3D Printing Need Help with 3D Printed Model Rocket (PLA)

[viper2788]

I know nothing of model rocketry (ironically as I'm on this forum), and I'm hoping some of you may point me in the right direction. I've done some preliminary research and I understand the general idea of how model rockets work, but it led me to several questions:

1) So far its about 13" in length and 1.25" in outer diameter. My CAD programs says it should weigh around 4oz (115g) without the motor or any weights added to the nose cone. I'm assuming a D12-3 engine should suffice? (I know its going to be tail heavy and some weights will be needed up top)

2) I'm planning on using PLA, simply because its easy to print and its what I currently have in hand. Do rocket engines get hot to the touch, and possibly cause warping issues if in contact with PLA? I'm thinking of making a threaded sleeve to house the rocket engine. Are there commercial sleeves that may shield the heat a bit? I'm really trying to avoid using PETG if possible, and currently my printers arent fit to print ABS/Nylon/ASA without an enclosure.

3) What size parachute should I go for? I'm going to assume its going to be up to 8oz or so with rocket motor/weights added.

I'm planning on having the "missile mounts" converted to guide a 1/8" launch rod.

If there's anything else I should know or consider, please let me know. Thanks in advance!

 

[Alan R]

Too, too much to get into.
Can you post the .obj and/or .stl please

 

[John Kemker]

Why avoid PETG? I've gone to almost exclusively printing in PETG, mostly due to the fact that my main 3D printing is for rockets.

Yes, motors get hot, even LPR motors.

 

[0011001100]

'm really trying to avoid using PETG if possible

Why? PETG is just as easy to print as PLA once the settings are dialed in. It may take more tuning than PLA but once you got it going it can do well. I've printed many kgs of PETG, more than PLA at this point.

o rocket engines get hot to the touch, and possibly cause warping issues if in contact with PLA?

PLA will work in a car in the sun, so yes. Typically in my experience, Estes motors get hot enough that I need to let them cool down before I can yank them out so I would expect they would easily warp PLA. It depends how much mass is around the motor though. If you add enough material, it won't warp because the thermal mass is great enough.

 

[cwbullet]

More than glad to help, be I need to see the files. Post the OBJ or STL files.

 

[Alan R]

Why? PETG is just as easy to print as PLA once the settings are dialed in. It may take more tuning than PLA but once you got it going it can do well. I've printed many kgs of PETG, more than PLA at this point.

I was switching over from PLA to PETG and spent most of Sunday trying to make something work. I have my PETG spec dialed into the slicer, worked flawlessly for years. But Sunday I couldn't get it to stick to my build plate at all. Tried every thing I knew. I've printed lots and lots of PETG, I like to use it for all rocket parts. No idea why it decided not to work. Possibly time for a new roll. I'll see if that helps.
In the meantime, the PLA parts I'm printing aren't heat critical, but they are hard-landing critical.

 

[Alan R]

I know nothing of model rocketry (ironically as I'm on this forum), and I'm hoping some of you may point me in the right direction. I've done some preliminary research and I understand the general idea of how model rockets work,

You say you don't know anything about rockets, but you're good at 3D printing. The latter is a bonus. The first part kind of bothered me.
Do you know you'll need a launch base for that?
I am going to suggest you invest in cardboard/balsa kit so you know what goes in a model rocket and how it works. As for the launching, I would suggest you pick up an Estes Tandem-X starter kit. That kit includes a launcher and a cardboard/balsa rocket to build. Price is $39.99 + shipping from Estes. You can possibly pick it up for less if you have a local hobby store. Note that this is the only starter kit with a cardboard/balsa rocket. All the others Estes sell are plastic pre-made fin cans.
Edit: or get an Alpha kit. It has plastic fins but still requires you to build the engine mount. Fin mounting can be frustrating for new builders. It's MSRP $35, a little less than the Tandem.

 

[Rschub]

Air is a good insulator, have you thought about not making a tube, but rather "fins" that hold the motor in place lengthwise. Or maybe a series of rings, although that would be a lot harder to print. More of a framework. this would also allow the heat to escape instead of being trapped in a tube.
We use tubes for motor mounts because they are cheap and available. Additive manufacturing allows you the freedom to try alternatives.

 

[thzero]

Model it in OpenRocket.
Print with PETG.
Use a standard motor tube as a liner.

 

[viper2788]

Why avoid PETG? I've gone to almost exclusively printing in PETG, mostly due to the fact that my main 3D printing is for rockets.

Yes, motors get hot, even LPR motors.

PETG works but I'll be printing lots for production. For one, it cant print nearly as fast as I can with PLA, and two, it can become a bit stringy when printing multiple parts at once. I may experiment with ABS or ASA to see if those print easier - should be better with heat as well.

I was switching over from PLA to PETG and spent most of Sunday trying to make something work. I have my PETG spec dialed into the slicer, worked flawlessly for years. But Sunday I couldn't get it to stick to my build plate at all. Tried every thing I knew. I've printed lots and lots of PETG, I like to use it for all rocket parts. No idea why it decided not to work. Possibly time for a new roll. I'll see if that helps.
In the meantime, the PLA parts I'm printing aren't heat critical, but they are hard-landing critical.

I started using Aquanet hairspray for anything I print and havent looked back. As much as I was initially against it, it gives me peace of mind and a near guarantee of proper bed adhesion. Its also dries very thin and doesnt leave lumps like some other brands. Hope this helps!

Air is a good insulator, have you thought about not making a tube, but rather "fins" that hold the motor in place lengthwise. Or maybe a series of rings, although that would be a lot harder to print. More of a framework. this would also allow the heat to escape instead of being trapped in a tube.
We use tubes for motor mounts because they are cheap and available. Additive manufacturing allows you the freedom to try alternatives.

Model it in OpenRocket.
Print with PETG.
Use a standard motor tube as a liner.

I'll def give tubes a try. I think I can make some small ribs inside to minimize contact with the motor and provide more air insulation.

Thanks for the replies everyone, I'll keep you posted on progress.

 

[cwbullet]

What printer are you using? I have no issue printing PETG fast.

 

[0011001100]

PETG works but I'll be printing lots for production. For one, it cant print nearly as fast as I can with PLA,

As someone working at a company that is printing PETG for production, you can print it just as fast. Like I said before you just have to get the settings right. This includes nozzle temp (we run at the top of the manufactures recommendation).

it can become a bit stringy when printing multiple parts at once

It is wet then and you need to dry it. This will happen with most filaments including PLA, although PETG and Nylon are some of the worst.

I may experiment with ABS or ASA to see if those print easier

Nope, they are more difficult to print with. ASA is easier than ABS although both will be much easier with an enclosure. Depending on the part size/shape, these two will warp without an enclosure no matter what.

 

[Alan R]

I started using Aquanet hairspray for anything I print and havent looked back. As much as I was initially against it, it gives me peace of mind and a near guarantee of proper bed adhesion. Its also dries very thin and doesnt leave lumps like some other brands. Hope this helps!

I had switched over the slicer settings from PLA without paying attention to the details (selecting my custom PETG preset) ... and I wasn't printing hot enough. Problem solved.
Edit: I print on blue tape over a glass bed, never had adhesion problems with that.

 

[beeblebrox]

I had switched over the slicer settings from PLA without paying attention to the details (selecting my custom PETG preset) ... and I wasn't printing hot enough. Problem solved.
Edit: I print on blue tape over a glass bed, never had adhesion problems with that.

I am using magnetic PEI sheets on my printers. Stuff works great. I use a little bit of glue stick. (The purple kind works best) I don't need to apply it very often, but it helps. as for PETG I have had too many problems with it cracking for no reason and it is not anywhere near as tough as PLA. (I made a bracket for the top of my printer to hold a bowden tube coming from my enclosed filament box. Just sitting there on my printer after a couple of weeks it cracked. No exposure to heat at all.) To get a bit more heat resistance use PLA+ I print that at 215C

 

[thzero]

I am using magnetic PEI sheets on my printers. Stuff works great. I use a little bit of glue stick. (The purple kind works best) I don't need to apply it very often, but it helps. as for PETG I have had too many problems with it cracking for no reason and it is not anywhere near as tough as PLA. (I made a bracket for the top of my printer to hold a bowden tube coming from my enclosed filament box. Just sitting there on my printer after a couple of weeks it cracked. No exposure to heat at all.) To get a bit more heat resistance use PLA+ I print that at 215C

Sounds like you have some settings not quite right for PETG then.

PLA+ does not have much more heat tolerance than PLA. if any. This was pulled from manufacturer specs (no, didn't got to every manufacturer).

	PLA	PLA+	PETG	ABS	3DXTech CarbonX PETG	Polymaker PA12-CF
Deflection temp. (C)	53	53	64	78	77	215
Density (g/cm3)	1.2	1.23	1.27	1.04	1.34	1.17
IZOD Impact Strength (kJ/㎡)	5.4	4.7	4.7	8.5		13.34
Flexural Strength (MPa)	90	74	58.1	66	80	169
Flexural Modulus (MPa)	1915	1973	1073	1177	5740	8339
Tensile Strength (MPa)	72	63	52.2	43	56	105
Elongation at Break (%)	11.8	20	83	22	3	3

 

[beeblebrox]

Sounds like you have some settings not quite right for PETG then.

PLA+ does not have much more heat tolerance than PLA. if any. This was pulled from manufacturer specs (no, didn't got to every manufacturer).

	PLA	PLA+	PETG	ABS	3DXTech CarbonX PETG	Polymaker PA12-CF
Deflection temp. (C)	53	53	64	78	77	215
Density (g/cm3)	1.2	1.23	1.27	1.04	1.34	1.17
IZOD Impact Strength (kJ/㎡)	5.4	4.7	4.7	8.5		13.34
Flexural Strength (MPa)	90	74	58.1	66	80	169
Flexural Modulus (MPa)	1915	1973	1073	1177	5740	8339
Tensile Strength (MPa)	72	63	52.2	43	56	105
Elongation at Break (%)	11.8	20	83	22	3	3

That polymaker stuff has interesting specs...have to look that up. But I will say that I have had rockets with fins made of PLA+ (I use eSun) that have sat on the pad for 30 minutes in the hot Maryland sun with no warping. I have seen regular pla rockets fins start deforming at 90°F BUT again, I did make a 3d printed cell phone holder for my car that has held up to the hot temps in there in the sun. I made a PLA+ one and it seriously warped... I wish I could use ABS but my printer does not have an enclosure...

 

[viper2788]

As someone working at a company that is printing PETG for production, you can print it just as fast. Like I said before you just have to get the settings right. This includes nozzle temp (we run at the top of the manufactures recommendation).


It is wet then and you need to dry it. This will happen with most filaments including PLA, although PETG and Nylon are some of the worst.


Nope, they are more difficult to print with. ASA is easier than ABS although both will be much easier with an enclosure. Depending on the part size/shape, these two will warp without an enclosure no matter what.

What printer are you using? I have no issue printing PETG fast.

Bambu Lab. I'm printing PLA at 250-300mm/s and PETG has struggled at half that speed, depending on part geometry. I'm actually printing multiple items at once for production, so speed/reliability is important to me. It'll also be printed at .01mm layer height so thousands of layers

 

[OzHybrid]

That polymaker stuff has interesting specs...have to look that up. But I will say that I have had rockets with fins made of PLA+ (I use eSun) that have sat on the pad for 30 minutes in the hot Maryland sun with no warping. I have seen regular pla rockets fins start deforming at 90°F BUT again, I did make a 3d printed cell phone holder for my car that has held up to the hot temps in there in the sun. I made a PLA+ one and it seriously warped... I wish I could use ABS but my printer does not have an enclosure...

The link for PA12 goes to a link for PA6 ( https://us.polymaker.com/products/polymide-pa6-cf )
The deflection spec you have is for PA6 so the material name needs to be changed from PA12 to PA6 as that's the data you're using. Good news is that PA6 is half the price of PA12...

 

[viper2788]

Scratching PLA altogether - I started test printing with ASA and was pleasantly surprised with default print speeds and results. I've got the thing modeled for the most part, just need to break it into a few sections to be assembled together. That being said, is a cardboard sleeve necessary to have around the rocket motor? I've got ribs that should keep it fairly snug and will also have a threaded cap to lock it in place. Thoughts?

 

[OzHybrid]

Cardboard tubes were historically used because they were available and cheap and relatively strong for their weight. Use 3 d printing to your full advantage. Just printing a tube where a couple of rings would work, would not be using it to full advantage. But make sure there are tapers at the top end to allow the motor to locate easily when you push it in to the top seating. If you are using motor ejection, make sure the ejection charge seals so your gasses don't escape....

 

[thzero]

That being said, is a cardboard sleeve necessary to have around the rocket motor? I've got ribs that should keep it fairly snug and will also have a threaded cap to lock it in place. Thoughts?

Looks like its around ~100C on the heat deflection; motor casing can get up to ~200C. For the 2 second duration? Probably not to big of deal, but the motor will put out heat for a much longer period.

I've seen some replacement engine holders using strakes done in PETG and Resin, and they've worked. But they also so signs of heat wear if you will after a couple of flights. So having them being replaceable seems to work out ok.

 

[viper2788]

Just about finished! I printed out a few in ASA and will be testing soon.

 

[cwbullet]

Right time of year to launch PLA.

 

[sed6]

Just about finished! I printed out a few in ASA and will be testing soon.

View attachment 609241

Could you share the STL with us?

 

[Tech 68]

I'll def give tubes a try. I think I can make some small ribs inside to minimize contact with the motor and provide more air insulation.

The motor ejection/deployment charge needs to be kept away from the printed parts if the part is providing structural support.

 

[thzero]

The motor ejection/deployment charge needs to be kept away from the printed parts if the part is providing structural support.

Depends.

 

[zeketrimmer]

I know nothing of model rocketry (ironically as I'm on this forum), and I'm hoping some of you may point me in the right direction. I've done some preliminary research and I understand the general idea of how model rockets work, but it led me to several questions:

1) So far its about 13" in length and 1.25" in outer diameter. My CAD programs says it should weigh around 4oz (115g) without the motor or any weights added to the nose cone. I'm assuming a D12-3 engine should suffice? (I know its going to be tail heavy and some weights will be needed up top)

2) I'm planning on using PLA, simply because its easy to print and its what I currently have in hand. Do rocket engines get hot to the touch, and possibly cause warping issues if in contact with PLA? I'm thinking of making a threaded sleeve to house the rocket engine. Are there commercial sleeves that may shield the heat a bit? I'm really trying to avoid using PETG if possible, and currently my printers arent fit to print ABS/Nylon/ASA without an enclosure.

3) What size parachute should I go for? I'm going to assume its going to be up to 8oz or so with rocket motor/weights added.

I'm planning on having the "missile mounts" converted to guide a 1/8" launch rod.

If there's anything else I should know or consider, please let me know. Thanks in advance!

View attachment 605240

I would use something like petg. Motor mounts do get hot and will cause warpage. Also. Petg is more resilient to impacts and imo, not that difficult to print with. It is also generally the same price. Why don't you want to use petg?

 

[thzero]

I would use something like petg. Motor mounts do get hot and will cause warpage. Also. Petg is more resilient to impacts and imo, not that difficult to print with. It is also generally the same price. Why don't you want to use petg?

PETG against motors isn't really ideal either, PETG is better than PLA as far as heat goes, but not as good as ABS.

"Do you know that model rocket motors are permitted to reach a case temperature of 200C (392F) and high power rocket motors are permitted to reach 220C (428F) during or after operation? These limits are in NFPA 1125, Code for the Manufacture of Model Rocket and High Power Rocket Motors. Long-burn-time motors are the types that most often approach these limits."

I do from experiments that the Estes A-C caused significant warping when up against the motor itself. Most people I've seen have either used cardboard motor tubes as a insulator, or other insulators, or even throw away plugins.

 

[zeketrimmer]

Cardboard tubes were historically used because they were available and cheap and relatively strong for their weight. Use 3 d printing to your full advantage. Just printing a tube where a couple of rings would work, would not be using it to full advantage. But make sure there are tapers at the top end to allow the motor to locate easily when you push it in to the top seating. If you are using motor ejection, make sure the ejection charge seals so your gasses don't escape....

I did a lot of petg prints when I had to comply with competition guidelines. Petg is definitely worth it. I have broke countless pla nosecones. I've had one petg nose cone and still use it. Even after a bolistic launch. Though, I also use parabolic nose cones so there really isn't any weak points

 

[viper2788]

Turned out alright! ASA has been holding up great to the heat. The original version couldnt handle the ejection pressure and broke in half, but after some reinforcement its been going well.