100 Watt CNC Laser Installation

spam.xls

a frog I made recently.

Made the hack-a-day logo while I was performing nail surgury.

I did burn the hell out of my self today.

remove support grate
remove lens housing, clean lens
replace lens housing

unscrew metric aperture tube
place tape over hole of english aperture tube
use prick punch to locate center
draw cross hair on tape using scalpel as a scoring tool
place triangle on side of aperture tube using blue tape
run air brush compressor
screw in aperture tube/scotch tape assembly
pulse laser
adjust beam
repeat

screw in metric aperture tube and aperture
power test:
75 watts was delivered with the aperture

I put together some web pages on

http://www.nilno.com/laser_intro/

describing the whole system. You'll notice it is mostly of regurgitation of all the pages that have collected here.

It happened.

Brought the oxygen up to 40 psi, blew a gasket in the optics, re-aligned everything, brought the oxygen back up to 40 psi, and cut a 1 inch line cleanly through 1mm thick stainless steel.

I am so grateful to everyone for their help.

Ramos, Chris, Mica, Imani, MonkeyGirl, Kevin Radloff, Mike Klos, Gilbert Haas.

Thank you all.

Alignment. Originally I thought this was going to be voodoo engineering because you cant see the beam of the laser. It turns out that its not that hard. First set up a system to mark circles or edges of your beam path with cross hairs in the center of scotch tape.




The place your targets on the beam path. If the item that gets the tape can be threaded into place it makes it easy to mount the target.




Using this system, I started with a target on the cut quality enhancer, and then moved on to the elbow that points the beam towards the floor. The elbow has allen head screws that allow you to microadjust the mirrors in the beam. This took a little while to figure out the impact of changing these screws and where the beam lands, so for a while I would take to shots on one piece of paper, and view the where the beam moved after making a change. After I got the hang of this, I went back to the targetting system to adjust the beam as best I could to be on center.




The cutting head has a nozzle on it with a port that is roughly half a millimeter in diameter. If the beam is not exactly on center, it gets reflected off the side when it comes out of the nozzle and forms a characteristic pattern that looks like this:




(picture courtesy of Romos)


Another alignment method I used to cure this problem was to remove the nozzle, and shine a short pulse on thermally sensitive paper. There are some examples of that this looks like below. Carefully adjust the beam so that it produces the same spot shape with and without the nozzle to ensure it is going directly through the port of the cutting head. Romos also recommended that acrylic works as an alternative to the thermal paper.




Height adjustment. Brother Romos created a nice picture of laser beam height adjustment. The issue is that the beam forms a waist and the most power of the laser occurs at the minimum waist diameter. The sweet spot of the beam waist can be placed in path of the beam by adjusting the height of the cutting nozzle.

To find the best height for minimum beam diameter, I used the thermally sensitive paper and looked at the beam diameter as a function of height. The markings on the card are based on 100ths of an inch are relative; they do not reflect the actual distance of the focussing lens to the paper. What you can see from this experiment is that the beam size gets smaller down to a distance of 650ths of an inch and then starts to increase in size.



I would not claim that is a good method to determine the beam diameter. I dont know if there is a way to determine what the beam size is, however, it was still interesting to look at the spot under a 100x microscope. This is a picture of my smallest possible spot on the thermal paper. The microscope was focussed on the stainless steel below the paper. You can see burnt edges around the hole. The burns are not a result of reflection as shown here, at least they dont occur like this repeatedly. It seems more like the results of a heat flare coming off of the beam.




This is a picture of the underside of the paper. I bought a microscope to look at items cut by the laser. It was cheap but it works very well. I found that it was even possible to put my camera on the opening and get pretty good pictures. The scope has a grid inside of its optics. Large lines are 100 micron apart. From this picture you can see the hole is roughly 200 micron.




This is the underside of 1/8th inch thick plywood which was cut at 10% power levels on the laser. The kerf width is roughly 200 micron as well.



I had some help this weekend. The guy on the far right is a buddy that came in from Chicago, my stepson is in the middle, and I'm on the left:



Another picture of some of us:




A video of a short pulse for the laser. I dont know the actual time length of the pulse. Its based on a microcontroller program that creates pulse lengths that increase by a factor of ten. By flipping between different lengthed pulses I was always able to find a pulse that worked well enough for my application.

This is a video of a longer length where I was hoping I would pierce the metal. Not working so far.