Issues cutting through wood with K40

Hi everyone
Firstly totally new to the forum and have had a good look around before posting and all I can say is I have a lot to learn but looks like I am in the right place.

Now for my “current” issue, I have a K40 and I am trying unsuccessfully to cut though some small pieces of oak about 5mm thick but just does not seem to be working for me.

I have the speed around 15 - 30 and no matter how many passes I do it just does not cut through… I gave up at about 30 passes

Is what I am trying to do just not possible or is there something I am doing wrong?

Thanks
TK

Welcome to MakerForums!

I would expect this to be possible.

Here are a few questions to get started:

  1. Have you added air assist to your K40? Any other modifications?
  2. What cutting power are you using, and how are you measuring it?
  3. Do you have an analog ammeter?
  4. How old is the tube?
  5. How are you cooling your laser tube?
  6. Have you noticed any loss in cutting power in other jobs?
  7. What speed were you cutting at?
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  1. Have you added air assist to your K40? Any other modifications?
    I have added an air assist fan but that is the only thing I have added

  2. What cutting power are you using, and how are you measuring it?
    Cutting power I have tried between 60% - 80%, my K40 does not have the digital readout but has a know that I have marked 0% and 100% and then just guess the rest

  3. Do you have an analog ammeter?
    Yes though I did not know what it was called - i think this is usually hitting between 10 - 15 mA

  4. How old is the tube?
    Only about 4 months but run only 30 times

  5. How are you cooling your laser tube?
    Water pump using distilled water

  6. Have you noticed any loss in cutting power in other jobs?
    I have not tried cutting before trying to do this oak, was going to try it on ply tomorrow to see how that goes

  7. What speed were you cutting at?
    i have tried between 15 - 30

And thanks for the reply :slight_smile:

The machines are very sensitive to focal height, if your bed isn’t in quite the right place it will never be fine enough to cut the full 5mm. I saw a recommendation elsewhere to prop one end up slightly and cut a straight line right across, see if a particular height is working.

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I would recommend:

  • Complete optical alignment
  • Ramp test
  • Then start by cutting thin non-composite materials, even cardboard, and work your way up to the plywood and oak.
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Ok great - thanks everyone this gives me some things to try

Is the ramp test the same thing that Frank suggested?

Yes, what @Frank_Fisher said …

It’s a simple method. Lay material on the bed with one end propped up so that it is sitting at an angle to the cutting head. Like a ramp.
Etch a line(s) down the length of the material.
Look for the thinnest portion of the line.
This is the correct focal length. That is, the distance from the head that the object must be set to.
Measure the distance from the head to this point on the incline (ramp).
Make a gauge that is this length so that you can easily set the objects height from the head.

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Your travel speed is way too fast. Slow it down to 5-10.

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I’ve cut 6mm oak before and, based on your initial post, the thing that jumps out is the speed. For single pass cutting your speed will need to be around 5mm/s.

Also it is important that the bed height is set so that the focus point is halfway into the workpiece because of the beam divergence around the focal point.

I would not go above 60% on the power for any significant cutting time without a current meter to verify you aren’t exceeding 18ma on the tube. To preserve tube life it’s recommended to max at 16ma. When I still had the digital control on mine 55% gave me 16ma.

You said you are cooling with a bucket and distilled water. Are you adding frozen water bottles to cool the water?

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ok - thanks, this is making a lot more sense

No I just have the distilled water but I live in Tasmania (Australia) and at night when I use my machine is usually between 5 - 10 C (about 41 - 50 F)

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To preserve tube life it’s recommended to keep the tube under 23C while running. Lower is better but usually we recommend around 18C at the low end due to condensation issues.

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Thanks Ned - so ideally temp of the water is between 18C - 23C? It’s not a huge window but I will order a temp gauge today and do my best… i might have to add in bottles of hot water :rofl:

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You can go lower but you have to be careful of getting too much condensation on your tube. How low you can go before you get condensation will depend on your local dew point).
Of course you don’t want the water to freeze or it will crack the tube. If your machine will be exposed to freezing temps then would want to keep the pumping running continuous with an aquarium water heater in the bucket.

I use a couple of frozen 1/2L water bottles to chill my bucket. These will last me anywhere from 30-60 mins depending on how much cutting I’m doing. I actually have a stash of about 12 bottles in my freezer.

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Typically you want a thermocouple on the tube to measure the temp. Most k40s typically come with one. Another one in the bucket is also nice to have.

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Did I miss something … they come with a thermocouple?

Well…at least mine did. I think it was part of the “upgraded” k40 version with the digital control panel.

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And it was mounted on the tube?
They measure water temp on the tube??

Actually it’s taped on the water “out” tubing. Would there be an issue with it attached to the tube instead though?

I have one on my laser tube but that just monitors the tube’s outer temp. That is not sufficient to protect the tube.
I have my main water temp sensor in the bucket. I would think that if the sensor is literally attached to the water tube vs the actual water stream that there would be a delay and error as to what the actual water temp is.

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You can get 18B20s in stainless cans. I imagine one could use a T in the tubing and silicon to have the tip of the 18B20 just touching the water going through. They respond pretty fast. But I don’t know if the stainless is isolated from the 18B20 and if so to what voltage rating; I’d hate to kill a mainboard that way. :frowning: