[Updated on: Sun, 10 January 2010 20:51 UTC]

[Updated on: Mon, 11 January 2010 22:50 UTC]

I've been dealing with the walls issue too.

A few months ago I submitted a handful of small, ~ 3.6 cm high typography models which I had hollowed out to save $ and weight. They successfully printed, but since then I have been submitting additional similar models which pass uploading but are subsequently rejected at manufacture.

This made me curious about my original letters. Since I modeled them entirely hollow with no front or back, I didn't really know if they were actually hollow.

So today, I cut one open. Lo and behold, it was solid! It could have been made with a laser cutter.

So, SW, was it easier to just charge me for less material ( as if my models were really hollow), send me the models as is and never tell me, or what was the issue?

here's the hollow model just prior to STL export:


and here's the cut-open model:

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reecejames wrote on Sun, 13 February 2011 11:27

...In my case, I managed to make the tiny gear teeth on my traction engine using a bunch of 1mm squares, arrayed around the perimeter of the cylinder.

Hi Reece;

Would you mind posting a closeup of the area circled in green? I'd like to see what those squares look like up close and what the spacing is between each square on the gear. You used 1mm squares because the depth (or wall thickness) of the wheel rim the gear teeth attach to is 1mm, right?

Just to double-check your explanation of how surface detail versus wall is calculated: Lets say I add an item extending from the surface of a wall 0.7mm thick (built with WSF material). To check the item I draw a cube on the wall surface centered on the item with dimensions equal to the thickness of the wall (0.7mm x 0.7mm x0.7mm in this case).

If the item falls within the boundaries of the 0.7mm cube it is considered to be a surface detail and will be printed even though the dimensions of the item are less than 0.7mm (the minimum allowed wall thickness permitted for WSF material). If the item extends beyond the boundaries of the 0.7mm cube it is considered to be a wall and must have a minimum thickness of 0.7mm (because it's built of WSF material) in all three dimensions.

That steam engine is freaking awesome!! I hope to produce models with that level of detail too.

Scott

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Certainly



You are quite right.

For WSF
If the item falls within the boundaries of the 0.7mm cube it is considered to be a surface detail and MAY be printable even though the dimensions of the item are less than 0.7mm. If the item extends beyond the boundaries of the 0.7mm cube it is considered to be a wall and must have a minimum thickness of 0.7mm in all three dimensions.

The may is something to do with the angle of intersection with the wall. For instance, the rivets on the engine are printable as they are wider than they are high. I guess that's a good rule of thumb, if it classifies as detail, make sure it is wider in the two dimensions on the wall than it extends from the wall.

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I would expect that to be rejected. That is because it will become a wall somewhere up to the 0.4mm mark from the wall. As it is a long length, it will certainly exceed the the 0.7 in one dimension, thus counting as a wall.

Remember a detail has to be under 0.7 in all 3 dimensions.

My recommendation is to make it 0.701 and then sand it down. You could also do it as a series of small separate details with a small space between them. (Think of like a dotted line of details along the ridge.) That would be allowable.

[Updated on: Fri, 18 February 2011 00:45 UTC]

Here's a shape that was accepted for printing. Dimensions shown are in inches (0.1mm roughly equals 0.004 inches):

The thickness at the center of the column is 0.028" (0.7mm), the minimum thickness allowable for White Strong & Flexible material.
The four 'points' of the column extend from the 0.7mm wall 0.35mm and taper from a thickness of 0.7mm at the wall to 0.35mm at their tips - all within reecejames' rule-of-thumb for allowable surface detail dimensions.

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Thank you, Noshaper.

I didn't explain that the column is an extrusion attached to a larger 4cm x 4cm x 20cm body. I suppose if you wanted to print just the column you could add a small piece of sprue to the 1.4mm side protruding 1.1mm and another piece to the 1.75mm side 0.75mm long to meet the 2.5mm x 2.5mm x2.5mm minimum dimension requirements.

I'm waiting for the model to be printed and shipped (assuming it can be printed and it arrives in one piece). Here's a 3D closeup shot of the model

There's a sprue connecting the top of the columns together to hopefully prevent anything from breaking.

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It's here - the columns turned out pretty good. Here's a quick shot of one end.

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Thanks, Reece! Your advice was crucial to making it work out on the first try.

The posts are 38mm tall - it's right on the edge of what can be printed as an unsupported extrusion. See how the post in the middle has twisted slightly to the left? I'm going to add some sprue to the center of the posts to stabilize them.

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I think the most annoying "feature" of Shapeways is the seemingly arbitrary rejection of parts due to thin walls. I just had a model rejected because of this.

What's ironic is that I made the new parts thicker than the same part which had successfully printed many times before.
The image below shows the ""thin wall" error, with the successfully printed thinner parts below (all more than 1.7mm thick at the thickest). I believe that the error is in the large wings at the bottom of the image.



So why does a thicker part (2mm thick at the thickest) get rejected when in the past I've had at least six of the large wings printed - with absolutely no errors? The new wings are as thick as the smaller wings in the image above.

It's like throwing darts -blindfolded.

Frank

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OK, I can see where detail becomes wall thickness. I can see that a tapered edge could get flagged. But I still can't see what's wrong with the following models. Both have been printed many times and now they are being flagged as having thin walls.

In both cases the walls are 1.5 or 2.0mm (well above the 0.7 for SF) the the section flagged seems to be across the face of a curved surface. Support could find nothing wrong with it but could also give me no remedy other than to "adhere to the design rules for the material."

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Here's the second model that was also flagged for thin walls across a curved surface.

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