Thin Walls

Discussion in 'Technologies and Hardware' started by joris, Oct 22, 2009.

  1. joris
    joris New Member
    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





     
    Last edited by a moderator: Aug 5, 2015
  2. woody64
    woody64 Well-Known Member
    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

     
    Last edited: Oct 22, 2009
  3. dadrummond
    dadrummond Member
    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.
     
  4. coines23
    coines23 Well-Known Member
    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.
     

    Attached Files:

  5. Inlite
    Inlite New Member
    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.
     
  6. stannum
    stannum Well-Known Member
    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.
     
  7. dadrummond
    dadrummond Member
    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!"
     
    Last edited: Oct 23, 2009
  8. woody64
    woody64 Well-Known Member
    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
     
  9. joris
    joris New Member
    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.
     
  10. woody64
    woody64 Well-Known Member
    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
     
  11. dadrummond
    dadrummond Member
    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.
     
  12. joris
    joris New Member
    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.

     
  13. stannum
    stannum Well-Known Member
    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.
     
  14. woody64
    woody64 Well-Known Member
    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
     
  15. Designmodeller1
    Designmodeller1 New Member
    Hi all, I too have had a few models rejected due to thin walls. :(

    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. :D
     
    Last edited: Oct 28, 2009
  16. joris
    joris New Member
    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.

     
  17. BillBedford
    BillBedford New Member
    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.
     
  18. joris
    joris New Member
    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
     
  19. BillBedford
    BillBedford New Member
    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.
     
  20. BillBedford
    BillBedford New Member
    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......