Difficult print for strength

[Levi Smith]

So, any ideas for how to best print this for strength? 

I've been doing it in petg with 3 or 4 walls, 50%(recently upped to 75%) and recently tried changing infill pattern from default to honeycomb. 

I've been printing it as shown with organic build plate only support.

As expected those flanges are occasionally breaking. 

PLA wont hold up to temps.

I tried abs but never got one to even stay layer fused when you get to the top of the inside. (Though I haven't tried it on my new Anycubic S1)

Petg works pretty well but there's still a visible line all the way across the piece when it does the support layers.

On a different topic I tried printing the support layer in PLA but I've try to get it to keep the petg together at that layer.

Are there other settings that would be more likely for success? 

What are the chances I could get TPU to print this decently and be stiff?

Is there some other material I should try? 

Thanks!

Levi

[Ray Price]

What's the use case and environment?

Can't see if the cavity goes all the way through, but can you split the model across the cavity and print in two pieces?

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[Sean]

CNC Kitchen just released a video a few days ago about a branch of Orca Slicer that has the "Brick Layers" algorithm baked in. He reported some pretty interesting results when he tested some different samples and configurations of settings. He offered a few suggestions that seemed to add to strength values that may help with printing with a traditional slicer algorithm. 

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[Levi Smith]

Cavity goes all the way through. 

It gets wire wrapped around it for part of an electro magnet. 

That being the case I'd never get it stronger by gluing or melting it back together would I?

Which was also why I didn't think printing it laying down would be as good since I was thinking I'd want the layer lines perpendicular to the wire wrapping.

On Wed, Jun 4, 2025, 8:35 PM Ray Price <r...@theraypriceshow.com> wrote:

[Levi Smith]

Hmm, now that's something I hadn't heard of before. I might see if I can give that a shot.

[3D Printing Tips and Tricks]

Armadillo TPU or even better annealed HTPLA.

Currently testing TPU LW at 230c which seems more rigid and way more durable than Nylon.

[Petr Ptacek]

How big is the part? What is the wall thickness? Is there a fillet on the inside between the flanges and the tube?

What I would do:

- I would print this as a tube with one flange placed down and the second separate flange that goes onto the tube with friction fit and glue. You can design a groove into the tube to catch the second flange in the right place. No supports needed.

- I would increase temperature so layers are fused

- I would print this with plastic that has as high Tg as possible and does not creep under the heat, likely ABS (Tg is ~105C). I would not use PLA ot PETG at all (Tg under 80C). Nylon creeps when heated and it is pain to glue it. I would not even touch TPU for this application.

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[Levi Smith]

You think Armadillo, annealed HTPLA or TPU LW would all be significantly stronger than just something like  a 64D TPU?  Or just different things to try?

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[Levi Smith]

It's about 117x82x152mm.  The inner walls are about 4-5mm thick.  Yes, it's filleted.

I'm not the designer but I like your idea with the friction fit.  You think there's enough space to make that happen and keep it strong?

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[Scott Bussinger]

Another option - custom support. Design a part that fills the area between the flanges. Cut it in half to make it 2 "U" shaped pieces. Print the pieces in PLA. Coat the top surface with glue stick as a release agent. Print the main part in TPU with the flange face down. Have the slicer pause printing just before starting to print the top flange. When it pauses, insert the two support pieces, glue side up. Resume the print. When finished, the support pieces should come out pretty easily because of the glue.

I've done this before myself for a similarly shaped project in TPU and it worked great.

I've left out details to keep the explanation shorter, but they're minor details (like tolerances so the supports fit in without being too tight and using some magnets to hold the supports in place so they don't slide around while that first layer prints over them). But it's a very handy technique for clean overhangs without a dual extruder system.

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From: 3d-printing-...@googlegroups.com <3d-printing-...@googlegroups.com> on behalf of Levi Smith <levig...@gmail.com>
Sent: Thursday, June 5, 2025 9:53:10 PM
To: Petr Ptacek <pjpt...@gmail.com>
Cc: 3D Printing Tips and Tricks <3d-printing-...@googlegroups.com>
Subject: Re: Difficult print for strength

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[James Fackert]

TPU more rigid than nylon?

That is totally wrong 

TPU whole purpose is flexibility.

Glass filled  or carbon fiber filled nylon, polycarbonate or petg would be the strong and rigid end.

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[Levi Smith]

Ah yeah... I had some vague thoughts about something like this...  

[Petr Ptacek]

Wow, that is huge. I'm baffled that such a thick plastic part can actually break. Do you have pictures of the broken parts for us to see where the parts are breaking and why?

Are you printing the parts with shells only, or are you using an infill? This is an example where infill will significantly weaken the part, and if the walls are 5mm, you need 5-6 shells (0.4-0.5 extrusion width) with 0.4mm nozzle, which is certainly not the default.

Btw, with part of this size, I would never print it in one piece with supports. It is so big that making a very robust and reliable connection between the flange and the tube is very easy.

[Levi Smith]

Yes, actually I just got a picture back.

Now the black one they dropped on the floor.

The gray one they just said broke really easily. 

These were likely both with 50% infill because at the time I looked I was reading that would be the strongest. I left it at default I believe. 

I've since switched to 75% honeycomb for the last batch I did and that seems maybe stronger....  I believe I upped the walls as well though I almost think the orca slicer based Anycubic slicer I'm using stops at 4 for some reason. 

What bothers me is the lines that run across right at the flange layer, though that didn't seem to be where the gray one broke...

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[Kurt The 3D Printer GUY!!]

Petr mentioned ABS above - and I am a HUGE fan of that. Print it in Two parts - then Acetone weld parts together - and maybe even Vapor smooth the whole part. 

But, for REAL STRENGTH - seriously - TRY Pro-PCTG from 3D Fuel!!!

  Pro PCTG - Midnight Black - 1.75mm | 3D-Fuel - Made In USA

-K

[Petr Ptacek]

Too weak adhesion layer, suboptimal part orientation, and 3d printing unfriendly design.
Just my 2 cents.

[Levi Smith]

Hmm, another interesting option it looks like!

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[markni...@gmail.com]

Levi,

An outside the box solution, if you don't need to make many of these, is to trace the end of the part on to a peice of fiberglass cloth, cut it out with scissors.

Then cover the end of your printed part with epoxy resin, place the the glass cloth on your printed part, then cover the glass with another coat of epxoy resin.

You part will be as strong as phenolic sheet, and will not break.

[Levi Smith]

Yeah that would certainly be a lot more labor intensive but a lot stronger! 

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[3D Printing Tips and Tricks]

Jim

It is not "totally wrong"!

Have you actually tested it yourself? Yes there ARE versions of TPU(including the LW I'm currently testing) that are more rigid than nylon AND more durable. 

https://ninjatek.com/shop/armadillo/

but NOTE... Armadillo is about to be discontinued, But we're finding TPU LW (at faster speeds and lower temps) to be as rigid as PETG and ABS and PLA. But it is not cheap.

Every version of Nylon which we have tested and is available commercially are relatively flexible as compared to PETG, ABS, etc.

Also, In our experience infused filaments, of any kind, are compromised at the fusion lines and are quite brittle as in easy to break.

The rigid forms of TPU are probably the most durable materials we have, but HTPLA (if you can secure the part during annealing and retain your tolerances) is the optimum for rigidity and durability. After complete annealing it is almost as machinable as PEEK! It's also a lot less expensive than the rigid TPUs or infused nylons and as easy to print as... PLA.

IMO...

Don't bother with a redesign.

Print the part with a custom support structure as described by another post but forget about the glue stuff... instead print the support part in  PETG and be sure to make the support almost hollow, minimal outlines and easy to remove. I'd print it in two halves so it can be reused. Print the actual part in HTPLA and insert the support part before the overhang starts. Then anneal the part before you remove the support structure. How to anneal? Get a large pot, fill it with water. Cook it until you see bubbles forming at the bottom. Then turn off the heat and drop the print in and keep it fully submerged for about 15 min. When you remove it be careful to not let the material move, it will likely be soft. The crossover happens after the part is removed from the bath and cooled over about 24 hours.

[Dan Flemming]

Levi,

I watch a YouTube video on strongest bonds a few days ago.

Plastic welding was strongest. 

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[Kurt The 3D Printer GUY!!]

You should share video link. 

Plastic Welding - like Acetone Welding with ABS & Acetone???

-K

[David]

The  squared edges combined with the layer lines are major stress risers in the part printed as-is. Even with a material change, each layer corner wrap is an area of concern for breakage. I would change sand those edges with 100-200 grip sandpaper and follow up with a heat gun pass to remelt them slightly. You're not fully melting those edges, but just enough to re-seal them after the layer lines have been ablated.  

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[Levi Smith]

Are you saying it would be better if the edges were changed to print rounded?

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