Thickness Inconsistencies

Discussion in 'My Work In Progress' started by thetimpotter, Oct 12, 2012.

  1. thetimpotter
    thetimpotter New Member
    I am having issues printing a triangular column that has the minimum thickness. When the model is measured by the shapeways team with netfabb, some column edges return a .73 height, while most others return something between .06 and .6.

    What might be going on here? Why would the .stl have different measurements than the sketchup file?

    Are triangles not allowed when the thickness is at the edge of design guidelines?

    Triangle = .7 mm thick x 1 mm wide in sketchup
     
  2. stonysmith
    stonysmith Well-Known Member Moderator
    The production team should be sending you a picture of their measurements along with the rejection email.
    Could you possibly post that picture here?
     
  3. Fredd
    Fredd New Member
    This individual had a similar problem in SU. http://www.shapeways.com/forum/index.php?t=msg&th=11125& amp;start=0&
    One thing to remember, if your program can set unit lengths in its native format, and you export it as a STL, the unit lengths you set originally are disregarded in the STL. So uploading a STL to SW you have 2 options, each unit can be either a mm or an inch.
    Posting a link to the file wouldn't hurt, also a photo as Stoney suggested.
     
  4. thetimpotter
    thetimpotter New Member
  5. stonysmith
    stonysmith Well-Known Member Moderator
    Okay.. there is another topic at work here. (in addition to the notes above)

    In this case, if you will study the Design Guidelines, look at the difference in definition between "Supported" and "Supporting"

    mSVXB.jpg

    It's a matter of physics.. the bars in yellow are likely to break because they support the area to the right that has more mass, but the bars in red are "protected" due to the fact that they are enclosed by a support structure. I can tell you this.. even IF your item was printed successfully, due to it's shape and thickness, it's likely to never survive being shipped. That yellow area is going to break EASILY. For this model, I wish that Shapeways had some way to pack it using two peices of cardboard sandwiched together.. this will never survive the baggie.

    One possible way around this is to place a thicker "sprue" around the whole thing such that everything is "supported" , and then cut the sprue off after it's printed. Unfortunately, that's going to add a bit of cost to the price.

     
  6. stonysmith
    stonysmith Well-Known Member Moderator
    To answer your original question..
    triangle.jpg

    From what I've been able to determine, the tool that Shapeways uses to measure walls does so via a line perpendicular to the wall that they select.

    In the case of both of these shapes, the "Diameter" may be 0.7mm, however, as you see, if they measure the triangle slightly off-center (in red) then it comes up short. What is a bit tough is the (purple) measurement. Even though the model is actually only 0.45mm in that direction, their measurement software won't report it.. it measures straight across, and will report all 8 faces of the octogon as 0.7mm.

    But, also notice that the triangular shape has about half of the area of the octogon. In the printer, the octogon is much more likely to "hold together" than the triangular shape will because it has more mass to it.
     
  7. thetimpotter
    thetimpotter New Member
    RE: Triangle - Hexagon

    How interesting. Perhaps a deformed hexagon that mimics a triangle would print? What is causing the software to misread the measurement, a non-horizontal face?

    I will think about how I might add a "sprue" that is easy to detach. I will at least add a quick one to see if that would solve the printing issue.