Cutting Glass for Overflow

Bret · Mar 6, 2023

Planning to run something very similar to the Innovative Marine ETX style overflow, but will need a way to cut out the notch on an already assembled tank with 1/2" glass.

Plan of attack right now is to drill holes in the corners of the weir, then use a diamond cut off wheel on an angle grinder to make the linear cuts. Has anybody done this before? Any suggestions?

fishyjoes · Mar 6, 2023

I wouldn't even try it. I'd use a different style overflow where you just drill a couple of holes.

Aside from that, if you're really on a mission and want to give it a try - get some pieces of glass to practice on first and see how it goes before you risk the real thing (assuming it's a rather large tank to be 1/2" thick glass)

Bret · Mar 7, 2023

Yes, I'll definitely be practicing before cutting the tank

MoshJosh · Mar 7, 2023

Think you would need to drill holes in each of the corners, then score lines connecting them. Not sure how you go about breaking/snapping the glass once the holes and scores are done. . .

Local glass shop should be able to do it pretty cheap. . . probably a lot cheaper than buying a new pane of 1/2" glass if things go wrong.

Soren · Mar 7, 2023

Bret said:
Planning to run something very similar to the Innovative Marine ETX style overflow, but will need a way to cut out the notch on an already assembled tank with 1/2" glass.

Plan of attack right now is to drill holes in the corners of the weir, then use a diamond cut off wheel on an angle grinder to make the linear cuts. Has anybody done this before? Any suggestions?

What are your primary reasons for wanting this particular type of overflow?

I don't have a lot of first-hand experience, but I have looked into similar topics before.
The use of an angle grinder seems hazardous to me, though it seems possible. One slight movement in an unintended direction could stress the glass and cause it to crack. When I once drilled a 10g tank, a slight bump of the drill chuck after popping through caused a crack from the hole out to the edge of the glass pane. Not the same as your case, but something to keep in mind. Angle grinders are difficult to keep in a precise, controlled line.

Drilling the holes in the corners is a good idea. Scoring the glass and tapping it to break it may be an option instead of using an angle grinder.

Do you have a local glass shop from which you could get advice or maybe consider having them do the cutting for you?

One obvious point is that you need to confirm whether or not your glass is tempered before attempting this. I don't know if you already know, but did not see this mentioned, so wanted to clarify.

MoshJosh · Mar 7, 2023

why not something like this?

Bret · Mar 7, 2023

Soren said:
What are your primary reasons for wanting this particular type of overflow?

I don't have a lot of first-hand experience, but I have looked into similar topics before.
The use of an angle grinder seems hazardous to me, though it seems possible. One slight movement in an unintended direction could stress the glass and cause it to crack. When I once drilled a 10g tank, a slight bump of the drill chuck after popping through caused a crack from the hole out to the edge of the glass pane. Not the same as your case, but something to keep in mind. Angle grinders are difficult to keep in a precise, controlled line.

Drilling the holes in the corners is a good idea. Scoring the glass and tapping it to break it may be an option instead of using an angle grinder.

Do you have a local glass shop from which you could get advice or maybe consider having them do the cutting for you?

One obvious point is that you need to confirm whether or not your glass is tempered before attempting this. I don't know if you already know, but did not see this mentioned, so wanted to clarify.

Two main reasons for wanting this style of overflow:
One is aesthetics. Even the smallest internal boxes are still rather large. My tank is only ~14" deep, so the boxes take up a disproportional amount of space.
The other is cost. The aftermarket external overflows are all pretty expensive, especially to have to compromise on the aesthetic.

Tank is definitely not tempered, so not worried about that.

I have lots of experience running angle grinders. I'm mainly concerned about what kind of wheel to use. There are several varieties out there for cutting glass/stone.

I'll ask the glass shop what they think when I go to pick up the material to construct the external box. If they can do it for me cheap enough, I may do that.

Soren · Mar 7, 2023

Bret said:
Two main reasons for wanting this style of overflow:
One is aesthetics. Even the smallest internal boxes are still rather large. My tank is only ~14" deep, so the boxes take up a disproportional amount of space.
The other is cost. The aftermarket external overflows are all pretty expensive, especially to have to compromise on the aesthetic.

Tank is definitely not tempered, so not worried about that.

I have lots of experience running angle grinders. I'm mainly concerned about what kind of wheel to use. There are several varieties out there for cutting glass/stone.

I'll ask the glass shop what they think when I go to pick up the material to construct the external box. If they can do it for me cheap enough, I may do that.

I had guessed both of the primary reasons, but wanted you to confirm.
Good to know that the tank is verified by you as un-tempered.
Experience with grinders is definitely beneficial, but there is still risk involved with using them for glass-cutting due to the alignment being controlled by hand. The brittleness of glass (even un-tempered) is why this is more risky than cutting less-brittle materials. A diamond-coated disk designed for glass-cutting seems the best option if you go the angle-grinder route. It just depends on how much risk you are willing to take, which of course comes down to a personal decision in the end.

Obviously, a glass shop is no guarantee for a perfect result, but I would still consider advice from those with more experience than me, especially if they have experience specific to your application.
A glass shop may also justify their experience by offering a guarantee, which might be worth the added cost to limit your own risk.

For what it is worth, I am a professional engineer with some experience with tools and materials, and I might consider your original plan a worthwhile risk for my own tank in a similar situation. Definitely drilling out the corners first should limit stresses during the cutting. If you can keep the angle-grinder under good control, your plan seems sound enough to me if you are willing to take the risk.

TheBear78 · Mar 7, 2023

MoshJosh said:
why not something like this?

This is what I was thinking aswell. Small weir box inside then a simple bulkhead connector or two to connect to the drain and emergency pipes on the outside.
Two relatively easy round holes, no lines to cut and minimal impact on internal space.
This is what the back looks like showing the bulkhead connector connectors.

FSP · Mar 7, 2023

Best (and only for my money) is find a fab shop with a water jet. Might not find anyone willing or able to do it to a complete tank. Grinding/scoring usually turns out badly ime, but whatever you do, make sure to get a good radius in the corners of the cut. Radius = depth of cut is a good place to start but it can be less.

Simpler one would be to make a small 2" or so deep box connected to an external box with holes. No bulkheads, why bother with a custom job on a glass tank. Cheaper and better than a prefabed one, especially the ones that put the external box lower than the top of the tank and splash.

Bret · Mar 7, 2023

FSP said:
Best (and only for my money) is find a fab shop with a water jet. Might not find anyone willing or able to do it to a complete tank. Grinding/scoring usually turns out badly ime, but whatever you do, make sure to get a good radius in the corners of the cut. Radius = depth of cut is a good place to start but it can be less.

Simpler one would be to make a small 2" or so deep box connected to an external box with holes. No bulkheads, why bother with a custom job on a glass tank. Cheaper and better than a prefabed one, especially the ones that put the external box lower than the top of the tank and splash.

I considered the the custom internal box connected to the external box as well. Still end up with a pretty big box in the tank though.

If you look at all the commercially available external overflow kits, they are all full of compromises. Differing box heights create noise, internal boxes are fairly large, double gaskets are prone to leaks, cost, etc.