Probably stupid question about baffles

tpw2000 · Mar 8, 2017

I want to make a baffle expansion system where it transitions between 29mm tube and 66 mm tube and 3D print the design. I would expect it to easily and rapidly melt, though- is that an accurate guess? If so is there any way to prevent it (different filaments or something) or would i have to make the system out of something else?

Incongruent · Mar 8, 2017

tpw2000 said:
I want to make a baffle expansion system where it transitions between 29mm tube and 66 mm tube and 3D print the design. I would expect it to easily and rapidly melt, though- is that an accurate guess? If so is there any way to prevent it (different filaments or something) or would i have to make the system out of something else?

Hmm... I'm not sure; this scenario is quite baffling.

Based on what I've read, the ejection charge will eventually coat the baffle with enough residue to make it impervious to future ejections. It might melt earlier, though. You might want to coat the baffle in epoxy, which should help somewhat, but without experience I can't say for sure.

Bat-mite · Mar 8, 2017

I know nothing about 3D printing, and very little about baffles. But considering the purpose of a baffle, which is to allow the gasses to pass through while blocking the burning grains of BP, I would want info on how hot burning BP is, and how hot the gasses are, and what the heat tolerance of the various 3D printing compounds is? My guess is that there is no printing material capable of withstanding a BP explosion ... but then, see my first sentence.

Good luck!

fyrwrxz · Mar 8, 2017

That's what we're here for. There are no stupid questions if you don't know the answer! First- a baffle is meant to protect your chute from still burning particles of BP, so- a little distance does a lot for you to allow the flame to 'snuff'. A 3d printed baffle needs only to have some aluminum tape to protect it as the hot gas quickly cools the further from the motor it gets. As stated before, carbon may build up quickly after a few flights to give you more protection. Most concerning is the mass added to your bird and where that would be centered and accounted for in your cp/cg calcs and the overall mass of the bird vs the motor you are trying to fly. Estes motors tend to produce more burning 'chunks' compared to a 4f charge due to the manufacturing process where the BP charge is compacted beneath the clay cap used to keep it dry and in place. Also you may design this with the 'shelves' with risers on them to prevent the pressure from peeling them away from the walls-a little thicker if you will. I say go for it and give us a report (and photos!) YMMV. Straight smoke and good chutes!

K'Tesh · Mar 8, 2017

I feel that there are no stupid questions except for those that aren't asked. Those who disagree are free to... vent.

If you can design something for a 3D printer, I'm sure you could design something for a laser cutter. I'd suggest that you try using a wood such as bass or a light ply coated with JB Weld's Steel Epoxy to protect it against the heat/burning fragments.

qquake2k · Mar 8, 2017

Could you put half moon baffles in the motor tube to help protect the transition?

cjp · Mar 16, 2017

qquake2k said:
Could you put half moon baffles in the motor tube to help protect the transition?

qquake2k showed me how to build mine ,only thing I do is add a top uncut disc with holes drilled around the outer edges and a eye hook in the center that the shock cord is attached to.This is where the rocket separates for my zipperless design.With these baffles all you do after you remove the motor casing is shake the residue from the tube left over from the discharge.Tubes stays clean.I coat the bottom of all the discs that face the motor with epoxy.Works out great for me.I use 3 half moon discs,spaced out around a inch and a full drilled out disc that's the top of the baffle.On 3" tube I use a coupler that is 3 or 4 inches.

vic20owner · Aug 29, 2017

I do the same but with a bit of chore boy (copper wool) under the top baffle (with the holes in it).

I'm not sure 3d printed ABS would hold up to the heat well. Easy enough to test on the ground.

HandsomeRob · Aug 30, 2017

cjp said:
qquake2k showed me how to build mine ,only thing I do is add a top uncut disc with holes drilled around the outer edges and a eye hook in the center that the shock cord is attached to.This is where the rocket separates for my zipperless design.With these baffles all you do after you remove the motor casing is shake the residue from the tube left over from the discharge.Tubes stays clean.I coat the bottom of all the discs that face the motor with epoxy.Works out great for me.I use 3 half moon discs,spaced out around a inch and a full drilled out disc that's the top of the baffle.On 3" tube I use a coupler that is 3 or 4 inches.

Whoa. I never thought about just putting the baffle in the motor tube before. Do you just use a longer motor tube, a couple half moons, and you're good to go? This seems like such a simple "duh" solution, I feel stupid for not thinking of it myself hahaha!

rharshberger · Aug 30, 2017

Only issue with the baffle being in the motor tube is that unless the tube is fairly long you may end up limiting yourself on motor selection, ie the longer motors may no longer be an option.

Sent from my SM-N920V using Rocketry Forum mobile app

qquake2k · Aug 30, 2017

HandsomeRob said:
Whoa. I never thought about just putting the baffle in the motor tube before. Do you just use a longer motor tube, a couple half moons, and you're good to go? This seems like such a simple "duh" solution, I feel stupid for not thinking of it myself hahaha!

In my case, I use the half moon baffles with zipperless designs. There is another baffle plate in the coupler.

https://www.rocketryforum.com/showt...t-Thump-In-My-Down-quot&p=1690127#post1690127

https://www.rocketryforum.com/showt...t-Thump-In-My-Down-quot&p=1690256#post1690256

AfterBurners · Aug 30, 2017

fyrwrxz said:
That's what we're here for. There are no stupid questions if you don't know the answer! First- a baffle is meant to protect your chute from still burning particles of BP, so- a little distance does a lot for you to allow the flame to 'snuff'. A 3d printed baffle needs only to have some aluminum tape to protect it as the hot gas quickly cools the further from the motor it gets. As stated before, carbon may build up quickly after a few flights to give you more protection. Most concerning is the mass added to your bird and where that would be centered and accounted for in your cp/cg calcs and the overall mass of the bird vs the motor you are trying to fly. Estes motors tend to produce more burning 'chunks' compared to a 4f charge due to the manufacturing process where the BP charge is compacted beneath the clay cap used to keep it dry and in place. Also you may design this with the 'shelves' with risers on them to prevent the pressure from peeling them away from the walls-a little thicker if you will. I say go for it and give us a report (and photos!) YMMV. Straight smoke and good chutes!

you can also include a cooling mesh inside the baffle

qquake2k · Aug 30, 2017

AfterBurners said:
you can also include a cooling mesh inside the baffle

Doesn't cooling mesh need to be cleaned and/or replaced periodically? If so, it would need to be removable, which with my design is not possible. Unless you shoved a piece in the top of the motor tube against the half moon baffles.

AfterBurners · Aug 30, 2017

qquake2k said:
Doesn't cooling mesh need to be cleaned and/or replaced periodically? If so, it would need to be removable, which with my design is not possible. Unless you shoved a piece in the top of the motor tube against the half moon baffles.

thats what I meant to say thanks

qquake2k · Aug 30, 2017

So something like this?

https://www.amazon.com/dp/B01E42C6O2/?tag=skimlinks_replacement-20

OverTheTop · Aug 30, 2017

If you are 3D printing the baffle consider running something like radial vanes from the middle to the outside. The vanes running in line with the airframe will give them some strength. The pressure pulse might crack a thin flat 3D feature like the half-D shapes above.

I have a 3D printed NC that has had about 10 flights (maybe more). The ABS on the NC base has stood up well to the ejection charge (3 grams in a 4" airframe) but the charges are facing the other way.

You might need to think about the flammability of the material if it is taking the charge directly.

Also, you could rig one up just to experiment with before getting the final solution. 3D is good for that.

boatgeek · Aug 31, 2017

OK, here's a nutty idea. What if you incorporate the cooling mesh into a 3-D printed part that is fairly thick and heavy-wall. If the edges get a little burned/melted, it's not a big deal. The main guts of the baffle are held together on the other side of the mesh, where exposure to burning BP is minimal. Heat wouldn't be too bad, since it's a transitory rush of hot gas.

Something like this:

Fire - Mesh retainer ring - Mesh - 3-D printed body - Chute

You could probably make it removable for cleaning, inspection, and mesh replacement with some rivets or something into the main body.

OverTheTop · Aug 31, 2017

OK, here's a nutty idea.

Not nutty at all. You could even provide thicker edges where they face the ejection charge, and thinner behind for support.

Probably stupid question about baffles

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