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Laser calibration

Fireman

First of all, I have to deal with fire !

Well, Whatever parameters I was using the laser cutter always wanted to burn things to hell. I tryed for hours to figure out what’s mistake I was doing… I remember that We moved the laser cutter from a building to another a few weeks ago. So I checked the whole installation…

  • Particle filter was OK
  • Water cooling was OK
  • Lens was OK
  • Mirrors was OK
  • Air compressor was’nt !

There is a small air compressor behind the laser cutter which wasn’t neither powered nor pluged into the Air duct. This problem cause flame because no air was comming frome the laser head. Immediatly after fixing that, The laser cutter works way better !

Some of the following pictures may have suffered the flame problem, but it is fixed now.

Focus lenght

To characterize the laser cutter, I first decided to check the focus. The focus is the ideal distance between the final converging lens and the material. Too high or too low and the laser isn’t focused enough and the less energy you have on the material. The more energy you concentrate on the material, the more easily it will burn.

To set the focus, I place a piece of wood diagonaly into the laser cutter. Then I placed the laser head on the most left, just a few millimeters above the material. This way :

Then I draw a straight line on my laser control software (Lasercut) and started the machine. Ass you can see, the line is cleaner on the left, and very large on the left.

I mesured the distance between the material and the laser head using a caliper. The ideal focus distance is 8mm (+-1mm without big changes)

I drew a little mark on our focus calibration piece to remember the ideal focus :

Kerf calculation

To calculate the kerf, I look for inspiration on the net. I found this tutorial which was very useful. To caculate the kerf, the guy cut a series of tangent rectangle. Then he push all the rectangle to the left and mesure the remaining gap.

Here is what I did.

Finally the gap was about 5mm wide.

kerf = \frac{4 mm }{20} = 0.2 mm

Power/Speed characterization

I tried to cut one of my parametric piece just after calculating the kerf. As expected it didn’t went trough the material.

To characterize power and speed of the laser, I creater a bunch of square on inkskape. Using the laser control software I set a different parameter for each square. The top left square was set to power 40% and speed 5 mm/sec. Then I decreased the power used on adjacent square. Finnaly, on the plate, power decrease on the horizontal axis and speed increase with the vertical axis :

Parametric kit

Fusion 360

For my parametric design, I started by creating a parametric polygon using fusion. I drew this sketch on Fusion 360 :

This sketch is very simple, I used the circular pattern function of fusion 360 to copy un side of my polygon. In the parameters I created a new input named edgeCount. The problem I had was to find a formula to calculate the length of the edge. Which is of course dependent of the edgCount. I used this formula to do so :

Apothem = \frac{ c }{2 * tan(\pi / n)}

Where

  • n : Edge count
  • c : edge lentgh

I was using a radius instead of the edge length to draw my polygon so I had to adapt the formula. By reversing the formula I got :

c = 2 . r . cos(\frac{\pi}{n}) . tan(\frac{\pi}{n}

Where

  • n : Edge count
  • c : edge lentgh
  • r : polygon radius

Here is my final sketch

The formula I used for the apothem :

The set of parameters I used:

The part is mostly finished. I just extrude it and add some filet to the edge. Here is the final render :

I mesure the wood planks thickness and the kerf and updated my parameters. I used this formula to calculate the gap where part attach together :

Gap = thickness - (2.kerf)

Here is a cutted view of

I then exported the sketch as a DXF. I convert it using inkskape to DXF Autocad R14 format to be able ton open the file with our laser control software. Then I Lasercutted a bunch of them :

Result

I decided to try another material which I never experienced, foamboard. Foamboard is a type of cardboard composed of to sheets of paper separed by plastic foam.

This material is very light but strong enough th fly a little plane for example. I had to find the corect power and speed parameters to cut it. Unfortunately my past methods didn’t worked. this material is very easy to cut. But there is two problem. Firstly, it burn easily. (Keep water near you) But the foam is also melting away. Giving this strange cut :

After a few try I sucessfuly cutted the material without melting too much foam. I used these parameters : Speed 65mm/s, Power 50%, Corner power 25%

Here is what I got :

The paramters were very good, the board wasn’t burning at all, The foam doesn’t smell very good but our filter does a very good job managing the smoke and particles. (It smell like burn paper)

I decided to cut a bunch of them :

Here is how it looks when assembled :

Files Download

Here is my files : - Fusion project : Link

  • Triangle DXF : Link
  • Square DXF : Link
  • Pentagone DXF : Link
  • Hexagone DXF : Link
  • Heptagone DXF : Link
  • Octogone DXF : Link

Last update: September 23, 2021