Mirror and beam alignment

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Joined: Sat Dec 09, 2017 4:16 pm

Mirror and beam alignment

Post by Eaglewood » Sat Dec 09, 2017 4:31 pm

OK, here is my problem, and while it is probably an easy fix, I just cant seem to get it right

I am aligning my laser beam on my mirrors.
1. I set beam to first mirror in dead center-- check
2. I set beam to second mirror in dead center while all the way in back left corner closest to first mirror--check
3. I move second mirror all the way to front and fire laser to find out location--wayyy off center. I reset mirror to put beam in center--check. I move second mirror back to left back corner-- beam is wayyy off . I reset to dead center and move it back to front-- wayy off.

I cant seem to find the happy area where the beam is dead center in both locations. What am I doing wrong???

Studio T
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Joined: Sun Dec 31, 2017 3:25 am

Re: Mirror and beam alignment

Post by Studio T » Sun Dec 31, 2017 4:36 am

Make sure your tube is nice and close to the first mirror and your tube is level and parallel to your frame. Make sure the frame is level and square. If you can’t do this make sure the machine is level. If you can’t do this make sure the thing your machine is on is level. Make sure the laser head is perpendicular to the bed. MaKe sure mirror 2 mount is parallel to your y axis and directly opposite your mirror 1 mount. Make sure the gantry is running parallel to the frame. Use a vernier calliper for this. Make sure the bed is level!

Can you see where I am going with this? ;)

Remember at rear left, mirror adjustments do nothing

( unless there is something like a 50-100mm gap between mirror 1 and 2 but i’d still follow my instructions.)

At this point It’s all down to the tube position and the mirror mount position.

At rear right mirror 1 is doing nothing. It’s all mirror 2
At front left it’s all mirror 1
At front right it’s mirror 1 and 2.

If you go around adjusting the mirrors at these positions repeating you should get it. In my experience what they say to do (and you are doing) isn’t enough.

I’d recommend you put your mirrors in the zero position before adjusting. Measure the thickness of the pivot point and adjust the mirrors so the points furthest away from the pivot points are the same measurement. You can use a vernier calliper for this. I usually try to make the dot hit the centre by moving the mirror mount before I even adjust the mirrors. You may need to adjust the z position of the laser head on the gantry if at rear left you can’t get it hitting the centre of the laser head aperture.

When you have done your initial calibration check the difference in spot location between rear right and front right where it hits the final mirror aperture on the laser head. I bet there is a difference. What people don’t tell you is aligning these mirrors once is not enough. You need to go back to the start and repeat the whole process about 4 times getting more and more accurate each time.

When there is barely any difference between rear right and front right adjust the third mirror. You will not get it perfect on a large bed but it’s possible to get it within 3mm circle; think of bullet holes within a 3mm bullseye.

When you get the dot coming out of the laser head at front right move it to rear right and try it. Move it back and for finding a happy medium. Try it in the middle of the bed and the other corners.

It is a black art, it will drive you crazy but it’s like tuning by ear, eventually it will be ok. One more thing, if you have lots of trouble make sure the rods/rails are straight. One tiny kink that is 0.5 of a degree out at one end can be 5 degrees at the other.

Have fun!

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Joined: Sun Jan 07, 2018 8:52 am

Re: Mirror and beam alignment

Post by Cosmo888 » Fri Jan 19, 2018 5:41 am

I have a Chinese 50W machine that blew a tube, in the process of replacing the tube it blew the laser power supply (don't think these issues are related).


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