Block Printing and Mold Making

Written by
Lizabeth Arum

Start with a 2D drawing, turn it into a mold, then cast copies
Based on work by Dan Steele, this tutorial shows you how to combine mold making and 3D printing to create silicone block prints.

   

block_printing

Preparing and cleaning up your your 2D image

The three requirements for a model capable of generating a mold are:

  • Manifoldness – A model must be manifold in order to turn it into a mold. For a model to be manifold, it must make up a volume that could exist in the real world. The most common cause of non-manifoldness are “holes” in a mesh. If the mesh isn’t “water tight” and there is no clear inside and outside volume, a model is not manifold.

  • No internal structures – Often when models are created, they are made by jamming multiple other models together. If these models aren’t stitched together properly with their internal structures removed, then we need to fix this before we attempt to make the mold.

  • Low-Poly – To use OpenSCAD to create a model, the poly count on the model must be less than 20,000. While this number may sound low for most objects, a higher poly count doesn’t get you any more detail anyway.

Preparing your 2D image

  1. Find an image to start with. I found this image on DelhiDaze Etsy shop:

       

    Etsy Image


  2. In an image editor clean up the image so that you end up with a black and white image. In Photoshop, I removed the background using the pen tool, inverted the image, and did some clean up with the eraser:

       

    clean up


  3. Save the cleaned up image as a PNG.


  4. If you do not have Inkscape, download, install and open it. Otherwise just open Inkscape.


  5. Import your PNG file by selecting File:Import and navigating to your file:

       

    Import PNG


  6. Select Embed and press OK:

       

    Select Embed


  7. Move the image to the top left corner of the document:

       

    Move to left


  8. You want the image to be a path. Select Path:Trace Bitmap:

       

    Trace bitmap


  9. Enable Live Preview:

       

    Enable Live Trace


  10. Adjust the trace settings so that you have black lines, then click OK:

       

    Adjust the trace settings


  11. Close the window by clicking on the red button on the upper left of the window:

       

    Close the window


  12. Move the top image in the stack to right:

       

    Move top image to right


  13. Delete the original image (the image on the left):

       

    Delete the original image


  14. Move the image on the right to the left:

       

    Move to left


  15. Change the units to millimeters:

       

    Change the units to mm


  16. Click on the lock to constrain the proportions:

       

    lock


  17. Scale the image up so that the width equals 200:

       

    resize


  18. Select the Edit path by node tool:

       

    Select the Edit path by node tool


  19. You want to expand the outline. Select Path: Outset or type CTRL+):

       

    Select outset


  20. You want to disable the fill, set the stroke to black, and set the stroke style to be 2mm:

       

    Edit stroke


  21. It's time to save. Click on the File Menu:

       

    Time to save


  22. Select Save As. Save as an SVG:

       

    Save as svg

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Going from 2D to 3D

  1. Open Tinkercad in your browser. Sign in or create an account. Then create a new design.


  2. Click on Import and navigate to your file. Set the scale to 100% and the height to anything. You will be changing the dimensions shortly:

       

    Import SVG


  3. Hold shift and click and drag on a corner node to resize the model until the length of the object is a bit less than 60mm:

       

    Shift and resize


  4. Drag the ruler onto the workplane:

       

    Set the height


  5. Set the height of the model to 3mm:

       

    Set z


  6. Set the model to be 16.75mm above the workplane:

       

    move up


  7. Create a base for the stamp by dragging a box onto the workplane and resizing. Make the height of the block 17mm:

       

    Create a cube


  8. Position the block underneath the design:

       

    Adjust placement


  9. You want to rename the design and download it. Start by selecting Design: Properties:

       

    Open properties


  10. Rename the model:

       

    rename


  11. Select  the extruded SVG and the block, then select Design: Download for 3D Printing, and click on STL:

       

    Download STL

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Making the Mold with OpenSCAD

  1. If you don't have OpenSCAD installed on your computer, download and install it now. OpenSCAD is another free modeling tool. You can find it at openscad.org.


  2. You’ll also need Dan Steele's Mold Generator scad  file. It can be found here.


  3. Put the Mold Generator scad script in the same directory as your model that you downloaded from Tinkercad, and load the script in OpenSCAD. The code editor window will look something like this:

     

     

    openscad script


  4. Change model_filename to the name of your STL file. In my code, the model_name was on line 21.


  5. Press F5 to render a view of what the script is doing. If you're lucky it will be perfect right away, but chances are it won’t be. Note that this script creates a negative of your model and pushes it into the two halves of your mold:

       

    Change values


  6. Negative space is difficult to see and position so there is a small change you can make to the script to see the model you are trying to place in the mold halves.

    Notice the six comments (//)  added on the left-hand side. Add those and press F5. You should be able to see your model in the preview:

       

    Add //


  7. You can now move the model around and put it halfway into the right-hand side of your mold.

    To move your model around  you need to tweak the variables.

    For model_rotate and model_translate the 3 variables are X, Y, and Z respectively. model_scale is a multiplier applied to the size of your original model. Adjust the mold_width, height and depth as needed so that the model sits nicely in the middle of your mold:

    *************************************************/
    // Model parameters
    model_filename = "elephant.stl";
    model_rotate = [0,0,0];
    model_translate = [22,0,-1];
    model_scale = .9;
    // Mold parameters
    mold_width = 85; // Measured along X axis
    mold_height = 60; // Measured along Y axis
    mold_depth = 20; // Measured along Z axis
    mold_spacing = 3; // Space between mold halves
    rounded_corners = true; // Rounded the corners to lessen warping
    edge_radius = 8; // Radius of rounded corners


  8. Press F5 after you make the adjustments to see the results. When you have all the variables set correctly, your preview should look something like this:

       

    Adjusted


  9. Once it looks right, you’ll need to remove the 6 comments and hit F5 again. It should now look like this:

     

    Remove comments


  10. Render the mesh by pressing F6:

       

    rendered


  11. Export the mesh as an STL by selecting File:Export and Export as an STL.

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Casting with Oogoo

Oogoo is corn starch and clear silicone caulk mixed together and then molded by hand or by forms to create just about anything you can imagine that needs to be adhesive initially and solid yet flexible when cured.

The original instructions for making Oogoo can be found at instructables.com.

Here are a couple of tips for using Oogoo:

  1. Add essential oils. Just add a few drops of vanilla (or whatever other fragrance strikes your fancy) essential oil to the silicon before adding the corn starch. It will somewhat replace the yucky vinegar smell.


  2. Add a bit of oil-based paint even if you don’t care about color. The extra oil from the paint and essential oil makes the Oogoo a bit thinner and delays the curing process a bit.

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Making The Oogoo Block Prints

  1. Add silicone to your container. To estimate how much you need figure a little more than what would fill one side of the mold:

       

    Add silicone


  2. Add the essential oil into the silicon before stirring in the paint:

       

    essential oil

  3. Add the oil-based paint:

       

    Add paint

  4. Stir until paint is mixed evenly:

       

    mix


  5. Mix in corn starch. Add the same amount of cornstarch as silicon by volume. Stir until it was well blended:

       

    cornstarch

    mix


  6. The mixture is stinky at this point, you might want to open a window:

     

    mixed

       


  7. Put on some gloves:

       

    gloves


  8. Smoosh the mixture into both sides of the molds (more than you think you need):

       

    smoosh


  9. Squeeze the mold halves together as tightly as you can. Oogoo should push out from all four sides if you've added enough. Use a clamp to keep the halves together:

       

    clamp


  10. In about an hour (wait longer if you have patience), carefully pull the mold apart. Make as many as you would like.

  11. Use a brayer and some block printing ink. Roll out the ink on a flat surface, then roll over block. Print on paper:

       

    ink

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Source for mold and Oogoo tutorial:Pinshape

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