me. I would go further than just roughing the inner surface of the tube and cut a shallow thread in it, or even drill holes like Daccel did for extra grip for the epoxy.

spudamine wrote:any chance your epoxy ran down the inside of the tube, insulating it?

No, I was aware this might happen so I poured it dropwise down the side where the schrader was farthest from the cartridge wall so I'm sure that's not the issue.

How do you get all that rubber crap off of your schraders, it's always looked like a bit of a pain to me.

Three words, drill, vice, file

I would go further than just roughing the inner surface of the tube and cut a shallow thread in it, or even drill holes like Daccel did for extra grip for the epoxy.

I use a file to cut grooves in it so it's pretty secure. But yes, a couple of holes drilled in would be a good idea which I have also used in the past.

I'm going to try and make another one tonight, I have some 0.55" steel tubing that should do nicely (unless I liberate some stainless offcuts from the maintenance department ) so keep watching this space

edit: version 2 made and curing, I checked for spark beforehand and it seems consistent actual internal volume is only 1.8mL so I'm going to have to be very careful with metering, even at 10x it will be just 0.7mL but with a 1mL syringe it shouldn't be an issue.

update 25/10/2009:

Can't get it to ignite I've taken it to 5x, reasonably confident of my metering and I definitely have spark. Bollocks.

How did the v.2 prototype perform?

In short, it didn't. I definitely have spark and the BB-seal arrangement is holding pressure, I've tried to up to 5x but no ignition in apparent. To be honest I've chickened out of trying it at high mixes, my conclusion is that I've gone a little too small with the volume to allow for effective syringe metering.

I might try a bigger version but for now I'm thinking aboutpneumatic cartridges again.

I agree that this is getting on the small side with syringe metering. I had problems at this scale. How about a mix metered with a venturi? There was one using a shock pump a while back that worked fine.

What about metering fuel in a "bulk tank" (which can still be quite small) and filling from that? On this scale it can't really "go nuclear" anyway.

Oh, and after shooting, can you push a new BB through the seal? (Without the seal coming loose)

psycix wrote:What about metering fuel in a "bulk tank" (which can still be quite small) and filling from that? On this scale it can't really "go nuclear" anyway.

That might be an idea, but I'd still prefer an individually metered cartridge.

Oh, and after shooting, can you push a new BB through the seal? (Without the seal coming loose)

Depending how far I push the BB in, just by pumping air it will pop out between 50-400 psi, the seal stays put. If you look at the way it's cast, the thing can't really pop out forwards or backwards.

jsr,

I think the idea of a hybrid cartridge without burst disc is brilliant, and even though you are putting this project on the shelf, I'm still going to give it a shot.

Have you considered using a presta valve instead of a schrader valve? This could solve the unwanted arcing since it is smaller in diameter. Also, it might improve the volume of the cartridge since it is thinner (albeit longer).

Could I know what you used to seal your bb? And also did you just epoxy the seal onto the metal cartridge casing?

Have you considered using a more powerful ignition source other than a piezo? - Since you said the mixture wouldn't ignite.

I noticed you said "pour epoxy". Do you mean your epoxy is in liquid form? Because mine is mold-able, and I was wondering if your liquid epoxy is stronger than the conventional mold-able epoxy. Anyway, what epoxy would you recommend?

zomgwtfbbq wrote:Have you considered using a presta valve instead of a schrader valve? This could solve the unwanted arcing since it is smaller in diameter. Also, it might improve the volume of the cartridge since it is thinner (albeit longer).

Sounds like a good option, I've never used presta's though. might be worth investigating as pilot valves though, I think hotwired had suggested them around the time I made the first pengun. Don't know how they handle high pressure either.

Could I know what you used to seal your bb?

3mm internal diameter silicon tubing, something like this.

And also did you just epoxy the seal onto the metal cartridge casing?

Yes, but if you look at the diagram you can see I slipped it over a length of barrel tubing to keep it locked in.

Have you considered using a more powerful ignition source other than a piezo? - Since you said the mixture wouldn't ignite.

Piezos are all I have but a stronger ignition might be the answer, though I'm more inclined to think it was poor mixing and I had good spark.

I noticed you said "pour epoxy". Do you mean your epoxy is in liquid form? Because mine is mold-able, and I was wondering if your liquid epoxy is stronger than the conventional mold-able epoxy. Anyway, what epoxy would you recommend?

The epoxy I use is liquid, something likethis. You can get a gallon for 50 bucks, it might sound like a lot to spend on adhesive but you use so little per project that it will last you a long time. Since it tends to flow throughout the whole of the casting it's stronger than putty.

Sounds like a good option, I've never used presta's though. might be worth investigating as pilot valves though, I think hotwired had suggested them around the time I made the first pengun. Don't know how they handle high pressure either.

Presta valves are made to handle higher pressures than schrader's, or at least that was what the bicycle shop guy told me.

The epoxy I use is liquid, something like this. You can get a gallon for 50 bucks, it might sound like a lot to spend on adhesive but you use so little per project that it will last you a long time. Since it tends to flow throughout the whole of the casting it's stronger than putty.

How did you pour the epoxy into the cartridge casing without the epoxy sticking to your table since the bottom of the cartridge is hollow? Did you also inject the epoxy in with a syringe for more precise work?

zomgwtfbbq wrote:How did you pour the epoxy into the cartridge casing without the epoxy sticking to your table since the bottom of the cartridge is hollow? Did you also inject the epoxy in with a syringe for more precise work?

It's all explained here. I do occasionally use syringes with finer jobs.

It is worth noting however that on this scale even with 800 psi+ pressures I'm comfortable using Araldite only: