Unable to align mirror 2 in the horizontal direction when testing front and back locations

Here is what I got when using the Clamp meter with a setting of 200 ACA


OK, so how are you setting the power on your machine? I was assuming you had a digital control panel on your k40 but I’m confused by your use of max and min. @donkjr thoughts?

I don’t know were the clamp meter is placed and what type it is. I doubt a clamp meter will measure the tube current accurately.

Also do not understand min-max settings and the last columns data?

I advise installing a meter that can read (ma), in series with the tubes return (cathode). Then plot tube power setting vs tube current.

Since the power is so drastically reduced I would remove the air assist nozzle and see if it cuts better, verifying the beam is not being internally reflected by that housing.
Alternatively, you can fire with the head held at a fixed target on the bed, leaving the target and head in the same place, move the bed up/down and fire again to see if the burned dot moves. If it does, the beam is not traversing through the objective lens perpendicular to the surface.
You can also inspect the inside of the objective lens housing and see if there are burn marks.

Do I understand your FL test correctly, you burned lines at different heights and looked for the thinest one?? It may be hard to find the right point with that method especially since the head is in differing x-y positions??

I suggest doing a conventional ramp test where the target is on an incline and one horizontal line is used to find the FL?

Picture of control panel?
Picture of LPS connectors?

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I’m sorry for the confusion about this. Through a friend, I bought it from a guy who hadn’t used it in over 2 years. He didn’t know anything about it and said that it was a K40. The one I have is here:


On the unit itself, I don’t have a the power adjustment button nor is there a meter showing the power.

I have been using Lightburn and I was using it to control the speed and power. From my research, the ‘Max’ power is used for the majority of the time, but the ‘Min’ power is used in corners so the material doesn’t burn when the laser changes directions.


For the chart I made, I was using the power cord that goes into the entire unit, which includes the little LCD, external fan, gantry motors, and the C02 laser…. I used a clamp meter around the individual white power cord, the black and green cords were outside the clamp, I’m assuming the units are amps. But since I was measure a host of other items at the same time, I don’t think that it was a valid test. For comparison purposes, my wife’s hair dryer was 10.7 using the same clamp meter setting.

I’ll have to get my multimeter and put it just on the tube and make a chart of power setting vs tube current.

For the focal length test, originally I did the ramp test and saw where the line was the thinnest, it was somewhere around 24. To verify this, I did the lines at various heights and looked at the results. There was burning at the shorter distances and at the further distances it was more out of focus.

I’ll also take out the air assist nozzle and see if it has any effect.

Here is the front and back of the focal lens. I didn’t see any burn marks, but there are some slight scratches on the concave side.

Here is what I got when I put my multimeter inline with the tube. My multimeter wouldn’t go any higher then 50% but the lower half is pretty much a straight line.

A clamp ammeter might not be super accurate for milliamps, but also and especially AC amps isn’t the right setting for measuring DC amps. I’m pretty sure there are clamp ammeters that don’t even have a DC amp range, though mine does. I don’t expect milliamp accuracy from my clamp ammeter.

The above chart I did with a multimeter using the mA setting. I put it inline between the tube and the power supply. So I think I finally got that part correct.

Ok those readings look fine. You would not want to run higher than 50%. 15mA is the recommended limit for best tube life. It deviates from linearity at the low end because you are getting close to the ionization threshold of the tube.

So as a reference, if everything is set up correctly, you should typically be able to cut through 1/8" wood with settings of around 8mA power and 10mm/s speed.

Can you provide a picture of your mirrors? Just want to see what condition they are in.

I can only assume that I’m in the market for new mirrors. :slight_smile:
And probably a new focal lens also?
Any links on Amazon of good mirrors?

Yeah, those mirrors look toasted, may be your issue. Your lens is probably fine. Some light scratches won’t have much of an effect. For replacement mirrors and lens I would recommend Cohesion3d. The people who run it are long time members of this community and sell good products at reasonable prices.


Thanks for all of your help. I’ll update when the new mirrors get installed!


I got the new mirrors installed and realigned. They helped a little, but at around 8mA power and 10mm/s speed I can barely cut through a business card…

Below is the ramp test at 8mA power and 10mm/s speed that is .125 thick. I think it is most narrow where I drew the pencil marks, which is right around 50mm from the focus lens.

Even though the milliamps look correct, could the laser tube still be bad? Could there be an issue past where I measure it at the end of the tube?

Hmmm…if the tube is significantly degraded you usually do not get a straight line in a mA vs % power. Typically it would plateau off before you get to 15mA tube current. What do you think @donkjr? Can you provide pictures of how your machine is wired?

One other thought, when you do a test fire when doing a mirror alignment do you get a single round spot or distorted / multiple spots?

Will it punch through a business card anywhere in the optical path with a test pulse?

When I do a test pulse, I get a single dot.

When pulsing the laser, it is purple.

Yes, it will go through a business card, but it takes around 3 seconds at 99%. I did this after the second mirror.

I think the issue lies somewhere with the focal lens.

Using the focal lens, to put a hole through a business card it took several seconds longer than just putting the card inline before the lens. I flipped the lens (concave side down) and it only took about 1 second to put a hole through it.

I’m going to do some more experimenting though with the height and see if the focal length needs to be adjusted.


definitely had your lens in backwards then, they always go “bump” up or convex up, concave down. Regardless I am glad you sorted it out!

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make sure that the beam is traversing perpendicular to the table and down the middle of the opbjective lens. If the beam enters the head at an angle or off axis it can hit the side of the tube on the way down.
You can test if the beam is perpendicular to the table by taping a piece of paper to the table and pulse a dot. Then move the head up or down and pulse again. The dots should stay close to each other as you move the head up and down and fire a dot on the surface.

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