3D Printing Printed Charge Wells?

[KilroySmith]

So, has anyone printed charge wells before?

I'm thinking of printing a cap on top of my AvBay bulkhead with a charge well incorporated. The AvBay bulkhead (a nicely machined piece of Aluminum from Madcow) will provide strength and protection to the Avionics, the printed cap will simply provide a lightweight, mechanically fixed place for the ejection charge.

I was originally planning on just putting a nipple on the cap that an Aluminum tube would fit over, then gluing the tube in place. The tube would contain the charge, and the nipple would rigidly hold it in place. But then my mind asked "Self, could I eliminate that aluminum tube and just print the whole thing?". My printer is currently loaded with PETG, but even that wouldn't hold up to sustained temperatures of the sort that a charge could generate; but I figure it might just work fine for the few milliseconds that it'll be exposed to the temperature.

Thoughts?

 

[mbeels]

I've never done 3d printing, but the charge wells on the AV bays that come from Mach 1 Rocketry are 3D printed. I don't know what the material is, though.

 

[KilroySmith]

And here it is: https://www.mach1rocketry.com/store/p243/Full_Electronics_Bay_for_54mm_x_7_inch_(Standard)_.html
Yep, those look very 3D printed to me; can't tell the material from here though. But none of the commonly printed plastics will hold up to sustained charge temperatures, so I'll buy into this being a valid thing to do. I figure I'll find out when I test....

 

[rharshberger]

I've never done 3d printing, but the charge wells on the AV bays that come from Mach 1 Rocketry are 3D printed. I don't know what the material is, though.

Pretty sure Steve at SMT uses PETG.

 

[roytyson]

I finally got mine all printed up. It was quite a journey. I think I printed enough charge wells for 20 people before I ended up with a good product. The contour will fit a 38mm bulkhead, and I made two different sizes. I intend to make a few more sizes for larger wells. Then came printing. I was having major "zit" issues on the exterior, it became a battle of man/machine. I finally got it dialed in, I think. Pretty happy with these two sizes.

 

[OverTheTop]

Lots of people have used them. I would make the charge wells removable in case you get a crack from the detonation.

 

[cwbullet]

Lots of people have used them. I would make the charge wells removable in case you get a crack from the detonation.

Yup - absolute requirement in my book.

 

[crossfire]

So what is the advantage of 3D charge wells?

 

[Cl(VII)]

So what is the advantage of 3D charge wells?

You have more flexibility in shape, and therefore where they can fit.

 

[cwbullet]

So what is the advantage of 3D charge wells?

They are cheap and easily reproducible.

 

[cwbullet]

I finally got mine all printed up. It was quite a journey. I think I printed enough charge wells for 20 people before I ended up with a good product. The contour will fit a 38mm bulkhead, and I made two different sizes. I intend to make a few more sizes for larger wells. Then came printing. I was having major "zit" issues on the exterior, it became a battle of man/machine. I finally got it dialed in, I think. Pretty happy with these two sizes.
View attachment 417613

What filament?

 

[crossfire]

They are cheap and easily reproducible.

That is good on the price. What do you think it cost to run a pair?

 

[cwbullet]

For you, I will do it for free. Does anyone have a good file to print that I could try out?

I have a couple but I would not say they are my best work. Give me the weekend.

 

[roytyson]

What filament?

PETG

 

[roytyson]

For you, I will do it for free. Does anyone have a good file to print that I could try out?

I have a couple but I would not say they are my best work. Give me the weekend.

I will throw my prints on thingiverse tonight.

 

[Joe Bruce]

My only warning would be on "directionality." My first DD rocket -- a LOC Deployer that hasn't flown yet due to COVID -- had a very tight main chute compartment. The very directional 3D printed charge well I designed (similar to what I see above -- inspirations for my own design) blew holes in my Nomex and chute.

For this rocket, I abandoned the 3D printed charge wells and switched to nitrile glove tips (not directional) and increased the volume of the main chute compartment with some NC surgery.

All that said, the PETG charge wells held up fine (no melting) to repeated ground tests until I abandoned them, and I would consider 3D printing again for my 5.5" LOC Patriot, which has roomy drogue / mains compartments.

 

[Ez2cDave]

I would make the charge wells removable in case you get a crack from the detonation.

Rocketeers should NEVER use the word "detonation" . . . May I suggest using "activation" ?

 

[OverTheTop]

I am not sure if you are being sarcastic or not.

 

[Ez2cDave]

I am not sure if you are being sarcastic or not.

"Semi" . . .

It all dates back to the 10-year long BATFE lawsuit over APCP ( Ammonium Perchlorate Composite Propellant ) .

The Government was claiming that APCP "functions by detonation", thus making it an Explosive.

NAR & Tripoli argued, successfully, that APCP "functions by deflagration" ( rapid burning ), rather than by Detonation.

APCP was removed from the BATFE Explosives List and, as a result, the LEUP ( Low Explosive User Permit ) requirement was dropped.

Dave F.

 

[OverTheTop]

I would argue that if you haven't seen a detonation in rocketry you haven't been doing much rocketry . Things go wrong occasionally, but the safety code keeps everyone safe.

 

[Ez2cDave]

I would argue that if you haven't seen a detonation in rocketry you haven't been doing much rocketry . Things go wrong occasionally, but the safety code keeps everyone safe.

APCP motors can over-pressurize and rupture, but the propellant itself does not detonate.

BP motors, on the other hand, can detonate. Black Powder is classified an Explosive, but APCP is not.

Dave F.

 

[OverTheTop]

You missed hybrids. The detonate under fault conditions.

I would think APCP would almost "detonate" under a blocked nozzle condition as the burn rate is exponentially proportional to pressure. Might not be a true detonation but the pressure spike is wicked.

 

[John Kemker]

You missed hybrids. The detonate under fault conditions.

I would think APCP would almost "detonate" under a blocked nozzle condition as the burn rate is exponentially proportional to pressure. Might not be a true detonation but the pressure spike is wicked.

There's an actual, real-world, scientific definition of detonation: In a detonation, the substance ignites ahead of the flame front, by the shock wave passing through it. The shock wave propagates the explosion. Deflagration is the rapid burning of a substance, usually generating large volumes of gas in a short period of time.

Hybrids do not detonate. Neither does APCP. Neither type of motor is shock sensitive, which is the requirement for detonation. Nitroglycerin detonates. Nitrocellulose (smokeless powder) detonates.

 

[jbr]

personally I don't see the need to have a directed charge cannon, we aren't launching projectiles inside our rockets
I have used non directed for over 300 flights

 

[Ez2cDave]

personally I don't see the need to have a directed charge cannon, we aren't launching projectiles inside our rockets
I have used non directed for over 300 flights

If that method does not appeal to you, use whatever you are comfortable with.

However, if using Pyrodex or Triple 7, charge cannons make it much easier to achieve the necessary compression for proper operation.

 

[AeroAggie]

Longer containers (i.e. cannons) can be beneficial for high altitude deployments where the air is thin, and you need to contain the charge longer for it to fully burn and develop enough pressure to actually deploy the chute. I don't know if 3d printed ones are up to that task, but I do intend to find out.

 

[Ez2cDave]

Longer containers (i.e. cannons) can be beneficial for high altitude deployments where the air is thin, and you need to contain the charge longer for it to fully burn and develop enough pressure to actually deploy the chute. I don't know if 3d printed ones are up to that task, but I do intend to find out.

Good point !

Also, place your e-match ON TOP of the powder, before sealing . . .

It gives more complete combustion ( e-match on bottom blows un-burned powder out of the canister, making it less effective ! )

 

[jbr]

the surgical tubing method works for high altitude

 

[cwbullet]

I just stick them in the middle.

 

[Ez2cDave]

I just stick them in the middle.

Chuck,

There was an interesting YouTube video where a guy was testing ejection charges.

When the e-match lit, at the bottom of the well, it forced the charge up, out of the holder, resulting in a lot of un-burned grains.

When the e-match was on top, the powder was retained in the holder and worked well, with very few un-burned grains.

Dave F.