3D Printing Fin Bracket

[Bruce]

I saw in a back issue of Rockets Magazine (Vol 10, #1) from about 5 years ago that a student launch team had made a 3D printed fin bracket for their rocket.

"This system had three slits for the fins to fit inside, and the fins were then bolted to the 3D printed piece. The entire piece was then screwed into the body tube into wood strips that were attached to the rocket’s motor mount. This created one system that was attached to the rocket using bolts and screws."

This seems like a great idea!

We've made 3D printed fin cans before, but the weak link is always the fins. And when one breaks, you can't just replace a single fin either. With the bracket idea, you could use fiberglass or wood for the fins which could be stronger than 3D printed fins. The fins would be removable for transport and individually replaceable. If the fin bracket itself broke, you could print another bracket and make the next one thicker where it broke. You would only have to unbolt the bracket and bolt the new one in its place instead of having to deal with removing a glued in broken part.

Has anyone on this forum ever tried making such a fin bracket? How did it work for you? Might you have a .STL file that you would be willing to share?

 

[Bruce]

I mentioned this fin bracket idea to my son. He modeled it in Fusion 360 for a BT-60 tube, 1/8" fins and 4-40 screws and printed it out today. It looks like it could work to me. We'll make a rocket for it and see how it goes. The .STL file is below in case anyone else wants to give it a try.

Any guesses on whether it will work or how it might fail?

What are the drawbacks of a fin attachment system like this?

 

[rocketjet787]

I have seen several collegiate teams use this idea, granted on much heavier projects, and they tend to fail between layers as a result of the bearing stress from the bolts.

 

[Bruce]

I have seen several collegiate teams use this idea, granted on much heavier projects, and they tend to fail between layers as a result of the bearing stress from the bolts.

Yes, that's a good point, separation between the layers by the bolts sounds like a very probable scenario.

What could we do to reduce the chances of this happening?

Larger bolts?
Make the bracket thicker in the layers by the bolts?
A sleeve of stronger material around the bolts?
Orient the print so the layers go in a better direction?

What else?

How could we test the strength of the fin bracket to gauge how much improvement each modification is making?

Perhaps hang weights off the fins until the bracket broke?

Any ideas?

 

[ether]

what forces are you expecting the rocket to handle? what is the purpose you are trying to achieve? replaceable fins? better alignment, ease of building? is this min diameter build?

answers to those questions will help you design what you need and if plastic component can work.

If not min diameter, you could put this bracket all internal and use it to align the fins, while using other material to lock in place (removable method) and not place that stress on the plastic component