Assignment 4: Make A Molecule

Introduction

According to Wikipedia, "the largest single use of ethanol is as a motor fuel and fuel additive". It's also used in medical wipes, hand sanitizer gels, paints, and perfumes. It's a good general purpose solvent and an effective antiseptic. And some people like to drink it.

Using a free, open source molecule editor like Avogadro you can construct your own molecular models, solve for low-energy configurations, and read out the bond lengths and bond angles. But for this assignment we've done all that work for you. All length values given in "inches" below are really in picometers, and all bond angles are physically accurate.

In this assignment you will construct an ethanol molecule in SolidWorks that is hollow inside and has a removable threaded cap. You will then 3D print the molecule and the cap.

Making the Cap

  1. Start a new part.
  2. Create an extruded base on the Top Plane
  3. Draw a circle centered on the origin and dimension the diameter to 2.05 inches. (Note: This value was formerly 2.1 inches but has been adjusted to make the threads work better on the NVPro printer.)
  4. Set the extrude depth to 0.75 inches.
  5. Click OK to complete the extrude. This produces a disk.

  6. Create a Revolved Base feature on the Right Plane.
  7. Draw a horizontal line along the top edge of the disk, starting at the midpoint of the top edge (directly above the origin) and running leftward to just past the left edge of the disk.
  8. Dimension the horizontal line to 1.2 inches.
  9. Draw a vertical line upward from the top edge of the disk, rising from the midpoint.
  10. Add an Equal relation between the two lines.
  11. Draw a 90 degree centerpoint arc connecting the ends of the two lines. To assure that the arc merges properly with the line endpoints, follow these steps:
    1. Select the Centerpoint Arc tool
    2. Click on the point where the two lines meet; that will be the arc center.
    3. Click on the top of the vertical line.
    4. Move the mouse down and to the left to form an arc, but stop before reaching the horizontal line.
    5. Press Escape to exit the arc tool.
    6. Click on the bottom endpoint of the arc.
    7. Control-click on the left endpoint of the horizontal line.
    8. Select "Merge" in the Property Editor to merge the two endpoints.
  12. Exit the sketch and use a 360 degree revolve of the quarter circle around the vertical line to form a hemisphere.

  13. Click on the flat bottom of the cap to select it.
  14. Use the Shell feature to hollow out the cap; set the shell thickness to 0.2 inches.

  15. Save your part as Cap.SLDPRT

Threading the Cap

    CUTTING PROFILE

  1. In this step we'll make an equilateral triangle to cut threads in the lip of the cap.
  2. Make a new sketch on the Front plane.
  3. Draw a vertical line about 0.2 inches long, somewhere below the bottom left edge of the lip. The exact position doesn't matter. Dimension the line to 0.2 inches long.
  4. Draw a diagonal line starting at the top of the vertical line and moving down and to the right, with about the same length as the vertical line.
  5. Add a third diagonal line to complete the triangle.
  6. Add an Equal relation between the two diagonal lines.
  7. Dimension the angle between the two diagonal lines to 60 degrees. Now you have an equilateral triangle.
  8. Click on the vertical line.
  9. Shift-click on the left vertical edge of the cap lip. (There may not appear to be a line there, but click on the edge and a silhouette edge will appear.)
  10. Add a Colinear relation.
  11. Click on the point where the two diagonal lines meet.
  12. Shift-click on the bottom edge of the cap lip.
  13. Add a Coincident relation.
  14. Now the sketch should be fully defined (black).
  15. Click OK to exit the sketch.
     

    CUTTING PATH

  16. Now we'll make the helical path that the cutting sketch will follow.
  17. In the Features tab, open the Curves pulldown menu and select "Helix and Spiral".
  18. Select the bottom face of the cap lip (the very bottom of the cap) as the plane for your sketch.
  19. Use a Normal To view so the cap edges form perfect circles.
  20. Select the outer edge of the cap lip. (This will be the middle of three visible circles.)
  21. Click Convert Entities to copy the circle into the current sketch.
  22. Click OK to exit the sketch.
  23. In the Helix/Spiral property manager, select a constant pitch of 0.25 inches.
  24. Set the revolutions to 3 and check the Reverse direction box so that the yellow spiral ascends into the cap.
  25. Set the Start angle to 270 degrees to ensure that the start of the helix coincides with the location of the triangular profile sketch. (If you layed things out slightly differently you might need a different start angle.)
  26. Click OK to complete the helix.

    THREAD FEATURE

  27. In the Features tab, select Swept Cut.
  28. Open the feature tree in the top left corner of the graphics area.
  29. For the sweep profile (blue box), select the triangular profile sketch.
  30. For the path (pink box), select the Helix/Spiral feature.
  31. Click OK to complete the feature.

  32. Save your part as Cap.SLDPRT
  33. Then do "Save As" and set the file type to STL. In the save dialog box, click on the Options button and select Fine resolution.
  34. Save the file as Cap.STL.

Making the Molecule

  1. Create a new part.

    FIRST CARBON:

  2. Create a Revolved Base Feature, sketching on the Top Plane.
  3. Draw a vertical line extending THROUGH the origin and dimension it to length 3.4 inches.
  4. Select the line's midpoint and make it coincident with the origin.
  5. Use the centerpoint arc tool to draw a left semicircle bounded by the vertical line endpoints:
    1. Select the centerpoint arc tool.
    2. Click on the origin; that is your centerpoint.
    3. Click on the top point of the vertical line.
    4. Move the mouse down and to the left, approaching but not touching the bottom point of the vertical line.
    5. Left click to draw the arc.
    6. Select the arc endpoint.
    7. Shift click on the bottom point of the vertical line.
    8. Click on Merge in the properties tab.
  6. Exit the sketch and use a 360 degree revolve of the semicircle around the vertical line to form a sphere.
  7. In the Feature Manager Tree, rename the feature Carbon1.
  8. Color the entire sphere (the Carbon1 element in the Appearances pop-up list) pale green.

    SECOND CARBON:

  9. Create a new sketch on the Front Plane.
  10. Draw a vertical construction line upward from the origin and dimension it to 1.54 inches.
  11. Exit the sketch.
  12. In the Feature Manager Tree, rename the sketch to Backbone1.
  13. Create a Linear Pattern feature and set the vertical line of Backbone1 as Direction 1.
  14. Set the distance D1 to 1.54 inches.
  15. Set the # of instances to 2.
  16. Set the Revolve feature as the Features to Pattern (just click on the sphere to select it).
  17. If the Reverse direction button (to the left of the Direction 1 box) is selected, click it to deselect. We want the yellow outline of the new carbon being constructed by the linear pattern to be on the same side as the dashed Backbone line. (If you don't see a yellow outline, click on "Full Preview" in the linear pattern dialog box on the left.)
  18. Click OK.
  19. Rename the feature Carbon2.

    FIRST HYDROGEN:

  20. Create a new Revolved Base on the Front Plane.
  21. Draw a diagonal construction line from the origin downward and to the left.
  22. Dimension the line length to 1.1 inches.
  23. Dimension the angle between the line and the vertical Backbone line from the previous sketch to 109 degrees.
  24. Draw a new vertical line (solid, not a construction line) through the bottom left endpoint of the line you just drew.
  25. We want the midpoint of the new vertical line to be coincident with the left endpoint of the diagonal line, so add a relation to enforce this property.
  26. Dimension the line to length 2.4 inches.
  27. Use the centerpoint arc tool to draw a semicircle to the left of and bounded by the vertical line. Merge the second endpoint.
  28. Exit the sketch, and in the Revolved Base dialog box, make sure that the axis of revolution selected is the solid vertical line, not the diagonal construction line. Use a 360 degree revolve of the semicircle to form a sphere.
  29. Note: if there is a problem with your sketch and SolidWorks wants to make the Revolved Base a "thin" feature, cancel the feature and then edit the sketch. Once a feature is marked "thin" there does not appear to be a way to undo this, and a thin feature is not suitable here. One possible cause of this problem is if the vertical line was made a construction line instead of a solid line.
  30. In the Feature Manager Tree, rename the Reolved Base feature to Hydrogen1.
  31. Color the sphere (Hydrogen1 in the Appearances pop-up list) white.

    SECOND AND THIRD HYRDROGENS:

  32. Create a Circular Pattern feature (in the pulldown menu from Linear Pattern).
  33. For the axis/surface of rotation parameter (first box in the "Parameters" section), select Backbone1.
  34. For the # of instances, select 3.
  35. Check the Equal Spacing box.
  36. For the Features to Pattern, select Hydrodgen1.
  37. Click OK to complete the feature.

    OXYGEN:

  38. Make a new Revolved Base on the Front Plane.
  39. Draw a diagonal construction line from the top end of the Backbone line up and to the right, and dimension it to length 1.43 inches.
  40. Set the angle between the vertical and diagonal construction lines to 120 degrees.
  41. Draw a solid horizontal line centered on the endpoint of the diagonal construction line, and dimension is to length 3.04 inches.
  42. Select the midpoint and add a relation to enforce this property.
  43. Use the centerpoint arc tool to draw a semicircle above the horizontal line.
  44. Merge the second endpoint.
  45. Exit the sketch and make sure that the axis of revolution is the solid horizontal line, not the diagonal construction line. Use a 360 degree revolve of the semicircle to form a sphere.
  46. Rename the feature to Oxygen1.
  47. Color Oxygen1 red.

    FOURTH HYDROGEN:

  48. Go the Features Tab, and in Reference Geometry, create a Plane.
  49. Set the first reference to Top Plane
  50. Set the second reference to the top point of your Backbone line and click OK.
  51. Rename the plane Carbon2Plane.
  52. Create a new Revolved Base feature on Carbon2Plane.
  53. Draw a horizontal construction line from the origin to the left.
  54. Draw a diagonal construction line from the origin up and to the left, and dimension it to 1.1 inches.
  55. Set the angle between the two construction lines to 70 degrees.
  56. Draw a solid horizontal line with its midpoint being the top point of the diagonal construction line.
  57. Add a relation to enforce the midpoint constraint.
  58. Dimension the horizontal line to length 2.4 inches.
  59. Use the centerpoint arc tool to draw a semicircle above and bounded by the horizontal line. Merge the second endpoint.
  60. Exit the sketch and use a 360 degree revolve of the semicircle to form a sphere.
  61. Rename the feature Hydrogen4.
  62. Color Hydrogen4 white.

    FIFTH HYDROGEN

  63. Create a mirror feature.
  64. Set the mirror face/plane to the Front Plane.
  65. Select Hydrogen4 as the feature to mirror.
  66. Click OK to complete the mirror.

    SIXTH HYDROGEN

  67. Create a Revolved base on the Front Plane.
  68. In the Feature Manager Tree, expand the Oxygen1 feature to reveal its sketch.
  69. Right click on the sketch and click "Show" (the eyeball icon) to make it visible.
  70. Add a new construction line from the end of the oxygen diagonal line, running almost vertically but slightly to the right.
  71. Dimension this construction line to 0.94 inches and set the interior angle between it and the diagonal below the horizontal line to 125 degrees.
  72. Draw a solid horizontal line centered on the endpoint of the new construction line, and dimension it to length 2.4 inches.
  73. Use a midpoint relation to ensure that the horizontal line is centered properly on the endpoint.
  74. Use the centerpoint arc tool to draw a semicircle above the horizontal line.
  75. Merge the second endpoint.
  76. Exit the sketch and use a 360 degree revolve of the semicircle to form a sphere.
  77. Rename the feature Hydrogen6.
  78. Color the sphere white.

    CAP OPENING:

  79. In the Features tab, under Reference Geometry, create a new Plane.
  80. For the first reference, hover the mouse over the boundary circle where Hydrogen6 meets Oxygen1. The boundary should be highlighted in orange. Click to select it.
  81. The plane is now fully defined; click OK to exit.
  82. Rename the plane to Hydrogen6Plane.

  83. Create an Intersect feature. If you don't have the icon for Intersect (it's not visible by default), open the slide-out menu at the top of the window and select Insert -> Features -> Intersect
  84. In the Selections box, add both Hydrogen6Plane and Hydrogen6.
  85. Click on the Intersect button. The entire molecule should turn green.
  86. Now we need to specify regions to exclude. Click on on the Hydrogen6 sphere in the graphics window (not the feature in the feature manager tree); it should turn pink.
  87. Cllick OK to complete the Intersect operation.
  88. Right click on Hydrogen6Plane in the feature tree and hide it.

    SHELL:

  89. Click on the flat surface at the top of the Oxygen1 sphere.
  90. Create a Shell feature.
  91. Set the shell thickness to 0.2 inches.
  92. Click OK to complete the shell.
  93. Save your part as Ethanol.SLDPRT

Threading the Molecule

    LIP:

  1. Create an Extruded Base feature on the flat lip of the opening in the Oxygen1 molecule.
  2. In the sketch editor, click on the inner circle of the Oxygen molecule opening.
  3. Click on Convert Entities to import that circle into the sketch.
  4. Reselect the same inner circle and click on Offset Entities to create a slightly bigger circle outside it.
  5. Set the offset distance to 0.2 inches and click reverse if necessary to make sure the new circle is outside the inner circle. Click OK.
  6. Click OK to accept the sketch.
  7. Set the extrusion depth to 0.75 inches.
  8. Adjust the direction (the button with the arrows to the left of the "Blind" menu setting) so that the extrusion extends into the molecule's interior.
  9. Click OK to complete the extrusion.
  10. Rename this feature Lip.

    CUTTING PROFILE:

  11. In the feature manager tree, open Hydrogen6, right click on its sketch, and select Show to make it visible.
  12. Make a new sketch on the Front plane.
  13. When you select a Normal To view, notice that the lip in Oxygen1 is tilted slightly down and to the right. That's fine.
  14. Above the lip in Oxygen1, near its left edge, draw a vertical line about 0.24 inches high that isn't snapped to any other feature.
  15. Form a triangle by adding two diagonal lines to the left of the vertical line.
  16. Add an Equal relation between the two diagonal lines.
  17. Dimension the angle between the two diagonal lines to 60 degrees.
  18. Add a construction line connecting the two midpoints of the diagonal lines.
  19. Dimension the construction line to length 0.12 inches. The result should look like this:
  20. Click on the solid vertical line and remove its Vertical property.
  21. Click on the construction line and remove its Vertical property as well.
  22. Click on the solid vertical line, shift click on the circular edge of the lip, and add a Perpendicular relation between them. This should tilt the triangle slightly upward, matching the lip.
  23. Click on the point at apex of the triangle (the leftmost point), and shift click on the circlular edge of the lip.
  24. Add a Coincident relation between the point and the circle.
  25. Dimension the distance between the formerly vertical solid line and the near-vertical construction line in the Hydrogen6 sketch to 0.925 inches.
  26. Now the triangle should be fully defined (black).
  27. Click OK to exit the sketch.
  28. Hide the Hydrogen6 sketch.

    CUTTING PATH:

  29. In the Features tab, open Curves and create a Helix and Spiral feature.
  30. Select the flat face of the Oxygen6 opening as the sketch plane.
  31. Click on the circle that forms the inner edge of the lip.
  32. Click on Convert Entities to import the circle into this sketch.
  33. Click OK to complete the sketch.
  34. Set the helix pitch to 0.25 inches and the number of revolutions to 3.5.
  35. Set the Start angle to 0 so that the yellow line in the preview begins at the triangle that forms the cutting profile.
  36. The spiral should extend down into the red oxygen molecule; if it's extending upward, click on the Reverse Direction box in the Helix/Spiral dialog pane.
  37. Click OK to complete the helix.

    THREAD FEATURE:

  38. In the Features tab, select Swept cut.
  39. Click on the triangle to select it as the proflie (blue box).
  40. Click on the helix to select it as the path (pink box).
  41. Click OK to complete the feature.

    BASE:

  42. Add a thin base to your molecule. The base should be a thin platform that you connect to your molecule in a method of your choosing (stand), so get creative! In our example we simply used a circular platform and three cylinders as the stand, but feel free to innovate and choose something more creative. Note: when creating the extrusion(s) for your stand, check the "Merge bodies" box so that you end up with a single body; this affects how your part will scale.

    INITIALS:

  43. Cut your initials into the platform by following the steps below. Place your initials somewhere visible so the molecule can be easily identified as your own.
  44. Create an Extruded Cut feature. Place the sketch on the top surface of the base.
  45. In the sketch tab, draw a construction line to indicate how the text should be aligned.
  46. Click on “Text” tool, and select the construction line as the "curve" parameter.
  47. Type your initials in the text box.
  48. To change the font and size: uncheck “use document font” and click “Font..” Set the size to 15mm under Height and Units. You should probably keep the same font, but if you change it, make sure that the lines of the letters don't cross at any point. Also make sure the final letters are legible at this size.
  49. Exit the sketch and set the Extruded Cut parameters. You should cut all the way through the platform ("Blind"). Note that the triangular cutout inside the "A" in the figure will be lost if you cut all the way through, unless you add a connecting piece (as a separate extrusion) to keep it connected to the base; in that case the "A" would look like a stencil.

You can make an assembly containing the cap and the molecule. The result will look like this:

But for 3D printing purposes you should have the cap resting on the ground next to the molecule, not floating in space above it. One way to do this is to mate one face on each part to the Top plane. (You'll need to remove the Fixed attribute from whichever part you inserted first into the assembly, so that it's moveable.) Note that the cap actually requres less support material if you orient it upside-down (threads facing up).

Printing on the Stratasys

  1. In SolidWorks, scale both the cap and molecule to 40%. You can do this for each part by going to Insert > Features > Scale. If your molecule plus base consists of more than one body, make sure to select scaling by Origin, not scaling by Centroid.
  2. To save the assembly as an STL file, do File > Save As, then select "STL" as the file format.
  3. In the save dialog, click on the Options button. Set the resolution to "Fine" and check the box that says to combine all parts into a single STL file.
  4. Go to skylab.ideate.cmu.edu and upload your STL file.
  5. Set the Resolution to "Fast" (0.10 in) and density to "Sparse".
  6. The interface will show you six different orientations for your print. Choose the one with the fastest print time and least support material, unless you have some reason to prefer a different orientation.
  7. In the Comments field, put your course number 15-294 and your name and Andrew id. This helps IDeATe staff track usage, and allows them to contact you if there is a problem with the print.
  8. Click on the "Order" button to submit your job for printing. Once you've done that, you'll see a list of your orders. Ignore the cost estimate; it's bogus.

What to Hand In

  • Hand in your SolidWorks parts files and STL files via Autolab by the due date shown on the class schedule.
  • When you get your parts, post a picture of your molecule on Piazza, in the thread provided there. The picture should show the cap threaded into the molecule body, and your initials should be visible.

Grading

  • 7 points for a correct Molecule body in SolidWorks
  • 1 point for a correct molecule cap in SolidWorks
  • 3 points for a good stand design in SolidWorks
  • 4 points for a complete printed molecule and cap with working threads, with a picture posted to Piazza
Back to 15-294 course home page

Last modified: Mon Sep 26 23:31:46 EDT 2016