So, I exceeded the limits of a 3D printed fin can

[cwbullet]

Seeing as how you got the rocket back in one piece instead of confetti, I'd say it was a successful flight.

Now I wouldn't want to fly that rocket again, that would be pushing your luck.

True. You can always replace the fin can.

 

[FlyBy01]

I agree. I am claiming some success! Sounds like just a little more reinforcement of some kind will make that fin can work on similar extreme flights.

I didn't fly it again, and the fin can has been donated to the Additive Aerospace Museum of 3D Printed Coolness.

I did rebuild the Wildman Mach2 with the stock fins.

Any files you would like to share? This goes out to all participants in this thread.

 

[Landru]

For strength, print fins separately, in spiral outline (Vase) mode. Leave root open, print with top 3 layers solid with 100% infill. Fill the cavity in each fin with thin epoxy. (System Three, West Systems, Tap Plastics, etc.) You can also add a piece of 0.030" fiberglass sheet inside for more strength. Utilize the 3d printing as a nice surface shape. Not strong enough by itself for high velocity applications. Use PLA+ (eSun makes the best) It has better heat resistance than regular PLA and is much tougher than PETG. Also has far superior layer adhesion. run it a bit hot, 215-220C

You want the fins oriented so the extruded filament flows as if you were laying up fiber reinforcement. The fins can be up to 50% stronger this way. I've had a bunch of samples tested by Lehigh university confirming this...

The fins can be hollow (all my 38mm and 54mm cans are hollow, and only 3 perimeters thick) , the center core adds essentially nothing to the fin strength, unless it prevents the exterior skin from buckling.

 

[cwbullet]

You want the fins oriented so the extruded filament flows as if you were laying up fiber reinforcement. The fins can be up to 50% stronger this way. I've had a bunch of samples tested by Lehigh university confirming this...

The fins can be hollow (all my 38mm and 54mm cans are hollow, and only 3 perimeters thick) , the center core adds essentially nothing to the fin strength, unless it prevents the exterior skin from buckling.

Does that not depend on the infill type and filament used?

 

[Landru]

Does that not depend on the infill type and filament used?

As for infill style, if loading is primarily tension, many perimeters beats all other infill styles. I'm trying to find the test data from Lehigh, but it was about 6 years ago. The caveat is you can get some odd delamination's if the process is not well controlled and there is not good bonding between perimeters.

Just to clarify, a solid core technically adds some stiffness, just very little compared to the exterior skin.

Its just like comparing a tube vs solid bar. Strength per unit mass is much higher with the hollow core.

 

[thzero]

You want the fins oriented so the extruded filament flows as if you were laying up fiber reinforcement. The fins can be up to 50% stronger this way. I've had a bunch of samples tested by Lehigh university confirming this...

Not sure I follow this with the way the fin can was printed.

My 3d fins (not a fin can) are printed as if the layers were grain, so the grain goes along the leading edge.

 

[cwbullet]

As for infill style, if loading is primarily tension, many perimeters beats all other infill styles. I'm trying to find the test data from Lehigh, but it was about 6 years ago. The caveat is you can get some odd delamination's if the process is not well controlled and there is not good bonding between perimeters.

Just to clarify, a solid core technically adds some stiffness, just very little compared to the exterior skin.

Its just like comparing a tube vs solid bar. Strength per unit mass is much higher with the hollow core.

That makes sense for strength per unit mass, but stronger overall would be with come infill patterns.

 

[Landru]

That makes sense for strength per unit mass, but stronger overall would be with come infill patterns.

At the end of the day we must come to terms with some constraint.

Perimeter only also makes for minimal stringing from less infill stops and starts, and faster printing (less material)

Not sure I follow this with the way the fin can was printed.

My 3d fins (not a fin can) are printed as if the layers were grain, so the grain goes along the leading edge.

Fin failure usually happens from flutter/side loading. Think diving board. With fins printed with layers along the grain, the stress is going to put the print in tension between layers, the weakest part of a print.

Additionally, printing the unit as a fin can nearly guarantees good fin alignment, and can make large fillets which also helps reduce stress.

The one place the fincans are sub-optimal is drag. The layer lines are definitely not the sleekest, and fins will need to be thicker than a comparable fiberglass/cf fin for a needed stiffness.

I am going to have to do one with the markforged printer at work and see how it holds up.

 

[Buckeye]

Any files you would like to share? This goes out to all participants in this thread.

I have no files. They belong to Additive Aerospace.

 

[thzero]

There was one or two fin can files on thingieverse

 

[Michael L]

It looks like this has been analyzed very well by the group. In one of the photos it looks like the edges flowed, as in melted. One of the guys at our club flew a minimum diameter rocket at near Mach 2. He had plugged the camera hole with using a glue gun. The glue melted and flowed out of the hole a little.

 

[cwbullet]

I have no files. They belong to Additive Aerospace.

I have a pretty good one. What type of tubing?

 

[Buckeye]

I have a pretty good one. What type of tubing?

Wildman Mach2, 54mm thin fiberglass.

I did not design nor print any parts, nor do I intend to. I purchased the fin can from Additive Aerospace, and I posted my experience with it in this thread.

 

[cwbullet]

Wildman Mach2, 54mm thin fiberglass.

I did not design nor print any parts, nor do I intend to. I purchased the fin can from Additive Aerospace, and I posted my experience with it in this thread.

I was going to offer to print another. I just asked the type of tubing. I will keep the print time for more appreciative flyers.

 

[hball55]

THAT IS AMAZING! Finally a flight with guts to push the can to its limits.

There has been quite a bit of debate on what an aero heating failure would look like, or whether the fins would rip off first. I always guessed the leading edges would fold over first.

The PET plastic softens about ~80C, and is actually less stiff than PLA, but much tougher.

The previous record was a 38mm flown by me to M1.3 without any fin damage.




The fact this can stayed intact despite folding over the leading edge shows the can is plenty stiff and strong. There is a lot of headroom to go faster if not for the temperature limits of the plastic. These types of cans are often flown with J motors and this is the ONLY 'failure' I've ever heard of.

Always been meaning to ask you about your name . . . Landru. My guess is the original Star Trek “Return of the Archons.”

 

[hball55]

Fiberglassing and epoxying the fin can defeats the purpose of the printed part, IMO. If I need to do all that, I might as well use the stock G10 fins in the kit!

A coating of finishing epoxy adds very little weight and possibly could have mitigated the damage.

 

[cwbullet]

A coating of finishing epoxy adds very little weight and possibly could have mitigated the damage.

I wonder what a thin coat of JB weld would do?

 

[Burner]

You can also print ABS and use vapor smoothing, finish comes out pretty nice when done correctly.

 

[cwbullet]

You can also print ABS and use vapor smoothing, finish comes out pretty nice when done correctly.

And in many cases, it is stronger.

 

[dr wogz]

Acetone bath:

I did that on a part a few months ago./ it turned out quite.. smooth & shiny! My work-mates were all quite impressed!

Pro:
Smooth & shiny & sexy (Like a fetish star in Latex!!) there is the odd bump here & there. I did notice that the surface on mine isn't 'glass smooth' but you do see the odd divot where a layer would be..
I would say that it will fuse the layers together. it does melt them all into one lump. Mind you, surface only

con:
Finding a bowl big enough!
Dealing with Acetone!!
Trying to determine the correct amount of time to 'soak it'
Trying to figure out the best suspension method & one that easily allows the object to be placed & removed
NOT touching it once it's in / been in the vapour bath for a few minutes.
making sure you & no one else touches it for the 'cure time' once removed!
sharp edges become rounded..

for whatever reason, when I did mine, I had sanded one area to see how it would 'smooth out' and despite it all being sexy smooth, you could still tell what & where it was sanded.