PETG-HF weird layer problem

[user_265483612]

Hey folks,

im trying to print a bottle cage for my bicycle using PETG-HF. Generally the print works just fine and looks great too.

Its only two sections that i cant get to print properly. The look bad and are also very brittle (orange arrows):

The problem starts on the same layer on both sides (blue arrows) and gets worse the higher the print goes (orange arrows).

The bottle is pushed into the cage from the side, so the cage itself needs to have some flex. I figured printing it upright and having the layer lines horizontal to have lateral flex would work best.

The problem is repeatable with every print and always looks the same.

• filament was dried for 8h in Creality dryer
• used default Bambu PETG-HF profile
  • as a test i completely disabled cooling but that does not change a thing, in fact the pictures above are from that print without cooling
• tried another spool of also dried PETG-HF

Im looking for any suggestions and how to get this print to work properly.

[ElektroQuark]

It looks like the is no enought support and the model oscilates with the print head movement.

[Rosch]

in my eyes it looks like the two uprising parts are not stiff enough as long as they were reconnectet by the end ring of holder.
i would place a breakout conneting part between these two flanks with has a very thin connection line. easy to clean after breaking away

[Olias]

@user_265483612

Im looking for any suggestions and how to get this print to work properly.

I’m assuming you don’t have access to the original CAD. If you do, then the answer is different from what I might offer to simply optimizing printing. So I will focus on print optimization.

1. If this is going to be mounted on a bike and subject to shock and vibration, the vertical printing method you’re using will most likely produce stress fractures along the weakest lines of the print. I’d recommend running the print in both vertical and horizontal orientations and see which one cracks less.
   

   

2. It appears that one of your goals is to produce an attractive print. You can have strong and you can have pretty, but unless the design is 3D printer-friendly–this one isn’t–you will likely be unable to achieve both. So choose which one is more important to you, a part that will be functional and last or one that will look like it came out of a mold but will quickly succumb to vibrational stress cracks from the weight of the water bottle.

3. The choice of tree supports is ideally suited for artistic or cosmetic prints but as you have learned on your own, they are not well suited for functional prints with straight and long geometries. Again, turning the print horizontally just might give you better results but the best tool is to use grid supports and increase the wall distance from the default of 0.35mm to 1.35mm, this will give you more space in the vertical vector to pull the supports more easily away from the plastic but you will still have the grid to contend with.
   

   

4. Try using the Manual Grid supports and to paint where the supports need to go. This will mitigate the areas of contact to those trouble spots. This is how that works. Select grid(or if you want, tree) manual version and then select paint supports. Left-click paints green(supports), right-click paints red(Block supports). You can micro-manage where supports go and do not go.
   

   
   
   
   

5. The last tip is that you can further improve but not completely eliminate, the attachment grid lines when using grid supports by increasing the spacing of the grid. You will have to experiment with your model to find out the magic ratio. This feature is also available with tree supports but may not be as effective as grid. Again, there is some trial and error involve here.
   

   
   
   
   

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BTW: When I say 3D Printer-Friendly, here’s an example of a water bottle holder that has a geometry that is self-reinforcing. Notice that the designer created a repeating pattern whereby supports likely wouldn’t be needed at all and the surrounding material helps distribute the stress evenly throughout the structure.

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[user_265483612]

Thanks a lot for the responses so far! They are great ideas i can try. Before i do though…

I’m assuming you don’t have access to the original CAD. If you do, then the answer is different from what I might offer to simply optimizing printing.

I actually do have access, I designed this myself in fusion

So before i try fixing the print somehow, i’d be interested in input for the model.

The most important requirement is that their needs to be lateral flex to be able to push in the bottle from the side. The bottle cage you gave as an example might work great, but it requires space above to be able to put the bottle in.

This the case im trying to solve for:

[Olias]

@user_265483612

So before i try fixing the print somehow, i’d be interested in input for the model.

That’s actually great news!!! It means you really can control the print much more accurately.

So here are just a couple of tips, some you likely are already aware of gauging by the design.

1. Chamfers are better than fillets when it comes to transitioning angles with FDM printing. I often use chamfers to relieve the first transition angle and then use finer filetts at the chamfer boundaries. This ensures that the lines of force are spread more evenly.

2. Wherever I have a surface, transition where there is no “perfect” orientation, I’ll thicken that part of the wall and use lofts and sweeps to make the transitions smoother. So as an example, in this section of your photo, the model could greatly benefit from using a smoother loft that would ease the transition and make the need for supports far less if at all.
   

   

3. In this section here, I’d go for full-rounded fillets or two fillets on each edge. This will cause the filament to curve around more smoothly. I do see evidence of the need for filament fine tuning, particularly with max flow rate calibration. combined with fillets, rhat will ease the harsh curve

   

So in this example, I used a full rounded fillet which is easier to print. In this example of a cup rim, I chose the inside and outside of the cup as the fillet entities and then chose the top of the lip as the surface being rounded.

Here, I’ve tried to do the same using two fillets on each edge of the cup lip. This is not quite as smooth but if your CAD doesn’t have the full rounded feature, it’s a way to force it into a full round.

So in this section here, I see evidence of a fillet.

I’m guessing that this is how a fillet likely started out in your example.

Here’s how I might have done the same thing using chamfers instead.

First Take the corner and chamfer.

Then take the transition boundaries at the chamfer edges and use a fillet on them to gain the max advantage.

When you’re done, the shape should look more like this.

Most chamfers at a 45 degree angle will normally not need supports but you may have to do some test shapes to find the sweet spot as far as angles go.

Now the last point I might suggest may be controversial because it uses more filament and takes much longer to print but in exchange you will get a stronger part. That suggestion is to mimic the “swiss cheese” appearance of the model above and see if you can fill in these areas with a hole pattern.

Turn this:

And make that empty middle look more like this:

I’m sure others will have more suggestions but that’s the things that come immediately to mind. Some of these may not work in your model but the concepts can be applied as you see fit. My strongest suggestion is to design test models of equal scale of the final product and verify which of the methods work best for your filament and design.

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One last note. Don’t rely on infill. Instead, make your wall loop overly thick by increasing them to an amount that will ensure 100% wall thickness. This will override any infill and make for a really strong part.

vs