Thin Walls

Of course! I'm just finishing tinkering with it so that I get a version which is usable by other people than myself. It works, even now, although my degree of faith in its results is not yet high.

After that, my sincere hope is to toss it to you guys, get you to run it on a whole bunch of known-good and known-bad meshes, and work with you to refine a version which can receive the Shapeways seal of approval - if it passes this, we'll print it.

Armed with that, I think my next project will then be a script which runs the thickness scan, nudges vertices outward in proportion to their degree of violation, and repeats until everything passes. I expect this to be slow - a "start it and leave for work / go to bed" kind of affair - but given the existence of the first script, it should be easy enough to continue on into the second.

Perhaps this is already answered or is common knowledge but I could not find it.

I once read that if you create a hollow object that is closed, the support material will (obviously) be trapped inside. In such a case, should we still be careful with wall thickness? Or can we treat it as being a single solid when considering wall thickness?

You must still worry about wall thickness. Wall thickness restrictions are primarily about stability, secondarily about preventing printer problems. Neither of those issues are helped by trapped support material. HTH...

Hey there Minimum Wall Thickness Discussion folks!

This new colour material has a minimum wall thickness of 3mm I see. I did some pretty detailed reading about what that means as opposed to a surface "feature".

So my question is ... how does minimum thickness apply to shells? Because there is more stability in a closed or semi closed structure than on a straight or stressed wall, I have noticed in some materials you can sneak in smaller wall thicknesses and have them work. I have, in some cases, gotten away with .5mm walls for shells.

I ask this because:

I'm sure the Bowie Bunny, which is created as a shell, has a less than 3mm thickness. Hold on, I have one in black detail here, I will measure ...

It is somewhere around 1mm thick.
(poor lil Bowie Bunny ... He is now dissected lol. I will order a new one - he is so cute)

Is this also true for the Bowie Bunny that Shapeways folks have advertised as a colour print? It must be, because it doesn't seem that Bowie Bunny solid, or 3mm could be that price. Or could it?

-Whystler

Peter,

Good info.

Is the Bowie the Bunny you printed out in the Coloured Sandstone material, the same as the small Bowie Bunny available as a shell in the catalogue that I ordered in black detail? Or is the coloured Bowie Bunny solid?

-Whystler

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:

From the looks of it, you didn't leave the filling material anywhere to get out, and they missed flagging it upon submission. And then the trapped filling material got solidified somewhat (maybe in some postprocessing step, maybe in shipping, maybe just over time) and is what you see there. Betcha it's weaker than the exterior if you test it.

Yes, give the surface a scratch. My guess is that it's just packed in tight. You'll probably be able to excavate quite extensively. Do you think?

-Whystler

In practice, the answer seems to be YES unfortunately. This seems to be the problem I'm having. Tapered shapes are being flagged as walls now when before they were not. Here's an example:



1-43 driver by Dattodesign, on Flickr

Same here!!



I'm seeing the same problem here with gear teeth. The gear is a nice large wall, but the teeth themselves, which only extend out 0.4mm, are causing the issue.

Considering how many previously (successfully) printed models are coming back with the thin wall error, Is there any way to streamline how this affects an order? If we could have 24 or 48 hours to edit our models, and re-submit them, and maintain the same order (paying the price difference , of course) That would be very much preferable to the coupon code applicable to the next order. Next order? What unneeded model shall I choose to fill the order out to the $25 minimum

I'm sure it's great for Shapeways to have another order with another $25 minimum, but from the customer standpoint, it's unsatisfactory.

Well I've successfully had the model above enter production! Big thank you to Kevin for his detailed explanation.

Things to take away in the case of my above post;
• A detail becomes a wall somewhere between 0.2 and 0.4.
• Detail comprised of 1x1x1mm squares or circles is acceptable geometry. (Make small gearteeth out of lots of little cubes)
• Lots of detail seems to crash mesh medic with a too many polygons error. (The model was around 44000 polys when submitted)

Basically a detail with an edge or corner less than 90° and or in a complex shape that does not fit into a 90° angle will be flagged as not printable.

To check if it's safe, draw a 1x1x1mm cube and see if it fits within the geometry touching the outermost surface, if it doesn't, it's not printable.

Best rule of thumb I could come up with.

thanks for your explaination, but I'm not sure I understand this correctly:

• A detail becomes a wall somewhere between 0.2 and 0.4.

To check if it's safe, draw a 1x1x1mm cube and see if it fits within the geometry touching the outermost surface, if it doesn't, it's not printable.

Are you saying a detail smaller than 1mm at any axle can't be printed? I hope I misunderstood you....

I'll see if I can explain a little better.

If you create a wall of material. Any item that extends out of that wall, is either a wall or a detail. If a cube of the wall size x wall size x wall size fits within, it's a wall. If it can't, then the maximum it can extend from the wall is somewhere between 0.2 and 0.4 depending on wall thickness and angles on that detail.

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. Physically there isn't much difference and in actual fact, the teeth are smaller.

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

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.

Thank you, Reece!

I'm going to modify the extrusion shown here:

https://www.shapeways.com/forum/index.php?t=msg&th=4553&a mp;start=0&

I'll make the extrusion 0.7mm thick up to the cutouts, then taper the "teeth" from 0.7mm to 0.4mm over the remaining 0.5mm of the extrusion.

If this is rejected I'll just make the entire extrusion 0.7mm thick and use a sanding stick (https://www.walthers.com/exec/productinfo/232-525) to taper the edge down to 0.4mm.

The car will have a few rivets on it - I'll follow your advice.

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.
:laughing: