For safety always wear protective goggles when machining.
To Mill a Cube
The making of the parts of the motor sledge and film gate requires the knowledge and skill to “mill a cube”. Essentially every face of the block must be at 90° to its adjacent sides and parallel (180°) to its opposite face. This ensures all subsequent machining operations of slitting and grooving of the parts can be correctly aligned.
- Choose face side 1 and mill flat. With a marker pen number it 1.
- Choose face edge side 2. Using face 1 against 90° angle plate set side 2 level and mill flat. Side 1 and side 2 should now be flat and at 90° to each other. Mark it 2.
- Place side 2 on parallels with side 1 against 90° angle plate and mill face edge side 3 flat. Side 3 should then be at 90° to side 1 and parallel (180°) to side 2. Mark it 3.
- Using side 1 on parallels and side 2 against 90° angle plate mill reverse face side 4 flat. Sides 1, 2, 3, and 4 should then be at 90° to each adjacent side. Mark it 4.
- Using side 1 against 90° angle plate, set work piece vertical using a square. Mill a reference on end face side 5 from side 4 to side 1 to at least the width of an available parallel.
- Using side 2 against 90° angle plate and reference flat on side 5 set on a parallel mill end side 6 flat. This ensures end 6 is at 90° to sides 1, 2, 3 and 4 and parallel to end side 5 in one plane. Work piece is inverted and rotated through 90° on the axis through the end sides 5 and 6. Mark it 6.
- Using side 1 against 90° angle plate and end side 6 on parallels mill end side 5 flat. This ensures side 5 is parallel with side 6 in both planes. Mark it 5.
I find that numbering the sides aids me when I plan subsequent machining operations, how the work piece is to be held and to avoid mistakes.
Deep Hole Drilling
The motor fixing screw holes in the motor sledge sides are considered “deep holes” i.e., greater than 3 or 4 times the diameter of the drill bit used. The technique of peck drilling must be used otherwise the drill bit wanders and the exit hole is not where it should be. Peck drilling is the process of drilling and full withdrawal of the drill from the hole to evacuate swarf at frequent intervals and allow the tip of the drill to cool. When deep drilling Acetal water is a good coolant. Typically for a 3.2 mm diameter 18.5 mm deep hole I use 5 or 6 pecks.
