How to Mount and Balance Mirrors for Spirograph Project

Motor-mounted mirror is a critical part of spirograph project which greatly affects final appearance  of whole device: www.instructables.com/id/Laser-show-for-poor-man/

Usually I use cooling fan as prime-mover for mirror. It's affordable part, easy to work with, plus it cools down electronic guts of hard running spirograph ;-)
Only drawback that we cannot change  direction of rotation but it's not significant feature for laser show.   

After many trials and experiments, I've finally developed  simple and reliable method to mount and balance acrylic mirror in order to achieve smooth and quiet performance and want to reveal it in this instructable.

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All described below is applicable only to plastic/acrylic  mirrors !!!
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Step 1: Rough Shaping

Usually mirror material comes as a sheet so we need to cut square piece of proper dimension, corresponding to size of fan.

Next, mark circle on your raw mirror then form round shape using  file.
It's not supposed to be perfect circle we are going to finish it later with aid of some machinery....
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BTW. I always have some leftover pieces of  mirror sheet so I can provide it upon request.
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Step 2: Mirror Mounting

To attach mirror I use 3/4" double sided sticky tape (mounting tape). I think this kind of stuff is available at any hardware store.

Make sure back side of fan is clean. Remove any label if there's one because its glue is not   designed to hold  anything heavier than thin paper so mirror may fly away at the middle of show.

Cut square piece of tape and stick it onto fan.
Remove protective film from tape, trim it, fold it in half  then put it back onto tape as pictured.
Make sure size of folded film is about 1/4 of whole piece length.
Now put  mirror onto tape. Try to align centers of mirror and fan as best as you can.
After you've installed mirror, folded film forms accessible pocket under mirror.

Mirror tilt can be set by inserting piece of paper into this pocket but it should be done  after balancing operation..   

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.

Step 4: Tilt Setting

To set mirror tilt insert small piece of thick paper into pocket under mirror.
Usually angle of tilt is very small so post card or business card works just fine.

And best thing is that you don't have to destroy your previous work in order to reset tilt ;-)

Remember, FS mirror requires gentle handling. Avoid touching it with bare fingers.
If you need to clean surface of front coated mirror use soapy water and soft cotton cloth.
Don't let water get into motor.
If you have heat gun dry mirror out with hot air. 

That's it.
Enjoy your new learned tips and play safe.