Possible source for high-quality mirrors

On: Fri, Jul 13, 01 12:33:13 AM

Steve wrote:

During one of my recent component binges, I took apart an old non-functioning hard drive, upon doing so I discovered an extremely reflective disc inside. After doing some basic tests, I found it to have nearly 90% reflectivity, and as far as I can tell, no light distortion whatsoever. This could be interesting, the local used computer store sells old 20-100meg drives for less than $10 each, if these dics are up to holographic imagery, it could mean spending a fraction of the amount on mirrors. Does anyone know of any tests I could run these through to determine their properties? Keep in mind I don't have a holographic setup yet, although I do have a laser and many different sizes of lenses, prisms, etc.
RESPONSES

J - Fri, Jul 13, 01 06:38:03 AM

Where are you located and where is this used computer store? 148.108.1.57

Colin - Fri, Jul 13, 01 09:36:00 AM

I assume you mean the hard disk itself. I guess my first test would be to expand a laser beam with a lens and bounce it off the disk and check the polorization. If you have a beam splitter you could make an interferometer using it as one of the legs. As far as testing its flatness the only method I know of is to check it against an optical flat. I am sure there is a purely optical method but I can't think of one right now. 64.167.151.174

John Klayer - Sat, Jul 14, 01 07:20:26 PM

A clever method for checking flatness is the Rayleigh Water Test it is explained very well at this site: http://netnow.micron.net/~dagley/Pages/coulterrayleigh.html It is a method of covering the mirror with a thin layer of water and observing parallel interference fringes under monochromatic light - a poor man's optical flat. 216.46.36.15

Michael S - Wed, Jul 25, 01 02:25:55 AM

So whats the scoop has anyone been able to get these hard drive discs to work for holography? 12.18.158.25

Michael S - Thu, Jul 26, 01 06:01:55 PM

I took one apart and answered my own question. There is a huge hole in the center and unless you don't mind having a 1.5" hole in the center or your hologram I don't see how they would be usefull. 12.18.158.25

Colin - Fri, Jul 27, 01 01:07:15 PM

Most often I am just bouncing a beam around the table. Would they be suitable for small size mirrors cut out of the disk? 63.193.192.12

Steve - Sat, Jul 28, 01 01:45:37 AM

Thats what I was thinking about doing 139.142.113.29

Michael S - Sun, Jul 29, 01 07:26:11 PM

The hard drive discs themselves are a very hard substance. So I don't know how tough it would be to cut them. The dimensions of the 3 plates from a 6.4 gig drive that I have, are apx. 5" outside diameter, 1 3/4" at the widest part of the plate, and an inner circle diameter of 1 1/2". An easy way to picute their size would be if you added 1/4" to the outside edge of a common Cd and removed the the inner circle up to the reflective material. Keep in mind that this drive is the larger of the two sizes. Having a footprint of 5 3/4" x 8". The 6.4 gig drive that I took apart had 3 double sided discs. I'm assuming its a magnetic surface. It has a reflective suface coated on a metal disc. So best case scenario you could get 4 (1.5" x 1.5") and 4 (1" x 1" )mirrors per disc. I haven't tried to cut one with a hacksaw but if anyone is interested I could give it a try. 12.18.158.25

Steve - Mon, Jul 30, 01 01:08:35 AM

4 1.5"x1.5" and 4 1" x 1" from a harddrive you can pick up for free (just call the local second hand computer store and ask them to keep hold of any garbage hard drives they get) isn't bad, considering it'd be well over $50 to order them off the EdSci. 142.32.208.231

Colin - Mon, Jul 30, 01 11:48:00 AM

For inexpensive mirrors try: http://www.imagesco.com/catalog/holography/HolographySupplie s01.html I got some of the 6x7 mirrors for $12 and traded one of my holograms to a stained glass maker for instructions and help cutting them. They are just float glass but are inexpensive and disposable. I use them to debug new ideas and save my 1/10 wave mirrors for good shots. (I have lots of dust in my work area). Years ago I took apart a 20mb seagate drive and had the disk hanging on my wall. It was sort of goldish. My guess is it must be at least as flat as float glass because the heads must fly so close to the surface. Even in the old days a smoke particle was thicker than the head height. I am a little worried about three things about the disks. 1. The reflective surface is beneath a clear coating and could make a double reflection. 2. I am still curious if it has any effect on the polorization. 3. Once they are cut the metal film will be exposed to oxygen and may begin to oxidize from the edges. I remember trying to break one. They are tough. A cut off wheel in a Dremel might work. I am sure a hacksaw would work. 63.193.192.212

Steve - Mon, Jul 30, 01 01:07:34 PM

If it is only a thin metal membrane, a hot X-acto knife might work. You'd have to heat it red hot. However I don't know if that might warp the rest of the disk. And are you sure there is a clear coating? The only ones I have I am almost positive are solid metal. Most likely aluminum with a magnetic coating. 139.142.113.232

Colin - Tue, Jul 31, 01 09:27:49 AM

This sound different than the one I had apart. The one I had apart was 12 years ago. 64.167.151.250

Steve - Tue, Jul 31, 01 12:27:58 PM

Thats true. I assume that a 20mb drive may use slightly different technology than a 6.4 gb :) 142.32.208.231

Michael S - Tue, Aug 14, 01 02:23:43 AM

I'm sure most of you already know this but a good source for mirrors is copy maching repair shops. They periodically toss out old machines that can't be fixed. 12.18.158.25

Michael S - Sun, Aug 19, 01 08:17:35 PM

Does anyone know if you can get mirrors any larger than 2"x12" out of copy machines. I was hoping to find 4"x5" or even 8"x10" but all I was able to find were 2"x12". 12.18.158.25

Colin Kaminski - Mon, Aug 20, 01 04:36:31 AM

If you only need float glass mirrors, you can get them new fairly cheaply from: http://www.imagesco.com/catalog/holography/HolographySupplie s01.html#fsm 6x7 inch mirrors for $12 64.167.148.132

john@myszkowski.net - Tue, Nov 13, 01 01:47:52 AM

I would be very careful about cutting these disks. The coating and even the substrate may be toxic. Find out first... maybe thats why this thread died out... 24.141.80.235

a 14 year old says! - Tue, Dec 18, 01 02:17:20 AM

hard disks are very hard { but presuming ure using a solid ruby laser ect or any class 3 or higher laser you could cut this disk into what ever shape u want to do not cut the disk with normal tool dont touch the disk it will always permanently smudge they are tought disks but they can "fray' and hte layers come apart some disk are coered in a anti humitdidy crstal base so pease dont even think bout licking it ect { lol } you wil never eailly get one off it ball bearing spindle without touching the disk if you can afford a laser that can be used for holograms y are you using 10 hard drives? and yes im 14 from ohio how bout that 202.67.97.122

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