How to cut a carboy: IE what to do with a broken carboy!

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So you have a nice collection of carboys under your kitchen table. One day you bump the table and knock a beer bottle off said table. Down falls the bottle when you hear that soul crushing crash sound. Glass on glass is a unmistakable sound all brewers have come to fear, hell even have nightmares about. You peer over the table fingers crossed, saying a silent prayer. I mean it's a big thick carboy VS. a small thin walled beer bottle, surly your pricey carboy won the battle. Your eyes clear the edge of the table, and there it is. One of your beautiful and expensive glass carboys busted.
As was the case for me. The gravitationally accelerated beer bottle blasted a gaping hole in the side of my precious carboy. One I had just bought to finish my "perfect" brewing setup. The comment about it being a soul crushing event is truly spot on. At least for me. There's something special about those sparkling carboys. I think they are pretty pricey too. Funny as we spend so much on other things for brewing, I still think carboys are just to much money. The insult added to injury of the whole deal? That damn beer bottle is still intact! Argh!

So what do you do if you are "lucky" enough have a half smashed carboy? You cut it up!
Now, you may be asking yourself "why the hell don't I just through it away?" Well sure you could, but I'm to, umm, well, let's call it "Thrifty" to just toss something I see potential in. My carboy was broken so that there was nothing missing lower than 10.5" from the bottom. So while examining my broken blob of pricey glass, I saw the potential to make a huge bowl out of it.
Why would I (or you) want a giant bowl made from a carboy? I'd like to say here that is you can't see the cool factor of having a carboy bowl, than you really are on the wrong site. Instead I will go ahead and give you some ideas. My first thought was punch bowl!
I mean those lovers of skeeter pee, the extra hard lemonade and even my hard punch will love this idea. You could even so some fun homemade sangria in it. This thing is huge! You could use it as a giant fruit bowl, even a chamber pot!
So mine turned out to be 10 inches tall. That give you about 4 gallons of volume to fill with whatever. I love it! It's neat to have another piece of brewana that's a pretty nice looking addition to my serving armada.
Now, how to do it:
I built a jig for the cutting. I wanted it to be very clean top edge, and of course I didn't want that top line to wonder.

The jig was very simple. Just a scrap of 3/4" plywood, 4 casters, some scrap 2X4's and a brand new glass wheel cutter.
The casters, used for bottle rollers, are mounted about 8 inches apart. You will see in the picture that it looks crooked from the edge of the board. This is correct. I mounted the bottle stop (the board to the left) first and then mounted the rollers using a square. That way everything lined up correctly. Mind where you put your rollers as you don't want them to roll to close to the busted area of the carboy.

You see in the next picture how it bottle fits the cutting jig.

Next I mounted the brand new cutter 10 inches from the end of a "T" setup of 2x4's. Let's talk a moment about the cutter. Why did I get a brand new one? Cause I wanted to make sure it would make a perfect score. I will be cutting wine bottles into vases for xmas presents so I figured the $2.88 price was well worth it to insure a nice cutting wheel.
In the next image you see the cutter being held close to the carboy as if it were about to be cut. This was a two person job. I had a friend push the cutter against the carboy as they are not perfectly round, while I held it firm against the stop and turned it.

The next picture is of the perfectly scored straight line around the carboy.

So, now you have a scored carboy. How shall we separate the two halves? Big damn hammer? I think not, but if you disagree make sure to video it! This site is full of engineers and scientists so lets go the science way. Thermal shock baby.
A quick search of YouTube will find you thousands of, "how to cut a bottle" videos where people use fiery strings or even the intense heat of a torch. Neither of these techniques are really a good bet. Both of them will produce very inconsistent results and often will ruin your project. Even a "good" result from the string or torch method will leave you with hours of sanding just to get a mediocre finished product. I can't tell you enough that these methods are crap. Very often the glass does Not break where you have told it to. The string method tends to spread the heat over a to wide of area to get a fine break. Where as the torch is simply to much heat for our needs.
So what method do I recommend? Hot and cold water! Simple enough. Way safer, no flammables, no torch flame, just hot and cold water. Don't get me wrong, I love to over due things, and I'm no stranger to doing dangerous crap it's just simple not the way to get a perfect edge here.
Right on the bottom of your carboy it said "NOT FOR HOT LIQUIDS" Why? Simple the carboys are very cheaply built. You know this if you have ever broken one, and will see this when you cut yours. One side can be half an inch thick while the other less than 1/8" thick. Cheap or standard glass, IE anything that does not contain additives such as lead or Boron, has a pretty impressive thermal expansion rate. This means when you heat it up, she grows! So what happens if you pored boiling water (I mean wort) into a glass caryboy? The hot liquid hit the bottom first, heating the bottom up very fast, while the top is not hot at all. So the bottom starts expanding, while the top does not, crack, she goes. This my brew loving friends is the basis of thermal shock.
Why doesn't my measuring cup blow up with hot liquids? Great question! Simple answer. Remember those additives I talked about earlier, lead and Boron? Your measuring cup (Pyrex is a brand name) is made of glass by adding a select amount of Boron to the mix. Your measuring cup is borosilicate glass.
Ok now that we have the techy stuff out of the way, let's get going on slicing up this carboy.
I put the carboy in the sink with the hottest water I could get out of my faucet. While it sat I heated 4 gallons of water up on the stove. I think it would be 180-200 deg. I definitely could not keep my hand in it, but did not measure the temps. This water was poured into the carboy. Allow some splashing around the outside too, we want it to heat as evenly as possible.
So, we cracked open a beer and sat back to let it heat. Give it a good half an hour to fully settle the internal stresses of expansion. I took a beer pitcher and filled it with ice and water and stirred it good to get the water as close to 32 as I could. I then took the carboy out very carefully and pour the hot water back into the pot which was placed back on the store to recharge to 200. The carboy was laid on it's side over the sink and each of us held one end firmly. Next pour the ice cold water directly on the scored line. Remember we are trying to induce massive amounts of thermal stress here. Pour the water in the wrong spot and you're likely to bust it in the wrong spot. Just be careful and pour out a thin stream that will run around the carboy right along the score line.
Why did we recharge the hot water? It took us twice to get a perfect effect. It may take you a few times. Just be ready for this!
So after two heat and cool cycles, pop and the top literally just fell off in our hands.
So if you have a carboy you want to save as a giant bowl, here's how you do it. You can use this technique to cut any glass bottle from beer bottles to carboys. Use it and enjoy! Just remember to use your new found superpower for good!
The last two pictures are the "Before" with the carboy steaming in the sink and of course the after, with a perfectly split carboy top.


nice work, and nice write up. If I ever break a carboy (and survive), I'll give it a shot. That being said, I use buckets whenever possible for exactly this reason
Careful, Pryex measuring cups haven't been made with Borasilicate since 1998, Corning sold the "Pyrex" name to World Kitchens who changed it to "pre-stressed soda lime glass" again because Boron is expensive.
It does not perform like lab glass against thermal shock any longer
"What did you do to ease the edge?"
This. People definitely need to know how to dress those edges. They'll be surgically sharp.
Well I wrote this in August and now that's it's an article there's no editing it. So the stupid auto correct changes will have to stay.
As far as easing the edges I used a diamond plate lap I had, but you could use any sand paper. Start with 180-220 and then 400 and finish with 600-800. I just went at the edge at 45 deg to the edges.
I've done plenty of wine bottles, but never something this large. I like the casters.
When dressing edges, it helps to keep the sandpaper wet. Wet glass is fairly easy to grind, but dry glass is extremely aggressive. Also, glass dust isn't something you want floating around. I use cheap 200-400 grit aluminum oxide with a little vegetable glycerine for wetting (higher viscosity means it dries slow, but plain water is fine) - it doesn't take long at all to take the evil edge off.
slick, almost makes me want to bust a carboy...if you have a good top, it would make for a great dome for seedlings, etc
I like the idea of turning lemons into lemonade....
And I think this is a cool outcome from a broken carboy.
I just question the extra expense of buying 4 casters, wood and a glass cutter in order to feel better about breaking a $39.99 carboy.
Unless you have these things laying around...
Looks like you could use it as an open fermenter for a 2-3 gallon batch of brew. Especially with some fermcap in it.

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