# New build - AirMail

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#### Dustin Lobner

##### Well-Known Member
TRF Supporter
Hi everyone,

Working on a new build that some people might find entertaining. I ordered some dowels from McMaster and got one of those thick-walled shipping tubes, decided to turn it into a rocket because why not? (OK, yes, the "why not" is that the tube is 10x's thicker than needed and is thus HEAVY). It's a 3.3" OD, so nothing "stock" will fit, so I'm 3D printing a fin can/motor mount and nosecone.

The tube still has all of the packing list and UPS stickers on it, so I'm going to add some more ("this end up", lol) and just fly it in its "bare" cardboard state with all of the shipping stickers on it and call it "AirMail".

Started the fin can/motor mount print last night. Computer says it's an 88 hour print, reality will be closer to 110 hours because my slicer underestimates for some reason. If we have a power outage or something I'm going to cry.

Hoping to fly this at Bong in April.

#### kuririn

##### BARGeezer
TRF Supporter
How come two of the fins have jaggedy surfaces?

#### Dustin Lobner

##### Well-Known Member
TRF Supporter
That's the support material to support bottom of the fins. For whatever reason, the slicer only orients those in a direct X-Y orientation, so it ends up being a series of squares oriented X-Y but the part is at an angle. ...image paving a walkway with squares that you aren't allowed to cut down, that you have to orient in the north/south direction, but your walkway goes southwest. The outside will be jaggedy.

If you look closer to the body, you can see some of the fin coming in looking "smooth".

Edit: clarity

#### kuririn

##### BARGeezer
TRF Supporter
Thanks, got it. Wishing you an outage free 5 days and plenty of filament on your spool.
Laters.

#### wsume99

##### Well-Known Member
TRF Supporter
That's a nice looking design. What is the MMT dia and what impulse class are you planning to fly the rocket at? What material are you using for the print? Are you printing this with solid infill?

(I'm interested in printing my own fincans as well and just want to learn from others so I can cut the number of iterations I'll need to get a usable part.)

#### David Schwantz

##### Well-Known Member
TRF Supporter
My Ender 5 will resume printing after a power loss. Yours will not?

#### Dustin Lobner

##### Well-Known Member
TRF Supporter
It's the bog standard CR-10...it claims it can, but everyone online who tried it had it not work, so I'm not planning on it working that way.

#### David Schwantz

##### Well-Known Member
TRF Supporter
Guess I would not test either!

#### Dustin Lobner

##### Well-Known Member
TRF Supporter
That's a nice looking design. What is the MMT dia and what impulse class are you planning to fly the rocket at? What material are you using for the print? Are you printing this with solid infill?

(I'm interested in printing my own fincans as well and just want to learn from others so I can cut the number of iterations I'll need to get a usable part.)

38mm motor, plan to fly on either quick burning Hs or most Is, biggest concern is having enough punch to get it stable before clearing the rail. I ran a few sims and they were coming out about 1-3k feet.

Material is Matterhacker's Tough PLA. I use it all the time at work for test fixtures and it's startlingly resilient...it isn't remotely brittle, it bends without breaking. Good stuff, just that it's $52 for a spool, so if the print goes wrong it's$52 down the drain. Calling it a PLA does it a disservice, it's more like ABS in terms of properties.

The bottom inch or so of the can is 100% infill (which in reality is maybe 50% plastic?). The goal was to make the interface with the motor as strong as possible. Everything above that is 25% infill or thereabouts so I can print the whole thing on 1 spool.

This is the 3rd fincan I've done. it's very doable, the main issue is designing the can to be easily printed. As far as iterations go, I print a couple smaller pieces beforehand where there's a critical interface. For example, if I have a 38mm motor, I know I have to print the motor mount bore at 38.6mm dia to get the right clearance. For where it meets up with the tube, I printed a 1" long ring with the ID drawn to "match" the OD of the tube...I had to hammer the ring on and off, so I opened it up 1mm on the diameter and that seemed about right. Short version, to get fitment right, you don't have to print an entire fincan, just print bit and pieces of it. Saves time and filament.

My favorite things about 3D printed fincans...1) you can do fin root to tip taper, makes the fins really stiff and sexy and 2) because they're as "perfect" as can be easily done, they don't rotate on flight...just a wonderfully straight boost. Rotating is something I didn't realize my "standard" rockets did until I flew a printed fincan. It was startling the first time.

#### wsume99

##### Well-Known Member
TRF Supporter
This is the 3rd fincan I've done. it's very doable, the main issue is designing the can to be easily printed. As far as iterations go, I print a couple smaller pieces beforehand where there's a critical interface. For example, if I have a 38mm motor, I know I have to print the motor mount bore at 38.6mm dia to get the right clearance. For where it meets up with the tube, I printed a 1" long ring with the ID drawn to "match" the OD of the tube...I had to hammer the ring on and off, so I opened it up 1mm on the diameter and that seemed about right. Short version, to get fitment right, you don't have to print an entire fincan, just print bit and pieces of it. Saves time and filament.
That is the exact same approach I use as well. Whenever I design a part to 3D print I focus on the critical interfaces first and print some test articles to get the design perfected. Then the rest is all about printability.

What infill pattern are you using?

That filament is very pricey. Have you ever tried using PLA+? I just finished my first spool of PLA+. I was quite impressed with it and it's under $20 per 1kg spool. I am 100% confident I could design and print a fincan to withstand flight on H-I motors using that material. The only unknown for me is how it would handle environmental exposure. I suspect it would be fine other than being left inside a car on a sunny, hot summer day. #### Dustin Lobner ##### Well-Known Member TRF Supporter That is the exact same approach I use as well. Whenever I design a part to 3D print I focus on the critical interfaces first and print some test articles to get the design perfected. Then the rest is all about printability. What infill pattern are you using? That filament is very pricey. Have you ever tried using PLA+? I just finished my first spool of PLA+. I was quite impressed with it and it's under$20 per 1kg spool. I am 100% confident I could design and print a fincan to withstand flight on H-I motors using that material. The only unknown for me is how it would handle environmental exposure. I suspect it would be fine other than being left inside a car on a sunny, hot summer day.
Infill...honestly not sure, lol. Either rectilinear or a honeycomb thing.

#### wsume99

##### Well-Known Member
TRF Supporter
Thanks for posting these. Helps give me lots of ideas. I like the thought of removable fins. I'm pretty sure with enough experimentation that a good solution could be designed.

#### Dustin Lobner

##### Well-Known Member
TRF Supporter
One of the neat and also mentally taxing things about 3D printing is you get to see things "grow"...but too slowly! Drives one slightly crazy.

Status as of this morning below. Should start going faster because after passing the tip of the fins there's no more support material, and things are getting smaller/layer.

#### wsume99

##### Well-Known Member
TRF Supporter
Just occurred to me, with a 3 fin design I would have only put three stringers between the OD and ID. I would have oriented them to be inline with the fins. This allows the load to more directly transfer thru to the MMT and also reduces the weight, material used and print time. Obviously it's your design but that's what I would do.

#### Dustin Lobner

##### Well-Known Member
TRF Supporter
Just occurred to me, with a 3 fin design I would have only put three stringers between the OD and ID. I would have oriented them to be inline with the fins. This allows the load to more directly transfer thru to the MMT and also reduces the weight, material used and print time. Obviously it's your design but that's what I would do.
Agreed. I originally had this as a 4 fin but couldn't print it in 1 spool so cut one off. There's a lot of "meat" to the design so I'm not worried about it, but in the future that's the plan.

EDIT - also, this way the rail button is sunk in solid.

#### wsume99

##### Well-Known Member
TRF Supporter
Agreed. I originally had this as a 4 fin but couldn't print it in 1 spool so cut one off. There's a lot of "meat" to the design so I'm not worried about it, but in the future that's the plan.

EDIT - also, this way the rail button is sunk in solid.
For sure strength is not going to be an issue with your design. I was just pointing out I thought three would be just as strong and a little cheaper and faster to print in case you hadn't already thought of it. I'm excited to see the finished product.

Looks like you are using Capricon tubing and you mentioned a bondtech extruder drive. Any other mods to your printer?

I have an ender 5 plus. Only mods I have done that affect printing are Capricorn and the creality all metal extruder. I did install a raspberry pi running octoprint, a webcam for remote monitoring, LEDs so I could actually see what was happening on the webcam, and two relays to turn the printer and LEDs on/off.