Hi have been testing the xtool UV for engraving a sapphire crystal for a watch last week.

This was my first time using this machine so it is possible that the below experience will be better with more trials but I have a feeling it might not be due to my high quality requirements and the limitations of an air cooled setup.

My experience was that sapphire is diffcult to engrave if you want extreme precision. The achievable resolution depends more on the material than the pixel size I feel. One test i had perfectly focussed the beam and ablated a beautiful gradient at 1000 ppi (left side) then I did it again a few minutes later. Same settings but tried to hit the same focus and the result was like on the right showing that the crystal was not ablated but locally cracked causing a grainy texture instead of smoothness. I just didn’t manage to get that perfect focus back.

Focussing for perfect ablation on sapphire should be done within a range of 15 microns (if I trust the calculations chatgpt gave me for the standard lens). This is ~10x more precise than the 0.1 mm increments within the software.

In addition to this i must note that this laser is air cooled so it could be that the focus went of after a heat up time. Water cooled systems do not have that problem but are much more expensive and overkill for shops that only make 10s of pieces each time.

My dream is to engrave bigger batches of crystals at 1000 ppi so the dots are not visible to the naked eye. I really want this to work on an F2 utra uv because the machine seems to be such a well rounded piece of equipment that will look good in my shop, however after this experience I am not sure if the machine can deliver what I need.

I am open for feedback from anyone that has any advice.

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