Laser mirror alignment and lens focusing

[athul]

Hi,

I've a few doubts about laser mirror alignment and been to few forums but couldn't get much help.
While aligning laser is it necessary to strike laser at the centre of all mirrors?

Some people told me it's necessary for 3rd mirror(laser head), but all they have is a fixed mirror. Mine is a adjustable one(3 screws) also my nozzle head(laser head) is adjustable(I can increase or decrease distance from 3rd mirror to lens by around 10 cm).

1. But is it really necessary to strike laser at the centre of 3rd mirror?

2. Even if doesn't strike the centre of 3rd mirror , can I make strike the centre of lens by adjusting 3rd mirror(by adjusting screws)?

3. One guy in reprap forum told me that I could hit the centre of lens at both shortest and longest distance of laser head( even if it doesn't reflected from the centre of 3rd mirror. I just want to know is that possible??Laser mirror and lens allignment

This is what i'm thinking,
Suppose laser is hitting the top of 3rd mirror at 45 degree so it will be reflected to the same angle but wont strike the centre of lens but corner. For a fixed length of laser head by adjusting screws on 3rd mirror (my all mirrors are adjustable ) let's say I could make it fall at the centre of lens. but if I change the head length laser will shift from centre of lens(???). So How could I strike the centre of lens at all position of laser head when beam doesn't reflected from the centre of 3rd mirror??
I can make it fall at the same spot at every position but not centre?
Also what would happen if beam enters the lens at an angle, would it still be focused to focal point?

Please help me and correct me if I'm wrong

Thanks



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[Downunder35m]

One of the worst problems you encounter with misaligned mirrors is inconsitent cutting power and wrong cutting angles.
1. Yes, as you want the laser beam to go down exactly 90° and into the center of the lens.
2. Yes and no. You want the beam to stay in the same spot on the first and second mirror when you move the axis from mim to max.
The 3. mirror can be out of alignment if the other two are fine, in this case you adjust the mount of the mirror/head to get the beam center.
In any case you don't want the beam to wander on the 3rd mirror.
3. No problem at all hitting the lens alsways dead center if all mirrors are aligned properly.

Good results come from good hardware, even cheap hardware can be aligned properly if you take the time to do so.
The reward is that you have even focus and power wherever your head is working.

[athul]

@Downunder35m Thanks for the reply

Yes, as you want the laser beam to go down exactly 90° and into the center of the lens.

Are you saying if laser doesn't hit the centre of 3rd mirror it won't fall at the centre of lens?? In that case can I use the alignment screws on the 3rd mirror to make the beam centre of the lens? But if I do that won't the spot shift as the laser head moves up and down (please see the picture = Here assumes that laser hits the top of mirror-3 instead of centre and mirror-3 is adjusted to make if reflect the centre of lens but as the lens moves closer laser shifts from centre)????

Yes and no. You want the beam to stay in the same spot on the first and second mirror when you move the axis from mim to max.

yes and NO?? Can you explain both

The 3. mirror can be out of alignment if the other two are fine, in this case you adjust the mount of the mirror/head to get the beam center.

How come laser will hit the centre of lens if 3rd mirror is miss-aligned.?

By mount of mirror or head are you referring to three adjustment screws on the top of 3rd mirror or the entire head assembly

In any case you don't want the beam to wander on the 3rd mirror

Can you please explain this too????

[Downunder35m]

There isn't really much to explain if you check Google for optics and how light is reflected.
But just to be clear:
Light is reflected in the same angle it hits a mirror, so you can use paper and simple line art to illustrate "what if?".
Is it quite obvious that seemingly it does not matter where exactly the first two mirrors are hit as long as the beam goes straight from the last mirror into the center of the lens.
But if you consider a few ° of angle difference then this can quickly add up!
The more difference you accumulate until you reach the lens the harder it will be to get the beam in a true 90° angle onto the lens.
To make it fully "visible":
Image your laser beam will hit the lens, somehow and that it wanders a bit over the mirrors...
You make a cut with fixed settings in the top corner of your machine and it goes all the way through in one pass - doing the same in the opposite corner can mean you need 3 or more passes.
If you need to cut a true circle with wandering beams you will create an ellipse but not a circle - you can check this with a thigh kerf by simply turning the cut out disc by 90 or 180° and trying to get it back into the hole.

In case you still struggle to get the point then grab a cheap laser pointer and some mirrors.
Put pointer in a fixed position and see what happens if you slightly change the angles of the mirrors.
Keep in mind that the change in reflection will be much bigger in a system where the mirrors move.

[consurelaser]

Hi friend,

Here is our complete user video for co2 laser engraving cutting machine. You can check laser path adjustment.



Hope that can help you.

Regards
Lucy
Consure Laser

[Downunder35m]

Why is it that basically every thread is sooner or later hijacked to advertise chinese machines?