What is the cause for this? Help needed, problem since 5 Months now

Community Laser Talk
21

I make a shot in front position and then in far postion and then i know where i have to move the far position spot so that i alignes perfect with the close shot. For mirror 1 to mirror 2 i align it that they hit the exact same spot in near and far position on the y axis. And then i move on to calibrate mirror 2 so that i hit mirror 3 dead center in every corner of the bed.

Thats how i do it, and then i calibrate mirror 3 that the beam gets out in the middle of the nozzle. So many people in the facebook groups thought it is a focus problem but it isnt a focus problem, its the tube in my opinion. Because i aligned everything again and again and again so many times now that im sure everything is perfect aligned, you cant align it more accurate then perfect.

Just to show all the people that think my bed isnt level or im out of focus i just did a ramp test in the bad corner and the good corner. And you can see very clearly that in the good corner i get a way thiner line as in the bad one, thats because i get a way thicker dot out of the bad corner and no one could explain me why that is so far.

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22

Itā€™s an incredibly narrow point, Iā€™ve never seen such a thin one before. How many ms is that shot with?
btw, I donā€™t think there is anything wrong with the tube, as long as there are no more points or an offset circleā€¦ but on the other hand, it is not in the center according to what we can see in the photo.

23

For my understanding it is not important to hit mirror 1 dead center. It is important that you hit the same spot in the x and y axis in near and far position.

Or do i have to hit mirror 1 also in the center? I dont see a reason why i should have to hit mirror 1 perfect in center, the laser beam just has to travel parallel to the axis what i know

24

Today i aligned mirror 3 that it gets down in the middle of the nozzle, just made a circle again in the bad and good corner and the difference is just soo big i dont understand what can cause this. :face_exhaling:

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25

To the best of my knowledge, the tube should be parallel to x and level with the rest of the frame.

How big is your machine bed? On my ā€œsmallā€ machine, there is one meter from M1 in position home to furthest away, in the diametrical corner. I canā€™t remember exactly how many percent you lose in a meter, but I would think that a 100 watt tube is meant for rougher cutting jobs and you might be looking for tolerances that this machine doesnā€™t have.
Put another way, if you cut 10mm plywood, 10x10mm square in each corner of your machine bed, can the machine handle it at the same speed and power setting?

26

My bed is 50x70cm, i also did a test card 5 months ago in every corner. The machine should be able to get the same result over the whole bed and not only in one corner, because all the others i know with the same laser dont have that problem.

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27

ā€¦or they never tested it properly.

Assuming a mirror reflection of 1% for each mirror,(which is optimistic in real life) that means 99% of the light energy will be reflected on each mirror, while only 1% will be absorbed or scattered away.

For three mirrors, the total efficiency of the system will be 0.99 * 0.99 * 0.99 = 0.970299 (approximately 97.0%). This means that 3.0% of the original energy will be lost on the mirrors.

Now we need to take into account the distance that the laser beam travels. As mentioned earlier, the energy loss will depend on factors such as the wavelength of the laser light and the humidity and density of the air. For a typical CO2 laser beam with a wavelength of 10.6 micrometers, the energy loss will be around 0.15% per meter of distance in dry air. For a distance of 1300 mm, the total energy loss will be 0.15% * 1.3 m = 0.195%.

The total energy loss for the system will be the sum of the energy loss on the mirrors and the energy loss due to the distance.

Energy loss on mirrors = 3.0%
Energy loss due to distance = 0.195%
Total energy loss = 3.0% + 0.195% = 3.195%
(I have not taken the loss in the lens into account)

This means that the laser beam will lose 3.195 watts of its original power of 100 watts when it moves through three 90-degree mirrors with a mirror reflection of 1% each and a distance of 1300 mm.

28

Yes that may be, but my problem is not energy loss, my problem is that i get a total different line in one corner and the other corner. It should be able to produce the same fine line over the whole bed.

Now i cant male anything small on the left side of the bed because it looks like crap as you see in those test cards. It only looks good and with nice detail in the right front corner but i need it to be everywhere the same. Other guys with the same laser get the same fine engraving everywhere on the bed, it is just not the case here with my laser and i just wanna find out why.

29

Donā€™t take this wrong, but put yourself in our position.

Everyone tells us itā€™s aligned and focused, so we take that with a grain of saltā€¦ In actuality itā€™s usually something occurring in the alignment procedure and it is not aligned properly.

I trust you wouldnā€™t be here if you didnā€™t think youā€™ve done all you canā€¦

We are assuming that you did in fact properly align itā€¦ however, as you can tell, most seem to think itā€™s a focus issue. To have a proper focus you have to have a proper beam from the lasers source, the tube in this case.

  1. unequal burn areas (corners)
  2. performance change, need more power for same job
  3. variations in the tool line, looks like in/out of focus
  4. tool path and surrounding area varies in a small areaā€¦
    a. you can see this in your circles

All of these are symptoms of a failing tube.

Iā€™m also concerned over the size of your output beam, itā€™s smaller than Iā€™ve ever seen.

Usually the higher the power the larger the beam.

Pulled this chart off Cloud Ray for CR tubesā€¦ looks like it should be about 5mmā€¦ how big is yours?

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I try not to use the term level, what should be used is square in all three dimensions. A cnc should operate the same, mounted on the wall as on level ground. Level just is a handy tool to use, but it can be deceiving.

So to be square, the mirror also have to be square within the 3d area. If you start with m1 off center, you have to follow it down the pathā€¦ in fact m1 is the basis of the path the rest of the way so it should be centered. Donā€™t redesign it if it isnā€™tā€¦ there is some slack room, but the closer the better.

Also keep in mind that an 18mm mirror has an X axes size of around 12mm when viewed from the tube or lases beam. If itā€™s a 5mm beam then 12mm-5mm is 7mm/2 is leaving only 3.5mm each side and youā€™re off the mirrorā€¦ somewhere around half the beam widthā€¦

Being off from the start means all the following mirrors have to be off that amount from a true 3d square.

The closer to the center of the mirror, the more room you have for error or to correct anomalies.

The only mirror that probably wonā€™t be centered is m3. You have to catch the beam from m2 with the head (m3). Moving m3 along Z will move beam from left and right going down the lens tube through the lens to the work table. Itā€™s much more important to be going down the center of the tube striking the center of the lens. If it hits the lens at an angle, your cut will be slanted as a resultā€¦

This is a good explanation of how to align a laser. It probably has adjustments that are not available to you, but the theory is great. You do have to put with some British humorā€¦ :face_with_spiral_eyes:

Hang in there, Iā€™m sure we can resolve thisā€¦ Itā€™s much more difficult remotely :exploding_head:

:smiley_cat:

30

Is there anything you need to see from my alignment, i can post photos of everything so you can see my alignment if that would help. :blush:

31

I know itā€™s repetitive, but ask yourself what it takes to achieve itā€¦
same power
same focus
same speed
same material
if one of the conditions is missing, you are out of the race.

I want to do a test in the ā€œbadā€ corner, where I want to change the original focus in plus and minus 3 mm, in 0.5 mm steps. Itā€™s worth a try.

32

I already did a ramp test today in the bad corner and the good one, and in the bad corner i dont get a fine line. Here in the picture you can see it

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33

I just filmed inside mirror 1 so you can see the lense from the laser tube, it looks like there is something burned in. Maybe that is causing my problems. I cant upload videos here but here is a screenshot from the video.

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34

It is not certain that it is the cause of the problem itself, but of course that spot must not be there.
I assume you ordered some new mirrors?, itā€™s always nice to have some spare parts. A complete set should be a must :wink:
I hope that solves your problem, keep us informed.

35

You are limited to size and type of files you can upload.

If you wish to post a video, put it in something like Google drive and just post a link here to it.

Ensure you set the protection so anyone with the link can access it.

I still think the spot size is way too smallā€¦ :thinking:

Iā€™d try to wipe it offā€¦ then some solventā€¦

:smiley_cat:

36

Yeah i replaced all the mirrors with new ones.

Does anybody know if you can replace that lense? Because i cant find any information about it, and some said in comments in fb groups and youtube videos that you cant change it because the gas would be gone if you change it but i have no clue.

37

But maybe that is causing it, there is no other explanation for my problem so far, everthing else is perfect and that spot in that lense shouldnt be there so im very convinced that it has to be the reason for it.

Alread tried that, but you can wipe it away. Its a damage in the lense.

Here the video WeTransfer - Send Large Files & Share Photos Online - Up to 2GB Free

Im already in contact with Omtech Tech Support about it. If you cant replace that lense it would be little bit frustrating, that would mean i need a new tube for about 500$, i just hope omtech would send me one for free because the problem did occur after 11 months after i bought the laser but i dont know because i contacted them only a week ago and i also didnt order the laser from their webpage directly, i bought it brand new from an ebay seller.

38

Take your lens tube out and have a look at itā€¦

:smiley_cat:

39

I didnā€™t read this post properly, sorry. I thought it was the M1 that has that spot. I donā€™t know if the lens in your tube can be changed, but you can always try to clean it. In my tubes (without metal end caps) I cannot change the lens.

40

Bummerā€¦ On your OMTech?

:smiley_cat: