I have both oxygen and nitrogen on hand and I tried 'em both.Originally Posted by CNCadmin
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Owen,
2mm distance between metal sheet and nozzle is ok.
Try with 3 bar oxygen pressure.
Adjust the distance between nozzle and focusing spot (not nozzle and metal) at 3mm. (look the attachment)
In the picture you can see 3 cases.
Case 1...the focusing spot is under the metal. (wrong case)
Case 2...the focusing spot is above the metal. (wrong case)
Case 3...focusing spot is in the metal. (correct)
Romos,
I think I have it at the right distance. In the picture I have attached, it shows a test wher I used thermal sensitive paper at different lengths away from the nozzle. The numbers that I wrote are based on an adjusting system on the side of the cutting head and are in 1/100ths of an inch. (They dont just really reflect the actual distance from the lens to the part, just how much the head is moved from a relative position of zero).
What the paper shows is very similar to your picture where first I started a little bit too far away from the paper, and moved in closer, and then around 625 it was too close. It looks like from this experiment that the best distance was around 650-700, which is what I used.
Still no cut, which is frustrating, but I will also try changing the beam width going into the focusing lens, and a different lens with a focal length of 3.75 inch. I forget right now what the beam size is when it goes into the lens but I think its larger than yours, which might be part of the problem.
owen
Owen,
Are you sure that your beam is centered?
If not, a part of the beam will reflect in the nozzle creating a secondary beam.
You can see it if you make short shootings on a clear acrylic.
It will look like the pattern in the picture.
Romos,
Where are you getting all these great pictures? They are very good, do you make them? These pictures will make some very good documentation.
I did alignment by making targets out of tape, as shown in my attached picture. I used these to center the beam as much as possible. Then I removed the nozzle of my cutting head and shot the beam at thermal paper. Then I would compare that result to the beam shot at thermal paper with the nozzle on the cutting head. At first I was getting results that look exactly like your picture, but after more alignment I was able to get a nice beam point when I run it with the nozzle of the cutting head on, and when it was off.
Owen,
I make the pictures.
What was the thickness of the metal?
What was oxygen pressure?
What was the cutting speed?
In most of my tests the metal is 1mm stainless steel, I also tried 1.5mm carbon steel. I dont know the pressure of the oxygen because the regulator set to be fairly low. Does the pressure make a lot of difference? When I can make my next set of tests I will try increasing the pressure. In most cases the cutting speed was zero inches per minute, because I was just trying to see if I could pierce the metal first. I did try moving the sheet metal just to see what would happen, it was at a rate of 25 inches per minute.
the pictures are great and if you like I think we should eventually make some documentation to help the next person that is doing alignment.
owen
<< Does the pressure make a lot of difference? >>
SURE Try with 2-4 bar.
By moving the sheet with your hand, you don't have stable speed.
One other question.
What was the frequency and duty cycle?
I didnt move it at all, the metal was stationary.
The frequency I am not sure about, I will have to test that on an oscilloscope. The duty cycle was at the maximum for the G100, which is 65%.
I will test the laser at increased oxygen pressures.
Additional information. This is a video of a short pulse that was used
to make the tests:
http://www.nilno.com/laser_dir/align...ulse_video.avi
This is a longer length
http://www.nilno.com/laser_dir/alignment/test1.avi
This is the result of the tests when the laser was just pulsed for a
short time on thermal sensitive paper. The laser distance was changed
from 900/100ths to 625/100ths of an inch:
http://www.nilno.com/laser_dir/alignment/pulse_card.jpg
This is a picture of looking at the paper that was pulsed under a microscope:
http://www.nilno.com/laser_dir/alignment/650_hole3.jpg
This is the same paper on the reverse side:
http://www.nilno.com/laser_dir/alignment/650_hole2.jpg
This was a test cut at when the laser was set at ten watts. What is
nice about this is by using the markings inside of the microscope you
can see the width of the cut is 200 micron:
http://www.nilno.com/laser_dir/alignment/plywood1.jpg
owen
watching and listening the test1.avi everything looks OK.
I listen frequency 1-2 Khz.
I thing that the problem is the oxygen pressure.
I mostly work with pounds per square inch (psi) when measuring pressure. I was very surprized to see that 3 bar = 43.5 psi -- I had no idea that pressure had to be that high. I would guess that I was operating at less than 5 psi. I will try a higher pressure when I get home.
this must mean that you use up the tank of oxygen rather quickly.
owen
I cut with 2-3 bar.
Don't try more than 4 bar. There is a possibility to break the lens.
It happened.
I 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.
Romos, thank you for all your help
Owen,
Welcome to the club
Romos
Thanks!
so the first thing this laser is going to do is start contributing to its construction. I need to make some housings for the power supply to make that more safer. I think I will use plastic sheet. I think I have heard that plexiglas should not be cut on a laser, do you know what specific brand is okay to cut? (I will probably also look on the synrad site that has a lot of documentation).
Check this link for varius materials for laser cutting.
http://www.franeklaser.com/laser-cut...plications.htm
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