Introduction: Bottle Cutting: Some Thoughts

Picture of Bottle Cutting: Some Thoughts

I've recently been doing a lot of bottle cutting.  My last Instructable, Snapple, Steel and Green Fire, had a short section on bottle cutting.  Since then, however, I've been wondering about what I can do to improve my success rate with cutting bottles.  Wondering might not be the right word ... obsessing?  At any rate, here's what I've come up with so far.  

Warnings: This project involves cut glass, very hot water and tiny glass pieces.  I don't tend to use gloves, and I'm not sure if gloves might cause more problems than they solve because of loss of traction/grip.  I don't tend to cut myself when I do this, but that doesn't mean it's not possible to do so.  You will also be grinding glass.  If you are cutting bottles infrequently, using the manual grinding methods described here, you will be inhaling little to no glass dust.  If you do this a lot, if you use a dremel or other high speed power tools for grinding, you will kick up much more dust, and you will need to use a suitable dust mask.  Finally, I have never had a bottle fail in such a way that glass flew any distance.  However, the little flecks of glass that fly off during the scoring process can go a couple of feet, so you will want to use safety glasses or at least sunglasses to protect your eyes.  I don't even want to think about getting one of those little things out of my eye.

Much later: Hey!  I was a finalist in the Green Design contest!  I had actually written this as an addendum to the lantern instructable mentioned above, and didn't really see it as prize material.  Thank you to everyone who voted for me and to all the contest judges!  I'm super psyched!

Step 1: The Right Tool for the Right Job?

Picture of The Right Tool for the Right Job?

I'm going to proceed with the idea that whoever is reading this either has a bottle cutting jig, or knows how to get one.  For those interested in using one like mine, or who want to see what I did and improve upon it, I'm showing what I use here.  As you'll see from my pictures, mine is pretty primitive.  It consists of a vertical board, a board at a 45˚ angle and a base post.  In the pictures that follow, I had removed the base post, and instead had the entire cutter positioned vertically on the garage floor.  I'll explain why in a moment.  

I just did an Autodesk 123d mockup (this is my first time using the tool, and I literally just did this moments ago, so be gentle - it is a pretty damn cool tool though) of my jig.  To hold the bottle cutter in place, I cut notches into the vertical board as I need them.  This set-up has allowed me a fair amount of versatility over the size of the bottle I cut and where I make the cut.  I would not call it a precision instrument.  The scoring tool is a basic glass cutter from a hardware store.  They run about $3.

(However, the lumber for the jig was entirely free: Big box stores (like Lowes and Home Depot) cut wood to their customers' specifications.  The customers then take what they want and the big box store worker throws the "waste" into a scrap pile or bucket.  I've found that if you ask nicely, and don't take more than a couple of boards, they will give these to you for free.  Don't be greedy!  Don't make them feel like they're giving you stuff they could otherwise sell to you!  It probably helps if you approach the worker with a cart containing other stuff you are (or appear to be) buying.)

Edit: A quick note on the jig design.  A reader below suggested a wheeled design, which I like, but in the end didn't go with.  My reasons for this are flexibility, simplicity and security.  The wedge shaped slot here can accommodate a wide variety of bottle/jar diameters without any moving parts.  With the base peg in place, the bottle is supported/secured in virtually all directions except up.  It is far from a perfect design, but it is easy to build and fairly efficient.  However, for those who will be cutting only beer and wine bottles, the wheeled version of jig may be more efficient than the one I show here.  Here are a couple of alternative designs:

https://www.instructables.com/id/Glass-Bottle-Cutter/

https://www.instructables.com/id/Drinking-Glasses-from-Wine-Bottles/

https://www.instructables.com/id/Simple-Adjustable-Glass-Bottle-Cutter/

https://www.instructables.com/id/Want-to-cut-wine-bottles-Build-this-jig/

Mine could be called a variation on the last of these.  I wanted it to be able to cut at many different heights, hence the wedge with an unfixed cutter/scorer.  I cut slots in the vertical board to hold the cutter at the place I want to make the cut.  Step 3 will show this in greater detail.  I'm also including a picture of a small San Pellegrino bottle and a large mayonnaise jar I recently cut.  The former has a 2 inch diameter, the latter, a 4 inch diameter.  A wine bottle falls in between these two, at about 3 inches diameter.  This flexibility is one of the advantages of this style of jig.

Step 2: The Bottle!

Picture of The Bottle!

More important than the jig, in many ways, is the type of bottle or jar you decide to cut.  Different bottles are made to different specifications.  The water bottle shown here is pretty, but very irregular.  The glass is on the thicker side, but the wall thickness varies quite a bit.  Beer bottles are thinner and, in my experience, more regular in wall thickness.  Fancy square vinegar/olive oil bottles are extremely irregular.  I have yet to get one to cut right.  The corners are half the thickness of the walls or less.  They are also a bear to score with the cutter.  Don't start with them.

Step 3: The Score!

Picture of The Score!

As I mentioned earlier, this bottle was very irregular.  So irregular in fact, that it refused to rotate evenly in the jig.  This created a problem, as the way I keep the bottle placed on one of its three axes (the Y axis) is through gravity.  To solve the problem, I removed the peg shown in the 123d mock up and in picture 2 above, tilted the jig vertically, and allowed the base of the bottle to rest on the floor of the garage.  I generally draw a line with a Sharpy where I intend to cut, but in this case, I ignored the line and cut a bit below it.  Picture 2 shows a bottle I cut for the Snapple, Steel and Green Fire instructable.  This is the way I usually use the bottle jig.  It's a bit easier to control than the vertical method, sans peg (see inset for picture 2).

A note on cutting: I've gone from heavy scoring of the bottle to a much lighter touch.  I do try to make sure that the score line is uninterrupted around the entire perimeter of the bottle.  It's also important to make sure the score line meets itself as closely as possible.  It can be tough, because the cutter's wheel does tend to waver a bit as you score the bottle.  This is the reason I started drawing the Sharpy line: if I follow that, I don't generally go too far off track.

Step 4: Like Water for the Elephant ... in the Room

Picture of Like Water for the Elephant ... in the Room

Scoring the bottle is the easy part.  Getting the glass to behave itself and break the way you want it to is where things get tough.  Nearly all methods of doing this involve thermal shock.  The idea is that the glass will expand and contract with the alternating application of hot and cold, and a crack will propagate along the line you scored.  Some people use a piece of string dipped in a flammable liquid, some use a butane or propane torch, some use water of differing temperatures.  I use the last method, and in general, it's served me well, but my success rate hasn't been as high as I would like.  Because of this, I've been trying to standardize the part of this process I can control: water temperature.  

Nearly every instructable/online resource describing this method says to alternate between "almost boiling water" and "cold tap water."  I realized just recently that I have no idea what that statement really means.  Does almost boiling mean 210˚ F?  180˚?  What temperature is "cold tap water?"  I wanted to codify the obvious thing that wasn't being addressed: what's cold; what's hot?

Here's what I found out: if I run the tap for a few minutes, the water temperature steadily drops to about 70˚F.  There is some variation, but it doesn't get much colder than this.  Early on, I tried using ice water, for the cold water part of the cut, and it was a disaster.

The same has been true (though to a lesser extent) when I use boiling water, or water just off the boil.  I've found that water from 175˚F - 185˚F works best ... however ... only in conjunction with straight cold tap water.  It's easy to forget that you aren't cutting with hot water or cold water, but rather causing thermal stress by using both.  Not enough thermal stress, and no cut will propagate along the score line.  Too much thermal stress, and the crack will ignore the score line and wander freely.

This means that the difference between those temperatures - 105˚F-115˚F - is optimal.  If my tap water ran at 60˚F, then I would want to bring the temperature of the hot water down to 165˚F-175˚F.  

There are other factors at play here as well.  The type of glass, how it is annealed, its thickness, etc, all affect how it responds to different temperatures.  You can probably rule out this method in trying to cut pyrex, whether it's lab-grade borosilcate or consumer-level annealed.  My suggestion is to start out with jars or bottles that you don't care too much about, find the temperature of your cold tap water, and add 110˚F for the hot water temperature.  If your cold tap water is significantly below or above 70˚F, you will probably need to do a little experimentation to find the best temperature interval.

Step 5: The Kindest Cut

Picture of The Kindest Cut

Although this is where the actual cutting gets done, this is actually the most straightforward part.  If your score line was straight and your water temperature is under control, making the cut is really no more difficult than pouring a steady stream of water on the score and rotating the bottle to ensure that the entire score line is heated evenly.

However, you will probably have to make repeat applications of the hot and cold water to propagate the cut.  I generally start with the hot first, then the cold, hot, cold etc. until the bottle splits.  Lately I've been placing a silicone hot pad underneath to stop the cut off piece of glass from getting damaged when it falls away from the part I'm holding.  Alternatively, you can do this in a PVC utility sink.  You could use cloth or a piece of polyurethane foam, but I wouldn't recommend it.  It's hard to see here, but little tiny shards of glass pop off the score line, and I imagine that eventually your cloth or foam would become quite unpleasant to touch.

The last picture here is of the cut bottle.  As you can see, it's a pretty clean cut.  However, it's still gonna need some work before you would want to touch the cut edge with an unprotected finger - let alone drink out of the bottom part.

Step 6: The Inside Story

Picture of The Inside Story

So what kind of bottle did you choose?  Are the walls of  regular thickness?  Here's where you find out.  This one, as I suspected during the scoring phase, is of varying thickness, and not terribly circular.  You can also see that, although the cut is pretty even, it still needs some work.

Step 7: Grindin'!

Picture of Grindin'!

So this part is also easy, but man, is it tedious.  Before you can do really anything with the bottle you've cut, you've got to fix that lethal edge ... unless you're just trying to accessorize for your next bar-fight.

I use plain 220 grit sandpaper here.  It's super-cheap and you can get it at the dollar store, Ace Hardware, True Value, etc.  Unless you're taking off a long jagged bit from a bad cut, I wouldn't use anything below 120 grit, as little pieces of glass are going to be forever flaking off from the edge and making your life miserable.  Anything over 320 grit is going to take forever to do the bulk of the grinding, but you might want to finish up with something in the 400-600 range to make the lip as smooth as possible.  I don't find sanding pads/sponges to be particularly useful.  They tend to fold around the rim of the glass and scratch the glass in places you would like for it to be scratch-free.

The other thing to avoid at this point is setting up unwanted vibrations in the glass, as these also tend to cause chips and breaks in the glass.  If you hold the paper in one hand, and the bottle in the other, there will be no unwanted vibrations, but it's not a very ergonomic arrangement, and its gonna get old real fast.  I find placing the sandpaper on top of a piece of non-corrugated cardboard (think cereal box, notebook cover or thick poster board), turning the bottle upside down and twisting the bottle back and forth against the paper is the most effective and least painful approach.  If you hear a screeching sound from the glass while you're doing this, you need more dampening.  Try putting some sheets of newspaper under the cardboard.

The pictures here are of the process, as well as the progress at the 1, 2 and 5-minute marks.  At this point, it's clear that there are some dips that are going to take a while to grind out.  Basically, you'll have to grind down everything else to the level of the dips, and then keep sanding until it's all even.  However, as we're not going for perfection here, we can work with the dips and just try to make the glass as smooth as possible, without worrying too much about the edge being perfectly even.  It's worth noting that these dips and the unsanded glass are not particularly sharp or dangerous at this point.  

You can work on the dips by folding the sandpaper around your finger and rubbing it back and forth inside and over the dip, but this has the same drawback mentioned before: it's tiring.  I prefer to take a piece of wooden dowel (or even a reasonably smooth stick), and wrap the sandpaper around that. Doing this allows you to apply more pressure, and apply it more evenly.  

At this point, the glass is drinkable - not pleasant, but drinkable.  The human lip is pretty sensitive, and while the edge is not a hazard, it's going to feel uncomfortable.  We can solve this by beveling the edge.  To do this, keep working with the sandpaper covered dowel, but this time, keep it at roughly a 45 degree angle to the glass.  Do a couple of passes around the outer and inner edges of the rim.

Now, wash the glass.  You're done!   The whole process, from score, to cut, to grind, to bevel should take between 15 - 30 minutes for a cut without any significant jags.

Additional resources:

Green Power Science: I don't know if he originated the water method, but he's certainly done a lot to popularize it.  There is definitely an infomercial-like feel to the video, and he is trying to sell you something, but there's good information too.
The Encyclopedia of Working With Glass: this was referenced in the Wikipedia article on cutting glass (which I strongly suspect the above gentleman, Dan Rojas, wrote).  I got the book from the library, and it really is the bomb. 

Comments

robotobor (author)2017-01-02

I have seen a guy use silicone rings on each side of the score line to focus the heating and cooling. If anyone knows of a source for cheap silicone rings please post it here. ALSO, you should consider adding a little water to whichever grinding method you use. The dust may not seem very noticable, but it is there and very bad for your lungs, eyes, etc. I use a flat lap grinder with a steady stream of water. Not only does this cut the dust, it also controls the heat generated in the grinding process.

Wow, is this a late reply! Sorry about that! If you have a bit of time on your hands, and don't care about re-using the silicone ring, the cheapest route is to make your own. I use rubber bands as borders, and then smear silicone in between. After about twelve hours, it's cured. It binds to the glass, but you can cut/scrape it off with a single-edged razor (watch out for your fingers) or one of those Scotch Brite copper or stainless scouring pads. You can make them as wide as you want. Honestly, though, I would try duck tape first. It's water and heat-resistant, and you don't have to wait! Just make sure the glass is dry before application. Let me know how things work out!

no_one59 (author)2016-04-24

Thanks for the "obsessing" about it!

Jcbubbadawg (author)2015-12-31

I was having issues getting a clean break. I used the pouring method with almost boiling water and cold tap water. Worked like a charm. Clean breaks with just a few mess ups. I was able to get 4 bottles cut in about 30 minutes.

Awesome! I'm glad it worked for you!

dogxtc (author)2015-09-01

i am a bottle cutting fanatic and my husband built me a cutter which works fine... plastic wheels and stainless steel frame and bars, It is for wine bottles but I can adjust where I want to cut it. I have made drinking glasses and just sanded them but there must be a better way of finishing the top edges, I use a dremel grindstone at present but I find the sanded area wears down with use and needs re sanding... what am I doing wrong?

I'd love to see a picture of your jig! As far as sanding goes, i do it all by hand. If the cut is a good one, it doesn't take very long. I haven't found that the areas wear down, but have found that if you progress in grits to around 600 (150,220,320, 400, 600), it's almost as though the glass was never cut - visually and to the touch. I also tend to sand the glasses upside down on a thick piece of cardboard, to minimize unwanted vibrations. I feel these tend to cause additional chipping. Check out step 3 here:
https://www.instructables.com/id/Tealight-of-the-Apocalypse/
I show the difference in finish between the grits.

Instructadam made it! (author)2015-03-03

followed your method with great results. Not regulating the temperature as well as you have, just hot then cold. however it worked beautifully for thicker glass and not so well on thinner glass (champagne bottle vs corona beer bottle). I am going to try with better regulation of opposing temperatures to see if that Improved the success rate. A nice instructabke, from the views it seems to be a sort of 'glass cutting bible' for a lot of people :)

Hey thanks! In one of the comments (C I A H) a reader suggested using a coffee maker to heat the water, and it works really well. I keep meaning to do a part two to this one. I think I'll be able to finish my second part in the next couple of weeks.

bretinc (author)2014-12-29

very well written and informative, great work

Thank you! I loved your whale!

hms1018 (author)2014-04-17

Thanks GG, I will keep doing it til I get it perfected.

hms1018 (author)2014-04-14

I have a bottle I cut and want any ideas on how to do this a little better than I did. To note, I did score it all the way around after taping it up to keep the line of cut as close to even as I could, because the top of the bottle is larger than the bottom and it's a little more than square. I had no problem with the hot/ cold water but I may have ventured a little off course with the cutter as I was cutting free hand or because of the shape of the bottle. It was I can say an extremely clean cut except for that 1 little hiccup.Help!!!

That's really not bad at all! Square is tough! The only thing I would say is that the bottom half is going to be easier to salvage than the top. You can try gentle tapping along the score-line with the hammer end of the cuter along the inside of the bottle. A little vinyl electrical tape on the round hammer end can be helpful. Many small taps is better than a few large ones. If you want to use the top, you'll probably need to re-score and re-cut. Otherwise you're in for a tremendous amount of sanding. If you have an understanding workplace, you can keep a piece of sandpaper under your desk and, with your foot on the paper, give the bottle a couple of turns back and forth every half-hour or hour. People will think you're crazy, but probably in an entertaining kind of way. At least, that's what I'm hoping they thought of me when I did this.

mwilliams68 (author)2013-10-25

Just wondering, have you tried the yarn method? If so, what are your thoughts and which do you prefer?

C I A H (author)2013-09-26

just a suggestion but i have had alt of good results just using a coffee maker to heat the water instead of trying to get it to a certain temp every time, the coffee maker gets it pretty close to the same temperature every time and it is as they say just below boiling but not ho enough to let it get away while cutting, not sure the exact temp it gets but i get nice clean cuts with it with no shards from any of the bottles i have cut so far

Interesting! I'll give it a try! Thanks!

londobali (author)2013-05-26

Hi Green Gentleman,
Thanks for your i'ble and in-depth R&D in the matter.. I'm just starting to do my own too..

I've been cutting a couple of bottles with this trick:
https://www.instructables.com/id/Easiest-way-to-cleanly-cut-bottles/
I was using the string way (step4) until i made a turntable for the bottles (still finger-powered at the moment)..

The small nick is enough to start a crack that will propagate as you heat it along the circumference of the bottle.
It seems that if I score all the way around, I'll have tiny fractures along the score that might propagate to the wrong direction and makes a jagged edge. most of my fails are with all-around scoring. Maybe my cutter is too cheap?? or my jig not sturdy enough??
*just read an earlier comment from bulwynkl that confirms just a nick is needed!
*and i just read the comments from Benstar & hrollinson.. +1
 

I've tried with different kinds of bottles, thick, thin, big, small, even the square one..
It works well for me and I'm pretty satisfied with this method..
Check out my pictures, all done with the nick and pen-torch technique.
Notice the four similar ones are local beer bottles, very uneven thickness!
The square bottle works fine, only needs a bit more sanding.
The equil bottle is widening towards the top, although it's not a horizontal cut, it's very straight.
The super thick bottle and tiny-and-thin bottle also works great.. 
:)

I tried to sand the bottles by turning them with a cordless drill (low speed), with a bottle adapter/holder made from tennis ball, nut and bolt, and a couple of washers..

Hi londobali,

Thanks for reading! Although I have a pen torch, I haven't used it for this purpose, because what I've been reading has indicated that the cuts tend to be fairly jagged. In the link you provided, it looks like a pretty mixed bag between jagged and clean cuts - granted the pix are a bit blurry, so I can only say that it appears to be that way. This isn't to say that it would be impossible to cut bottles with a torch, a candle or a flaming string, or even cut them very well. The way I'm showing here is just a very simple way to make a cut, with a fairly high rate of success, that costs very little to set up, and involves nothing more dangerous than hot water, and the glass itself.

The adapter sounds interesting. Do you have any pictures of it in action?

suayres (author)2013-05-29

Really clear, concise, helpful information. Thank you!

Thank you! I tried hard!

filtercages (author)2013-05-26

I guess most folk that visit Instructables already know, but Sketchup is also a good alternative to Autocad123 - and free too.
I happen to have the Pro version, but for most requirements the free version is more than adequate.

hrollinson (author)2013-05-24

ever tried this?
http://www.youtube.com/watch?v=rQmhspsyJxg
i've found it creates a straighter edge than using a jig.

londobali (author)hrollinson2013-05-26

Thanks for the link hrollinson..
Just see that corningmuseumofglass is great resources for bottle cutting.

cheers!

Benstar (author)hrollinson2013-05-26

Yep! "Cracking off" is the easiest, fastest way to get a nice clean break. Here's the Corning Museum of Glass video: http://www.youtube.com/watch?v=E4yovEi7j7E
I just use a turntable from a lazy susan.

Arley1578 (author)2013-05-26

I have been cutting bottles for glasses, etc. for ;years. Here's my recommendation for those interested in less time involved than the usual ones posted require. First, buy or rent or find someone with a tile saw with a 'table'. Align the bottle against the back of the 'table' and push thru the blade. Wear a plastic apron, breathing mask and eye protection. Secondly, buy, rent or find someone with lapidary equipment and polish the cut edges of your glasses. I realize some readers may not have access to this equipment but if you do, things will be much simpler and easier to cut and finish.

ibwebb (author)Arley15782013-05-26

This is easier true... but either more expensive, MUCH more expensive, or you have some friends with good tools to borrow. I mean I could say as well o make it easier go out and just buy them. I think The Green Gentleman was trying to show us how the everyday person could do it more efficiently.....

bulwynkl (author)2013-05-26

I've seen a lot of these - and I've seen how glass blowers actually do it, since my Uncle is a glass blower and I used to skive off class by visiting his lab...

He had rig for it. It was a loop of thermal ribbon - Ni-Chrome I think - attached to a DC supply.

Nick the glass tube or bottle in one spot (only) where you want the cut.
place in the loop.
turn on the power.
Rotate the tube or bottle evenly on the line you want the cut. after about 60 seconds... a sharp crack. a single clean cut.

turn off the power, gently pull the glass parts apart.

It will be very sharp. You need to bevel the edge or if you have a glass blowing lathe and annealing kiln, melt the edge. :-)

I still have a few beer bottle glasses at home from the 70's...

chuckyd (author)2013-05-26

The cheap sandpaper is one reason for the slow, tiring process. It would be better, especially if making several projects to use a diamond chip abbrasive.

rippa700 (author)2013-05-26

This is great and always nice to see things done differently. I do the same score process, but then warm the score over a small candle, rotating the bottle over the flame. Then I run an ice cube over it. Usually takes 1 to 3 cycles to cut and works cleanly (excepting the carbon from the candle) every time. I then use carborundum powder on a flat steel plate and gring the lip flat on that but a glass worker friend says that really it is better to anneal the glass. Heat it to almost red hot in a glass link and let it cool. That removes stresses in the glass and also smooths the sharp and rough edge for a better finish. I haven't worked out a home made way to do that last part yet. So - great job and keep it going. NIce ible.

ArtisanEclectic (author)2013-05-24

I normally wouldn't say Here is someone that has got it right.

But since you acknowledge that you are exploring and that your cutter is still in it's primitive stages, I thought I would save you some time and point out that, in my humble opinion anyway, This guy has a great design for a bottle cutter. I'm not saying it perfect and can't be improved. But it would get you where you want be.

https://www.instructables.com/id/Glass-Bottle-Cutter/

Hi! I actually saw his cutter, as well as some other wheeled types. I like the design aesthetically, but I have a couple of issues with it mechanically. First, the bottle stability issue: most consumer cutters have some means of securing the bottle on all three axes. Gravity plus the wheels take care of one on the cutter you referenced, the base another. A little more stability is nice - I would like to replace one set of wheels with a wall or something. Second, flexibility: For wine bottles, the spacing of the wheels probably holds the bottle fairly well. However, I cut everything from small spice jars to large mayonnaise jars. The wedge shape can accommodate a variety of cylinder heights and diameters without a lot adjusting mechanisms. The wedge is simple, easy to build, and relatively efficient. My last concern is with the wheels he uses. Brass is a fairly soft metal, but I would be concerned about scratches on the glass. I would go with wood wheels from a craft store.

All this said, there is certainly room for improvement in my design. I do appreciate your reading and your comment. If you have any other thoughts on improvements please share them!

I def agree with you on the metal wheels. I think I would use plastic, or wood would be ok too but they would soak up the lubricant. (you should use Mineral spirits on the cutter)

And I like your wedge idea. The only issue I have with it is friction. Perhaps some strategically placed strips of mover's felt would solve this.

But your goal should be a clean smooth nonstop cut all the way around your bottle. Stopping and starting causes rough edges that are harder to make smooth.

I used to work in a custom glass shop where it was not unusual to make curved cuts in 3/4 inch thick plate. Our boss called these cuts "cute". lol

Ah, now that is interesting. I had not considered the starting and stopping thing. I'll see what I can do to mitigate that. Thanks for the advice!

rimar2000 (author)2013-05-23

Very useful tips, thanks for sharing.

Thank you! I'm a fan of your work too!

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