Noob : Laser is bad cutter

Hello all, I calibrate mirrors, moved the frame (which was not in line) on Y axis, I replaced the bed, and made one on my own (with glued and screwed aluminium angles), for a heigth of 85mm.
With the stock machine, I have cutted 3mm mdf wood in 2 passes (I didn’t wrote down the config speed, and percent power).
Since my setup, I took more than 20 passes to cut the same.
Speed is 70mm/s, power is 85%.
My K40 is not with AMP, but 100 digits.
Please, help me :wink:

Does someone know this machine K40 ?
Can someone help me ? :wink:

Are you saying:

  • That your machine no longer cuts 3mm ply in two passes?
  • It now takes 20 passes to do what used to take 2?
  • You do not have an analog meter rather a digital one.

Usually these type of problems are caused by:

  • Mirror misalignment
  • Bad laser power supply
  • Bad tube

Describe what have you done to try and isolate the problem so we can proceed with helping your from that point.

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Also 70 mm/s is too fast for cutting 3mm stock. Cutting speeds are typically closer to 10 mm/s.


The first time I tried cutting 3mm ply took me 2 passes, and was fine.
I tried to realign the mirrors and messed it up.
So now, I think it could take more than 20 passes to cut 3mm ply, but I gave up at 18…

I’ll try to align mirrors again this week-end
Do you know where I could find a tutorial for that ?

I hope my laser tube is OK, and power supply, I don’t know.

and, sorry, I don’t have other meter than digital. Do I have to buy an analogic one ?

thanks anyway :wink:

Thank you for this info.
Problem is at that speed, wood is on fire.

Maybe a problem with the focal point ?

I’ll try this week_end lower speed. Could you give me a percentage idea for that ?
I don’t have other power gauge than percentage, as you see on the picture :frowning:
Thanks anyway for your help

I’m guessing you do not have an air assist? An air assist will keep the wood from flaming up.

For cutting the focus point should be halfway into the piece being cut which gives you the best cut profile.

For most tubes the max operating power is about 18mA. Typically you operate at a max of about 15mA for best tube life. The problem with the percentage power settings is that they can be variable for percentage relative to current. For my machine, before I converted to a permanent amp meter and variable resistor, 70% gave me about 18mA. At 10mm/s a typical power might be around 9mA which for me would have called for 30-35% power. A good mod to make to your machine would be to convert to analog power vs the digital controller. Knowing amps is better than simply have a digital controller.

Replacing the Digital Panel with an Analog one

You can also temporarily install a digital multimeter to read the mA as a function of percentage to have a better understanding of the relationship.

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In addition to what others have posted I would do a ramp test to determine that your material is at the proper focal distance. Its as easy as propping a piece of wood at an angle and burning a line across it. The thinnest/smallest part is your focal distance, measure this and use that to set your material height. I would make a gauge block of the right size to do a “quick check” when you put material in, its what i do with mine. Other than that mirror alignment is crucial to getting the power to the material, as is clean mirrors. Make sure your focus lens is installed properly(bump or curved side up) and that your water is between 15-20°C for optimal performance.
also BEWARE!!! The digital power panels are notoriously known for over-driving the tubes, and no two seem to be the same scale. Your best method would be to install a mA meter between the tube return line and the laser PSU(NOT the red wire! the one nearest the first mirror is the one you want).
As linked by @Nedman above check those links, along with more info on @donkjr His blog is very thorough and well documented.


Thank you, I thought I would have to check the focal point. I’ll do it this week-end.
Mirrors alignment was so frustrating (If you know a tutorial on youtube, I take !)… I cleaned the mirrors, but I believe the alignment is not efficient enough.
So many problems to solve :frowning:
Well, I am really glad to see a community around this machine which is so reactive. You’re great, guys.

Well I have to:

  • realign mirrors,
  • clean mirrors
  • test the focal point
  • try to
  • prepare to make a new bed (motorized)
  • replace digital panel with an analog one
  • make a air assist

Well. It’s time to work !!

I really thank you all for your kindness


This mirror adjustment guide is not for a K40 specifically, but it’s very thorough and helped me during my build of the Fabool. Most of the adjustment stuff should be the same for your mirror mounts.

One thing I would recommend that this guide doesn’t mention: use tape to center the beam on the mirror mounts WITHOUT the mirror actually in them. There’s no need to have nasty smoke (and potential tape fires) getting the mirror dirty.

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Or alternately put the tape on a thin piece of metal or aluminum foil so it doesn’t burn through and foul the lens. putting the mirror back in after adjusting can throw things off in my opinion.

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Here are some alignment guides.

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