View Full Version : Drilling Bigger Holes

Drew Jaeger
02-22-2012, 03:11 PM
Hello All,

I have a commission to create 6 pendant light shades for some friends of mine. The hardware they picked out has a massive (40mm) diameter opening needed. I have 2 brand new 40mm diamond core bits and last night tried to drill them. I broke 4 of the 8 I had made and gave up. The first one was my fault since I was drilling at a bit too high of a speed and the bit bound up and cracked the shade. I am using a clay dam and a cordless drill to keep the glass wet and cool. I added fresh water every few seconds and kept plunging in and out to keep the cut clear. Besides the one that bound up they just seemed to crack with about the last 10% of the cut to go. It's all Gaffer color and Spruce Pine so I don't suspect it's a fit problem. The opening on the top is cutting a fair amount of material, I'd say 75% of the base area so I don't know if that causes issues as well.

I am checking with my friends about hardware that can use a smaller hole but if they are set on 40mm I may have to keep drilling. Or start over from scratch and put the hole in hot.

Any tips? I searched the archives and didn't see anything about core bit drilling that big.


Mark Rosenbaum
02-22-2012, 03:56 PM
That is not really that big....most of the medium socket holes (standard bulb socket) that we drill are 42 mm. We use a drill press on the ones we can fit underneath, or a hand drill for larger shades. We constantly spray the drill with water to cool the bit. Make sure that you are flushing out the hole and you keep the bit straight up and down. I know that it is a new bit, but check to see if it still has diamond on it....HTH

Pete VanderLaan
02-22-2012, 04:38 PM
It could also be underannealed. One of the things with knocking pieces directly off the pipe into the lehr is that frequently, they just go in too cold and need to be soaked at a much higher temperature.

Try making the piece in just clear. See how it does. If that cracks, then it's either Mark's suggestion about the diamond presence or it's the annealing... or you could be pushing it too hard with too little lubricant but assume one of the first two things before you get real crazy. There should be coolant on the work all the time, not periodically. Cordless drills says to me that the bit is not staying stationary and that too is a problem. Ideally that should be done on a drill press with a thru the waterway drill bit.

Kenny Pieper
02-22-2012, 07:24 PM
Just because it is gaffer does not by any means say that it is not a compatibility problem.
A drill press is a much better way to go. Although I have drilled glass with a cordless drill I always feel like I have gotten away with something. Even a slight change in angle when the bit is in the glass can cause a major stress and crack it. You do want a pretty high speed with not much pressure for diamond drilling

David Hopman
02-22-2012, 10:35 PM
I only break about 1 in 100+ shades on drilling now that I changed my procedure, doing shades up to 18" diameter. I use a drill press , belgian center feed and 42mm bits, but instead of bringing the drill down onto the shade, I hold the shade up against the drill. I also rock the shade around as I push up, which makes the hole a bit larger and pretty much eliminates the bit grabbing the glass when it finally cuts through. It also helps a lot to have a flat surface to start on that is at least as wide as the bit.

Josh Bernbaum
02-23-2012, 06:35 AM
Ideally that should be done on a drill press with a thru the waterway drill bit.

Agree with this and what was said in the other last 2 posts, that a drill press is the way to go. I've had much better luck making good holes when a constant water feed is going through the center of the core bit while drilling. You can buy this apparatus to attach to your drill press.

Rick Sherbert
02-23-2012, 06:41 AM
i drill A LOT of lights. Stability is your friend. I have hand drilled ones (40+ for a commission) that wouldn't fit in my drill press but it was really sketchy. Some pressure is ok but let the bit do the work. Any time you get at an angle you risk binding the piece up on the bit. If you are properly annealed as recommended in previous posts, then it's all mechanical. Are you generating too much heat? More coolant. Too much pressure? Back off some. Unstable and binding? Figure out some kind of jig. Not much more than that.

Pete VanderLaan
02-23-2012, 06:57 AM
Again, just try one in clear.

Drew Jaeger
02-23-2012, 07:04 AM
Again, just try one in clear.

That's my plan. I'm out of the studio until Monday but I will make up a couple test blanks in clear then and test them out.


Michael Mccain
02-23-2012, 10:26 AM
don't know the shape of your shade, but once you get the water fed drill press from Amazon, if at all possible start your hole on one side, and once you're halfway through flip it over and drill through the rest of the way. This is easiest with flat glass, obviously. Assuming the glass is annealed correctly.

Bob Meyer
02-23-2012, 04:01 PM
I take a different approach, and am obviously in the minority. I blow the shades somewhat cone-shaped, then use a flat disk to take the opening nearly up to the desired diameter, then use one of those cylindrical grinders that fusers use to grind out the inside to the exact diameter I want. I guess that evolved from already having the equipment I needed to do it that way. But I've never had one crack doing it that way.

Virtually all the shades I do go with a 1.5" diameter socket.

Pete VanderLaan
02-23-2012, 04:16 PM
Virtually all the shades I do go with a 1.5" diameter socket.

well, given that one inch is about 25mm, 42 mm is pretty close to that.

Brice Turnbull
02-23-2012, 04:21 PM
Gee, I almost hate to post this, but my experience has been different than everyone else I guess. I broke shades when I used the drill press (maybe 1 in 3 on a bad day, and 1 in 5 on a good day). I used a water-feed chuck and slow revolution and light pressure. The problem was binding when the piece was drilled almost all the way through.

After trying a few things, what I've been doing now for the past 3 years (?) and 1000 shades has brought my broken ratio down to 1 in 10 on a bad day and none of 12 on an average day.

I use a cordless drill, with a mid-speed to slow speed. I dip the bit in a cup of water about every 3 seconds of drilling. I don't grind the socket-end of the shade flat first (I used to), instead I finish with a bit of a cone at the socket-end so I can center the drill bit fairly easily.

I start on the inside of the shade, and drill about 3/16" (?) deep, turn it over and when I've ground from the outside to see a lip around the bit, I start to gently, slowly wobble the drill in all directions, still re-dipping the bit an inch and a half deep in a cup of water every 3 seconds or so. The wobbling has eliminated my main problem, which was binding inside the hole in the glass. I let the drill stop before I dip it in the water and don't start it again until it's down in the groove on the glass again.

It sounds to me like this is your problem (binding in a hole that is only exactly as wide as the bit itself), so if you want to take other's advice on how to solve that problem, feel free. Your goal is to solve the problem of the bit binding in the glass. Another way to help with this is to tighten the chuck of your drill hand-tight, so it holds the bit in, but will slip if the bit binds. This takes finesse with a key-chuck, but works more naturally with a keyless-chuck.

Also - by using a hand-held drill, my arm moves if the bit does bind. My arm is flexible, and the glass is not. A fast revolution will either snap the glass or hurt my arm, but a slow one will let me live without injury and seems to keep the glass in tact.

The other thing I will mention is that lamp shades are more tricky to make correctly than vessels and paperweights. They need to be as warm as possible when put away. Preferably just less than maleable. They should also be a little extra hot at the socket end (where the punty is attached).

Of course all of this is only my opinion after about 1600 or 1800 shades blown and drilled with my own trial and error methods.

Cheers, and best wishes - lights offer great design possibilities if you can just spend the months it takes to learn to make them stable :)

Bob Meyer
02-23-2012, 04:52 PM
well, given that one inch is about 25mm, 42 mm is pretty close to that.

That's why I said 1.5"! I was trying to tell Drew that most of them ARE really that big.

Pete VanderLaan
02-23-2012, 05:26 PM
What! Not 1.5973"?

Mike Hatch
02-25-2012, 08:20 AM
It looks as though this is another "glassblowing" scenario where there are lots of different ways to get the desired result and one must chlose what works best for them with the tools available.
It appears most replies stress the stability of the piece of glass being drilled. What type of jigs are you using? Pictures?