3D Printing Material to use for 3D printed bulkheads and E-Bay sleds

[DaHabes]

I'm starting to build out 3" and 4" RDD E-bays for various rocket builds I have in process or upcoming. I intend to use the same sized sled in each E-Bay with the same components (Eggtimer Quark & WiFi, Eggtimer Quantum and Featherweight GPS) for ease of use and transferability if necessary (e.g., one component in an E-bay gets borked for some reason - each E-Bay will have a sled but the sleds will be identical so they can be field swapped easily). I am going to use Blue Tube couplers and switchbands (for component survivability in the event of an ungraceful landing) in case of a since I primarily build with Blue Tube & LOC airframes. I have designed the sled and bulkheads using FreeCad and OpenSCAD, respectively. I do not have a 3D printer, I always outsource the printing to CraftCloud by All3DP.

First question, which materials would be recommended for printing the bulkheads and how thick should they be to hold up to deployment loads? Drogue will obviously be at apogee and should be a minimal stressor, but main deployment always puts some load on the upper bulkhead. I'm assuming deployment under drogue at about 50 mph. I am assuming either PETG or ABS are fine but want to get some expert input.

Second, I'm assuming the sled(s) can be made out of anything. Is PLA sufficient or is something stronger preferable?

Thanks in advance.

 

[cwbullet]

PETG. It is the easiest to print and will last longer.

 

[DaHabes]

Sweet. Thanks.

 

[DRAGON64]

PETG is also my material of choice for strength and heat resistance.

 

[cwbullet]

Sweet. Thanks.

If you want a little more strength, use PETG with CF.

 

[alexzogh]

If you are willing to spend a little more and have a printer that can handle high temps (260+ nozzle, 60-100 bed) I found Filamentum's carbon fiber nylon to be stronger than wood with a higher temperature resistance at the same thickness. The main issues are it's out of stock often, very expensive, and a bit of a pain to print.

If this is your first foray into alternatives to PLA or ABS, I'd follow Chuck's recommendation.

 

[dr wogz]

for a structural part, such as a bulkhead, I would stick with ply-wood. stronger, easier to work with, and glues easily (plastics and glue [epoxy] are 'iffy' at best!) And likely cheaper when laser cut..

 

[jdsmith39]

I've been doing what you are going to do for the last two years. I've used PLA and PETG for bulkheads and sled. Both are fine. Though I'm using PETG more often now because it's on the printer more often. I have/had zero issues with either one.

As far as thickness of bulkheads. I have a range of thicknesses depending on diameter. It's from 7mm to ~12mm. You'll be surprised at how strong these can be.

I've posted all of my bulkheads and sleds. These are all designed around 3" diameter and larger. All sizes have been used multiple times. These are all made for two altimeters.
Link to my 3D models
I have one AV sled that is used in all of my rockets.

I'm currently designing a new sled/bulkhead to work with 2.6" tubes (LOC). I printed the AV coupler with a built-in switch band, which worked much better than I thought it would. Currently the sled will work down to ~1.8". My ultimate goal is 1.6" for the sled. This is also made for two altimeters.

I admit, this would work MUCH better if you had your own printer. I use a Prusa MK3S. I've had it for just about 3 years now and it still is going strong with nearly zero maintenance. There are cheaper printers, but it is an upfront cost and a learning curve no matter the printer you get.

 

[Chad]

I use PLA for sleds and ebays and haven't had any problems but will switch to PETG pretty soon as my PLA spool is almost done. I bit the bullet and got a prusia mk3s last year and 3dprinting has been a game changer for me in the hobby, i love it.

btw if you're doing plywood and need something custom cut, PM me. I have a laser that makes short work of 1/8" and 1/4" plywood.

 

[dvdsnyd]

PETG can have adhesion issues.

 

[Zyzzyva1000]

I have been using PLA (or mostly PLA+) for fin cans/nose cones and ABS or polycarbonate for smaller stuff (retainers, rail buttons, etc). I cannot for the life of me make PETG work. But I figured out ABS and PC so there's that. I have started coating my PLA parts with a long cure finishing resin and that has made the parts much stronger (also makes finishing easier)

 

[ghuber]

FWIW, I do a lot of internal ebay components and nose cones with PLA (Polymaker has a product call Polylite PLA Pro that is both both strong and doesn't crack). One nice thing about these components is that one can then put in heat set inserts to accept mounting screws, for example for the bottom bulkhead of a nose cone (where the GPS lives) or to secure the top of the ebay to the upper body tube. The danger with PLA is that it is sensitive to heat in the summer--left in the sun or even a very hot car and it will deform.

At the same time, I still tend to lasercut plywood bulkeads for more structure pieces that will take a load. So it is not uncommon for my ebays to have a PLA internal part with a plywood bulkhead that is doing the structural work on the outside.

 

[cwbullet]

I have been using PLA (or mostly PLA+) for fin cans/nose cones and ABS or polycarbonate for smaller stuff (retainers, rail buttons, etc). I cannot for the life of me make PETG work. But I figured out ABS and PC so there's that. I have started coating my PLA parts with a long cure finishing resin and that has made the parts much stronger (also makes finishing easier)

It must be your printer or technique. PETG is one the easiest filaments to print for me.

 

[cwbullet]

I use PLA for sleds and ebays and haven't had any problems but will switch to PETG pretty soon as my PLA spool is almost done. I bit the bullet and got a prusia mk3s last year and 3dprinting has been a game changer for me in the hobby, i love it.

btw if you're doing plywood and need something custom cut, PM me. I have a laser that makes short work of 1/8" and 1/4" plywood.

That works north of the Mason-Dixon Line, but in the hot south where it can get 130 F in your car or truck, PLA tends to become a little too flexible.

 

[DarthMuffin]

PETG for me. I'm in the NW, but many launches are in the desert where it can be over 100 degrees and much more than that in a car or rocket.

CF PETG (atomic filament) works well too, and is a little stiffer with a few more degrees heat tolerance. I like it for printed bulkheads. Also a little heavier. You wouldn't think so with CF, but that's what my print tests say. I have not found any CF impregnated filaments to be conductive or a hindrance to RF.

I also use ABS sometimes when I need less weight, more strength and heat tolerance, and something easier to glue (welds with acetone). So basically min dia/competition/extreme things.

I have a roll of polypropylene (what blow molded nosecones are made from) and it can work for the right shaped parts (i.e. not a flat sled). It is very light and tough with excellent layer bonding. Boy does it like to curl up though, if you think ABS is bad for that you ain't seen nothin' yet... Also it's borderline "unglueable" without some exotic expensive stuff. If it didn't have those drawbacks I would use it everywhere.

 

[thzero]

Ive only done printed bulkheads in smaller rockets but use PETG. All the parts going onto rockets I use PETG like others mention. PLA finds use for drill guides, etc.

 

[OverTheTop]

Remember when designing bulkheads that many will need to take the pressure generated by ejection charges. As rocket diameters go up the forces become significant so you need to design appropriately. Additional thickness or support from something inside the bay are two ways of helping with this.

Also, consider what happens if the bulkhead fails, by designing for off-nominal outcomes. Remember the z-axis weakness if using an FDM printer. Make sure a bulkhead failure won't lead to the recovery components separating.

 

[Zyzzyva1000]

It must be your printer or technique. PETG is one the easiest filaments to print for me.

I think I am going to have to get some different PETG, because I have only ever tried this one roll but just can't get it to work no matter what I do

 

[cwbullet]

I think I am going to have to get some different PETG, because I have only ever tried this one roll but just can't get it to work no matter what I do

PETG is very very sensitive to the amount you squish it and hydration.

 

[manixFan]

I think I am going to have to get some different PETG, because I have only ever tried this one roll but just can't get it to work no matter what I do

On my Prusa I find Windex gives me the best adhesion for PETG (original bed type). If anything, I have trouble with it adhering too strongly. I'll clean with alcohol or acetone if the bed is really mucked up, but Windex has solved a lot of my over-adhesion issues. Of course a lot depends on the type of bed you have, but my guess is if you try different cleaners you'll find one the works best for you. Just make sure it's compatible with your bed.

As stated, PLA does not get along with typical summer temps in the south, certainly not in Texas. I've used a few PETG 3D bulkheads, and as mentioned, they don't standup as well as plywood or certainly G10. But for areas where the load won't be great, they do work well. However, I basically consider them expendable after a few launches. I've also tested some printed charge holders (sized for .38 special cases) and they stood up quite well to the charges, but again, I consider them expendable.

If you do try PETG, you need to keep it sealed when not in use so it does not absorb moisture, and really work on getting your first layer height dialed in. The other setting that made a big difference for me is retraction – that's what I found best controls stringing. (Tiny strings of filament between sections.)

Good luck,


Tony

 

[Zyzzyva1000]

On my Prusa I find Windex gives me the best adhesion for PETG (original bed type). If anything, I have trouble with it adhering too strongly. I'll clean with alcohol or acetone if the bed is really mucked up, but Windex has solved a lot of my over-adhesion issues. Of course a lot depends on the type of bed you have, but my guess is if you try different cleaners you'll find one the works best for you. Just make sure it's compatible with your bed.

As stated, PLA does not get along with typical summer temps in the south, certainly not in Texas. I've used a few PETG 3D bulkheads, and as mentioned, they don't standup as well as plywood or certainly G10. But for areas where the load won't be great, they do work well. However, I basically consider them expendable after a few launches. I've also tested some printed charge holders (sized for .38 special cases) and they stood up quite well to the charges, but again, I consider them expendable.

If you do try PETG, you need to keep it sealed when not in use so it does not absorb moisture, and really work on getting your first layer height dialed in. The other setting that made a big difference for me is retraction – that's what I found best controls stringing. (Tiny strings of filament between sections.)

Good luck,


Tony

Its not adhesion to the bed (I have an adventurer 3 with a textured flexible bed, never had a problem with adhesion (in fact usually its hard to remove prints). My issue has been layer adhesion and such bad stringing that the prints are unusable or just fail from layers not adhering. I have a filament dryer and even recalibrated my bed (higher than usual to take PETG's need to not be squished) - still failure.

Anyone have a brand of PETG they like? I think Im just going to toss what I have and try something else.

 

[manixFan]

Its not adhesion to the bed (I have an adventurer 3 with a textured flexible bed, never had a problem with adhesion (in fact usually its hard to remove prints). My issue has been layer adhesion and such bad stringing that the prints are unusable or just fail from layers not adhering. I have a filament dryer and even recalibrated my bed (higher than usual to take PETG's need to not be squished) - still failure.

Anyone have a brand of PETG they like? I think Im just going to toss what I have and try something else.

Poor layer adhesion is often a print temp issue or over cooling via fan (kinda the same thing). Before printing a lot with PETG I did some testing to find the best temp for my printer and filament:

https://www.stlfinder.com/3dmodels/?search=PETG+Temperature+Test&free=1
Once you get the temp and the extrusion rate dialed in, you really should not have any problem with layer adhesion. As I mentioned earlier, stringing can often be minimized by adjusting the retraction amount. One issue I have had is very thin parts sagging or deforming due to heat buildup. For things like nosecones, as the part tapers to a point I'll adjust the fan speed or add a layer pause to allow the filament time to cool. I could also reduce the printhead temp, which would probably be a better solution.

Good luck,


tony

 

[Kane]

PETG bulkheads, 9 mm thick. They survived a forward closure impact ejected from a CATO.

 

[Lt72884]

I've been doing what you are going to do for the last two years. I've used PLA and PETG for bulkheads and sled. Both are fine. Though I'm using PETG more often now because it's on the printer more often. I have/had zero issues with either one.

As far as thickness of bulkheads. I have a range of thicknesses depending on diameter. It's from 7mm to ~12mm. You'll be surprised at how strong these can be.

I've posted all of my bulkheads and sleds. These are all designed around 3" diameter and larger. All sizes have been used multiple times. These are all made for two altimeters.
Link to my 3D models
I have one AV sled that is used in all of my rockets.

I'm currently designing a new sled/bulkhead to work with 2.6" tubes (LOC). I printed the AV coupler with a built-in switch band, which worked much better than I thought it would. Currently the sled will work down to ~1.8". My ultimate goal is 1.6" for the sled. This is also made for two altimeters.

I admit, this would work MUCH better if you had your own printer. I use a Prusa MK3S. I've had it for just about 3 years now and it still is going strong with nearly zero maintenance. There are cheaper printers, but it is an upfront cost and a learning curve no matter the printer you get.

interesting. I printed some up last week and noticed during stress testing that they had A LOT of flex. I used 20% infill, 4 walls and a little hotter on the temps to get some good fusion of layers. Takes about 2 hours to print a quarter inch thick bulkhead on my cr10 for a LOC-IV av bay. I have seen your files before and they are very well designed.

For my LOC-IV i calculated about 50Lbs of force and then multipled that by 2. I may use a 1 inch diameter washer to help spread that force out over a larger area. I was able to hang about 40Lbs from the 3d printed bulk head, but i did not dare try a snatch force test by dropping the 40Lbs from a 6 inch height.

 

[jdsmith39]

interesting. I printed some up last week and noticed during stress testing that they had A LOT of flex. I used 20% infill, 4 walls and a little hotter on the temps to get some good fusion of layers. Takes about 2 hours to print a quarter inch thick bulkhead on my cr10 for a LOC-IV av bay. I have seen your files before and they are very well designed.

For my LOC-IV i calculated about 50Lbs of force and then multipled that by 2. I may use a 1 inch diameter washer to help spread that force out over a larger area. I was able to hang about 40Lbs from the 3d printed bulk head, but i did not dare try a snatch force test by dropping the 40Lbs from a 6 inch height.

I have several versions for 4-inch diameter rockets. For LOC Precision AV bays (has the thinnest bulkhead) the bulkhead is 7mm thick, 40% infill and 3 perimeters. Mine have very little flex with these settings. Also keep in mind, the threaded rods will squeeze things together which helps the 3D printed part.

Madcow AV bay 4inch version is 12mm thick, 25% infill and 3 perimeters. I have a fiberglass AV bay 4inch which uses the same settings as the Madcow. I've had no issues with any of them. They've all been used many times now. I've cracked one (surface only) by over tightening the rods. It was still fine in the launch. Printed a new bulkhead afterwards just in case.
Definitely use the biggest washers that fit. Of course, I'd do that even with any other material, too.

 

[cwbullet]

My four-inch AV bay is 25% infill and is 7mm think. The key to infill is the method of infill you use and its direction.

 

[Lt72884]

I have several versions for 4-inch diameter rockets. For LOC Precision AV bays (has the thinnest bulkhead) the bulkhead is 7mm thick, 40% infill and 3 perimeters. Mine have very little flex with these settings. Also keep in mind, the threaded rods will squeeze things together which helps the 3D printed part.

Madcow AV bay 4inch version is 12mm thick, 25% infill and 3 perimeters. I have a fiberglass AV bay 4inch which uses the same settings as the Madcow. I've had no issues with any of them. They've all been used many times now. I've cracked one (surface only) by over tightening the rods. It was still fine in the launch. Printed a new bulkhead afterwards just in case.
Definitely use the biggest washers that fit. Of course, I'd do that even with any other material, too.

Thanks for the reply. Ill increase the thickness a bit and the infill. Im starting a new build this work and it will be my first dual deploy setup. Im using the lociv rocket kit with a j270. This will be my beginning stages of hopefully getting to a bigger and better rocket. Maybe by next summer (2024) ill begin my personal level 3 process.

 

[Lt72884]

My four-inch AV bay is 25% infill and is 7mm think. The key to infill is the method of infill you use and its direction.

Exactly. I just use plain rectangular infill because 99% of my parts are not functional haha.

Also, rectangular infill seems to be pretty strong.

What infill are you using? I use prusa slicer or ideamaker at times

Thanks

 

[caveduck]

I use PETG because ordinary PLA isn't suitable for use in the desert heat (though I think some of the newer PLA+ formulations have higher deformation temperature). PETG is pretty strong, rigid without being brittle, and machinable. For me the brand matters quite a bit - I only use Atomic or Prusa PETG now. Hatchbox and similar gave me more problems with stringiness and very narrow first layer tolerances. I've never had any moisture absorption problems with Prusa and Atomic.

For infill I'm usually doing either 100% rectilinear or 15-25% hex, and try not to push overhangs beyond 45˚, though I can go a bit higher at the risk of an occasional blown part.

 

[cwbullet]

Exactly. I just use plain rectangular infill because 99% of my parts are not functional haha.

Also, rectangular infill seems to be pretty strong.

What infill are you using? I use prusa slicer or ideamaker at times

Thanks

I have had pretty good success with Rectilinear, Triangular, and Honeycomb with the last one being my favorite. I use a lot of Atomic PETG with CF.