Cura settings for really, really strong print?

[aag 6]

I am trying to print some M10 screws with tough PLA. With the AA0.25 nozzle, the resolution is very good and the threads are usable without modifications. However, the screws are simply not strong enough; the threaded part snaps away from the head as soon as I give some torque. I thought that my Cura settings would be really strong, but that was not the case.

Which settings are critical in order to achieve the strongest possible print? If push comes to shove, I'd even print everything solid (100% infill) but when I tried that setting Cura would still leave a lot of open space (maybe because of the gradual infill, or something).

[burtoogle 514]

Hello @aag, I would say 100% infill, solid, not gradual. Also, print as hot as you can while still obtaining good definition.

[Smithy 1,144]

It would be better to print it horizontally, but in case of a screw, you can only print it with PVA, which makes no sense.

 

I am not sure, but I think there is a difference if you say 100% infill, or increase the wall count to a high number that you also get 100% infill. The pattern is different because then only walls are printed. Give it a try.

 

[yellowshark 153]

 and I am wondering if you might be stronger with a bigger nozzle; every time you print two adjacent lines you have a join and I wonder if that  introduces a weakness. What would be stronger, 10 lines from the 0.25 nozzle or one line from a 2.5 nozzle?

[aag 6]

...or is PLA simply not the right material? Would I obtain more strength from e.g. polycarbonate?

[ahoeben 1,955]

The problem with printing a bolt, is that the skin of the thread is printed on top of infill structures of the head. Unless that part of the head is printed solid, the connection between the head and the thread is going to be weak.

 

You don't have to print the entire thing solid though. You can add something like a cube to the scene and change its Mesh Type to "Modify settings for infill of other models" in Per Model Settings, and then overlap it with the bolt head. Then you can add the "Infill density" setting and set it to 100%. That way only the bolt head is printed at 100% infill.

[Smithy 1,144]

5 hours ago, aag said:

or is PLA simply not the right material?

 

You can use ToughPLA which is quite stronger than normal PLA but still easy to print. 

I guess the best material for screws would by Nylon.

[eldrick 65]

I agree with Smithy - use a high number of walls, like 50, so it prints solid.

In any case, a small printed plastic screw is unlikely to be strong enough to be useful, because the unthreaded core is only around 8mm at most.

Edited January 21, 2019 by eldrick

[Asger-P 3]

Hi Aag

 

Just set the wall thickness to 8,5mm (34lines), which is just over the half of the nut size, this will give you a solid bolt.

If you use something less e.g. 5mm then you will get some layers of infill right where the thread and the head meet, this happens even if you set top and bottom to 20 layers, probably a Cura bug.
 

Good luck

Best regards

Asger