DIY Drill a Glass Tank

[size=10pt][color=blue]When a Fellow Reefer needed a hole drilled it seemed like the perfect opportunity to explain how to drill a glass tank. The pictures below are from Cdangel0 75-gallon build along with his 20 long fuge tank.
One of the first requirements to even starting this project is to determine if you are capable of doing it. It will require tools (diamond bit, drill) and a lot of patience. This is one job where it is not a race to the finish.

Disclaimer: Drill your tank at your own risk. I am a Diy’er and have done this with a lot of tanks but I am no expert. These are the technics I used and they worked for me; they may not work for you.

[size=10pt][color=black]Determine if the tank can be drilled.

[color=blue]Not every tank can be drilled. There are standard plate glass and tempered glass tanks. Some manufactures label their tanks but a lot do not. If you are unsure contact the manufacturer or search on the internet. DO NOT DRILL UNTIL YOU ARE SURE. The difference becomes apparent if you have ever broken both types of glass. Tempered glass breaks in a unique way. If any part of the glass fails, the entire panel shatters at once. This distinguishes it from normal glass, which might experience a small crack or localized breakage from an isolated impact. Tempered glass might also fail long after the event that caused the failure. Stresses continue to play until the defect erupts, triggering breakage of the entire panel. Although the video uses a Dremel the principal is the same; If you drill a tempered tank it will shatter.
If the tank is older and you can’t find any info on whether it is tempered or not I have 2 suggestions to test for the glass being tempered. Put the tank outside on a bright day and with a pair of polarized sunglasses look through the tank if you see what appear to be little circles or squares the tank is tempered. Another way is to use a glass cutter. In the spot you want to drill apply some cutting oil to the inside of the tank. Using a glass cutter, roll it across the glass. If the glass cutter scores the tank it is most likely not tempered if it leaves no mark then it is hardened and tempered.

[size=10pt][color=black]What Size Hole Depends on the Bulkhead.
[size=10pt][color=blue]I created this chart to help you determine the proper hole size you will need. Most of the bits you will buy will be sized in millimeters (mm). Because the bulkhead will have some overlap of the tank you will have a bit of play with the bit size. The below chart is a guide and you should buy your bulkheads in advance and use the manufactures directions for hole size. Round the mm size below to the nearest whole mm.

Most of the tanks I have seen use the schedule 40 fittings. They work well and are solid. If you have the extra cash and want the beefy upgrade, the schedule 80 are top notch. Most high end manufactures use the schedule 80 fittings when building custom tanks. All my fittings are schedule 40. When I refer to bulkheads in this post I am referring to the schedule 40 bulkhead. Besides being schedule 40/80, bulkheads have different connection styles such as slip-slip(s-s) or threaded-threaded(t-t). Other combinations: s-s, s-t, t-s, t-t. This refers to the inside of the bulkhead where you go to attach plumbing to the bulkheads. I prefer to use a threaded-threaded(t-t) connection. The benefit of this is it allows you to change your plumbing around with out having to scrap the bulkhead. On a s-s type bulkhead you glue the plumbing into place. Once glued it can not be removed without cutting the plumbing and starting over.

Opinions will vary on whether you are better to use slip or threaded.

Once you select your bulkheads, order them and confirm the bit size.

This is the bit we used to drill 1 1/2" bulkheads into the tank. These were not the high end bits but the $6 specials.

Apply backing to the tank. I use 5 layers of tape or another solid material to keep the glass chipping to a minimal. In the picture below you will see a board clamped to the tank. If you use a board it must be tight to the glass to give support as you break through the glass. I have seen a lot of tanks drilled using no backing what so ever and I also usually see that they have lots of glass chipping.

Measure the placement of your hole twice. In the case of this tank we are going to use a 1 1/2" 90 degree street elbow. Once you determine the water height and what you will be using to collect the overflow water, mark the hole. Since we will be using threaded bulkheads we made sure the pvc elbow was able to spin around so it could be put on and removed with ease.

What speed (RPM) should you use to drill the hole
[color=blue]This seems to be the least asked question when people go to drill a tank. If you google video of tanks being drilled the average tank is drilled at an incredible speed of 5-10 minutes per hole. I have always use a slower speed and taken 15-30 minutes per hole. In drilling Cdangel0’s tank it was about 25 minutes per hole. Which is correct? I asked an infamous Diy’er who has created some awesome tank equipment for the answer.

[quote=“Jim K. aka greeneyeblackcat”]
[size=10pt]The slower the better if using a diamond hole saw (300 or so rpms) with plenty of water for coolant (glass cracks when overheated) Zero pressure is a must. I like your setup. I have always cut my holes with a dremel tool and a burr. Just punch a small hole in the side of a McDonalds type drink cup to cool the bit and cut away.[/quote]

To start the hole I use a drill press to allow the bit to cut evenly around the tank. If you don’t have a press you can make a template out of wood and clamp it to the tank. This will keep the bit from skirting around the glass. These are the preferred methods but in a pinch I have angled the diamond bit off of 90 degrees to the tank. This will start the bit cutting a “curved slice” that is maybe 1/4 of the circle that you are cutting. Once this is started some you can remove the bit and begin cutting again at 90 degrees to the tank wall and shouldn’t have the skipping/sliding around problem. If you try to start drilling with the entire face of the bit on the glass it will want to slide around and result in an ugly scratchy mess before it starts making the hole.

As you can see from this picture, when the hole is started at a 90 degrees without skirting around it makes a nice clean hole.

Keep the bit clear of debris and keep it cool. Some have suggested using anti-freeze, while this will work I do not recommend this. Anti-freeze is used as an automotive coolant where the car will be exposed to extreme cold and extreme heat. Drilling the tank will not get to these extremes. Running water across the cut will keep it cool and remove any debris. If you have the ability to move the tank outside the water hose works very well. I clamp mine in place when I am working alone to ensure while I am cutting the hose does not fall away. If you have to drill the tank inside a water dam works well to keep water on the bit. You can use putty or even duct tape to create a dam.

As you drill the tank you can see the depth through the side glass. Although we stopped a few times to take pictures, when you drill try to drill without stopping; it is hard to realign the drill bit after you stop.

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