How to mount and balance mirrors for spirograph project

Step 3 Balancing

Unbalanced mirror causes noise an vibration so balancing procedure is necessary and important step in spirograph building.

In early projects I had to use manual Dremel for this operation but later I've developed more advanced method of mirror balancing using drill-press and Dremel sanding drum.

To hold fan I've built  simple attachment using scrap plywood and couple of screws.
Fan is locked between two crews on rotating lever.
Compressed spring pushes lever toward drill chuck so edge of mirror is always in contact with sanding drum.
While sanding drum spins mirror I use file to shape mirror.
Simple, easy and quite fast.

Few words of caution.
First, safety glasses are must!
Next, set drill at slow speed.
Make sure fan is properly secured.

At the beginning work with coarse file but don't push hard.
When mirror stops wobbling and revolutions become smooth switch to fine file to finish edge.

After some practice, if initial rough shaping done properly and mirror is centered, whole operation may take just few minutes.