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 Post subject: Most cost effecient assembly for Shapeways
PostPosted: Mon Aug 20, 2012 7:22 pm 
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Hey, I looked before asking this. Does anyone know the most cost effecient way to lay pieces out to be loaded onto shapeways? Like place seperate pieces to form an overall cube shape? I mean the overall size is just LXWXH, so I guess it just depends on the puzzle and what allows pieces to be the most compact. I do know, however, once the file is a certain size (on either length, width, or height) that it requires a larger, less exact, printing proccess.

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 Post subject: Re: Most cost effecient assembly for Shapeways
PostPosted: Mon Aug 20, 2012 7:39 pm 
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As far as I can tell, the resolution of WSF is the same no matter the size of the print. I think they just have one SLS printer configuration.

As for reducing cost, there are a few competing factors.

1) The total amount of material to be printed (the volume) is what you are charged for. You want to make your pieces as hollow as possible. Solidworks calls this "shelling" which is a different "shell" than the "shell-mech". .8 mm walls will do. You must make a hole between the inside and the outside of the piece so that Shapeways doesn't register the inner volume and charge you for it.

2) Shapeways has a density discount. If you can make your model at least 10% dense then you can get a big discount. The way they calculate this is to draw a bounding CUBE around all of your pieces. If the volume of your pieces / volume of bounding cube is greater than or equal to .1 then you get the discount.

Because the bounding box is a cube, you want to make your parts packed as close to a cube shape as possible. Having even one dimension wider than the other three costs you a lot of volume. It can be very hard to manually pack parts into a cube. TomZ has written a program to automate this and it does a much better job of achieving a high density than you can do by hand.

There is a way to cheat Shapeways and always get the density discount. If it gets abused too much though I think they'll catch on and close the backdoor. See http://www.shapeways.com/blog/archives/564-How-To-3D-Print-High-Polygon-Models-with-Shapeways.html

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 Post subject: Re: Most cost effecient assembly for Shapeways
PostPosted: Mon Aug 20, 2012 7:56 pm 
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bmenrigh wrote:
As far as I can tell, the resolution of WSF is the same no matter the size of the print. I think they just have one SLS printer configuration.

As for reducing cost, there are a few competing factors.

1) The total amount of material to be printed (the volume) is what you are charged for. You want to make your pieces as hollow as possible. Solidworks calls this "shelling" which is a different "shell" than the "shell-mech". .8 mm walls will do. You must make a hole between the inside and the outside of the piece so that Shapeways doesn't register the inner volume and charge you for it.

2) Shapeways has a density discount. If you can make your model at least 10% dense then you can get a big discount. The way they calculate this is to draw a bounding CUBE around all of your pieces. If the volume of your pieces / volume of bounding cube is greater than or equal to .1 then you get the discount.

Because the bounding box is a cube, you want to make your parts packed as close to a cube shape as possible. Having even one dimension wider than the other three costs you a lot of volume. It can be very hard to manually pack parts into a cube. TomZ has written a program to automate this and it does a much better job of achieving a high density than you can do by hand.

There is a way to cheat Shapeways and always get the density discount. If it gets abused too much though I think they'll catch on and close the backdoor. See http://www.shapeways.com/blog/archives/564-How-To-3D-Print-High-Polygon-Models-with-Shapeways.html


Wow, thanks for the info! TomZ's program sounds interesting. I had been wondering if there was a program for that.

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 Post subject: Re: Most cost effecient assembly for Shapeways
PostPosted: Mon Aug 20, 2012 8:40 pm 
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Just a small correction: the bounding box isn't necessarily a cube, it can be a cuboid of any dimensions. It's just the smallest box that fits around all of the parts such that the box's edges are aligned with the model's X, Y, and Z axes.

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 Post subject: Re: Most cost effecient assembly for Shapeways
PostPosted: Mon Aug 20, 2012 8:45 pm 
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will_57 wrote:
Just a small correction: the bounding box isn't necessarily a cube, it can be a cuboid of any dimensions. It's just the smallest box that fits around all of the parts such that the box's edges are aligned with the model's X, Y, and Z axes.

Hmm I thought for sure it was a cube. Assuming similarly-sized pieces you could just line them all up in a straight line and get the discount rather easily.

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 Post subject: Re: Most cost effecient assembly for Shapeways
PostPosted: Tue Aug 21, 2012 6:29 am 
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The bounding box is necessarily a cuboid because only three dimensions are used (x,y,z), but it does not have to be a cube e.g. x=y=z. The bounding box is used to:

1) Define the maximum (and minimum) model size which can be accommodated by a particular machine. For standard WSF the minimum model size is x+y+z ≥ 7.5mm and maximum is 660 x 350 x 550mm

2) Used to calculate the model's density which is the total volume of the WSF material used divided by the volume of the bounding box. If this is >0.1 then the cost of any material used over 20cm3 is discounted by 50%.

The size of the model does make a difference to the accuracy. The accuracy at any point in the model is +/- 0.15mm, but, if you have one large model (not a collection of small parts) then the accuracy is +/- 0.15% of the longest axis. This means that as long as any one part is less that 100mm long, the accuracy will be 0.15mm, but parts larger than this will be less accurate e.g. if it was 660mm then the error could be nearly 1mm.

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 Post subject: Re: Most cost effecient assembly for Shapeways
PostPosted: Tue Aug 21, 2012 8:42 am 
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Gus wrote:
The size of the model does make a difference to the accuracy.
This is incorrect. If a model exceeds a certain size, it will be printed on a larger, less accurate printer with greater layer thickness. However, this maximum size is very large it will usually not apply to puzzle makers.

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 Post subject: Re: Most cost effecient assembly for Shapeways
PostPosted: Tue Aug 21, 2012 9:23 am 
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TomZ wrote:
However, this maximum size is very large


Should we think then in > 30 x 30 x 30 cm^3 or so?
Or even furniture sizes?


I don't want to know the price of a Shapeways chair..... :?

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 Post subject: Re: Most cost effecient assembly for Shapeways
PostPosted: Tue Aug 21, 2012 1:10 pm 
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TomZ wrote:
Gus wrote:
The size of the model does make a difference to the accuracy.
This is incorrect. If a model exceeds a certain size, it will be printed on a larger, less accurate printer with greater layer thickness. However, this maximum size is very large it will usually not apply to puzzle makers.
The figures I quoted are directly from the Shapeways site; large models are less accurate, so the size of the bounding box has an effect on the accuracy. Once the model size gets over 100mm in any direction, the accuracy will be affected. Obviously, for TP puzzle designers 100x100x100mm is a very large puzzle :shock:

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 Post subject: Re: Most cost effecient assembly for Shapeways
PostPosted: Tue Aug 21, 2012 2:54 pm 
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Gus wrote:
The figures I quoted are directly from the Shapeways site; large models are less accurate, so the size of the bounding box has an effect on the accuracy. Once the model size gets over 100mm in any direction, the accuracy will be affected. Obviously, for TP puzzle designers 100x100x100mm is a very large puzzle :shock:

I've had plenty of models that are larger than 100mm in some directions, and the quality doesn't look any different. Are you sure these numbers are correct, or did you mean 100cm?

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 Post subject: Re: Most cost effecient assembly for Shapeways
PostPosted: Tue Aug 21, 2012 3:56 pm 
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Imagine you made a model which was like a 660mm long ruler with a small 1mm diameter peg at each end. The accuracy placement of the pegs could be out by just under 1mm i.e. +/- 0.15%. For models built with many parts, like twisty puzzles, this is not a problem, because even if the model was 660mm long, the accuracy for an individual part would still be +/-0.15mm because the part is only, say, 20mm in any direction.

So, for TP models, the +/-0.15% error would probably never apply, and all the parts are built to +/-0.15mm.

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