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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Comments

[ugman77]

Why are you not able to change the direction of the rotation of the fans? Wouldn't a simple current reverse switch accomplish this?
I have a spirograph using regular motors and I find that the rotation change increases the number of possible patterns tenfold.

[AP Digital light]

Fan is device to produce steady airflow only in one direction. It contains motor controller without reversible feature.

[FJMSoft]

Hey friend, where can I get this kind of mirror?
Very interesting!
Thank you.

[AP Digital light]

Acrylic mirror sheet should be available at any plastic supplier, furniture/hardware shop or Home depot,

[ajam123]

Oh my... I love your laser show machine! I just got my dvd burner laser and I'm definitely building something like this now! I'll try to use my arduino for it. Thanks alot for the great idea!

[paul30003]

I've alread done that with an arduino. Still working on the code a bit, but its come a long way now, If your stuck for ideas, let me know and ill send you my updated sketch. http://www.fxlasers.co.uk

[bratan]

Great tutorial! 2 questions. 1. Since I don't have drill press, is it possible to get by with just handheld dremel instead? :) 2. How do you know when to stop filing the piece? Is there any clear indication?

[AP Digital light]

1. You can if you make similar jig. You'll need free hands to hold file;-)

2. Indication is wobbling.
To check it place edge of file close to edge of mirror about 0.5 mm.
While you hold file still, slowly spin mirror with your hand (make sure drill press is turned OFF!!!) and monitor gap between edge of mirror and edge of file.
If mirror is not centered you will see that distance between edge of mirror and edge of fixed file is changing significantly (within 0.5 - 1mm).
I usually stop filing when distance change is about 0.3 mm.

[bratan]

Thank you! I guess I'm getting a small drill press :) BTW, what happens if mirror wobbles, or even if it's square? Does this affect laser beam, or might detach from the fan?

[AP Digital light]

It doesn't really affect shown patterns but noise and vibration may become very annoying factor especially if device employs high speed fans.
Risk of separation mirror from motor is quite real too.

Strong vibration may cause light device to wander around itself till it eventually jumps from the table;-)

Possible solution for square or unbalanced mirror is to install it onto balanced heavy flywheel attached to motor thus weight of mirror may be neglected.

[miketwo]

You seem like the guy who would know...

I'm trying to mount a mirror to a servo, to turn my IR sensor into an IR scanner.  Your instructable gave me some great ideas, but I might as well ask -- how would you do it?

(The mirror has to be weight-balanced on the servo and mounted at a 45-degree angle.)

Cheers!

[skowerr]

for a scanner i'd use a hdd head with a mirror attached to it so there would be a nice inline movement of the beam. head could move the beam in horisontal  plane and a servo could rotate the head vertically. if you would use only  servos it would  be quite hard to scan an object in straight lines. you would get a sinusoidal line which would diturb the scale of scanned object, and that you would propably like to avoid.

[AP Digital light]

I guess optical alignment of that system is real pain, IR beam, eh?
I would mount IR transmitter/receiver on a servo shaft to minimize all adjustment troubles. 

But if you want go with mirror, I think, servo is relatively slow device, so balancing is not so critical, even if you set it for continuous rotation, unless mirror is huge and heavy.

It would be nice to see your finished scanner here, on Instructables.;-)
Good luck!

[T3h_Muffinator]

Great idea! 
Got any videos of the finished product?  (The spirograph, that is!)

[AP Digital light]

Spirograph video and building tutorial
www.instructables.com/id/Laser-show-for-poor-man/

[T3h_Muffinator]

Ah!  Totally missed that - my bad!

[AndyGadget]

Clever idea. I made my own version of your laser show some time ago (but never got around to making it into an Instructable).  I cut discs from an old shaving mirror using a hole cutter, but getting them centred was a trial and error thing and because they weren't front silvered, I lost a lot of light.  I'll do a rebuild sometime using proper mirrors and your method for setting them up.