Engineer & Entertain

Ideas I grapple with

Spiraling into control

I am building a table for my Handibot as one of my biggest challenges thus far is registering the machine in the same spot when I move it to change bits. The table will have dog holes bored every 3 inches. The Handibot will have a fence and work pieces will be clamped against the fence via offset clamps.

The screw does not go through the center of the circle. It is offset so the circle rotates like a cam.

Rather than cut circles and mount them offset, I decide to make cams based on the Fibonacci spiral. I am not sure if there is any advantage or disadvantage to this. My reasoning was that a spiral would have a smoother transition in clamping. We’ll see how this works in practice.

I laid out a rectangle and spiral based on the Fibonacci numbers with a pair of dividers. Alternatives to using dividers/compass include:

  1. Multiplication – the 3″x3″ square is effectively the number 8 square in the picture below. To make the 5 square, multiply 3 by 5/8ths. The 5 square is 1.875″ x 1.875″. To make the 3 square multiply 3″ by 3/8ths and you will find the 3 square is 1.125″ x 1.125″
  2. Print a spiral. Adhere the paper to your work piece with spray adhesive and cut it out.

I laid out a 3″ x 3″ square on a scrap of 3/4″ thick plywood. I set my dividers to divide the square into 8ths.

The 3″x3″ square can effectively be thought of as the 8 square

From the outer corner of the 3″ x 3″ square I paced out five spaces. This is the corner for my 5 square.

Five little steps and I made the 5 square

I repeated this process to create the 3 square, 2 square, and 1 squares.

I used a compass with a pencil to trace the arc in each square. The compass legs are spaced the length of a side of a square.

Then I cut out a small rectangle from the 8 square. This provides a handle for me to grip when tightening the clamp.

Cut with a handsaw.

Next I used my fret saw to cut the spiral. I used a sander to sand down to the line.

Golden

I drilled a 3/4″ diameter hole in the spiral for a dowel. The dowel is 1.5″ long and glued in place.

Looks like a duck

The clamp does hold pieces against a fence, but I am unsure if it will be strong enough while using a CNC router. I’ll report back with those results eventually.

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