3D printing for HPR

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SolarYellow said:
So, essentially, painting an ABS filament print with this stuff should make it significantly stronger and reduce the tendency to split between layers?

https://plastruct.myshopify.com/products/ppc-2
Or if there's another solvent that could be purchased in a quart can at any decent hardware store outside CA for a lot less $/oz, that would be even better...
Click to expand...
Potentially......how much strength is hard to quantify, of all the 3D printer hobby filaments ABS is iirc the most easily bonded. Even a thin ABS slurry might work (ABS dissolved in Acetone or MEK) as a bondind agent.

Most of the "best" 3D printed rockets I have seen done were using Nylon 66(? I think) and were post print annealed and processed makingva very tough rocket....that was also heavy for its size, same model could have been built from FG for probaby 75% less weight or cardboard and ply for 50% less weight (specific to this particular rocket which was not just 3 or 4FNC). The printer was also not a hobby grade printer either.
 
JohnCoker said:
I haven't run sims yet, but I can fly most 54mm motors. Maybe a J250 first flight and then a J800 if it survives that?
https://www.thrustcurve.org/motors/guide/653fe2eb6ed72400026ca5ca/summary.html
Click to expand...
ok... was asking because my 3d printed fin 5.5" build just went up just fine on J350.
https://www.rocketryforum.com/threads/my-l2-project.167503/Next on docket is a J415,. J460, and J540.

Granted I did put a few layers of fiberglass over the fins. They are PETG that were printed out with the grain (i.e. layers) following the leading edge of the fin, and also airfoil shape. I did more of the fiberglass for strength on landing, etc. than anything.
 
rharshberger said:
Potentially......how much strength is hard to quantify, of all the 3D printer hobby filaments ABS is iirc the most easily bonded. Even a thin ABS slurry might work (ABS dissolved in Acetone or MEK) as a bondind agent.

Most of the "best" 3D printed rockets I have seen done were using Nylon 66(? I think) and were post print annealed and processed makingva very tough rocket....that was also heavy for its size, same model could have been built from FG for probaby 75% less weight or cardboard and ply for 50% less weight (specific to this particular rocket which was not just 3 or 4FNC). The printer was also not a hobby grade printer either.
Click to expand...

Yeah... annealing, if the material can handle it, certainly would help. I imagine that yes the slurry with ABS might work too.

Similar to the ABS slurry, a light glaze of epoxy on a 3d printed part seems to add some strength to it, at least with PETG it seems to seep into the pores (how deep though?!?). But not done any like real testing in a controlled environment to know if that really does any good.
 
rharshberger said:
Actually John, I think ABS is a better choice than PETG from the standpoint of bonding and post processing options/methods. PETG neither bonds well nor does it mechanically finish well (sand, file, etc) like ABS. You can also wipe a tin layer of solvent on ABS and it will chemically bond imperfections, PETG forget about it. ABS though has its downsides too, its more difficult to print with, temperature stable and vented enclosures or environment.
Click to expand...

What about ASA?
 
Rschub said:
There are many applications for 3D printed parts, I myself would not use them for any primary load bearing structure due to the inevitable scatter in actual strength that the manufacturing process produces by default.

Conventional materials are produced in controled conditions in huge quantities and tested for their physical properties. 3D printing is not that. Every machine, operator and material will be different from the others.

I am sorry, but in my opinion your test results will be only good for your process, only for as long as you don't change it. It will not necessarily be applicable to anyone else, except as an example of how to qualify 3D printed materials for oneself, which is a worthy goal.
Click to expand...
agree with you... sort of....

And gotta say John Coker does a great job of documenting and using engineering on his work (read Johns stuff!)

I do agree the materials and process need to be controlled, with equipment calibrated and all the variables listed, and those that affect the outcome controlled. Having said that, with some basic controls and calibration we could come up with something like a b-basis allowable. https://ntrs.nasa.gov/api/citations/20040111395/downloads/20040111395.pdf for reference. Having said that, i have other concerns...

1) Do you follow the recipe, exactly......
Material and process control is just that you need to CONTROL the critical processes and Monitor them to make sure they are correct. Very few folks on here have actually calibrated their printer (not just is the bed flat but actually calibrated). Some examples are;
  • use the extruder without a nozzle and heat and MEASURE the actual amount of material that is extruded when you feed out a theoretical 1M of filament, how does the actual length compare to theoretical
  • weigh a finished part to see if the actual weight correlates with the density and the volume
  • Print a cube, measure the corner heights and edges to determine; Overall height tolerance, squareness, shrinkage factors etc.
  • Verify the gap from the extruder to the bed
  • Measure the bed temperatures over a grid pattern.. how even and how close to the edge before it cools.

2) Do you know what you want....
I would be willing to bet that very few folks on her actually know what mechanical properties they need? Saying, i want it the same as (fill in the material here) doesn't work. Do I need the stiffness of wood, the bearing strength of fiberglass, the toughness of nylon? and how 'stiff or strong' do I need. Is it shear strength, do I need to thread a hole? is a one for one substitution of PLA for fiberglass good enough? most likely not. Most of the 3d parts I have seen fail were due to bad design not bad material choices - this includes designing in infill or using designed in ribs or stringers.
  • Do you understand what using infill does to the strenght of the part?
    • And how it is different in the X/Y direction vs the Z
  • Have you designed in ribs or just let the slicer do an infill?
  • Are structural filles built in?
  • Are you designing for hot wet or cold. Side note from testing, parts sitting in the sun got hotter then motor tubes during a launch, all aprts see heat!

3) are you controlling the process, really....

Following the process means doing EXACTLY the same things each time. For example:
  • Do you start with dry filament EVERY time (and yes PET-G does need to be dried)
  • Do you replace the nozzle frequently enough that the ACTUAL nozzle diameter is still correct
  • DO you have an enclosed machine? If not how are you keeping the temperature and humidity the same
  • Same minimum wall thicknesses? same feed rate? Same supplier for the filament?
  • Do you need to and should you aneal the parts ( I use a suis vide machine for this)
    • What is the shrinkage from aneeling?
4) How do the parts interface to the rest of the rocket...
  • How do your parts attach to the rocket and have you accounted for the limitations / benefits of the materials?
  • Remember the temperature and fit for heat inserts is also a process, just cranking up the soldering iron isnt process control.
  • Have I designed in bonding aids / bonding features?
Mike (actually works on material and process controls for materials) K

P.S. I did mention John is pretty good at this stuff.
 
Last edited:
kramer714 said:
agree with you... sort of....

And gotta say John Coker does a great job of documenting and using engineering on his work (read Johns stuff!)

I do agree the materials and process need to be controlled, with equipment calibrated and all the variables listed, and those that affect the outcome controlled. Having said that, with some basic controls and calibration we could come up with something like a b-basis allowable. https://ntrs.nasa.gov/api/citations/20040111395/downloads/20040111395.pdf for reference. Having said that, i have other concerns...

1) Do you follow the recipe, exactly......
Material and process control is just that you need to CONTROL the critical processes and Monitor them to make sure they are correct. Very few folks on here have actually calibrated their printer (not just is the bed flat but actually calibrated). Some examples are;
  • use the extruder without a nozzle and heat and MEASURE the actual amount of material that is extruded when you feed out a theoretical 1M of filament, how does the actual length compare to theoretical
  • weigh a finished part to see if the actual weight correlates with the density and the volume
  • Print a cube, measure the corner heights and edges to determine; Overall height tolerance, squareness, shrinkage factors etc.
  • Verify the gap from the extruder to the bed
  • Measure the bed temperatures over a grid pattern.. how even and how close to the edge before it cools.

2) Do you know what you want....
I would be willing to bet that very few folks on her actually know what mechanical properties they need? Saying, i want it the same as (fill in the material here) doesn't work. Do I need the stiffness of wood, the bearing strength of fiberglass, the toughness of nylon? and how 'stiff or strong' do I need. Is it shear strength, do I need to thread a hole? is a one for one substitution of PLA for fiberglass good enough? most likely not. Most of the 3d parts I have seen fail were due to bad desing not bad material choices - this includes designing in infill or using desinged in ribs or stringers.
  • Do you understand what using infill does to the streght of the part?
    • And how it is different in the X/Y direction vs the Z
  • Have you designed in ribs or just let the slicer do an infill?
  • Are strutural filles built in?
  • Are you designing for hot wet or cold. Side note from testing, parts sitting in the sun got hotter then motor tubes during a launch, all aprts see heat!

3) are you controlling the process, really....

Following the process means doing EXACTLY the same things each time. For example:
  • Do you start with dry filament EVERY time (and yes PET-G does need to be dried)
  • Do you replace the nozzle frequently enough that the ACTUAL nozzle diameter is still correct
  • DO you have an enclosed machine? If not how are you keeping the temperature and humidity the same
  • Same minuimum wall thicknesses? same feed rate? Same supplier for the filament?
  • Do you need to and should you aneal the parts ( I use a suis vide machine for this)
    • What is the shrinkgage from aneeling?
4) How do the parts interface to the rest of the rocket...
  • How do your parts attach to the rocket and have you accounted for the limititions / benifits of the materials?
  • Remeber the temperature and fit for heat innserts is also a process, just cranking up the soldering iron isnt process control.
  • Have I desinged in bonding aids / bonding features?
Mike (actually works on material and process controls for materials) K

P.S. I did mention John is pretty good at this stuff.
Click to expand...
A reply to my on post yah I know kinda lame.... but,

If this sounds like a lot of work to do, yeah it is. If you buy a sheet of material like G-10 someone else has done all this for you, even plywood has some very sophisticated inspection and process control, metal alloys come with certifications and test data. If you want o do this stuff yourself, either do the heavy lifting, or build TEST and fly with lots of margins.
Mike K
 
Having materials with known and reproducible properties is what allows us to construct the modern world.
There are too many unknowns with 3D printing to say we are there yet.
I usually suggest a direction with my posts and let others fill in the details, thanks Mike!
I guess I am a typical designer type.😎
 
I have done ABS prints for my Nike Apache 1/2-scale rocket. The 4" nosecone has dozens of flights on it. There was also a transition, 3"-4", that has flown to M1.4, and a 3" conical nosecone that has flown to M2.14.
https://www.rocketryforum.com/threads/hpr-transitions-materials-and-techniques.179653/post-2426734
If you design the part for the material properties, and how it interacts with the other parts, then you will succeed. It is like any other material really, although not quite isotropic.

Remember you can set up test forces using simple things like levers made from 4"x2" wood. That allows you to test for full flight loads plus margin, or take it to destruction if you like.
 
kramer714 said:
If this sounds like a lot of work to do, yeah it is.
Click to expand...
I want to strike a balance here. I also don't have any way of calculating the mechanical properties "needed." (Otherwise we could do this all through calculation and not need physical testing.) As hobbyists we develop a feel for what works and are familiar with our favorite materials.

My goal is to put 3D printed parts into context with more familiar materials and hopefully start a process that will make the general hobby community comfortable with 3D printing. By this I do not mean the 3D printing enthusiasts. (I doubt I can tell them anything anyway.) I'm thinking of the RSOs and maybe eventually TAP/L3CC members.

When someone comes in with a partly or fully 3D printed rocket, I want there to be a path to evaluating the fliers skill and design/material choices and not have the discussion stop with "3D printed parts are not allowed."
 
JohnCoker said:
My goal is to put 3D printed parts into context with more familiar materials and hopefully start a process that will make the general hobby community comfortable with 3D printing. By this I do not mean the 3D printing enthusiasts. (I doubt I can tell them anything anyway.) I'm thinking of the RSOs and maybe eventually TAP/L3CC members.

When someone comes in with a partly or fully 3D printed rocket, I want there to be a path to evaluating the fliers skill and design/material choices and not have the discussion stop with "3D printed parts are not allowed."
Click to expand...
Perfect scope, IMO. One can't test everything, but perhaps your (John's) well-known skills and discernment can demystify 3D printed parts for the betterment of both the builder and the RSO.
 
Over on the [*REDACTED*] there is a proposal to have a group of people make up identical batches of [*REDACTED*] using their own process and testing the results to see what the differences are.

If you put out a request with a simple .stl file, a material, and an infill percentage, and had people send you their samples for testing we would get an idea of just how variable the results are in the real world.

Sorry to be a pest about this, but the lack of data on the mechanical properties of these printing materials is a pet peeve of mine.

At any rate, I will be very interested in seeing the results of your testing. 👍
 
I agree with John Coker's ideas of striking a balance, and using 3D printed parts along side of the traditional materials.

Here is a 3D rocket that I printed using foaming PLA (the filament foams and expands when heated, making it about 50% lighter). It's intended to be combined with a phenolic airframe as the backbone and motor mount. This has a 54mm hole for the phenolic in the center, and 6x 6mm holes for pultruded carbon fiber rods, used in kite building. This is a 30cm section, about a foot long, and very light. I "slather it with fiberglass" on the outside, and on the flat areas where the 30cm sections meet, so it works like a fiberglass centering ring or bulkhead, and transfers the forces from the phenolic backbone/mm to the outside fiberglass skin. The carbon fiber rods stiffen everything, and help carry the thrust forces upwards through the rings and bulkheads. The 3D printed part has to be just strong enough to hold the form for the outer skin, and temporarily hold the carbon fiber rods in place, I'm not counting on it for structural strength. I use 1mm walls and a 10% 3D-cubic fill to keep it light. Because PLA can't handle high temps nor UV light, it gets sealed away. There is also a foaming version of ASA, which is stronger, can handle higher temps, and is UV resistant, but it suffers from warping: not as bad as ABS, but somewhere between PLA and ABS.
So, all the rocket related stuff goes inside (motor mount, e-bay, parachutes, etc.) in a sort of traditional rocket construction, but the outside skin can be anything you can print. Mine is a long needle shape made of about 8x 30 cm sections, making it 8 ft long, like a very long nose cone and tail cone. It opens up possibilities of making airplane cockpits and unusual printed details (rivets, window hatches and such) on the skin area, or as making aerodynamic transitions when staging. The skin needs to be able to hold its shape during flight, and transfer it's forces via bulkheads to the inside airframe, whether that be rods or interior tubes, or whatever. The skin no longer needs to be load-bearing for all the thrust.
The same can be done with exotic fins, whether fantasy related, aircraft related, or with a symmetric airfoil shape, but leaving a cavity for a structural piece of G10 fiberglass or plywood which gets epoxied to the internal airframe. John could strengthen his 3D-printed Nike fins with such a composite construction. The skin can be something other than purely structural.
I can imagine you could use this technique to make a good X15 plane, with it's unusual wing transitions and airfoil shapes, or a Star Wars X-wing fighter. Using 3D printed parts combined with traditional building techniques to make good rockets gives some interesting possibilities.

IMG_20231031_132135.jpg
 
I am definitely open to having other people contribute parts for testing. Right now, the blocker is access to a UTM and I need to get the first set of samples broken, particularly the plywood samples, so that I know where we're starting at. I think testing hypotheses 1 and 2 will be done soon, but 3 will be a more involved process and input from other people there would be perfect.
 
JohnCoker said:
As a side note, I'm also pursing a "just try it" approach with my best guesses. I built a 3" Nike-Smoke with everything 3D printed except the tubes and motor retainer. Of course there I took advantage of the ability to print things that can't be easily cut with a CNC router such as rings with integrated gussets and a 1-piece fin can.

It was during that process that I decided I wanted to know more about how 3D printed parts compared to traditional ones. The RSO/TAP/L3CC community is familiar with traditional materials, so if we could put 3D printed parts in context, it will help their acceptance.

These parts are printed in ABS on a Bambu X1C with 50% infill. Probably PETG would be a better choice as it is more easily printed, but ABS has been my go-to material so I wanted to start there.

View attachment 612714

I actually reprinted the fin can in 3 colors after this photo, and that's what I ended up using, but the picture below appears to be the only one I have of all the parts together.
Click to expand...

I'm sorry for being off-topic here, but have you shared STLs for that nose + fincan anywhere? Those look great!


On-topic, I've printed a bunch of nose cones in ABS and generally just made them thicker-walled and higher-infilled than I really thought I needed, continuing my general over-building habit. I'm intrigued to see your results!
 
DragonRocketry said:
I have 2 printed nose cone that I am working on to make molds from and I got a lot of time in them just getting them smooth enough to start the process of laying up the mold.
Click to expand...
I'm curious what your process is. I've sanded several printed NCs and fin cans not for layups but only to reduce the surface roughness. The first one was definitely a learning experience. I have found that wet sanding by hand produced the best results in the shortest time. I progress from 80, 220 and then 400 grit. I am satisfied with the surface after sanding with 400 grit.
 
wsume99 said:
I'm curious what your process is. I've sanded several printed NCs and fin cans not for layups but only to reduce the surface roughness. The first one was definitely a learning experience. I have found that wet sanding by hand produced the best results in the shortest time. I progress from 80, 220 and then 400 grit. I am satisfied with the surface after sanding with 400 grit.
Click to expand...
To me, if I care, putting a layer of a finish epoxy on top of the print will give you a better surface to sand and fills in the gaps, especially if its a colored piece,
 
JohnCoker said:
I finally have the second batch of results back from the testing lab, so I can report results for hypotheses 1 and 2:
https://www.jcrocket.com/printed-components.shtml
The most interesting part is next: how to design and print parts that are as strong as plywood on consumer 3D printers.
Click to expand...
The parts have to be stronger/unit weight than plywood. Or what's the point? Well, there is the fact you can include other design elements for other purposes in a single component. But that's some of the time, not all.
There's a parametric designer under my files.
The link is for the parametric centering ring designer. Shows in the description below as the header for the repository...

https://www.rocketryforum.com/threads/norms-scad-file-repository-and-3d-printing.170781/post-2541403
 
Depending on how the 3D printed part is incorporated, it's actual strength may not matter much...

My BALLS rocket was minimum diameter 75mm M that went to 26 K feet. the body/fins/nose were fiberglass but all interior components were 3D printed with simple PLA (!) including a test of 75mm "motor capture" with PLA printed "ben-wa-balls"... [video below] (I had an eye bolt as a backup in case they failed).

Nose cone AV bay had threaded 3D part printed and epoxied into the nose conde and the AV bay screwed into that 'coupler'. Buy my retention to the nose was kevlar that went past the side of the threaded coupler and was epoxied to nose cone itself. So the 3D printed AV bay doesn't really experience forces.

My mid AV bay was similar - all PLA with screw in AV bay for dual deploy - but the shock cord passed along the side of the av bay and was epoxied so that the forces should not be experienced by the plastic AV bay. [Ironically I used proline 4500 for the first time and apparently didn't clean / scuff the fiberglass coupler and so the epoxy bond to the fiberglass failed... I've only used Rocket Poxy before and never had a problem so I need to learn more about the Proline stuff...]

The shock cord was attached to the motor with 3D printed 'ben-wa-balls".... Not really ball shaped, there were four of them fit so that they gripped the forward closure of the AT motor simply by being held against the body tube (min diameter). Each one had a slightly different length of kevlar bonded into it with Rocket Poxy. The different lengths were to test how many would fail (if any) before there was a final eye bolt in case they all failed. Of the four, only one melted enough to release from the motor (if I had used more infill, maybe it wouldn't have failed). Here is a video from when removing the motor after the flight to see how they fared...


View attachment Ben-Wa-Balls-Motor-Capture.mp4

If I were to use 3D printed centering rings and the span was small enough, I'd probably use enough rocket poxy so that it provided the strength and temperature 'resistance' so that I didn't care - so I'd be using the CR more as a mold instead of structural....
 
thzero said:
It doesn't say, but did you use 100% infill on the FDM parts?
Click to expand...
I explicitly stated that all initial prints were with the printer defaults. That varies quite a bit by printer, with the X1C having the lowest infill and enabling fast speed by default.

I believe that increasing the infill percentage will be one way to increase strength, but that needs to be tested...
 
JohnCoker said:
I explicitly stated that all initial prints were with the printer defaults. That varies quite a bit by printer, with the X1C having the lowest infill and enabling fast speed by default.

I believe that increasing the infill percentage will be one way to increase strength, but that needs to be tested...
Click to expand...
Ah, yes I see under samples you did.

But yes, #of walls/shells and infill might indeed play a difference. Depends on the part too.
 

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