I'm looking to cut a glass bottle like a beer bottle and turn it into a drinking glass. I had the idea to cut the top of the bottle off with some NiCr wire but I'm not sure how I should wire the NiCr wire. Does it need a resistor or reastat of some sort to keep if from shoring out the circuit it is hooked up to?
I plan on wraping the NiCr wire around the top of the bottle and leting it heat up and hopefully the heat will weaken the bottle in that spot and then I can break it off..
Bottles are made of a glass that has a fairly high coefficient of expansion. If you don't heat and cool very uniformly, it will break due to unequal stresses. The method you propose won't work. A better answer is to just get a diamond saw and cut the top off. The edges will be sharp, so you'll need to grind them.
The wire is resistive, so no special control is needed, although most designs will vary the voltage to control the heat and some may have a feedback circuit to keep the heat constant and supply more voltage if the wire cools as it is cutting.
Interesting. I've heard of doing it that way, but not about the problems one might encounter.
Could he use the hot wire in "cheese-cutter" fashion instead?
The
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I've used hot wires to cut foam and it works great for that. I seriously doubt any hot wire cutting of glass will work. I've got a moderate amount of experience with molten glass - and with cutting bottles. The diamond saw works great to cut the tops off. I tried several methods to get a smooth lip. You can just heat the bottle 'til it's nearly molten, then allow to cool, but you'll bust most of them unless you heat and cool slowly. A grinder worked better. I've made some stretched neck bottles, that looked cool, but it's a tedious process without the right eq uipment. You need a controllable heat source (gas or electric) and an insulated kiln that drops the temp slowly.
As a kid I would melt glass using carbon rods from ordinary D-cells. They were wired in series with my moms laundry iron. The light was blinding. But I learned glass flows like honey when heated.
Lets assume for a moment the ni-chrome wire can melt glass. I can picture the glass congealing on itself on the backside of the passing wire. The diamond saw is a more practical idea, I've seen them offered on ebay and elsewhere affordably priced.
Dennis Harper snipped-for-privacy@gmail.com
It is necessary to score the glass with a glass cutter before applying the hot wire. Build a jig to hold the cutter and rotate the bottle against it. Helps immensely to dip the cutter in some light oil before starting and go around until you meet your starting point; Ideally in one smooth high pressure movement. The sound changes from a tearing paper sound (scoring) to a rough gravely sound when you meet the previous score.
Only go around one time, but make sure it is a good continuous score.
Bottles with small mold imperfections can be cut. Bottles with bubbles included in the glass take a lot of skill. Uniform glass thickness is easiest to cut.
The hot wire should wrap completely around the bottle if possible (or as close as you can get it without shorting the wire), directly over the score - we used flat nichrome from a toaster and it worked very well (cutting 8" 14" round CRT's open around the faces). We put the wire around the CRT's and then turned on the heat - the wire stretches a bit but we were holding it with pliers and kept the tension constant. We had a variable low voltage supply and kept it just cherry red where it WASN'T against the glass.
The coping saw / cheese cutter hot wire holder may also work. I'd rig a jig if I was going to try that method - less chance of drifting off the score mark.
Another excellent technique (better for bottles, in my opinion) is to tap it from the inside of the bottle along the score. You take a large piece of steel wire or rod ~1/8 - 1/4" in diameter. The wire is bent at a radius so it contacts the glass perpendicular to it on the inside.
It has to hit the score mark exactly - so the tapper rod should come to a rounded point. To hit the right depth each time (without a lot of effort) get a short piece of stiff reinforced plastic or rubber tubing and push the top of the rod through the center of it. Friction holds the setting of the depth once you get it set. The short tubing rides on the mouth of the bottle and provides a pivot and depth gauge for striking the inside of the bottle.
Hit in the same place until you see a crack form. (helps to have a desk lamp shining down on the glass). Once you start the crack tap
1/8" or so to one end of the crack - the crack should jump about 1/4" each time you strike it (moving forward about 1/8th inch each time).It rings like a bell until you get the entire periphery cracked, then the sound becomes "dead." At that point the top and bottom will usually come apart in your hands - if not gently keep tapping around the inside until it falls apart.
Wet or oiled fine emery cloth will take off the jagged edges. Using the part of the bottle that's to be discarded to rub off the jagged edges works well enough to keep from being cut on the edge - but for a drinking glass, use emery.
Oil the cutter wheel each time you use it. The scoring tool has to be in good shape - the old rusty one you've mistreated over the years may not work well.
For bottles - the tapper method is less hassle.
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Hello, Michael! You wrote on Mon, 7 Nov 2005 15:50:30 -0500:
MK> I'm looking to cut a glass bottle like a beer bottle and turn it into a MK> drinking glass. I had the idea to cut the top of the bottle off with MK> some NiCr wire but I'm not sure how I should wire the NiCr wire. Does MK> it need a resistor or reastat of some sort to keep if from shoring out MK> the circuit it is hooked up to?
MK> I plan on wraping the NiCr wire around the top of the bottle and leting MK> it heat up and hopefully the heat will weaken the bottle in that spot MK> and then I can break it off..
I think the diamond saw idea is the best bet, but I know what you're talking about with the hot wire method. I've seen it done that way on TV and was well impressed. If I remember rightly the wire was just wrapped in a loop the right size to fit the neck of the bottle and then the loop was heated bright red in a blacksmiths furnace and quickly fitted over the bottle before it cooled. The bottle with loop attached was then quenched in cold water and the top just came off clean. They didn't say how many bottles they broke before they got it right, but I bet it was a lot. :^) With best regards, 3T39. E-mail: snipped-for-privacy@hotmail.com
on ebay and elsewhere affordably priced.>> Dennis Harper> snipped-for-privacy@gmail.com
How do you cut flat glass? You score it so that when you bend it, the stress concentrates at the score line and it fractures cleanly. Do the same with the bottle. Score it all around where you want it to break. The concentrated heat causes the expansion that propagates the fracture along the score line. mike
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It does work, I've done it before. The cut was not as neat as a diamond saw would do, but it does break neatly.
Check out Ebay for the: "Fleming Bottle and Jug Cutter"
After you see the pictures, you should be able to make one from hardware store parts - I've made a few over the years.
The conical pivot they use for the scoring tool gauge, can be made from a tiny funnel (or not so tiny one for large mouth jars). Fill the funnel with polyester resin or epoxy and use it as a mold to get the conical shape then drill a center hole or put in a piece of drill rod, when casting.
1/2" X 1/8" aluminum extrusion is the basis for the other parts of the scoring tool holder.Armor All will work as a mold release agent. Hot melt adhesive works well to hold the parts in alignment and plug holes until the resin hardens.
Or spend $10 on ebay?
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This should work fine, although the diamond saw will give more reliable results, but if the bottles are free, who cares. Simply heating without scoring is not going to give the results desired. I assumed he wanted to melt the glass. That won't work. You can't melt part of the glass while the rest is cold. If he wants to crack the glass, it works fine, but you need the score to make it reliably crack in the right location, and if you're going to score it, why bother with the heating, just tap it from the inside. Results should be just as good. The results are far more dependent on the good score and type of glass than they are on the method of inducing the crack to propagate. Heat or impact should both work.
Diamond saw is probably the most expensive way to get a set of tumblers . . .
Hot wire is overkill for something like a bottle, and maybe less reliable than tapping a scored piece of glass - for run of the mill round bottles up to gallon size. If I were cutting square bottles or very thick glass, diamond or hot wire would be my first choices.
I've done some stained glass, built a few aquariums, and cut a lot of bottles. Scoring and tapping is the easiest, least expensive, method and almost as reliable as a wet diamond saw.
Diamond saw is the only way to cut some glass - like shatterproof safety glass, wire imbedded safety glass, some quartz glass', beveled glass, very expensive stained or textured glass, glass "jewels," glass block, etc..
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I must not know how to use a glass cutter.. Every time I try to score it and then tap it all that happens is the entire thing shatters.. I've always hated glass cutters...
- Mike
I too have heard of cutting bottles using only the wire, no cutter or other tools necessary. I believe I saw it for my first time in an old-timey scientific wizardry book. IIRC, the diagram showed a length of wire suspended between two posts, with plenty of slack, and the bottle or tube being cut was leaned against the loop and rotated to produce a groove at the desired cutting location.
You definitely don't want to give the wire full power; it's not resistive enough. A light dimmer would probably make a good regulator. Put the dimmer and a light bulb in series, and try to get the wire to glow brightly, but you don't want it to burn up. I did this once with a variac, but you may or may not have one of those lying around.
I never took the time to construct a sturdy base for the wire, and I learned very quickly that it is impossible to cut anything unless you have the wire securely tethered.
Mike, Here's a bunch of sites about doing this:
We tried both ways cutting bottles - score/no score - with a hot wire. No score only works well on very uniform bottles. With cheaply made bottles the internal strain and differences in thickness tended to cause a propagating crack to run off course.
With the CRT's we cut (from old scopes and radar displays) the no score technique worked very well. I assume the makers of the mil spec CRT's carefully anneal the glass to relieve stresses and there's no doubt the glass was a uniform thickness. (~3/8+ inches). Had one guy holding the CRT by the neck an inch off the carpet - one guy holding the wire with some pliers and another working the power supply. The crack didn't propagate around the glass like a bottle it just cracked and fell off in one go.
Bottles keep getting better. (I brew beer, so I inadvertently pressure test a few to their limits each year - sub orbital launch of the bottle necks).
The old style, thick Corona bottles from the late 80's, for instance are very weak. There's a lot of glass, but the thickness is not uniform. The newer ones (thin glass, mid-late 90's and on) will hold the pressure. Likewise the Fischer Bottles (French beer with a Grolch style bottle and cap) have to be treated with care - they are embossed with a design and relatively weak for all the glass they contain.
Modelo bottles may be the easiest to cut - almost no effort or care needs to be used. The shape wouldn't lend them to tumbler use.
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Those crummy old red devil cutters they sell in hardware stores usually don't work, except for very think pieces of well-made window glass. I use a carbide-wheel cutter to cut stained glass, and it works almost, but not quite, as well as Bugs Bunny's. Toyo and Fletcher make good ones. (Fletcher also makes steel-wheel cutters tho, so be careful shopping.)
Once you get really good at glass cutting, you can use a cheap steel cutter, but you'll never be happy with it.
A lot of people also make the mistake of tapping on the scored side of the glass. You have to tap on the other side (which makes it trick when you're cutting a bottle or a tube). Likewise, if you prefer to bend the glass to break it, you have to bend away from the score, expanding it; bending the other way almost always has an unfavorable outcome.
Mercury is really only hazardous when stupid people get a hold of it. Unfortunately the best way to keep mercury out of the hands of stupid people is to make it generally difficult to obtain.
Obviously you should not go sticking red hot pieces of metal in mercury in a confined space. But this is actually a very effective way to harden a drill bit. (Another very effective method for drilling glass is to go to Home Depot and buy a glass drilling bit. :)
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