endmill to grind or chip out glass?

[jkujawa]

Hi all:
This is probably a strange request, but I know one of you out there probably has some good advice on this.

We have products which have expensive machined housings with small round glass windows (2.5" dia) bonded into the housings. We need to remove the windows to re-work the fixtures. We can break the glass, but that leaves small glass shards/chips still attached to the housing with the high-strength adhesives we use. We need to remove these glass shards/chips.

I made a fixture and, using a rotary table on our Bridgeport I have been able to 'cut' out the glass, leaving a thin film (approx. .001" - .003") of adhesive on the housing. This thin film can easily be scraped off.

The problem is it obviously destroys the bit. The first time I did this I used a 1/2" HSS bit. It worked on one window, but the corners were badly rounded after removing one 2.5" diameter glass window. I tried a .25" carbide bit but that chipped. I tried a larger 6-flute bit approx. .875" diameter and that seemed to work on one piece, but I am not sure it won't start to dull or round after one or two more windows.

I need to do about 45 housings. I dont' want to go through 30 or 40 bits. Any ideas on what I can use?

Thanks!!
John

[rnponti]

I have not used a diamond bit in a mill but when I grind glass I use a diamond wheel and cool and lubricate it with water. The secret is 'slow'. Go to any stained glass shop and for $20 you can get the grinding wheel. (they have 1/8" shaft and 3/8" diameter with a 1/2 to 3/4 inch length.) They also sell the lubricant you put a couple drops in a quart or water. Works great. I have been using the same grinding wheel for 15 years in my glass shop. Granted it is not used heavily.

[tc26]

National Diamond Lab sells diamond tools for machining glass.
www.diamondtooling.com
Be sure to flood the cut with coolant.

[jkujawa]

Thanks Guys,
Unfortunately I have to go 'dry' because of the electronic components housed inside.

Any other thoughts??

John

[CalG]

A copper tube of the correct diameter or a solid rod charged with abrasive (diamond or even just valve grinding compound should do this task nicely.

Be generous with the grinding compound until the glass face is quite thin, then clean up for the final punch through.

CalG

[Konrad]

Perhaps take a chisel and skilfully chisel glass out first then clean with carbide endmill.

Konrad

[Boots]

You might try the Onsrud Diamond Bit #76-254 . It works well on glass. it's 3 flute 1/4 in. dia and has diamonds even on the end for plunging/ surfacing 1.125 in. cutting length 3 in. OAL. You can use it dry with a vacume cleaner to suck up the chips/dust. You can get it from Ballew Saw and Tool 1-800-288-7483 for around $137.00 . I bought 2 and have only used the one so far and it is still cutting good. I use them on G11 material but they work on solid glass as well.

[ImanCarrot]

A coupleof things you might consider trying: heat the assembly then cool it quickly. The metal and glass parts should cool at different rates and might fracture the adhesive bond betweeen the two.
Or, cool it rapidly- this will thermal shock the glass which should fracture.
Or, soak the lot overnight in Acetone- this might disolve the adhesive.