Selfie Ring Light Tutorial #5: Back Cover

Step 6: Screw Hole Placement

The two halves of the design are held together by screws.
(Not glue, because otherwise how will you change the batteries?)
These screws go most of the way through the design, so we need to make sure they aren’t blocked by any components.

Here’s a section view of one of the screws in the final design;

Not much wasted space!

Notice that:

  • The screws have to avoid every electronic component, even the LED ring.
  • There needs to be some extra space around the screw for it to attach securely.

The Layout sketch is a natural place for hole locations to live – we can see at once whether they’ll fit.
The screws are 3 mm in diameter, we can imagine that needed extra space by using a larger circle like 5 mm.

So let’s add them to the Layout sketch:

  1. If you’re not still inside the Layout sketch, right-click on it and select ‘Edit Sketch’.
  2. We’re missing one detail of the LED Ring outline – the inside size.
    1. Draw a Circle (press c) outwards from the origin,
    2. Dimension (press d) it to have a diameter of 75.65 mm.
    3. Mark it as a construction line. (select and press x)

    Now we can see where to locate the screws.

  3. Draw a 5 mm circle in the gap between the left of the Battery Holder and the LED Ring.
    (Press c, click to place the centre, type ‘5 mm’, press Enter)
    Draw another 5 mm circle in the gap above the Battery Holder, to the left of the Digispark and inside the LED Ring.

    TAKE CARE not to get these small circles stuck to the LED ring outlines.
    (If it happens, select the large circle to show the Coincident constraint, then select and delete that constraint)

  4. We can use dimensions to fine-tune the position of the screws; (Press d)
    1. Click on the horizontal line and the first circle’s centre, and set that vertical distance to 7 mm.
    2. Click on the first circle’s centre and the origin, move the mouse until you’re setting the horizontal distance, and set it to 34.5 mm.
    3. Click on the second circle’s centre and the vertical centre line, and set that horizontal distance to 15.75 mm.
    4. Click on the second circle’s centre and the origin, move the mouse until you’re setting the vertical distance, and set it to 31 mm.
  5. For consistency, let’s also make them construction geometry.
    (Select both circles, press x; they’ll turn into dashed circles)
  6. There are four screw holes, not just these two.
    We can Mirror the ones we’ve already drawn.

    1. Select Sketch > Mirror in the Toolbar.
    2. Click on each of the two circles’ edges.
    3. In the Mirror dialog select Mirror Line, then click on the vertical centre line in the sketch.
    4. When you see the preview of the mirrored circles, click OK.
  7. Oops, it looks like the switch outline is overlapping with one of the screws. Let’s move the switch up a little.

    That won’t work well…

    1. Zoom in to the area with the Switch outline,
    2. Click on the centre point to show the Horizontal  constraint we applied earlier.
    3. Select the Horizontal constraint and press the delete key.
    4. Now the Switch outline can be dragged up out of the way.
    5. Apply a vertical dimension of 4 mm to lock in in a sensible position.

    Much better.

  8. The Layout sketch is complete. Good job!
    Exit the sketch.

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