For athletes and tradespeople alike cross training has a benefit.

Anything that you can learn about something will help you understand more about everything.

Step 1:

One of my favorite tools that I've used to make the things shown here is a swing arm.

It can be used on any material or with almost any cutting or marking device.

Usually I use this tool to directly cut my material but with the concrete form and the cherry benches I used it to make a series of MDF patterns .

Step 2:

a lazy susan with bearing is great for a pivot point.

A nail through the arm of the swing into a solid substrate that holds it but allows it to rotate is ok too.

The radius is determined by the distance from the center of the pivot to the cutting edge of your saw, router, plasma cutter, torch or scribe.

The quality of your pivot-

The rigidity of your swing arm-

The ability to make micro adjustments to the radius (arm length)

The ability to record those adjustments on the arm to make repeat operations

And the slickness of the surface your arm drags over are the keys to making this an accurate tool.

Step 3: Unistrut Is Forever

a good adjustable swing arm can be made with two pieces of wood that are nailed together to fix the radius length... But unistrut is awesome and solid.

A fancy woodworker could make a great tool with a sliding dovetail but I'm more of a Brutalist.

Above are the swing arms I use at home mostly for metal and the one for work that is mostly for wood.

The one for home uses the lazy susan and the one for work uses a three inch round piece of brass that fits in the hole at the pivot end. this gets fastened to the concrete floor for stability.

Before cutting I usually draw the radius with a marker to optimize my material and to check the radius.