How do you cut delicate mirrors?

[pixpop]

As far as how straight the cut has to be - that depends... If you're talking a couple straight lines that intersect, that should be OK. But if you want to carve a complex curve, then you're going to want to cut the groove as deep as possible before you try to snap the mirror along the groove. Remember that glass is very brittle, and once the crack starts it will run very fast through the rest of the mirror. You want to be sure that the crack will follow the groove as it runs through the mirror.

On a really thin mirror, you probably won't have much trouble making the crack follow a curved path. But I woulnd't want to try and carve a circle out of a 3/8 inch thick mirror (or thicker) unless I had the groove cut down through at least 1/3 to 1/2 the thickness of the mirror before I tried to snap it the rest of the way.

I'm not wanting to cut a curve.. I want the cut to be straight. I'm just not sure how to cut a straight line with the Dremel. I mean, I can't use a straightedge to guide me as I would with a glass cutter.

I have a bunch of spare microscope slides, so maybe I'll practice on them over the weekend to see if I can make it work.

[buffo]

You don't need to be perfectly straight. Just work the dremel back and fourth with your hand - you can eyeball the line. If your line is a little wavey, that's fine. (mine was...)

Here's a picture that shows the result of my most recent cut:



If you look closely, you can see where the dremel groove was. As you can see, I didn't cut all the way to the edge, yet the mirror still broke cleanly. There is no damage to the optical surface of the mirror. (The green spots are artifacts caused by my cheap-ass digital camera...)

Also, on this next pic (below) you can see a spot near the bottom where I got the glass a little too hot and it started to crack, but fortunately it didn't crack all the way through.



Since you will be cutting a fairly thick rod, I'd suggest that you cut a groove on all four faces of the rod. That way you should be able to ensure that the mirror will crack in the right place.

One final piece of advice: If this really is an irreplacable piece, then you might want to follow Steve-o's advice and have a professional shop cut it with a lapidary saw. It shouldn't cost all that much, and if you are uncomfortable working on it yourself with a Dremel then getting a pro to do it will probably be a lot less stressful.

Out of curiosity, what are you going to use the pieces for? I'm trying to picture this thing in my mind... I'm guessing that you'll end up with 18 separate 1 inch tall cubes (or rather, rectangular boxes) with mirrored faces on 4 sides that are 1 inch high by 1/2 inch wide... What are you going to use them for?

Adam

[MechEng3]

I have 2 wet cutting diamond saws I use in my lapidary....gem faceting hobby. I could cut that materials easily without any heat or scratches. I can also cut and fashion crystals...even polishing desired surfaces. I would be happy to cut them for you. PM me if you are intrested. I also have a 4mm diamond unit as well...this saw is for expensive materials as to keep waste to a min.

[Laser Ben]

It came from a prototype scanner unit, it is coated for >98%R @ 650nm on one side and AR coated on the other side. I was thinking of selling these on eBay and keeping a couple for myself now that crutch doesn't want them. If anyone wants one I caold sell them for $25+Shipping.

[The_Doctor]

I was thinking of something like a thread saw. WHen I saw Buffo's mention of a lapidary saw I went Googling, and found an old image of the way the Egyptians used to do it. A bow saw. My idea was to use a couple of tiny cassette motor drive pulleys, the one on the motor to drive the thread, the other to support the thread on the other side of the work. To avoid knot problems, it could change directions at each end of a run of thread length, various crude methods would work to toggle that and avoid the knot hitting the workpiece. I think dacron braid fishing line would be a good choice, and maybe the stuff used for radio tuning dials, either is thin, strong, cheap, hard wearing, and doesn't stretch easily. I don't know what the abrasive should be, but that won't be the hardest thing to find.

Another idea I had was a tape saw, but I don't know how well that could work. If it can work, the loop can be spliced so thinly it can pass across the cut edge without the problems a knotted thread would cause, so it could run continuously in one direction. Guiding it might be more complex that a thread saw though, and I don't know if the edge will take enough abrasive to make the cut. I still like the idea though, mylar film is very thin and has similar properties to dacron (is same polymer, near enough) By choosing the right tape it might be possible to select one with a hard powder coating already on it. When repairing cassette recorders in the past I remember seeing what tapes can do to the toughest of ferrite and ceramic tape heads. I think it might be possible to make a very narrow cut in glass with microscopically fine edges, and to do it with a fairly simple bit of DIY, leaving it entirely unattended while it does the work. What I don't know is if it is worth the hassle, or how fast it could be made to cut. I tried looking for thread saw or tape saw on Google to see if there was a precedent, and couldn't find anything except that old Egyptian bow saw.

[Laser Ben]

http://cgi.ebay.com/BUTW-INLAND-SWAP...QQcmdZViewItem

[The_Doctor]

http://cgi.ebay.com/BUTW-INLAND-SWAP...QQcmdZViewItem

And if you want to cut one small mirror, and can improvise? That's a big spend. Sometimes the obvious answer isn't the best. I wouldn't be so concerned with how I cut it anyway, so much as how I grind a very fine edge on it afterwards.

[Laser Ben]

I just tried cutting it with an oxide cut off wheel under water and it works wonderfully, no sparks or high heat! Now just 16 more cuts to go!

[steve-o]

Under water! Nice!

[Hemlock Mike]

Besides cooling, the water also dampens vibration preventing shattering.

Mike