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[APD] Re: Drilling tanks

OK, folks. Here's the real word. :^) [Free advice, worth every penny!]

I have run precision optics shops and my own optical mfg. co. (over 30 years). I long-ago lost track of how many holes I have drilled in glass.

The ideal, for modest quantities of holes, is a hollow tubular drill bit with diamonds imbedded in the first 1/4" or so, with a water swivel to allow coolant flow down the center. [Oops! Without the drill press we are into a few hundred bucks for larger holes. :-( NO WAY!]

For hobby hole drilling, I like the use of the clay dam to hold a coolant puddle around the hole being drilled, but a thin-wall brass tube as the physical tool. Cut or file coarse sawtooth notches around the cutting edge, so coolant and grinding compound can flow in readily. I'd say cut away up to 30-50% of the end of the tube surface.

Mount the tube in a drill press or one of those portable drill jigs, so you can hold it very steady and very perpendicular to the glass. Run at pretty low speed at first, but play with speed to get optimum results.

I have used diamond powder, but valve grinding compound from the local automotive supply is way cheaper and works just about as well. Get the water-mixed kind.

The drilling technique is all-important. Too much pressure and speed with sparking will end up with broken glass. NO SPARKS! Gentle pressure, with frequent lifts to allow fresh compound to replace the glass slurry will send the bit through the glass at a maximum rate. Use feel and sound to learn the best rate. Press, lift, press, lift, etc.

Use a backing glass, temporarily glued behind the glass being cut. It will eliminate nasty chips and fractures on the exit surface. Paraffin (the wax, not the British stuff) and a little heat makes a cheap glue that is easy to remove and non-toxic to fish. [Gem/lapidary hobby shops have harder waxes that are much better.]

That said, I have found fittings through the wall have always been a source of breakage when moving or handling tanks, so I prefer the double J tube kind of overflow that needs no holes through the glass.


Wright Huntley - Rt. 001 Box K36, Bishop CA 93514 - whuntley at verizon_net
                    760 872-3995

"Do we really think that a government-dominated education is going to produce citizens capable of dominating their government, as the education of a truly vigilant self-governing people requires?" [Alan Keyes]

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