Cutting Glass With CNC

Breaking a pane of glass in half is easy – just score it, break it, and after practicing a few times, you’ll eventually get it right. What about cuts that are impossible with a normal glass cutter, like radiused corners and holes? For that, you’ll need CNC. Yes, you can cut glass on a CNC machine. All you need is a diamond burr or glass drilling bit, high speeds, low feeds, and lots and lots of coolant.

Cutting glass on a CNC machine doesn’t require any spectacularly specialist equipment. [Peter] is using an $800 Chinese mini CNC engraver for this project, but that’s not the only tool that was required. A fixture for holding a glass plate was also needed, but [Peter] quickly fabricated one out of acrylic.

Cutting glass with a CNC is something we’ve seen before. [Ben Krasnow] has been using diamond burrs, high speeds, low feeds, and lots of coolant to cut mirrors so expensive you don’t even want to guess.

While [Peter] isn’t getting the perfect finish [Ben] got a few years ago, he’s still milling holes and slots in glass. He’s wondering if it could be possible to mill an aspheric lens using this technique and a special spherical burr, something that would be very interesting to see, and could be a pretty good way to rough out telescope blanks.

32 thoughts on “Cutting Glass With CNC

  1. I wonder if he could mitigate the slight cracking problem by milling 40% from one side, then flipping it over and milling the other 60% from the other side. the kind of “knapping” flakes you see generally only happen when you apply pressure to a continuous edge of glass. It would make for a better finish, but would make code generation a pain.

    1. EMC2 can mirror your toolpath by itself (although that function is a bit glitchy).

      I’m thinking it will then just chip at the middle and not the end. Also, aligning the coordinate systems can be a massive pain if it turns out that my fixture is not mounted perfectly aligned to the axes (it’s likely not).

    1. The most useful suggestion from there was to try using some victim glass. I certainly should trying it out, seeing as my fixture can be easily extended to do this (just use two layers of acrylic)

  2. I suspect it’s possible the CNC3020 is not rigid enough and the minute vibrations are what’s causing the glass to chip. Also check for other sources of vibration such as form the spindle itself.

  3. A much quicker way to hog out a telescope mirror blank is to use a diamond cutting wheel chucked into an angle grinder attached to the end of a long extension bar with an adjustable pivot point, so you can grind out a successively larger radius. You’ve got to remove a _lot_ of glass to hog out a 16″ f/5 mirror…

  4. As for the chipping why not just make the piece you make slightly larger than you need and then use a sanding bit to polish the edge down to the final size while removing edge chipping?

    1. The chipping is not really a problem for the flange I needed, it would not degrade the flange much. However if I did, it would remove one of the key benefits of CNC, that is its precision. I don’t trust myself to sand it down evenly.

      Also, you can’t really sand down like that some of the features, such as the edge of the groove.

      1. Not a link, but some ideas to experiment with.

        1) Have you thought about working it while submerged in a layer of coolant?
        2) Have you considered using warm or even hot water? The colder glass gets, the more brittle, right? And it seems to me that in order to prevent serious cracking, you need to keep the temperature GRADIENT below a certain extreme rather than worrying about the workpiece or tool temperature directly. And dripping cool water onto the tool might be causing the gradient to go too extreme because as the glass gets hot when cut some of the water in the immediate area of the tool will be vaporized.
        3) What about using non-newtonian fluid submersion? Tape? Sacrificial wood? Glass is just… so tricky.
        4) Lift often?
        5) Get a piece of real, non-laboratory obsidian and grind that to see any differences between your chips and the chips on obsidian. Ideally, use obsidian that has been knapped manually for practice so its grain direction is known. I think you’ll find there are some non-obvious properties of glass which will suggest you should be more discriminating in selecting glass stock material.

        They look like impact chips. Did you happen to capture any of the chipped-off material around the workbench that you can analyze microscopically?

        Your tiny chips don’t seem to be a huge problem, but I’m betting you’d like to be able to do it reliably with no chips, because that’s a really cool skill to learn!

  5. A friend of mine is a professional glassworker. He showed me a trade secret that blew my mind.

    To create a perfect circular hole in a sheet of glass, all that is necessary is to score two lines of equal lengths in the glass; one vertical and one horizontal, to form a ‘plus sign’.

    Then using the opposite end of the scoring tool, tap the center of the ‘plus sign’, to knock out a hole which is proportional in size to the scored lines, AND the amount of pressure applied from the strike.

    Make the score lines longer to produce a larger hole, and/or apply more pressure when striking the glass with the back end of the tool.

    Ovals are created in the same way, with the exception that one line is made longer than the other.

    Don’t expect this to work the first time you attempt it. This technique takes practice to master the craft, but he makes it look so easy.

    Be mindful that glass is extremely sharp. I tell you this because my friend is missing a finger.

  6. Peter again. This guy is making awesome stuff with a 500$ CNC. He found out how to make the spindle software-controlled, how to add functionalities like endstop and so on… Just go to his website, you will be amazed of the level of explanation.

  7. Hi, first time posting. I am about to cut some glass on a CNC. Can you answer the following questions for me.
    1. What size diamond blur bit would you recommend?
    2. What type of lubricant would you recommend?
    3. Can I secure the glass to with two sided tape to our cutting bed?


  8. I have a much much improved modification that costs $80 and uses a heavy duty glass cutting wheel with a -5mm turning radius, using a glass cutting wheel is much better, cleaner, and faster, email me for info.

  9. Forgive my tangent post, but does anyone have thoughts on filtering the coolant while milling glass?I switch between glass and various metals and struggle with manually cleaning out my Haas coolant tank and related lines. Thanks!

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