Cutting bottles, buffing

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Doug Coulter
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Cutting bottles, buffing

Post by Doug Coulter »

I cut the first few bottles thussly:

Drill a couple holes in the edge of a drill press table (or anything like that that is really flat and smooth and stable). Bolt a piece of angle iron to the edge so the "cradle" it makes is vertical, then put a dremel tool in there with some hose clamps. Use a cutoff disk in the dremel, the littler ones that easily shatter work best for this. Adjust the dremel to cut at the height you want, just where the walls straighten up above the curve at the base. Gently hold the bottle against the cutoff disk while rotating it, going all the way around. Then I've used several tricks for parting them, but the one that works best is to put some 20 mil nichrome wire in the groove, hold it in tension, and heat 'er up. The bottom usually just falls off, and the cut is usually fairly clean. It can be sanded to a better smoothness with drywall screen (coarse sandpaper) taped to a metal plate, or with a lathe jig, then really smoothed up with lapping grit and lots of patience. When sealing with viton o rings, shiny surfaces seem to matter more than slight "waves". The ring will take up about a 1/16" "wave" if other things are right, but a sandblasted surface will always leak some.

The above works far better than the cheapie bottle cutters that spin a normal glass cutter around a bearing placed in the neck. With those a little overlap of the scratch mark causes failure, as it's very skinny and almost never truly overlaps, so the cut diverges there. The dremel puts a nice fat groove in there and if you're careful it will overlap if you go a little past a full turn.

I now do this in the lathe. I made a jig that allows chucking the neck end of the bottle (I actually chuck to a stepped piece of wood dowel going through the neck and held inside the larger part with a big wooden washer and screw). I made a tool post grinder by adding a mount to a dremel tool, and if you're careful (don't produce too big a thermal gradient in the glass, just take your time, and I even do this dry), you can just cut all the way through with this and the edge is perfect. It also works on things like fluorescent light bulb tubing and other fun stuff. I got a quick coupler for a couple of popular sizes of glass (3/8, 1/2, 1") and it turns out 15w bulbs are that latter size, very thin, but they do hold a vacuum. I make little baseplates for these out of teflon or peek on the lathe, and now have a bunch of little chambers I can try things quickly in on their own branch of the "good" system. I use Apiezon wax W or Hysol 1C to seal wires through the bases for quick experiments.

Hope this helps -- it worked so well here I was buying a bit too much wine to get the bottles...If you cut the tops off instead, you get nice basins for various uses such as ice baths in the chemistry room, washing hands, whatever. They make decent bells too, and were popular with the neighbors for various uses.

Buffing:

Any plating goes on a little bit porus, due to the fact that what you're plating it onto is not uniform -- there are little places in steel where there are non conductive (and thus non plating) impurities, which is easily seen in a microscope after acid etching the steel. So you wind up with little holes in the plating in the worst possible places -- who knows what those impurities were after all? Could be graphite, sand or just about anything that snuck in there during manufacture. This is one reason why there are extra high priced metals available that have been remelted in vacuum -- they skim the crud off the surface and you get much purer metals, but even then they might have the odd graphite inclusion.

Copper is most often used as a base coat (perhaps after a strike coat of something else unless you have an alkaline copper system to go straght on steel as I do) for one big reason -- it's easy to buff. When you buff it, you close up the holes -- you actually smush the metal around some, it is very soft as-plated. If this is not done, electroplating for corrosion protection does not work, and in fact makes things worse due to various metals in electrical contact in the presence of whatever corrosive is there. You learn this quick if doing electroplating for money, the stuff comes right back rusted with an angry customer if you skip that buildup and buff step -- in other words, even if the copper looks shiny enough it isn't, as plated.

Tip to all:

Weld all the little stuff on there first, then the big flanges so you don't warp them by welding close by. Maybe some of you are so good at TIG this isn't a problem, but here it was, and I warped one of the big ones due to weld stresses nearby, adding a new 2.75 cf with one side of the tube only about 3/4" from a big iso160. A few excruciating hours of interrupted cut machining making the "fingernails on chalkboard" noise on the lathe made it flat again, then I had to recut the groove for the o ring centering device as well -- it had warped over 80 mils. So I then had to also modify the clamps to work with the thinner flange. I'm back in action, but this is a problem better avoided. I now have an adjustable center I had to make for 6" tubing in my bag of tricks.
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Steven Sesselmann
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Re: Cutting bottles, buffing

Post by Steven Sesselmann »

On subject of glass, I just received these neat little glass KF25 to KF10 nipples, they were made by a local glass blower and cost me $50.00 each. The flange ends have been ground flat, but they could do with a slightly smoother polish as Doug suggests.

Steven
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https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG
001userid
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Re: Cutting bottles, buffing

Post by 001userid »

Nice write up Doug. I was using the wheel cutters, I'll retool for a dremel. Thanks for sharing.

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DaveC
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Re: Cutting bottles, buffing

Post by DaveC »

Using a hot wire will usually produce a good cut, in a lot less time. I have done a little bit of glass cutting with the Dremel... but I was never very good at getting the nice results Doug is getting.

For cutting any type of larger glass tubing, without using a diamond band saw... (this is the cat's meow, and McMaster Carr sells them, but they're not cheap)... try putting a clean, single line groove all the way around the bottle, using a good three corner file. I have left over from college chemistry days, that still works well. Be sure the groove closes on itself - no gaps. The use a piece of 18 - 24 Ga, Nichrome wire... or even plain steel picture wire.. and a 6 volt filament transformer.. with enough current capability to make the wire glow bright red... don't want to melt the wire.

Wrap the wire into the groove, and begin heating... it will take a minute or two...depending on the thickness for the thermal stresses to develop. Keep the wire snug in the groove, and don't let the ends cross and short out. After you hear the "tick" as the glass cracks, rotate the bottle about 1/4 turn and repeat.
after the second "tick" the top will fall off... leaving a reasonably square cut, very sharp edge.

I usually dress the edges with a diamond file, for safety.

This method works best with soda lime ( the soft) glasses, and not very well with Pyrex and not at all with fused quartz.


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Doug Coulter
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Re: Cutting bottles, buffing

Post by Doug Coulter »

Gee, this is a nice place where people share really good helpful stuff.

Thanks to all!

As I said, I now cut most glass on the lathe one way or another. I've found out that 15w fluorescent tubes are precisely 1" in diameter, or close enough to seal with one of those quick couplers I got from Lesker. As one of my hobbies is making analog bargraph neon tubes, this is a quick and cheap way of getting a large piece of soft soda glass to put them into. I cut them all the way through on the lathe and then clean them out outdoors with an air blast to avoid breathing mercury and rare earth oxides. It's very thin glass but holds a vacuum just fine. What I do is draw them down to a thin neck so that I can seal them off in vacuum (sometimes it's not much vacuum depending on the gas fill), and seal the bases with teflon or PEEK plugs made on the lathe, and either apiezon wax or lately Hysol 1C (not listed as such in mcmaster but just type it in and they have it). They do list a low viscosity version that adds -LV to the number, but I'm betting it is not as good around a vacuum.

BTW, you chuck these in the lathe after carefully wrapping them with duct tape, precisely one round, and don't chuck them hard. If you're putting any noticable torque on the glass, you are going too fast. The lathe is also a good place to have the stuff to evenly heat a small portion all the way around for the neck pulling operation.

Basically I use another dremel that I made a mount for so I could put it in the tool holder. This was a bit of a challenge as there's not much spare room inside a dremel for the screw heads to hold the piece of wood I carved to match the dremel's curves. Works great, and the worst problem with this is leaving it down on the lathe somewhere and hitting it with the moving table, or tripping over the wire and breaking the little cutoff disk.

Another thing -- the bulbs you can get for short wave UV are quartz, and it's quite a bargain getting it that way. These are extremely hard to cut any other way -- they tend to shatter weirdly when normal techniques are used. But slowly grinding through them works. I do most lathe work on glass at its slowest speed, about 60 rpm.
Why guess when you can know? Measure!
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