Which mirrors for 80W machine? (glass tube)

Lasers
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As I learned yesterday, the brand new mirrors in our 80 W machine (glass tube) at Dim Sum Labs are of type K9. According to k40laser.se, a K9 mirror “is the worst mirror you can ever put in your machine.”

Photos of the laser cutter at Dim Sum Labs
Photos of the laser cutter at Dim Sum Labs1600×1200 324 KB

I am happy to buy new mirrors from China, which is just across the border. On k40laser.se, I found:

  • Si mirror: “Good reflective index for our machines (less than 50w)” – I assume for 80W, it’s not suitable, or is it?

    On Taobao, 20 mm Si mirrors are dirt cheap at less than 40 RMB a piece (ca. 5 EUR / USD). Could they be fakes or of bad quality?

  • Mo mirror: “Good for up to 100w+ lasers.” – Is this the one to get?

  • Cu mirror: “Copper mirror, better than MO, a bit below SI when talking about reflective index” – Or better this one?

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We always use gold plated copper mirrors on our 100W CO2 laser. They last very long if you clean them regularly whith care (don’t scratch them). The problem with Si or Mo mirrors is, that they can crack easily when they get too hot if they are not clean.

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This is a very good point! Our machine is in a hacker space, and I know from other spaces that people just continue lasering into dirty optics. After painful searching on Taobao, I found a source:

直径20/25/30mm铜镀金反射镜片/聚焦镜片激光镜片/反光镜激光配件

At 80 RMB, such a Cu mirror is about double the price than an Si one. This is fine for me, and hopefully we get OK quality then. It’s still dirt cheap. I have not yet ordered.

Does anyone know which mirrors are used in the Trotec Speedy series? (totally different price range, I know, just curious as I have used these machines frequently in the past)

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The last mirrors I ordered was these:

We use them now for more than a year on our Lasersaur in the FabLab and they are still good.

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Thanks! MCWlaser doesn’t ship to Hong Kong, but I may just try the merchant on Taobao. It’s way cheaper too.

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Yes, I guess the prices on Aliexpress are more expensive because they target foreigners :wink:

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Could perhaps be better products too on Aliexpress, or ones that passed a different level of QC.

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How does a mirror made of 3mm thick solid molybdenum crack?

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I use MO mirrors from Amazon.

MCWlaser Mo Reflection Mirror x… https://www.amazon.com/dp/B07MFLPPGN?ref=ppx_pop_mob_ap_share

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Solid MO mirrors would probably not crack, but I saw cheap MO mirrors made of glass with Mo coating. They can crack from thermal stress or just from the grub screw in the holder.