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Thread: How to saw glass tubing?
02-05-2014, 11:43 AM #1
How to saw glass tubing?
I have 12mm OD x 8mm ID Pyrex tubing that I'd like to cut into short pieces, about 25mm long. Scribe and break doesn't produce a clean enough end, and its difficult to break off such short pieces cleanly. So I'd like to saw them. I see various Youtube videos of people sawing wine bottles etc on a tile saw so tried that out but it just shatters the tube. Not clean at all. So how do I do this? Very slow saw speed? some other method? What type of blade?
02-05-2014, 11:48 AM #2
Diamond blade under water is the surest way. The water can be a sponge and drip. I bought some nice little diamond blades suitable for a flex shaft or Dremel on eBay from China. A lathe to spin the tubing while you hold the rotating diamond saw against the glass will work nicely and produce a square end. I would not want glass powder and water on one of my lathes. It would be simple to build a special purpose machine for sawing glass tubing. For very small quantities, maybe a 1/2" drill motor and a Dremel could be rigged for a temporary setup.
Ron Hofer liked this post
02-05-2014, 12:03 PM #3
Easy way to try first might be:  with the edge of a triangular file, score the tubing all around, rolling it on the benchtop as you score to produce a single transverse scoreline as deep as you can go without crushing the tube,  with a piece of shop rag wrapped around the scored tube, break at the scoreline with your two thumbs straddling the position of the score and adjacent to each other, and your fingers wrapped around the far edges of the tube. And then there are the hot wire and other methods to try if that doesn't work. Probably best of all is Larry's suggestion.
02-05-2014, 12:09 PM #4
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02-05-2014, 12:38 PM #5
Metal Bond (Not Plated)
3500 or 1750 RPM (not critical) on 6inch blade
Slow speed saw=waste of time
Or scribe & break then square on 220 grit diamond wheel, flood coolant water.
Or scribe & break then square w/ loose Silicon carbide or Al-oxide grit on 300 rpm homemade lap.
Lots of ways to skin this cat.
How many do you need ?
Do you need to square or chamfer the ends?
Give us some more details.
This can be done fast and cheap.
N/A liked this post
02-05-2014, 12:46 PM #6
Diamond saw and coolant is the answer.
02-05-2014, 12:48 PM #7
I watched a youtube video a while back of an old guy hand-making valves. Looked like he cut the glass tube by putting a turn of wire around it then passing a current until it glowed red hot.
02-05-2014, 01:01 PM #8
Tile saw could work but tile blades are a bit course for glass… a diamond wheel 220-grit or so would be better
Wet diamond wheel is best choice for cutting glass but don’t try to chop through or chop off… better to bring glass to wheel and turn glass with making a score all around and then go deeper until you cut through. Glass held in wood v-block or larger tube so it can go straight to wheel OD with little side movement using an aquarium pump or the like for slow full flood would be good. Use water with a little washing soda added. Glass should have a little clearance at both ends when held so at cut-free there would be no binding to wheel. Held by hand in holder is good if that would be safe for you. Try to make wheel turn as true as possible to side and OD.
What equipment do you have and how many are needed?
02-05-2014, 02:19 PM #9
I have a "pro" tile saw that I just cut some thin (2mm) frosted glass plate on, did a nice job, very minor edge chipping, with hand feed. Flood water both sides of blade, SOLID rim (not segmented) 10" blade, 3600 RPM. Not sure why your tubing would shatter under those conditions, but the piece IS pretty short. I have found that support is required, but the support needs to be a tiny bit compliant in case the saw and table are changing relationships a bit during the cut. This same saw was also used to cut 2" thk glass disks, to create 2 flats on edge, using a leadscrew drive that was added to the saw as a special engineering project (sow's ear = silk purse).
02-05-2014, 05:26 PM #10
I agree with those who recommend a diamond wheel. For just a few parts, a regular thin abrasive cut off wheel is fine. You need to have it running true and low vibration. Water is pretty much necessary. You can do without it, but it will take a very long time because it has to cool as you go. Score and crack is difficult unless the tube is long compared to the diameter so the bending moment vs shear is large. The best way to score is with a very sharp diamond point, making a scratch that is almost invisible. The criterion is stress concentration, not total amount of stress. Filing a deep groove with a triangular file is not the way to go. You get a radiused groove that spreads the stress out. Every score and crack I did had at least a small wave at the bottom.
You want to support both ends of the tube when abrasive cutting or the glass will snap off at the end of the cut, leaving a "toenail".
02-05-2014, 05:48 PM #11
Back in the dreaded plumbing days, we replaced sight glass tubes in boilers. Used what was called ironically, a sight glass tube cutter. Sorta like a pair of pliers. One arm with a bushing would go inside. It also had a sliding stop gage for the correct length to be cut. The outside arm had the cutter. The good type had a diamond point for the scribe. Worked the best. The cheapos had a wheel. We used kerosene for both. Very nice even cut. That is, if the end was true to begin with.
02-05-2014, 05:51 PM #12
02-05-2014, 07:17 PM #13
Our lab glass blower would make a small score in a larger diameter tube and just touch it to the flame in the right way, off would pop the piece with a very neat break. Are you sure your tubing is properly annealed? Pyrex is generally very well behaved.
Last edited by mnl; 02-06-2014 at 06:54 AM. Reason: typos
02-05-2014, 10:32 PM #14
I cut the pyrex sight glass tubing for my locomotives with a Dremel and one of their diamond coated cut off wheels. I do it dry by rotating the tube in one hand while holding the Dremel in the other hand. Always get a good clean cut. If you need to you can dress the end with the diamond cut off wheel after you have cut it but I have never needed to do this.
02-05-2014, 10:41 PM #15
02-06-2014, 09:33 PM #16
Thanks for all the ideas. Some good suggestions here. I ended up turning the tube slowly in the lathe and cutting with a diamond blade in a dremel, as Larry suggested in post #2. I only had to do a few. I think Slicerman's suggestions are probably the best for larger quantities/more precise results. Shaybuilder must have some steady hands, I couldn't do it holding the tube and Dremel one in each hand. For what its worth the tile saw was a total disaster and I'm skeptical of the heated wire method. The point of Pyrex is to be able to heat it without breaking, the material is designed to have very low thermal expansion coefficient. Anyways, thanks again, now on to the next adventure.