I'm not sure I correctly understand "minimum detail size"

Discussion in 'Design and Modeling' started by A_Square, Aug 6, 2013.

  1. A_Square
    A_Square New Member
    I've been assuming that detail size refers to the minimum displacement along the normal of the surface that is needed for a detail to be seen. However, I just saw this (awesome) ring: http://shpws.me/oubJ

    Clearly, those craters aren't 1mm deep/high, but they show up great. I figure this means that I can be a lot less conservative in my designs, but I'm not exactly sure now what the limitations are. So, I'm wondering, what exactly does that 1mm minimum engraved/embossed mean? Is there a technical discussion of the design rule terminology somewhere?

  2. MrNib
    MrNib Well-Known Member
    There appears to be no good answer to this question. Sometimes designs are approved and sometimes they are rejected. About the only "rule" I can determine is that detail "transitions" are less likely to be rejected if the deviations in direction towards the normal of the surface plane are less than 90 degrees. So a detail that is formed by an angle of let's say 45 degrees might be ok but a sudden cliff wall transition gets rejected.

    I think the main problem is that the pass/fail is not exclusively determined by automated computer checking, which is also difficult to define in any computer algorithm if you tried to write one. In addition the definition of embossing versus engraving becomes rather nebulous for complicated surfaces and the numeric limits may be different. For example 0.35 vs 0.4 mm. I've had parts that break these rules passed for regular alumide and failed for polished alumide, and others passed for polished alumide and failed for regular alumide. These numbers can change over time and there is no public specification revision history you can reference, as far as I can tell. Nor is there a good defintion that distinguishes between intentional or unintentional surface noise, subtle decorative detail, or embossing/engraving that is intended to guarantee the visibility of text or logos. You also, as of yet, can't request a waiver to have something made and bypass what I would consider to be a non-fatal failure (as compared to a fatal wall thickness error).

    I already started a thread on this subject. I have several examples of fabricated parts I need to take photos of that intentionally break the rules when using the most strict definitions of the rules. Quite frankly I've had it up to here with this issue so I'm letting it breath before I post those results and any other thoughts or conclusions, but I'm suddenly beginning to feel re-invigorated to pursue this issue!

    https://www.shapeways.com/forum/index.php?t=msg&th=14874 &start=0&
    Last edited: Aug 6, 2013
  3. MitchellJetten
    MitchellJetten Shapeways Employee CS Team
    Hi there,

    If your model is below the minimum required detail size, we will not reject your model anymore.
    Instead we will proactively reach out to your to find out about your intentions.

    For example, WSF we require details to be 0.2mm and 0.5mm for readable text.
    If I spot that your model is below this, let's say there is text on your model which is only 0.2mm I will reach out to you and be like "hey I checked your model and spotted that the text might not be readable due to it's size, would you like us to print the model knowing that the text might not be visible?".

    This way we can still continue with the model even though you know the text might not be readable.

    For your example, the craters are below the minimum, thus we cannot guarantee that those details are visible and thus we reach out to you and ask if you don't mind.
    Clearly the moon ring turned out to be fine and looks great, but there is no guarantee if you go below the minimum detail rule.

  4. A_Square
    A_Square New Member
    Thanks Mitchell, that's very helpful! I'm still unsure of which dimension(s) the minimum size refers to, though. Is it the width of the feature, the depth/height, or both?
  5. MrNib
    MrNib Well-Known Member
    Well this is certainly good news. But another concern I heard was that Shapeways was worried about customers not getting what they wanted as compared to the computer generated previews on the product page. So when you reach out to customers to determine their intent does this only apply to designers or also to customers down the line? Is it ok'd for eternity after the designer gives their blessing and posts photos of the item?

    Speaking of rejections and cancellations I just had an item rejected today in gold plated brass but it was simply cancelled. This is a design that was previously made using the stainless steel process so it's definitely not ultra smooth since there is no major polishing step. In fact the roughness or fine stepping detail is a result of the CAD program method used at the time. I could remove the fine steps if I really had to but they are somewhat irrelevant in the larger scheme of things.

    In this case I thought the same design would be awesome in the gold plated brass process both because of the appearance and because it comes in contact with ink, so there's less chance of rust developing and it should be easier to clean the item after use in a solvent. It's a dip pen nib design that is designed to fit into a holder. Any roughness equivalent to what you get with SS is actually ok for holding ink on the nib so I'm not concerned about it. So can you build this part in gold/brass without polishing at the pointy twirly business end of the pen nib? Just consider this zone to be like the internal locations of a complicated design that can't be reached by polishing!

    The other end I'm not so concerned about since it is hidden from view in the nib holder so there's no problem with that end getting some polishing if you feel the need to do so. I'm also having this same part built in SS in the same order and its status is "In Production" so it appears to have passed the review stage.

    Order #280525.
    Reason: Details are too fine
    Additional information: details will be lost i finishing

    Last edited: Aug 7, 2013
  6. MrNib
    MrNib Well-Known Member
    Ok, this is the twirly nib design which was cancelled in gold/brass but was fabricated in stainless steel. What exactly is the reasoning that prevents this from being fabricated in the gold brass process? Is there a concern that any fine detail couldn't be faithfully reproduced? That any fine detail would be ruined by polishing and plating? That any fine detail could not be removed by polishing? Or that polishing is not possible in the groove spaces? Just to reiterate, I don't really care if there is any polishing on the pointy end. It can look just like this but with gold plating.


    Since I now have a credit for this part how do I get it uncancelled, fabricated, and sent with the original order? Is there a reach out appeal board that I can make my case to?

  7. stonysmith
    stonysmith Well-Known Member Moderator
    The Silver and Brass processes are done with a lost-wax casting method. Steel is an entirely different process.
    Small details such as the spiral ribs on this item may be so small that the molten metal may not flow into the crevices properly.

    Your best bet for a more in depth answer is to email service@shapeways.com.

  8. MrNib
    MrNib Well-Known Member
    I'm trying to find out if it's the spirals which are a problem or the fine micro-steps used to build up the spirals. The spiral section is one inch long so it's hardly small compared to jewelry that has been highlighted on the site. And it's a solid section so it should be rather robust.

    I think I will assemble a different version using a different technique to build the spiral avoiding the micro-steps. It's something that I planned on doing eventually anyway. I'll submit that using my credit, and then wait to see if it gets the big El Kabong. After that customer service if necessary to further clarify the issue if possible.
  9. A_Square
    A_Square New Member
    Hi there,

    I'm afraid the thread got pulled away a little bit from my original question, and I don't want that to get lost: which axis does the "minimum detail size" refer to? Is it perpendicular to the surface the detail is on (i.e. the height/depth of the feature), or parallel (i.e. the width of the feature)?

    In general, is there some sort of "visual glossary" for the design rules? That'd be awfully useful!
  10. MrNib
    MrNib Well-Known Member
    Sorry to hijack your thread....

    Your perspective is correct. In the simplest case embossing or engraving detail is the distance of the detail above or below the plane of a surface in the normal or perpendicular direction. If you were to consider a wall sticking straight up from this surface the wall thickness would be the thinnest dimension of the wall parallel to the surface. The height of the wall would be considered to be in the same direction as the embossing direction which would be normal to the large surface plane. It is my understanding, and I may be wrong on this, that you can have a wall thickness that is as thin as the minimum detail dimension as long as the wall is not taller than the width. I try to keep wall widths at or greater greater than the minimum wall spec limit value no matter what height they might be.

    Of course things can get more difficult to define on more complicated surfaces. If your engraving or embossing is not implemented with a 90 deviation from the surface plane, if your detail is on a tightly curved surface, or if there is no large definable surface plane it can become difficult to define these terms.

    I'm not aware of a great visual glossary around here. Some people have diagrammed things in the forums. The tutorial section may have something.

    or this info from a printing machine manufacturer should be helpful
    http://www.shapeways.com/tutorials/design_rules_for_3d_print ing

    so those would be a good start. Some of the design rule specification numbers in the tutorial documents may not be reflective of the latest values but any geometric definitions should have remained constant.

  11. stonysmith
    stonysmith Well-Known Member Moderator
    A bit of both. If you want to ensure that the detail to show up, it needs to be both wider and taller than the minimum.

    The thing you have to be careful of is that if the parallel distance is less than the perpendicular distance, then it will be declared a wall, and the minimum wall rule will apply also.
  12. MrNib
    MrNib Well-Known Member
    And sometimes a wall is considered to be a wire!

    Now my head hurts.