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Notes on using a glass cutting surface

Recently I have had some repeatability issues regarding focus. This is noticeable in inconsistent kerf size, as well as apparent varying laser intensity.

When trying to find the cause of this issue, I discovered that my 6mm sacrificial plywood board was slightly bowed. To eliminate this I experimented with using a 2.5mm glass sheet from a picture frame on top of the usual card or ply sacrificial material to get a flatter surface.

It should be noted that adding anything potentially reflective to the lasers path can cause unpredictable reflections, and should only be done with great care.

From these experiments I found that spacing a sheet of glass approximately 8mm above a sacrificial board creates a very reliable surface to cut on. So far, the glass has not shown any signs of wear, even after a test directly onto the glass running five passes around a 20mm circle, with a speed of 100mm/min and a power of 100%.
This also extends the life of the sacrificial material, as the laser is more dispersed when it reaches the board, and the surface is no longer critical.

These experiments also revealed a number of interesting results, which may prove useful for other more specific applications. These are as follows:

- Using glass directly on top of sacrificial card, I was able to engrave the underside of the glass with low speed and multiple passes. (100mm/min, 100%, 3+ passes)

- The glass has little effect on the lasers power. As such hazardous materials could potentially be cut in a glass enclosure, with fume extraction, protecting the user & machine.

- Focusing directly onto the glass, the lasers path can be seen traveling through the sheet, making it much easier to refine the beam width.

- With opaque materials, the ideal speed and intensity can be tuned by taking note of the amount of light that passes through the stock being cut, and the glass sheet.

Further experiments will hopefully refine the minimum spacing between glass and sacrificial board, to minimise the impact of this method on the available material thickness.

I may also trial clear acrylic on the same setup.image


  • Great idea. I have a question about this: given that the glass will extend the required focal length of the laser if placed on top of the stock (eg, if the standard focal length is 1mm from the black shield to the cutting surface, adding a 2mm thick glass sheet would give a focal length of 3mm), can the focal length be extended far enough to allow for that? As Lliam has said, we could theoretically cut more hazardous materials safely because of the glass plate. One of the projects I wanted to try was using the laser cutter to make toffee lace by melting sugar with it, but the fan would blow the sugar away and I am unsure of the effect the melting sugar would have on the laser itself. This would possibly solve both of those problems.
  • For the experiments I did cutting through the glass, I positioned the laser head just above the glass, then focused it as best as possible. I didn't spend much time on this but was able to easily cut paper with a normal appearing beam width.

    If I was to use this method regularly I think I would talk to Dominic about the option of printing a modified laser shroud.

    Something to watch is how the fumes from the sugar effect the glass itself. On one of the first tests I did, cutting a scrap of card with a printed face and the glass about 3mm above, the fumes seamed to condense on the glass, effecting the beam quality.
    To overcome time, I raised the glass to about 8mm, and used a fan to provide some cross ventilation.

    Let us know how this goes if you try it.

    - Lliam
  • I am using 2mm clear acrylic instead of glass and it seems to do the trick...
  • Great, thanks for letting us know!

    Keep us updated if you notice any permanent damage to the surface of the acrylic over time.

    I recently had to clean the glass on my setup for the first time, as it had developed a soot buildup along some of the paths cut at high power levels.
    It cleaned easily with some window cleaner.
  • So far no visible damage to the surface of the acrylic (have been using this setup for just 10 days or so) but do have the soot build up along the paths, which I clean with rubbing alcohol.
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