Uploading A 'negative' Stl File

Discussion in 'General Discussion' started by 1482054_deleted, Feb 22, 2017.

  1. hello everyone. New user here. I'm trying to make a mold (for resin casting). That means the image has to be a negative of what I want to make. So I've inverted my STL base file so it appears to be recessed in to the material. uploading it, what I get as a preview is a FLAT surface. Looking at the back of the preview I see a positive of the image uploaded. any hints on what I need to do to create this recessed mold? pictures attached.

    front.JPG should be a negative of this: two.JPG
     
  2. MrNibbles
    MrNibbles Well-Known Member
    You need to do a boolean subtraction of the model from rectangular piece of material that is larger and thicker than the fireman model. It looks like perhaps you simply inverted the sign of one of the major axis dimensions which would only create a mirror image of the original model or maybe you simply rotated the model by 180 degrees. You need the boolean subtraction operation with another object to create a mold.
     
    hanelyp likes this.
  3. elopez3d
    elopez3d Well-Known Member
    Making a negative mold will result in a lot of volume. You may want to order the printed model and make the mold yourself. If you do it this way you could also smooth out the master a bit more.
     
    hanelyp likes this.
  4. 3Dcarving
    3Dcarving Well-Known Member
    Hello,
    If you want, I can realize your mold for free, For that return me your drawing STL to analyze the possibilities.
    cordially
    Jacques Ronteau
     
  5. UniverseBecoming
    UniverseBecoming Well-Known Member
    Hey, Jacques, that's a nice offer! Props! :D

    I agree with MrNibbles and el_Lopez. I would just add to what el_Lopez is saying in that the main problem is print lines. All things 3D printed are done so in layers. These layers are visible on the surfaces of 3D printed objects. If you made a mold from Shapeways' Frosted Extreme Detail Plastic the print lines would be 16 microns in size and that is bearly noticeable to the naked eye, but noticeable nonetheless. To sand down those print lines on the inside of a mold cavity would be far more difficult than sanding down the print lines on a positive or master.

    If that is a bass relief you could easily make a mold of it using silicone putty. Here's how to do that. Smooth-On has lots of interesting information on how to make molds found on their site here.
     
  6. thank you, that makes sense. You're right - the model was done in Aspire and the Z axis is simply made negative to get the result which works fine for cutting this on the CNC in plastic. Still learning about real cad. thanks!
     
  7. I just wanted to add a big thank you to Jacques for his kind offer.
     
  8. Youknowwho4eva
    Youknowwho4eva Well-Known Member
    Just a note, our software will see an enclosed body and try to correct inverted normals. Besides that, it looks like you've been set on the correct path.