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I have a 3D object that I print with 0.6 mm nozzle and white PETG. At the moment I can't print the layers in another direction since I use 3D printed threads. The object is a de-seeder bit for the sorrel fruit. Some of the teeth break off when using it (see red arrow showing the missing tooth that breaks off when used below).

If you want to see how it's used, I have provided an animation/video of it.

Photo of various 3D printed models of de-seeders of various heights with an inset photo of sorrel fruit

Upclose photo of the 'bit' end of the de-seeder with an arrow showing where a tooth is missing

I was wondering if there was a way to increase the strength of the teeth on the bits from breaking. I was thinking of using some type of nail hardener but was wondering if that would work or if I should try and use something else.

I'm also willing to try a different 3D material but it needs to be able to withstand summer heat in Florida in a garage which gets to be 97 °F or 36.11 °C and be printed with an E3D Revo 6 nozzle (which is like a hardened steel nozzle). PLA will just melt/turn rubbery.

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    $\begingroup$ forces applied parallel to layer lines will provide the results you are experiencing. Even a surface treatment as you suggest will not add much strength. I don't have a materials suggestion, but you are on the right train of thought in that regard. $\endgroup$
    – fred_dot_u
    Commented Sep 14, 2023 at 0:08

2 Answers 2

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Alter geometry

You experienced one of several factors of print strength:

  • the layer-layer boundary is always weakest

So, we need to make sure to strengthen that as much as possible. Let's start with the shape as it is:

Teeth geometry

Now, how can we increase the strength? Layer-layer strength is linear to area, so can reduce the number of teeth. Next, thicken the walls - two is already more than twice as strong while 4 to 5 is hefty strong.

reduced geometry, thicker walls

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I think you already know that in this print orientation, the tooth breaks off easily. Maybe you can try to print this thing in two parts? Use a horizontal orientation to print the saw-tooth ( with its complicated structure, using organic support might be good) and later combine with the thread?

The other things that I can suggest are:

  1. Is it possible to make the saw-tooth base wider and thicker, although it will result in a reduced number of teeth in the circle and also make the centre hollow bore smaller? This will increase the surface area bonding the layers in the tooth, thus giving it more strength.

  2. Try altering the printing temperature and layer height. Generally higher temp and lower layer height result in greater strength. You can check out a great 3D Printing YouTuber CNCkitchen's articles:

  3. Yeah, using another material such as ABS would give better strength and heat resistivity. But it's also harder to print.

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  • $\begingroup$ Thank you for the interesting links... good stuff. $\endgroup$ Commented Sep 15, 2023 at 6:11

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