cutting glass tubing

So will ceramics such as firebrick when red hot. I wonder if there are really any insulators at 1000°C.

Best regards, Spehro Pefhany

Vacuum. But then, that's neither strong nor hot, in and of itself. And some materials have a habit of conducting through it anyway! :^)

Tim

-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @

Hello Ken,

I cut some 1/4 inch pyrex tube recently. Could not get a clean break so I used the edge of a wet ceramic wheel at my local optician's place. Sawed through with the edge of the wheel then used the wet wheel circumference to smooth the glass cut.

Come to think of it, the optician had replaced his ceramic wheel with a diamond wheel so that is what I used. But I would have preferred a ceramic wheel. A ceramic wheel is larger but it just feels better to me.

The inside edge of the glass tube still has some burrs. Opticans call them stars. I think a hand held cone shaped diamond or ceramic tool can clean that up. Leftover stars are susceptible to breakage so best to eliminate of possible.

Tom Hubin snipped-for-privacy@earthlink.net

Old Glasscutting trick, works on 'flint glass`, : (Might work on pyrex even with its lower coefficient of expansion). Once you've got it scored wet the score mark with water. Then touch the score mark at one point with a red hot piece of metal, (large nail, etc.). The thermal expansion does the cracking.

Pragmatist "Politicians are not born, they are excreted." - Some perceptive old greek.

Reportedly, turpentine works better, or is this just an old grandad's tale. He always dipped his cutting wheel in turpentine before scoring the glass. Gerry :-)} London, Canada

Just as an update.... I've tried a few different suggestions (with not much luck), even tried, just for the sake of it, the engraving tool with carbide point.... it would score the glass but I still couldn't get a clean break that I could dress up for finish. This is a borosilicate glass tube from McMaster Carr. I haven't tried the "hot rod/wire" as of yet, but nothing else is getting the job done. I may have to take it to someone with the proper equipment. Another poster questioned length - it is going to be eleven sixteenths (spelled for clarity, although a decimal would have worked ). I have tried several methods of "scratching" the outside - not much success. I'll succeed, but it may be due to someone elses help :-) Thanks to everyone for all the posts. I'll post a followup shortly. Ken.

Ken, this sounds like some type of tempered glass. I recall a highschool assembly put on by, I think, GE. This was in the 1950's. They demonstrated pounding a large spike into a wood timber using what appeared to be a common flask from a chemical lab. Then when done, just dropped a piece of carborundum into the flask and it shattered. Very impressive!

Do you have the ability to aneal the glass tube? Then try one of the cutting methods mentioned in other posts.

Paul

Many better grade glass cutters have an oil reservoir and a wick to 'wet' the cutter wheel. Since water will work, and saliva, and also oil and you say turpentine, it seems that MANY fluids will serve to aid the propagation of a crack in glass.

Dan Mitchell ==========

Hi Ken,

You sure did get a lot of tips most are right,.... sorta. Being that your cutting Pyrex, (Cornings brand name for a 33 expansion borosilicate glass), ( AKA, Kimax from Kimble, & Duran from Schott), (and most recently, Simax and Cinex from ......you guessed it,.... China) These and Quartz glass are considered a hard glass, meaning it takes alot of heat to soften it. They also have a lower expansion rate. Things like Coke bottles or windows are a soft glass. Actually there are about 50,000 formulas of glass on file at Corning. Each and every glass has it's own working characteristics and compatibilities. They can differ greatly with their coefficients of expansion.

This is what makes the difference when trying to cut the glass with thermal shock techniques. A string with lighter fluid will work on a coke bottle, but it won't touch Pyrex. Scratching with a glass knife and putting a hot rod on it will work as will using nicrom wire around it. However many things come into play for different reasons and therefore these tricks are not good for what you're trying to do. Basically because the piece your trying to cut is so short. Also if the glass is not annealed will make a difference in the outcome. Stress in the glass can make a crack run wild.

Because the piece is so short I am assuming that the ends need to be cut square so to make a seal on the ends. There isn't much room for an o-ring or compression fitting to work on the side walls.

The best way to get a square end that is not all chipped is with a diamond wheel with about 220 grit or finer. Carborendom wheels will work good on small diameter tubing , but not on large, the blade can drift and not cut square. And always use water to cool the blade.

Tile saws will cut heavy wall tubes OK, but they will beat the hell out of standard wall tubes. (a lot of chipping) Especially the ones with slots cut in the blade.

Harbor Freight has a line of very cheap diamond wheels. But again they're pretty rough for delicate cuts. They're better for ceramic tile and heavy walls or chunks of glass.

The best blade I know of for your situation is one for Makita portable saws. Makita offers two styles. One with slots in it and without. I have the one without and it seems to make a pretty decent cut. It's about a 3 inch diam. blade. Now if you only knew a good machinist that could turn up an arbor shaft to adapt to Jacobs chuck on a drill or a flexible shaft........Hummmmm.

Like cutting ceramic, you need to make a straight and steady cut. You cannot bind or tweak the blade or it will break out the glass for sure. That's why tile saws and glass saws usually have a carriage to hold the piece while you cut.

If you still just want to scratch the glass to break it, use a piece of tungsten carbide to make the scratch. Files are to coarse. You want to make a deep, crisp, sharp scratch about 1/4 to 1/3 around the tube. Drill a hole in a block of wood or 2x4 that is a snug fit on the tube. It should be just deep enough so that the scratch is just above or flush with surface of the block. Wet the scratch and pull back and away from the scratch. The wood will give the leverage you can't get buy holding it. Using pliers you will usually end up crushing the glass.

And if all else fails, Maybe I can refer you to someone in your area with a glass saw. I have been a member of ASGS (American Scientific Glassblowers Society) for 25 years.

Good luck,

Randy H. SC Glass Tech. Scam Diego, Comi-fornia

Thanks, Randy, for all the good info. I have a small diamond blade on its way to me, and I will turn up a nice little arbor to hold it. I am planning on water cooling while cutting. Should I go completely around the circumference several times, deeper each time, or simply cut straight down through the glass with the blade? I'm thinking of chucking the glass tube in the lathe, with the tube wrapped in a thin sheet of rubber, and indicating it to center, then mounting the blade in a dremel type tool on the toolpost, covering up everything involved and using a water drip. Does this sound feasible? Everything you mentioned in the post seems to be "holding true", and I did even try the hole in the block of wood method, but still no luck. I realize, now, that I'm going to have to cut clear through the tubing to get what I need, and then dress up the ends a little bit if necessary to get them square and smooth. This stuff is a little nasty to work with and to date I haven't had much luck with any of the methods I've tried. The diamond wheel will be my last attempt, then I'm off to someone that has equipment to do this job. Again, I appreciate the info and help. Ken.

I've had success using the lathe and a single mounted diamond.

michael

The diamond blade should work. You want lots more than just a "water drip". The saws I've used for cutting just about every variety of glass, ceramics, and quartz (except tempered glass, which can't be cut) were lubricated by a flow of water (lots!). We placed a copper tube, slit to fit over the saw blade just above the cut and plumbed it to the lab water supply.

I'd cut the tube all the way through rather than trying to score all the way around. And I'd rig a slide table so that the tubing can be handheld and hand fed into the blade. The way you are talking about doing it you won't be able to feel the cut and may force it, which will result in chipping/breaking. And hand holding the tubing gives it some "wiggle room" and lessens the chances of breakage. Using this I've 19mm (.5mm wall) quartz tubing for a Skylab crystal growing experiment.

If you need precise length dimensions and end squareness, consider cutting the tubing about 10-20 thou long and then grinding to exact dimensions using standard optical abrasives & techniques.

Hi Ken,

Your right on track. This is the best method to assure that your end is square. Even better than a fancy glass saw! Just feed the saw blade in slowly, don't force it through. You can cut a little faster at the start, but slow up before you break through. You might want to slip a piece of wire or wood dowel just inside the tube to catch the end as it pops off. You may have a little chipping on the inside edge, but most of the surface of the end will be OK.

If you use a heavy flow of water the blade will spray 360 degrees. You might want to make a shield. A steady drip should be sufficient and help keep the spray down. Just a long as you don't see the glass light up from friction. If you don't use enough water it will burn the edge. This putts stress in the glass causing it to crack.

If the blade is to coarse, you may have some saw marks on the ends form the texture of the blade . This may be problem for a good seal if this is for vacuum work. If this is the case, or if you have some minor chipping on the edges you want to remove you can flat grind the ends. To do this it helps if you put a slight chamfer on the outside edge using the side of the diamond on the blade, or with sand paper or Emory cloth. To do the inside edge wrap some Emory cloth around a dowel or anything round just to knock off the sharp edge. This helps to keep the edges from grabbing and chipping out more.

You can get piece of flat window glass to use as a lap table. (ask for some scrap at the hardware store) To coarse grind the end down past the chipping use about 150 grit silicon carbide grinding compound with water to make a slurry. Use a figure 8 motion. Then use about a 320 grit as a finish lap. Just make sure you clean everything thoroughly before using a finer grit size. If this is for vacuum service go down another step to 600 grit. If you don't have grinding compound try some wet sanding paper over the flat glass.