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I'm attempting to model and print a globe. The semi-circular arm that holds the globe has an outer diameter of 98mm and inner diameter of 92mm, so the arm is fairly thin. The arm has a small hole on either end that fits around a protrusion at each pole of the globe to hold it in place. The hole extends into the arm only a few millimeters, so it doesn't go all the way through.

I printed the arm in ABS and it ended up being a bit too flexible to hold the globe securely. Obviously I could do things like making the arm thicker or extending the globe's protrusions all the way through the arm, but I'd prefer not to if I don't have to (you know, artistic integrity or whatever).

Would printing in PLA result in a more rigid part? I've tried to do some googling on this, but couldn't really find a definitive answer. Most comparisons focus on strength which I assume doesn't necessarily correlate to flexibility.

I'd also welcome any other suggestions for making the part more rigid.

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  • $\begingroup$ Just curious... did you get around to solve this? $\endgroup$ – mac Jan 21 '18 at 23:39
  • $\begingroup$ Unfortunately, I haven't had much of a chance to play around with things. I did one test with PLA and while it did seem a bit more rigid, it was still too loose to securely hold things. I am hoping to try playing around with the infill settings in the next few days. Sorry it's taking so long to accept your answer. It's looking like I'm going to have to make some design modifications, though. One detail I neglected to mention in the question was that the outer ring is actually holding an inner ring of a similar thickness, so the idea of inverting the pins and holes sadly won't work for me. $\endgroup$ – Pak Jan 22 '18 at 4:05
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The flexibility of 3d plastics has a lot to do with the additives manufacturers use. The same base material with additive X may have very different properties than the one with additive Y.

That said, generally speaking PLA is known to be more rigid (and brittle) than ABS, but less strong. So: you have a fair chance at giving it a go with PLA, albeit you my end up with a more delicate object in the end.

There is a well known youtube channel, whose author has performed a lot of quasi-scientific testing on common brands of filament (PLA and not) where you can get an idea of the relative rigidity of the filaments. You can find the table with the results here (look for the "bend test" columns).

However the very firs thing that came to mind when reading your post, is that you could simply swap pins and holes by putting the holding pins on the arm, and the holes on the globe instead. This would allow you to preserve your design and to have longer pins.

Things you could try when it comes to printing (unless you are already doing them):

  • Print the arm flat so that the layers stretch from pole to pole uninterrupted.
  • Print with near solid infill (solid infill can be problematic if your extrusion calibration is not perfect), like 95% and cubic infill (for more uniform properties along the full length of the axis.

Finally, you could try to anneal the arm in your kitchen oven. This process works by warming the part until it becomes pliable and then letting it cool very slowly. The end result is that the molecules arrange themselves in a more "crystal-like" way and the part becomes stronger and more rigid. Beware that annealing changes your part dimensions so you should definitively do some experiments with a test cube and find out the direction and percentage of the shrinking before going "all out" on the arm.

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  • $\begingroup$ Besides Thomas, there's also Stefan / CNC Kitchen that does (quasi) scientific tests of filaments and print patterns $\endgroup$ – Trish Jun 27 '19 at 10:57
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To make it more rigid I would add more shells than to use solid infill.

There are higher strength PLA's, but they only gain their higher strength and temperature resistance after annealing. From reviews I've seen, there is only a percent or two difference in size, but this is more complex than it seems because the difference is different along the layer lines or crosswise from them. However, even normal PLA will anneal, so if you have any you could do some quick experiments.

If you have a high-strength nozzle, you could use NylonX. This is nylon with carbon fiber to make the part rigid. There are also carbon fiber PLA's ad ABS's, but I've never experimented with them.

Otherwise, I like the answer from @mac

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Print thinner layers. Also, you did not mention the other dimension of your arm. If you view the globe with the arm to the left, then you have said the thickness in the X direction (left to right) is 6mm. But what about in the Z axis (away from you)? You could make it thicker in that direction to improve its rigidity.

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