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K40 - Entry 5: Cheap Stock Mirrors

7 years of bad luck? A broken mirror., Rather a heat-shattered mirror

Lesson 2 in quality control, stock K40 units ship with notoriously cheap mirrors. This one cracked the first time I set the power up above 20%. I think I had it up around 60% as I was attempting one of my first real cuts. I heard a pop and thought it might be the tube. Fortunately it was just an inexpensive mirror.

I got onto eBay and Amazon and after a little research, I found these from CNCOLETECH. There is much to be learned about mirrors for lasers! These are Si gold plated mirrors. My laser a a bit shy or 40 watts, so these are the ticket. You can see how much the K9 mirrors included with my unit are respected.

Here is a chart that explains the nuances of laser mirrors:

  • Si Mirror: Silicon Glass Gold coated has a very good reflective index, however it is not very suitable for laser powers over 50 Watt. (lasts about a year before it should be replaced)

  • Mo Mirror: Molybdenum is by far the toughest material. It does not have the best reflective index but it is strong, requires the least cleaning and is an absolute must for higher power lasers. (lasts about 3 years or more before replacement is needed)

  • Cu Mirror: Reflectivity between that of Si and Mo, but stronger than Si. This material is easily scratched and some people make them in the DIY style (I wouldn’t do that)

  • K9 Mirror: Little can I say about this stuff… it is good for the trash bin. This is the lowest of the lowest quality and should be avoided.

Anyway, Amazon Prime got me three mirrors shipped with overnight shipping. I only replaced the broken one so far and the laser works far better. I'll wait a bit until I put the other two in. (Probably need to invest in a new lens as well)

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