drilling inconsistency - Why??

[treesprite]

Why on earth is my drilling so inconsistent when I've used the same drill for all of them? It seems to not matter whether I'm using an old worn out bit or a brand new one. Of all the holes I've drilled I've only had one crack, but the hole I just did in the 75g with a brand new bit, turned out very messy (but passable, thank goodness). Yesterday I drilled a clean hole in a 15g tank using an extremely worn bit.

 

One thing I discovered was that drilling from the inside of the tank while sitting on the floor, is easier than doing it from the outside of the tank while standing. Still, that didn't seem to matter when I did the 75 - the hole still came out messy.

[gmubeach]

Glad you got your tank drilled show us pictures!

[Coral Hind]

Using a guide helps to get a clean start without lots of groves in the wrong spots. Keeping the drill straight is important to make sure the side of the bit doesn't make contact with the glass or it can cause chips. When you get close to the end slow it down some with less pressure so as not to spall out the other side.

[Jon Lazar]

IME the "messiest" holes come from either letting the bit wander as you start to make the hole, or chipping on the inside of the hole as the bit completes the hole and punches through.

 

You can keep the blade from wandering by clamping a 1/2" plywood template where you want the hole. It holds the blade steady, and also helps keep it perpendicular to the cutting surface.

 

To minimize chipping as you finish drilling the hole, clamp another piece of wood to the other side of the glass.

 

If you use both techniques, you'll have a layer of glass between two layers of wood. This will solve most of your drilling problems. Or you can do the cuts freehand and slop on lots of silicone once you're done.

[Happyfeet]

Its easy. Nothing to get worked up over. Here is a little visual guide.

Make a mold from laminate hard board, Plywood, or anything of the like works as well. Cut 2x45 degree slices to make the "V" to guide the bit.

 

Tape it to the tank, or clamp it in place.

Tape underneath the hole as well to catch the glass and cut down on vibrations.

Put a towel underneath in case it falls through.

Mold Plumbers putty to make a water reservoir.

 

 

 

 

Put the bit in and drill in 3-5 second bursts until it begins to make a groove. Gradually begin doing 10-15 second bursts. I found at high speeds there are less vibrations. The slower the more vibrations...

 

Dont put any pressure. Just let the bit do the work.

Halfway through put the drill in high gear and full speed for 20-30second bursts.

With 3-5 seconds in between to let it cool.

 

Doing it like this seems to have turned out some pretty uniform results.

Edited May 17, 2010 by Happyfeet

[treesprite]

I need to get a hole saw to make a template really, but that still doesn't explain why sometimes I have trouble and other times I don't.

 

Now that I'm thinking about it, maybe it's the thickness of the glass that messes me up. Do other people have more trouble with thicker glass than thinner?

[Jon Lazar]

Wheb drilling freehand, sometimes you hold the drill perfectly steady, and sometimes you don't.

 

If you want to be consistent, use a jig.