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Thin Walls [message #7408] Thu, 22 October 2009 12:59 UTC Go to next message
avatar joris  is currently offline joris
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As per Woody's suggestion I'm opening up a topic here for you to discuss your thin wall issues.

The wall thicknesses per material:
White, Transparent & Black Detail: 1mm
White, Strong & Flexible: 0.7mm (I would personally always keep to and recommend 1mm).
Cream Robust: 1mm
Stainless Steel(depends)

There are a number of issues with regards to wall thickness:

1. Our filters are not good at checking them at the moment so your model might upload OK but once it is ordered we might still reject it.

2. Some models that have successfully been printed previously are currently being rejected due to thin walls.

3. With Stainless Steel it is difficult to determine wall thickness and if the model will print ahead of time.

4. It is difficult to measure wall thickness in a lot of modeling tools.

1. We are improving our filters and will get a major update to the wall thickness filter within two weeks. Additional updates will follow and each will make the problem a little less likely to occur.

2. We apologize for rejecting previously printed models. We should have communicated this better and in advance. We should also have been clearer to you. We screwed this up.

What has happened is the following: initially we were very experimental and wanted to help everyone push the envelope of 3D printing. We therefore printed models that might fail and happily printed them a few times if they did fail. We tried until we got it right and then sent that model to the customer. As more and more orders flowed in this became more and more difficult to do. A failed model is another process, another set of steps that one person has to undertake. These experimental models cost us money in the extra hours in materials and handling spent on them. They disrupt the normal flow of things from digital to your object. Production people gradually started to become more stringent on the 'printability' of a model. This to keep the ever increasing torrent of orders flowing to you. There are only so many hours in a day and they chose the path of getting the most orders out of the door in time. At the same time we generally became less adventurous and experimental. Whereas initially we were focused on pushing the envelope, we are now more focused on process optimization and keeping costs down. The goal after all is to make 3D printing as inexpensive as can be. To eventually turn 3D printing into a technology that everyone can use to make everything. Before we were completely aware of it we were rejecting models that we should not have rejected and becoming too boring. We don't want to be boring.

Over the coming two weeks we will reevaluate our criteria for accepting and rejecting models. We will strive to find the right balance between the optimal process and pushing 3D printing forward into the unexplored. We apologize for our poor communication on this matter.

3. Stainless Steel is a new material and process, there are no design rules. By Saturday I will put a tutorial live giving you a more in depth look into what will and will not work with Stainless Steel. This process however is likely to remain a 'hit or miss' one for some months. I hope however to give you significantly more clarity and information.

4. We are currently evaluating several tools that you can use to check wall thicknesses. Once we are done testing them we will do a blog post about the tool(s) that is(are) up to spec. I hope to be able to do this by Saturday but can not be sure.

To sum up:

by November 4th we will have a new wall thickness check live for you that will help in ameliorating this problem.

By November 4th we will have reevaluated our rejection guidelines and hopefully stuck the right balance between experimenting and cost.

By October 24th I will publish more information about the Stainless Steel guidelines.

Hopefully by October 24th we will have completed evaluating a suitable tool for wall thickness checking.

If you have a wall thickness issue, tell us about it below. Also, if you have any ideas, or concerns that we have not addressed, please tell us also.

Joris





Re: Thin Walls [message #7413 is a reply to message #7408 ] Thu, 22 October 2009 17:21 UTC Go to previous messageGo to next message
avatar woody64  is currently offline woody64
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High,

thanks for starting this discussion.

1. It would be very helpful if the designers knows which old models are in danger of beeing rejected next time due to too thin walls.
Is this information available?

2. Is there a guide how to deal with such objects:
http://www.shapeways.com/forum/index.php?t=msg&goto=7393

If an object has a peak then that results always in a thin wall at the end. Correct or wrong?

3. If rejected then a written advice where to search for the thin wall would be helpfull. Or does the printer software give an exact report/picture?

Woody64

[Updated on: Thu, 22 October 2009 17:28 UTC]


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Re: Thin Walls [message #7414 is a reply to message #7408 ] Thu, 22 October 2009 18:53 UTC Go to previous messageGo to next message
avatar dadrummond  is currently offline dadrummond
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Great to see this thread opened! Joris, I really appreciate the way you addressed things above, and the way Shapeways is thinking about the issue. I'd like to add my voice to the clamor for clarity.

To me, the most difficult concept is distinguishing between the detail resolution of the machine and the minimum wall thickness. I still cannot tell you what constitutes a wall.

One can imagine a precise definition of thickness, as follows: Take an imaginary sphere of diameter X = minimum thickness. If it is possible to position the sphere inside any solid portion of the model, tangent to any inner surface (that is, opposite the outer surface normal), and have any point on the sphere lie outside the model, then the model violates the thickness condition. If this inner-tangent sphere always lies inside the model, then the model satisfies the thickness condition.

The problem with this definition is that it refers to thickness, not wall thickness. Because the nominal resolution of the machines in question is more like 0.1mm, presumably the rule is not designed to forbid details below the wall-thickness limit. The question is, what's the difference between a "detail" and a "wall"?

What would help me (yet another wall-thickness rejection victim) is:

1) A precise, preferably algorithmic definition of wall thickness, similar to the thickness definition above. In other words, what is Shapeways checking? The tools Joris refers to are surely part of that solution. The definition should also be provided. I don't want to just build my model and then check it with a tool -- I want to design appropriately from minute 1.

2) Pictures! Along with such a precise definition, lots of "good -- bad" comparative pictures, preferably of the same model before and after, will help train our brains to recognize wall thickness issues, and distinguish them from appropriate detail, before they're submitted.


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Re: Thin Walls [message #7416 is a reply to message #7408 ] Thu, 22 October 2009 19:31 UTC Go to previous messageGo to next message
avatar coines23  is currently offline coines23
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I'm glad to see this thread too, since it hit a number of my models as well. In conversing with Ralph, I got some screen shots of trouble areas on my model which helped me find areas where I made a mistake, and where I think it was throwing a false positive. The attached image shows both. The 0.200 mark is indeed too thin, so I've fixed that, but the 0.198 mark is from a panel scoring line similar to those on model planes, which while being about 0.2mm wide, is also only 0.1mm deep.

  • Attachment: STL_56181.jpg
    (Size: 63.98KB, Downloaded 499 time(s))

Re: Thin Walls [message #7419 is a reply to message #7416 ] Thu, 22 October 2009 22:00 UTC Go to previous messageGo to next message
avatar Inlite  is currently offline Inlite
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I have had many many models cancelled due to wall thickness issues, despite trying to keep everything within the parameters, the problem I have is that unless we are told which parts of the model are under thickness then I could spend hours remodeling and still not get the specific part that is preventing the print from going ahead.

Also, I would like to see if there is a chance of getting "experimental" parts printed - meaning, I pay for them and Shapeways prints them with the understanding that if the print fails then I get sent whatever came out of the machine and I accept that I cant ask for a reprint/refund.
Re: Thin Walls [message #7424 is a reply to message #7419 ] Fri, 23 October 2009 01:26 UTC Go to previous messageGo to next message
avatar stannum  is currently offline stannum
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Yep, I'm all for some kind of "experimental path" too. Otherwise there is no way to submit test models and see where they fail. And not only where, but also how. Does it become a blob? Does it look like a cheese full of holes? Is the modelling approach giving the desired texture? Can it work when printed in any direction? Does a basic shape need more polygons? Is that zone wasting polygons that do not make it any smoother? Is X or Y shape the best one to imitate whatever real thing, when working at so small scale? Does it still work for double size version or better use Z shape in that case? And so on.

My experiment was a group of things, placed multiple times over support plates, in a try to see how things would work out in multiple orientations (I read some blog posts about that), and how simplified or detailed modelling would transfer to the final object or how many failures whould happen. I got busy with other things and postponed it altogether after the cancelation, but a friend "managed" to print it in a ZCorp and I got pictures of how it failed, so now I know what problems I would have with those machines, and what would work. The conclusion was that system is not usuable for what I want, too rough surfaces, and too brittle before applying cyano. The model failed, but the test "worked", basic "try and error engineering".

I would like to get back to the project, it was a pet project for the time being... but multiple upload and reupload trying to figure what was wrong with magic "non manifold" (yeah, right... STL or the printer software fusing vertices: I had to debug by uploading a part and then adding other more until I realized what was really going on) and then 2 weeks to get an sparse "not printable" wasn't very encouraging.
Re: Thin Walls [message #7428 is a reply to message #7419 ] Fri, 23 October 2009 04:04 UTC Go to previous messageGo to next message
avatar dadrummond  is currently offline dadrummond
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Another key reason for the "experimental" path is the need for prototyping in a less-expensive material.

I have a model -- my only model so far -- which I am designing to be printed in steel. However, this is a project with many phases, and I can't afford steel for all the prototypes along the way. Therefore, having spent the money to learn that steel beats the resolution of white detail (see here), I'm printing my prototypes in the detail material (black, under the assumption that the material properties of black approximate that of white, and knowing that details printed in white detail can be difficult to see).

I accept that black detail is not equivalent to steel, and I understand that there will be defects in the black detail print. What I want is 1) a way to tell Shapeways "print this, I'm trying to learn about proportions and connections and things that are difficult to see on a 2D screen", and 2) some assurance that, if there are gross printing defects unrelated to my design, Shapeways' exemplary customer service will still come to my rescue.

In short -- we should be allowed to print prototypes of future steel prints in WSF, and all that implies.

I believe this problem can be solved with a suitably worded page during the ordering process:

"WARNING: Your model violates one or more standards for printing in this material. In all likelihood, the print will show gross defects. By clicking 'OK' below, you confirm that you will accept whatever our printer emits, no questions asked, no complaints, no whining, no nothing. You are using our services for your own experimental ends. Good luck!"

[Updated on: Fri, 23 October 2009 04:34 UTC]


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Re: Thin Walls [message #7431 is a reply to message #7408 ] Fri, 23 October 2009 05:47 UTC Go to previous messageGo to next message
avatar woody64  is currently offline woody64
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Currently I have more then 6 items facing this problem.

I'm working on a solution but still don't know the exact criterias.

I another thread I asked also for a test print for designers:
- no $25 minimum
- no send
- only a report in kind of photo
- possible send with next normal order

Woody64


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Re: Thin Walls [message #7434 is a reply to message #7431 ] Fri, 23 October 2009 07:27 UTC Go to previous messageGo to next message
avatar joris  is currently offline joris
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I will try to answer all questions in one post, should be interesting.

Woody:

1. It would be very helpful if the designers knows which old models are in danger of beeing rejected next time due to too thin walls.
Is this information available?


We can calculate it but it would take some time to build the reporting tool and set up a way to communicate it to everyone. And it would take some time to go through the entire database. Good idea though, I'll see if we can do it.

2. Is there a guide how to deal with such objects:
http://www.shapeways.com/forum/index.php?t=msg&goto=7393


There is a wall thickness tutorial. http://www.shapeways.com/tutorials/3dprintingminimumwallthic knesstutorial

If you guys haven't seen it, I'd like to know if it answers some of your questions. I do believe that it does not completely illustrate the difference between a peak and wall. I will improve it.

If an object has a peak then that results always in a thin wall at the end. Correct or wrong?

I will first look into the matter more deeply before answering.

3. If rejected then a written advice where to search for the thin wall would be helpfull. Or does the printer software give an exact report/picture?

Currently the software just finds that the model is too thin. So there is no visual tool to help you find the thin walls.

dadrummond

1) A precise, preferably algorithmic definition of wall thickness, similar to the thickness definition above. In other words, what is Shapeways checking? The tools Joris refers to are surely part of that solution. The definition should also be provided. I don't want to just build my model and then check it with a tool -- I want to design appropriately from minute 1.

I like your definition but want to be absolutely 100% clear before I respond.

2) Pictures! Along with such a precise definition, lots of "good -- bad" comparative pictures, preferably of the same model before and after, will help train our brains to recognize wall thickness issues, and distinguish them from appropriate detail, before they're submitted.

I will see if we can add them to the tutorial.

coines23

Thank you for convincing me that the picture idea is a good one. Your (and dadrummond's) answer has also made me super careful in responding about the wall thickness definition. I will work on this.

Inlite

the problem I have is that unless we are told which parts of the model are under thickness then I could spend hours remodeling and still not get the specific part that is preventing the print from going ahead.

With the tools we are evaluating this should be very easy to do, for most models. The plate of spaghetti model will always be complex.

Also, I would like to see if there is a chance of getting "experimental" parts printed

This is an option but would require an extra process for us. Also in some cases a misprint could screw up other models. I'll look into this to see if it would be possible

stannum

I understand that belatedly getting a wall thickness error is a bad thing. I also want to reiterate that we want to encourage and make experimentation possible.

dadrummond

In short -- we should be allowed to print prototypes of future steel prints in WSF, and all that implies.

Since each process is very very different in terms of detail, wall thickness and printing issues a WSF part does not say much about a final Steel part.

But, I do believe in iterative design and in making it possible for people to prototype in series inexpensively as well as print out a final product.

I believe this problem can be solved with a suitably worded page during the ordering process:

This is a good idea.

Woody

I another thread I asked also for a test print for designers:
- no $25 minimum
- no send
- only a report in kind of photo
- possible send with next normal order


This is also an interesting idea. I'll look into it.
Re: Thin Walls [message #7439 is a reply to message #7434 ] Fri, 23 October 2009 13:51 UTC Go to previous messageGo to next message
avatar woody64  is currently offline woody64
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The tutorial only describes the rough basics.

WiKKiDWidgets tries to explain the difference between detail and wall. But I think it's not aligned with the tutorial.

It would be a good point to follow this explanation and to give a statement from shapeways point of view.

I've started to upload corrections for some of my items. How can we go on?
Do I have to order them, or do you have another proposal.

Woody64


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two blender methods for thickening walls [message #7449 is a reply to message #7439 ] Sat, 24 October 2009 04:26 UTC Go to previous messageGo to next message
avatar dadrummond  is currently offline dadrummond
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Just a quick tip for Blender users with thin walls: expanding along normals is your friend.

If you have a relatively irregular but subdivided and smooth object that's too thin, consider two strategies:

1) Easy. Select your object, go to Edit Mode (Tab), select all vertices (A, or A,A until all vertices are selected), then expand along normals (Alt-S). This will "puff up" your object. If you have deep creases in the object, the expanded geometry will overlap and you'll need to touch these areas up.

The disadvantage of this method is that it distorts geometry on all sides. Hence:

2) Hard but geometry-preserving on one side. If your object has an outside wall whose aspects are carefully designed and an inside wall that you don't care about -- I'm thinking here of something like a coat-of-arms shield with designs on the outside and nothing important on the inside -- this may be a better method. Select your object, go to Edit Mode (Tab), Face Mode. Now move your view until you're looking at (normal to) the inside wall, the wall you'd like to thicken by moving it toward you. Go to freehand select mode (B,B) and select all the faces that are facing you -- but avoid selecting those faces at the edges that curl over toward the outside surface. (If you do select some of them by accident, B,B,MMB or shift-RMB to deselect them.) Now Alt-S (expand along normals) as before, and thicken the inside faces selectively. If you don't like what you see, ESC (or Undo) and deselect the faces that seem to be causing problems. Save often -- Blender save selections!

The obvious solution might seem to be scaling your object along some axis. If that works for you, do it! But often (I find) scaling produces results that completely distort key geometry. The strategies above will thicken pieces while preserving at least some underlying geometry.

Hope this helps.


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Re: two blender methods for thickening walls [message #7450 is a reply to message #7449 ] Sat, 24 October 2009 07:38 UTC Go to previous messageGo to next message
avatar joris  is currently offline joris
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OK everyone,

There is a blogpost live about Netfabb it is a great tool to measure wall thicknesses, and it might automatically repair things such as inverted normals, non-manifolds and holes:
http://www.shapeways.com/blog/archives/312-Netfabb-is-an-awe some-STL-viewer-repair-tool.html

I've also put the initial design information about the Stainless Steel process live:
http://www.shapeways.com/blog/archives/313-Initial-Design-ru les-Stainless-Steel-3D-printing.html

I am still waiting from permission from some model owners to use renderings of their models, hopefully that will make things clearer.

Please tell me what you think of both blogposts.


Woody,

I am making sure we give the right answer before we respond.

Re: two blender methods for thickening walls [message #7464 is a reply to message #7449 ] Sat, 24 October 2009 19:32 UTC Go to previous messageGo to next message
avatar stannum  is currently offline stannum
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You can "puff down", Alt+s is shrink/fatten, so use the shrink effect to get a smaller inner shell. Requires flip normals afterwards. The issue is converting the Blender factor to mm, as the operation will not be even all over the shell. I just tried with the monkey head, different thickness in different zones.
Re: two blender methods for thickening walls [message #7471 is a reply to message #7464 ] Sun, 25 October 2009 19:42 UTC Go to previous messageGo to next message
avatar woody64  is currently offline woody64
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There's also a nasty problem with all the items customers get denied.
All of them were verified from me by ordering them myself to make sure it works. Now I have to redesign them and also to reorder them a 2nd time on my costs.
How will you deal with that at shapeways.

Woody64


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Re: Thin Walls [message #7518 is a reply to message #7408 ] Thu, 29 October 2009 01:51 UTC Go to previous messageGo to next message
avatar Designmodeller1  is currently offline Designmodeller1
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Hi all, I too have had a few models rejected due to thin walls. Sad

Some of my designs (jewelry) are small to begin with and overall structurally sound but some contain details (like flowers) that have pedals with tips smaller than .7mm. I understand the need to reject a part for the risk of the part being weak and fragile but are rejections also based on "expected" detail levels?

For example I know the part is strong enough to "hold up" on it's own but It will surely lose some of the details, and if loss of detail is OK with me and I understand that it will occur, (and will not expect refunds) Is there a way that I can still get the model printed?

As designers exploring a new medium I think we all know that there will be problems with our designs but if we can't see our failures how are we supposed to adjust/fix our design methods?

Perhaps there could be a way for those of us that are OK with the potential hazards and risks of loss of details and failures could "sign up" on a list. This could be a "print anyway" list of designers with the understanding that what we get is what we get, good or bad, try to print once only, no refunds.

A experimental "sign up" list would prevent Shapeways from having to re-print a model over and over again to try and get it right and also give designers the opportunity to push the envelope. Very Happy

[Updated on: Thu, 29 October 2009 01:55 UTC]

Re: Thin Walls [message #7520 is a reply to message #7518 ] Thu, 29 October 2009 08:39 UTC Go to previous messageGo to next message
avatar joris  is currently offline joris
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Woody,

With regards to this re-designing it would depend.

If the model is truly too thin, too fragile then you will have to re-design it.

But, if the rejection is based on us being too careful then you should not have to. I'd suggest that you email us the links to all the models that you are thinking of re-designing and we look at them once more.

Designmodeller1,

Such a list feature is a good idea. We are considering something like that.

Re: Thin Walls [message #7532 is a reply to message #7408 ] Fri, 30 October 2009 11:28 UTC Go to previous messageGo to next message
avatar BillBedford  is currently offline BillBedford
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Quote:

What has happened is the following: initially we were very experimental and wanted to help everyone push the envelope of 3D printing. We therefore printed models that might fail and happily printed them a few times if they did fail.

I would much rather receive broken parts so that I can make adjustments to my drawings. After all I am the one who knows what the part should look like and where compromises can be made.


Bill Bedford
Re: Thin Walls [message #7533 is a reply to message #7532 ] Fri, 30 October 2009 11:32 UTC Go to previous messageGo to next message
avatar joris  is currently offline joris
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Bill,

Thanks for giving another view to the testing idea.

Shipping is expensive for us though.

But, what several people are saying is that they would not need re-prints?

Joris
Re: Thin Walls [message #7535 is a reply to message #7408 ] Fri, 30 October 2009 11:50 UTC Go to previous messageGo to next message
avatar BillBedford  is currently offline BillBedford
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joris wrote on Thu, 22 October 2009 12:59

As per Woody's suggestion I'm opening up a topic here for you to discuss your thin wall issues.

The wall thicknesses per material:
White, Transparent & Black Detail: 1mm


I'm am not sure that I understand why this wall thickness is so conservative. I am trying to model some loco wheels where the full size examples where 5 or 6 feet diameter and the web between the boss and rim, because it was corrugated and reinforced, was only about 1/4 inch (6mm) thick. I don't expect to be able reproduce exactly that in 1:76 scale but I would expect something much thinner than 1mm ( say 0.2. or 0.3mm ) to be robust enough to survive manufacture.


Bill Bedford
Re: Thin Walls [message #7536 is a reply to message #7533 ] Fri, 30 October 2009 12:04 UTC Go to previous messageGo to next message
avatar BillBedford  is currently offline BillBedford
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joris wrote on Fri, 30 October 2009 11:32


But, what several people are saying is that they would not need re-prints?


Yes, My view is that if I don't follow the rules then I should take the responsibility for the failures. This is how most of my other suppliers (casters and photo etchers) work. But this will only be useful if I have the failed pieces sent to me.

Whether you would want to take on the extra support of explaining why models fail is a completely different question......


Bill Bedford
Re: Thin Walls [message #7537 is a reply to message #7535 ] Fri, 30 October 2009 12:19 UTC Go to previous messageGo to next message
avatar joris  is currently offline joris
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Bill,

A part of the wall thickness issue is simply a constraint of the process and the machine.

A printing head has to deposit material and this material must be surrounded by support material. The size of the drops, laser, extrusion nozzle etc. all have a minimum thickness. Any thinner and the structure collapses, the wall has holes etc.

These wall thicknesses are hard limits of the process itself. Over time they will improve.

But, as people have stated there is a difference between walls and details.

Where we made errors is in becoming too stringent in applying these and higher standards to adventurous models.

A wall is any structural element of your model.

So lets say you're printing a porcupine. The spines of the porcupine would have to be 0.7mm thick at least(in White, Strong & Flexible). For such a structure I would even recommend 2mm. Any thinner than 0.7mm and the pins simply would not print properly. Thicker than 0.7mm they should print but might be fragile. 1mm would be stronger, 2mm stronger still.

But...the spines each have a very fine point at the end of them. This is a detail and could be finer and thinner than 0.7mm. Because this detail is not a structural element the printer will simply try its best and then leave a tapered off end. This is similar to what happens with corners, edges etc.

So lets look at Laurana: http://www.shapeways.com/model/7842/laurana_50k_cropped___sh elled.html

The entire structure is a wall. This simply could not be any thinner or it would fail. The eyebrow is thinner at the very end, this is a detail.

Anything that if removed would cause a hole to appear in your model or mesh is definitely a wall.

Anything that can be safely removed in and of itself without creating a hole in the mesh is most probably a detail.

Details taller than 1mm, are walls.




Re: Thin Walls [message #7539 is a reply to message #7537 ] Fri, 30 October 2009 13:44 UTC Go to previous messageGo to next message
avatar BillBedford  is currently offline BillBedford
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Joris

Sorry, but in a passed life I used to help design ships, so I have a basic understanding of structural engineering, though I have forgotten all the maths.

Now the interesting thing about a large ship is that the plating on the outside is vary, very, thin compared with the volume that it encloses, but that there is a system of structural members inside the plating that supplies the structural integrity.

So applying this you our models, we could build a lattice out of robust members without any problem. If we then added a thin sheet to one side so we had a series of open boxes we could still print it if the sheet was thick enough. The problem is that there is nothing that I have read that gives me a clue about how thin I could make this sheet. I know this will be complicated because the further apart the lattice members are the thicker the sheet needs to be. Also the span of any particular thickness that could be supported would depend on the size of the lattice members as well as the distance between them. Would I be right in thinking that the thinnest possible dimension of this sheet would be close to the minimum feature size?

Software that only measures arbitrary minimum thicknesses will always give false negative in cases like our lattice, unless structural integrity is taken into account.


Bill Bedford
Re: Thin Walls [message #7540 is a reply to message #7539 ] Fri, 30 October 2009 13:59 UTC Go to previous messageGo to next message
avatar joris  is currently offline joris
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Bill,

I seem to not be explaining myself correctly.

I'm sorry for being confusing.

The thinnest the sheet could be is the minimum wall thickness. The thinnest the lattice could be is the minimum wall thickness.

The printer in principle can not make anything thinner than the minimum wall thickness.

However a detail such as a sharp point can be produced because the printer simply gives up at one point leaving some of the point intact.

An edge of an eyebrow could remain but if a wall would have the same thin features it could not be produced.

Sorry for using words like 'structural element.'

What I'm trying to say is if you're trying to stack golf balls one on top of another your structure would at minimum be one golf ball in width. You can not stack half a golf ball. This golf ball width is the minimum wall thickness.

And yes, if you look closely at some points on the stack of golf balls you can see that the width is less than one golf ball. But, if you'd want to add a layer to your golf ball stack you can not add half a golf ball. You can only add one golf ball.

Re: Thin Walls [message #7541 is a reply to message #7540 ] Fri, 30 October 2009 14:59 UTC Go to previous messageGo to next message
avatar BillBedford  is currently offline BillBedford
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Joris

Now I really don't understand what is going on as I have a lot of white detail pieces where the minimum size is about 0.6 x 1.1mm.

Unless, of course the minimum wall for white detail is really around 0.5 or 0.6.


Bill Bedford
Re: Thin Walls [message #7543 is a reply to message #7541 ] Fri, 30 October 2009 17:10 UTC Go to previous messageGo to next message
avatar afrodri  is currently offline afrodri
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I'm still somewhat confused about the "structural" definition. Is the goal to make the object structurally sound in the "will not fall apart under its own weight and/or shipping" sense, or is the issue "will it survive the compressed air post processing"?

For example, the three objects below:

index.php?t=getfile&id=1699&private=0

Assume the blue material is 1mm x 1mm in cross section, and we are using WSF. The object on the left should be acceptable, as no subcomponent is less than 1mm.

The structure in the center adds a red piece which is .5mm x .5mm. Adding this piece only increases the overall structural strength, but the red piece - by itself - is small and potentially delicate.

The structure on the right has the red piece "exposed" and not braced against other components.

Which of these would be printable?

  • Attachment: wall.jpg
    (Size: 21.50KB, Downloaded 5369 time(s))

Re: Thin Walls [message #7546 is a reply to message #7408 ] Fri, 30 October 2009 19:13 UTC Go to previous messageGo to next message
avatar woody64  is currently offline woody64
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Today I received another "walls to thin" hint.
The difference was, that there was a photo added which points at the troubled places.
In this case I made the error since the object was only designed fro white and flexible, but to thin for others.
This leads me to the proposal of storing the minimal wall size of an object and restricting the materials for printing:
An element < 0,7 has no materials
elements between 0,7 and 1 only white and flexible ....
elemnents between 1 and 2 only ....

That would save a lot of troubles. Is that considerable?

Woody64

[Updated on: Fri, 30 October 2009 19:14 UTC]


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Re: Thin Walls [message #7621 is a reply to message #7408 ] Thu, 05 November 2009 01:12 UTC Go to previous messageGo to next message
avatar coines23  is currently offline coines23
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I've got time to work on 'em now, so I've started replacing my Not For Sale models in my shop. Two down, three to go...

I'd appreciate it if you'd glance over this one:
http://www.shapeways.com/model/56589/jovian_schild_class_esc ort_cruiser.html

before I work it over, since it shares a lot of geometry with this older ship here:
http://www.shapeways.com/model/30103/jovian_lanze_class_stri ke_carrier.html

That one has been successfully printed very recently.
Re: Thin Walls [message #7861 is a reply to message #7408 ] Sat, 21 November 2009 13:20 UTC Go to previous messageGo to next message
avatar BattlegroundToys  is currently offline BattlegroundToys
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While I greatly appreciate that what you guys are telling us, and your efforts toward educating us to build better drawings, I would have to fully agree that there should be a way for the customer to request that the model be printed anyway. With such a request, you give up your rights to a reprint, unless you pay for another one.

The other thing that I've struggled with is that my most recent experiences have been with a model that has already been printed successfully and was then later rejected on a subsequent printing request.

I realize that the process is evolving, but this was a big surprise and now instead of sending out product I'm back at the drawing board.

Again, you guys (the fantastic Shapeways team, Joris and Bart rock!) are doing a great job helping us all figure this out, but sometimes we just need to get something done.

[Updated on: Sat, 21 November 2009 13:22 UTC]

Re: Thin Walls [message #7984 is a reply to message #7408 ] Mon, 30 November 2009 17:44 UTC Go to previous messageGo to next message
avatar woody64  is currently offline woody64
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Does anybody know an actual status?

Is there now a check done after/when uploading?

Do we get a hint where the problems are.

Is there a correct description of "detail" and "wall" now.

Are the old models checked, to prevent that another customer buys an item and get the response walls too thin.

If not. Is it guaranteed that the designer and the customer come into contact to check corrections possibilities?

Woody64


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Re: Thin Walls [message #8157 is a reply to message #7408 ] Tue, 08 December 2009 17:08 UTC Go to previous messageGo to next message
avatar EricFinley  is currently offline EricFinley
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Seems to me like there should be a simple solution. If you want your piece printed "Best Effort" then it goes into a pile of similarly flagged pieces; once there's enough Best Effort pieces for a full run, do one with just those.

This means that if you flag Best Effort you are accepting not only that you might have made a mistake, but there's a chance that someone else might have designed a piece which breaks the design specs and ends up messing up yours. [I don't know how likely this is; if Joris or someone wanted to weigh in with that data, that'd be helpful. It seems unlikely, at least in the SLS method.]

I'm guessing that there would in fact be enough of those that the Shapeways team would end up running one or more such batches per day - I don't know for sure. Presumably, if this is not the case, then Best Effort may also mean that you have to wait until a full batch is going to run, so the usual ten-day guarantee won't apply either. Wouldn't expect it to be a big deal, though.

So - add a checkbox for "Best Effort" to the upload page (with a "What's This?" popup explaining the terms). Checking this means that if your design uploaded successfully, it will go to print - when there's time and enough other Best Effort pieces stacked up. And you'll receive the result, whatever the result is. But it will be at risk from more than your own errors; that's the price you pay for having it bypass the checking process.
Wall checking software, was: Thin Walls [message #8344 is a reply to message #8157 ] Wed, 16 December 2009 11:05 UTC Go to previous messageGo to next message
avatar BillBedford  is currently offline BillBedford
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Does the new wall checking software find all instances of thin wall or is it stop after the first few hove been found?


Bill Bedford
Re: Thin Walls [message #8372 is a reply to message #7408 ] Thu, 17 December 2009 17:42 UTC Go to previous messageGo to next message
avatar EricFinley  is currently offline EricFinley
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Bill - unless I'm mistaken, there is no automatic wall checking software. The feedback I've received has always looked like someone manually looked at the design and identified the thinnest parts, and then measured them.

As it happens, though, I'm 90% done a Blender script which will in fact automatically check wall thicknesses... which is then 50% of a second script I have planned, to automatically fix them too. It's slightly approximate, but should be much better than visual inspection (and faster too). I'll be posting a link to the script in these forums as soon as it's ready, I promise - should be within a few days, could even be today.
Re: Thin Walls [message #8379 is a reply to message #8372 ] Thu, 17 December 2009 18:49 UTC Go to previous messageGo to next message
avatar BillBedford  is currently offline BillBedford
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Eric Finley wrote on Thu, 17 December 2009 17:42

Bill - unless I'm mistaken, there is no automatic wall checking software. The feedback I've received has always looked like someone manually looked at the design and identified the thinnest parts, and then measured them.

Great! More arbitraryness.


Bill Bedford
Re: Thin Walls [message #8384 is a reply to message #8379 ] Thu, 17 December 2009 19:29 UTC Go to previous messageGo to next message
avatar dadrummond  is currently offline dadrummond
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Just wanted to suggest that we give SW a bit of a break, here.

The "arbitrariness" should not be entirely (or even mostly) blamed on Shapeways. Wall thickness causes problems because of a) the laws of physics, b) the realities of handling during the printing process, and c) the capabilities of present-day printers.

a) Physics. You can easily model something that can't support its own weight. If you think that a manual check is arbitrary, please suggest any non-arbitrary way to predict -- without actually printing your object first (too expensive!) -- that it will or won't collapse even if left on its own. Humans are imperfect, but can assess whether objects are likely to collapse, bend, or chip better than a script. Unless you know of a script I'm missing.

b) Handling. Let's say you've written a decent finite-element analysis tool that can determine whether an object will support its own weight. Now: does it properly simulate the stresses when an object is lifted out of the printer, packaged, and shipped by UPS? Does the metal-print simulation properly simulate the un-infiltrated "green" state and the pinch of tongs reaching around the object? Etc. etc. Here, a well-informed human is your best bet.

c) Printers. Very tiny features can cause problems which can disrupt an entire print run. The basis of SW's business -- the reason their prices are so low -- is the ability to print many people's objects in one run. Printer-related model problems are probably most amenable to automated script detection.

I'm sure SW is deeply interested in reducing the arbitrary nature of some of the checks. Perhaps a fuller appreciation of the extraordinary difficulty of automating these checks would improve our patience and happiness. This process is really the difference between modeling stuff in your computer (almost anything is possible) and making it real (most things you can design are not printable).

Reality is arbitrary. The checks are primarily reality checks. There is no such thing as an automated reality check, and there won't be for a good long time.


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Elytra on Shapeways: http://www.shapeways.com/shops/elytra
Re: Thin Walls [message #8386 is a reply to message #8384 ] Thu, 17 December 2009 20:04 UTC Go to previous messageGo to next message
avatar BillBedford  is currently offline BillBedford
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dadrummond wrote on Thu, 17 December 2009 19:29

Reality is arbitrary. The checks are primarily reality checks. There is no such thing as an automated reality check, and there won't be for a good long time.

The accusation of aribtraryness comes from having bags full of pieces that have been printed but now fall foul of the minimum thickness rules. Almost all the professional suppliers (casters, photo-etchers etc) I have deal with supply me with pieces that have failed so at least I know what when wrong and I can design around the problem.


Bill Bedford
Re: Thin Walls [message #8391 is a reply to message #8386 ] Thu, 17 December 2009 22:09 UTC Go to previous messageGo to next message
avatar GHP  is currently offline GHP
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One of my Snowflake balls was rejected for thin walls, apparently because the text on the bars was too thin. When I pointed out that the text should print as part of the bar, adding its thickness to that of the bar, I was told that the text was "loose" and would fall off. The text was done as a separate mesh (or meshes), but it is immediately adjacent to the bar, so I would expect them to fuse together. Am I misunderstanding how the technology works?

Another Snowflake ball, ordered by Robert Schouwenburg and done exactly the same way (but with different text), is now in production, having apparently passed the printing checks.
Re: Thin Walls [message #8394 is a reply to message #8391 ] Thu, 17 December 2009 22:36 UTC Go to previous messageGo to next message
avatar BillBedford  is currently offline BillBedford
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GHP wrote on Thu, 17 December 2009 22:09

One of my Snowflake balls was rejected for thin walls, apparently because the text on the bars was too thin. When I pointed out that the text should print as part of the bar, adding its thickness to that of the bar, I was told that the text was "loose" and would fall off. The text was done as a separate mesh (or meshes), but it is immediately adjacent to the bar, so I would expect them to fuse together. Am I misunderstanding how the technology works?
I think you have just found one of the universal laws of unintended consequences. If you want to make two part that intersect but do not fuse you have to have a bigger gap that you would really like, but if you really want the two part to fuse they will always separate.
In general, if you want to build something without moving parts it should be a single mesh.


Bill Bedford
Re: Thin Walls [message #8398 is a reply to message #8394 ] Fri, 18 December 2009 02:42 UTC Go to previous messageGo to next message
avatar dadrummond  is currently offline dadrummond
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Hi GHP,

I think you just need to not build models that rely on fusing of adjacent parts. If you want two meshes to print as a single object, you must explicitly overlap them in space.

That is, even though two parts are 0.3mm apart, which will cause them to print as a fused object due to the statistics of the printer's resolution, SW will not allow you to claim that this printer-error-induced connection constitutes a real structure. (I hope you would agree -- what if the printer actually does what your model specifies, by chance! Yikes!)

When modeling for SW, I create virtually every part with a separate mesh. (Here I must respectfully offer the opposite advice from BillBedford.) In my Scarab and Scarab 2 models, there are more than 20 separate meshes, each carefully overlapped to create a continuous solid object. The downside of this is that I pay a bit more because overlapping material is double-counted by SW. Currently, they compute cost by summing the volumes of all meshes as an approximation to the true total material volume.

The upsides are: first, and most importantly, I can adjust each segment of the beetle independently just as if it were a real creature, which has helped enormously with the model refinement process, allowing me to quickly turn Scarab 1 into Scarab 2. Second, I'm lazy, and Boolean algorithms in Blender still frequently produce non-manifold problems that I hate debugging as much as anyone. No Booleaning at all in these models. (I did print signet rings for me and my girlfriend that used a rather elaborate Boolean difference operation to create the stamp portion. Worked fine, but it took forever to fix the non-manifold problems.)

So, my advice: act as though the printer will do exactly what you tell it to, and don't rely on its errors to produce solid models. Use explicit overlaps if you like, or unify your meshes. Both work. The former is more expensive and requires more thinking but is more flexible if you intend to make major changes to the model; the latter is maximally cost-efficient and foolproof but can somewhat inhibit editing later.

[Updated on: Fri, 18 December 2009 02:54 UTC]


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Re: Thin Walls [message #8399 is a reply to message #8398 ] Fri, 18 December 2009 03:33 UTC Go to previous messageGo to next message
avatar GHP  is currently offline GHP
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But the text and the bars weren't 0.3mm apart, or even close to that (I believe). I mapped the text onto the surface of the sphere outlined by the twisted bars, so there should only have been some very tiny gaps due to computational error.

On the other hand, I guess I did do some smoothing on the bars, which may have reduced them a bit. Just to be safe, I am now mapping the text onto a slightly smaller sphere.

Thanks for all your advice.

Gillian.
Re: Thin Walls [message #8450 is a reply to message #8372 ] Sun, 20 December 2009 16:37 UTC Go to previous messageGo to previous message
avatar pete  is currently offline pete
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Hi Eric.

using Blender to do Wallthickness checks? Wow!
We would be interested because it would help in removing the arbitrariness mentioned above.
Today it is indeed manual work.

Do you care to share?

best regards,
Peter

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