Cutting Glass

I'm trying to cut some glass but I'm having a bit of a bear of a time. I am needing a 1/2" dia. round piece of glass, 0.004" thick. Or 0.1mm thick, 12.2mm dia. I've tried carbide and glass bits to score it, and I've tried grinding it down with diamond files, but I can't get the glass round enough, and when I try to file it down with a diamond file, I often break the (fragile) piece of glass. Ideas?

4 Thou thick!!!

Have you tried using Dragonfly wings, they are about the same thickness, but much more flexible....

heat it with a torch?

Walrus said:

4 Thou thick!!!

Have you tried using Dragonfly wings, they are about the same thickness, but much more flexible....

Click to expand...

;D

They are for the diaphragms of an Altec M11 microphone. Dragonfly wings will pull in under polarization and arc to the centre electrode.

cast glass in a mold?

think it would be possible for me to cut it on my cnc for you?

I never cut anything that thin but you can try this if you haven"t already. It worked on stuff a 32nd of an inch.  First cut a square a inch larger than your circle on all sides. Score you circle in the center of the square then make about 8 relief cuts all the way around from the edge of the circle to the edge of the glass. take some pliers and gently break the glass around the circle.

Can you glue the glass to the face of a 1/2" metal cylindric something with something that can easily be removed (ordinary candle wax would be my first idea) and then grind it flush with the diameter, maybe even rotating the thing in a lathe/drill press?

CO2 laser.  No problem, perfectly round with very smooth edges too... 

-Chris

dale116dot7 said:

I'm trying to cut some glass but I'm having a bit of a bear of a time. I am needing a 1/2" dia. round piece of glass, 0.004" thick. Or 0.1mm thick, 12.2mm dia. I've tried carbide and glass bits to score it, and I've tried grinding it down with diamond files, but I can't get the glass round enough, and when I try to file it down with a diamond file, I often break the (fragile) piece of glass. Ideas?

Click to expand...

Have you tried to do it in water?
Also, I'd imagine some glass engraving company would have proper tooling.

Best, M  

A couple more comments....  RE: the laser, I forgot to mention that a Versalaser probably isn't up to the task.  Check out Potomac Photonics or Synrad as potential vendors.

I also thought about masking and etching since you are only at 0.004", but I wouldn't suggest dealing with HF acid.  As Marik Said, maybe a commercial glass etcher can help.

Perhaps I could try putting it on the lathe and cutting it with a carbide tool? I thought about a laser but I need more power than I'm likely to want. It's borosilicate glass which doesn't seem to want to etch very well, unless there's a trick to getting it to etch with acid concentrations. I found a commercial place that might be able to do it, I'm anxious to hear the price. I've tried heating it but I melt and warp it, and I need it to stay flat. I've tried cutting under water, and at least that keeps the glass fragments from flying around. I think the laser approach might be best, although I just read about an interesting approach that uses a very fine-tipped tungsten wire that is heated. I also saw a hand cutter from Schott specialty glass that is supposed to be set up to cut 0.002"-0.010" glass.

One other option, I suppose, is to make a new diaphragm holder (it's separate from the backplate in the Altec), and design it to accept a Mylar diaphragm and do what I'm already familiar with. I know what a M11 is supposed to sound like, so I could try it, I guess. That would basically require making two little rings, one of them 0.7mm tall, 14.20mm OD, 12.55mm ID, with a groove on one end to glue the diaphragm on, then a second ring 0.8mm tall, just lapped. I think I could make that work, too; just need some time on the lathe.

How about gluing it to a ring with a soluble glue like Canadian Balsam, machine the edge by breaking away the glass or using the diamond file, then dissolve the glue and remove the disk? You could also use a diamond drum to grind the edge, like the ones used for stain glass work.

The Canadian Balsam reads like a good idea.  I have some old ATM books and IIRC CB is mentioned for holding glass lens.

Water Jet Cutter? Not sure about them handling the thickness but I think it would probably be fine.
Kelly

I have a MAG light with a glass lens pretty close to 1".
Check your sporting goods store. Also do a goggle search for blank lens.

Just an idea.

RonL

> 1/2" dia. ...glass, 0.004" thick

125:1 slenderness, you gonna hafta support the heck out of it.

I'm thinking metal-lathe.

Chuck a 1.5" rod of Al or Brass, face the end very flat. Mount a stick of pine in the tool holder. Wax or Balsam your glass to the rod and while hot, rotate the chuck while working the pine over the glass to get it very parallel to the rod (perpendicular to the rotation). Cool.

Now mount a diamond ring in the toolholder. Actually, a carbide-tip tool should rub glass away. It may not be ideal economics for mass production but you are just a few parts. And a carbide tool will mount a lot easier than the diamond ring.

Aim the tip just outside the 0.25" radius, turn chuck slowly, feed tool into the glass very slowly. You want to hear some action (it may be ear-splitting), but you can't afford what a metal-worker would call "pressure". Just keep rubbing until you get through the glass.

If the glass is not perfect perpendicular, it will go-through at one part while another still has thickness, and probably shatter. I hope your blanks are cheap.

Alternately: face two very short 0.5" diameter rods, center-drill the backs. Sandwich the glass between them. Mount between lathe centers with high force. Now you may be able to nibble the bulk and file-down to finish, with the part you want to keep always well-supported.

Trying to do it without a good metal-lathe.

VERY good zero-wobble drill-press. Find a 9/16" carbide-tooth hole-saw which is really 1/2" inside. Wax the glass to hard oak or flat aluminum/brass. Clamp well. Feed gently.

Same as above except steel tubing with 0.5" ID. Build a dam around the glass. Fill the pond with toothpaste or auto valve-grinding compound. Let the steel work the abrasive against the glass.

Any wobble in the drill-press will at least give an undersize result, and may just break glass.

40 years ago there was a fine air-abrasive tool which, in the ads, would cut a neat square out of an egg shell. Also, of course, various watch-size products which pay better than egg-squares. I guess it was a tiny sand-blaster, and what we now know about abrasive dusts, it may no longer be available, though it may have re-birthed as this water-jet.

Very brave/brutal approach: wax the glass between two 0.5" rods, hammer the rod through a 0.5" hole. Anything outside 0.5" will be sheared off. Maybe most of what is inside 0.5" will survive. Same as a hole-punch, except because glass has low tensile strength and elaticity you support the leading-face too.

> Have you tried using Dragonfly wings

He needs the stiffness. Enough, but not too much.

> I have a MAG light with a glass lens pretty close to 1".

The 0.004" is sorta critical, sorta the whole point. "Right Stiffness".

It is a Plate Resonator. Like a cymbal, or floor, or sorta like a marimba stick. Your MAGlite glass would be like a 15" cymbal 1.5" thick! Stiffness rises faster than mass, so a too-thick plate has a too-high resonance. And specifically, stiffer than he needs for high sensitivity.

> accept a Mylar diaphragm

Yeahbut... limp-stuff must be stretched to stiffness, the degree of stretch is always uncertain and sometimes uneven. With glass, the stiffness is built in by design, by proportion and bulk material property. That said, you already know why glass diaphragms are rare and Mylar is everywhere. It is a lot easier to fiddle Mylar than to cut thin glass.

Good luck.

dale116dot7 said:

I thought about a laser but I need more power than I'm likely to want.

Click to expand...

I was thinking in terms of outsourcing the job.  A laser that has the wattage required to cut glass in a timely manner will be crazy expensive, but the actual job run time and CAD/CAM setup will be negligible.  Synrad and Potomac are two laser manufacturers that I have worked with, and I know that they both have lasers that are up for the job.  They should be able to direct you to to one of their customers that can do contract work.  Also, you can probably get each of them to do a few pieces for you as a demo.  I'm thinking that the cost per piece will be pretty low, especially in volumes of a few dozen.

-Chris

I have cut holes in glass many times but never thinner than 1/16 inch. I use a diamond hole saw. But frequently the exiting end of the glass may make splinters. I use putty around the hole to create a kinda volcano and fill it with water. To prevent the splinters you can stick the glass to some double sided tape. So there is something to hold the trailing edge in place.

But I am not optimistic about cutting such a thin piece of glass. But may be possible with a few trials if the trailing edge of the cut is supported to prevent splintering. Possibly even glueing several pieces together stacked with superglue then using acetone to release them later. The bottom one I am pretty sure will splinter some. But you may get a few good ones..


John