View Full Version : Quartz tube cutting in a lathe

07-22-2019, 09:06 AM
Have an interesting project at hand: a reflux column head for a brewhouse pilot production still. 304 stainless with a quartz sight glass section inbetween to monitor operation.
I need to cut a section from a hefty walled section of tube to make the sight glass. After some meditation as how to make that happen I chose to use the lathe for the purpose:


A fine diamond cutting wheel was secured into the toolpost and the tube fixed on PTFE supports between the chuck and a live center. Water was brushed over the cutting area and very slowly the disc ground away on the rotating tube.


After literally several hours of careful tinkering I managed to part a section of needed length from the tube stock.


Since the tube was far from being uniformly round I could not really get a totally clean break...bits were chowdered away from the internal surface, but it is good enough for the purpose.

07-22-2019, 09:13 AM
Further the support rings were machined from 304 stainless sheet and PTFE gaskets to accommodate the sight glass section.


The sight glass was test fitted into the reflux head:


Seems to fit like a glove, just tight enough to seal, but still enough clearance to allow for thermal expansion forces to relax.

Five special screws were machined to secure the flange section together and tighten the gaskets.




07-22-2019, 11:10 AM
Now that's a nice bit of work. And big kudos on thinking outside the box and using the diamond blade.

old mart
07-22-2019, 11:48 AM
I presume you stopped grinding just before it finally parted.

07-22-2019, 11:58 AM
I presume you stopped grinding just before it finally parted.

Lord knows I tried :D ! But it would not part off as such and I was afraid to break it completely by forcing, so i kept grinding very slowly to further weaken the system. Of course it broke through, caught on the shards, parted in the turning lathe and shred the internal corner before I could slam on the stop button. Well at least it remained in one piece and functional. The cutoff disk separated the pieces and would not allow them to catch too bad on each other.

07-22-2019, 12:35 PM
When I saw your first pictures my first thought was fill the tube with wax in the area of the cut to keep it from dropping off as you finish.

old mart
07-22-2019, 03:07 PM
If you have to make another, a liner could be made to keep the ends supported. A length of rolled corrugated cardboard might suffice.

07-22-2019, 05:31 PM
very cool! I hope you get some samplers as part of your payment! Cutting glass without chipping on break through is a major PITA. The only thing that's helped me is supporting the exit with wood or plastic. I'd further the comments above, but suggest a piece of PVC or delrin machined to the tube ID and slid down to where the cut is. You'd still have to cross your fingers and turn around on the spot three times to be in with a chance though :)

07-22-2019, 07:18 PM
Yea....quartz glass can be a treacherous beast! :D The problem with machining an internal support is the fact that the tubes are.....well how to say it, "crooked" at best.....and it seems to be a universal characteristic void of significance towards time or space of production. Hence machining a functional central support that actually contacts the internal surface of the tube in more than a few spots without splitting it apart upon installation is quite a challenge. And the wall thickness is not uniform, so one is going to break through at some point and inevitably a more or less unclean break is the result.
I've worked with the material a lot in my past days as a high temperature chlorination reactor maintenance engineer and really the only option to have a really clean contact surface is to cut off an ovesized lump and grind off the chowdered edges afterwards on a diamond grit surface. To be honest, for practical purposes it rarely makes a difference if there are a few bits missing from the edge.

I remember a rather humorous episode from the days when I was still young and beautiful and had the motivation to work an occasional late night shift welding quartz reactor cores or mixers in the lab workshop. I had just finished welding together a rotating bed reactor mixer from quartz....it was sitting on graphite blocks secured in vice. I turned off the oxy acetylene torch and took my welding mask off.....the task was completed. Off and away for the night....right? No!! The next moment the vice gave rise to a slight "tick" sound caused by thermal expansion from the heat of the welding process.....released the graphite block and dropped all of my hard work on to the workshop floor, shattering it into a thousand shards. As I floated there about two inches above the floor from just the pure horror of what just had happened, the clock struck midnight. At midnight the automatic alarm system of the premises armed itself and went off silently at the same time because of my presence in the workshop. About two minutes later the security patrol guys arrived, rushed in and were about to cuff me to the radiator. It took some explaining from my side to let them leave me be and mourn my heavy losses :D

07-22-2019, 08:20 PM
It looked like it worked out well for you. A bit time consuming on the cutting. You basically filed your way through it. I think the job would have went faster if you could have spun the diamond blade as well as the quarts tube like in a tool & cutter grinder and motorized work head. Might have been a cleaner cut especially when you start to break through.


07-22-2019, 09:05 PM
I did this using a 10" ceramic tile saw (spinning diamond blade and flooding with water). I then smoothed the edges by putting a diamond honing stone under water and slowly smoothing things out using a figure 8 motion. If you get bad chip-out, you can use the spinning diamond as a water cooled grinder to even things out.

07-22-2019, 09:48 PM
We tried to machine high temp ceramic parts from 3/16 diameter finished stock,part of in a lathe then drill several .025" holes through the wall. I put it in a lathe and carbide tooling would not even scratch it. I told the owner that we would need diamond tooling or at the very least PCD and I could do it, however I have no clue how you will drill .025" holes through them. He sent the supplied material back and refused the job.

07-23-2019, 03:53 AM
It looked like it worked out well for you. A bit time consuming on the cutting. You basically filed your way through it. I think the job would have went faster if you could have spun the diamond blade as well as the quarts tube like in a tool & cutter grinder and motorized work head. Might have been a cleaner cut especially when you start to break through.


Yes, that was my original idea also and back in the days I used to do it this way round. And I actually had a suitable rpm controlled tool to hold the diamond disc blade.....but it would not fit into the small lathe, so I would have had to build a special rack to hold the tube and be able to turn it smoothly against the rotating diamond disc. Way too much work! :D It was simpler and more productive to do it the way I did for this one occasion. But really I would not love to cut 20 of these with the method I chose :P
From pervious experience I can tell that even if I had spun the cutting disc against the tube I would not very like have ended up with a much cleaner break. It is possible, but not a norm.....more like a blind and unlucky coincidence.

old mart
07-23-2019, 04:08 PM
You could have used Pyrex borosilicate glass, but it would have been no easier to cut.

07-25-2019, 02:58 AM
Also watch out with quartz shards, they are nasty. Not only sharper than hell they have the same refractive index as blood so if you get a piece in a wound it basically disappears. I have been told stories by guys who work in fabs of doctors removing pieces and they only way they can find them is probe around until they hit something. Ouch!