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 Post subject: Is this part strong enough for 3d printing? (and a hint)
PostPosted: Fri May 31, 2013 2:04 am 
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Hello all,

I was doing a puzzle design, and it encountered some... problems with thin parts. (Bonus points if you can guess it)

Image

As you can obviously tell, the area of concern is that really thin area. That is a little smaller than 2mm. Would it be strong enough to survive shipping and such?

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 Post subject: Re: Is this part strong enough for 3d printing? (and a hint)
PostPosted: Fri May 31, 2013 2:12 am 
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It's certainly not ideal but it should work. It will survive shipping just fine.

WSF is quite flexible but it tears very easily, especially with a twisty motion. When assembling the puzzle, if you have to put that piece in near last you may have some trouble getting the foot in without breaking it or causing that stem to tear. I'd suggest printing an extra 10% of that piece just in case. Also, when you shell the part, make sure the stem stays solid all the way through.

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 Post subject: Re: Is this part strong enough for 3d printing? (and a hint)
PostPosted: Fri May 31, 2013 2:15 am 
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bmenrigh wrote:
It's certainly not ideal but it should work. It will survive shipping just fine.

WSF is quite flexible but it tears very easily, especially with a twisty motion. When assembling the puzzle, if you have to put that piece in near last you may have some trouble getting the foot in without breaking it or causing that stem to tear. I'd suggest printing an extra 10% of that piece just in case. Also, when you shell the part, make sure the stem stays solid all the way through.



Thanks. I shelled it extra thick at 1mm so it should be fine.

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 Post subject: Re: Is this part strong enough for 3d printing? (and a hint)
PostPosted: Fri May 31, 2013 2:25 am 
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Don't shell the neck, and 2mm should be fine. I occasionally split parts like this and only shell the large parts before combining again.
Can't wait to see it!

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 Post subject: Re: Is this part strong enough for 3d printing? (and a hint)
PostPosted: Fri May 31, 2013 2:27 am 
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Thanks for all the help. When I shelled the part, the thin bit was solid anyway. So that was ok.

Another hint: It is jumbling only, and unbandaged a bit.

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 Post subject: Re: Is this part strong enough for 3d printing? (and a hint)
PostPosted: Thu Jun 06, 2013 3:11 pm 
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Stress concentrates at sharp acute angles, which can cause fractures. On thick geometry there's ample strength for the material to resist stress fractures, but this piece is pushing the limits of the material. Don't forget, 3D-printed parts often exhibit tiny voids and variations--if an irregularity happens to occur at that sharp corner, the part will break!

Use a fillet to round out that corner. Not only does that distribute the stress over a larger area, it also keeps the tensile stresses more parallel to the surface which helps retain integrity around any irregularities in the part.

If an ordinary fillet would block other pieces then put the fillet in a gutter as shown in the lower-right diagram. That's not as optimal as a simple fillet, but it's more resilient than the sharp angle would have been.


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File comment: Fractures can start when stress is concentrated at sharp interior angles. Prevent fractures by spreading the stress with a fillet or a fillet-and-gutter.
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 Post subject: Re: Is this part strong enough for 3d printing? (and a hint)
PostPosted: Thu Jun 06, 2013 3:35 pm 
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I am not a puzzle builder, but have assembled many Shapeways puzzles, so I know the material.
It is indeed flexible enough to stand slight torsions. But the question is, if this piece might be caught
during a twist and upper and lower half are twisted by 90 degrees or more. The piece might stand this
once or a few times, but sooner or later it will be torn by the mechanical powers.

As mentioned already rounded shapes are evident.
Regarding the real dimensions, consider how much is left if ordered as e.g. as WSF polished. This
takes away a little bit more material. But might be even better, if this flattens the surfaces and allows
pieces to move aside each other much better.

For small pieces it is very important to have well working rails to lead them through.
AND: The rounded edges of larger pieces shouldn't be designed too "relaxed". This causes larger gaps
in the rails and small pieces get unnecessarily caught.

This all is only from my experience of assembling and playing. Anyway I hope my experience might be useful.

Kind regards - Frank

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 Post subject: Re: Is this part strong enough for 3d printing? (and a hint)
PostPosted: Thu Jun 06, 2013 3:51 pm 
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Adding an intermediate shell will strengthen the connection.

Oskar

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