I have recently bought a K40 laser cutter and came across something a bit

Lasers
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1

I have recently bought a K40 laser cutter and came across something a bit strange. When adjusting the mirror alignment I also did a final spot test with the masking tape over the final aperture (before focal lens) and I found that the beam was always offset from centre no matter what I did.

I took the laser head off, stripped it down, measured all the components and made a drawing. This what I discovered. To get the beam central on the focus lens, I need to be 1.45mm above the entry aperture centre.

Am I correct in this conclusion?

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2

You may be. I found mine had the same problem. So I added some washers to shim it up. However, I was replacing the stock lens housing with the air assist LightObject one at the time so…

The K40 alignment is challenging with the poor mechanical design they have.

3

may very well be true. Although it doesn’t really matter after the beam entered the laser head since it focuses to a fixed point anyway.

4

I had shim my head up as well.

5

This could explain why I have barely been able to cut through 1mm cardboard on 90% power. I haven’t had time to troubleshoot that yet. The other thing I noticed with mine is that the large hole where the beam enters the cutting head is off-center. Specifically, the center axis of the hole does not intersect the center axis of the vertical cylinder–not even close. I dismissed it as not being much of a problem, as long as the beam hits the center of the mirror. I will reexamine that latter assumption when I look into the beam height issue noted here. Thanks!
EDIT: this may explain how the beam wanted to burn through my 3D printed air assist nozzle before I could cut with it.

6

@SirGeekALot James, cardboard at 90% means you have a more of a problem than I had. Tip: when I was going through the mirror alignment procedure and had got them as good as I could (I was using masking tape) I too couldn’t cut cardboard, most frustrating … and then I cleaned the mirrors and focal lens with acetone and bingo, straight through 3mm acrylic at about 10mA and 10mm/sec. (38%/40%) on my dial. The glue from the masking tape had deposited on the mirrors and diffused the laser beam.

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@Duncan_Caine I might have to try that. So acetone is safe on the lens and mirrors?

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I wouldn’t. I don’t know about anyone else but I use alcohol and distilled water 50/50 and good cotton balls. softly dragging the soaked ball over the surface but never pushing down on it .

One wipe around get another clean cotton ball do it again one wipe only. As many as you need until clean. You know it’s right when it dries clean.