Laser mirror and lens allignment

Hi,

I've few doubts about about the mirror alignment and laser focusing. The reason why I'm asking this is that , the edges of my cut piece are not square. After searching through lots of forums I found that if laser do not hit the exact centre of the lens, result will be beveled cuts. Some posts says that beam should hit all the mirrors at the exact centre, and some other says It should be on the centre of 3rd mirror other wise beam would be slanted.

I'm not using a factory made machine, Mine is a modified X carve and It's placed inside a home made casing.

I'm really confused about this. Should the beam strike all the mirrors at the dead centre or it doesn't matter as long as the beam strikes same spot at every position (inside mirror not exact centre). It must be important for the 3rd mirror but what about others. Most post I've read have fixed 3 rd mirror but mine is adjustable one(3 screws).

can I use the screws on 3rd mirror to make the beam strike exact centre of lens even if it doesn't strike the centre of 3rd mirror.

Thanks

Not dead centre on the two first mirrors. After all, they just forward the beam and if they do it a bit off centre - who cares? Don't get the beam at the edge or outside the mirror though.
It is not really a matter of dead centre of the third mirror. What you want is the beam in the centre of the lens. If you have a head with adjustable length the beam should be in the centre of the lens at both the shortest and the longest distance. That is what is important. Adjust the third mirror so this happens.

Edited 2 time(s). Last edit at 04/29/2016 02:54AM by falwty99.

Quote
falwty99
If you have a head with adjustable length the beam should be in the centre of the lens at the shortest and the longest distance. That is what is important. Adjust the third mirror so this happens.

My head is adjustable, and it's already at the maximum length so that it will few mm away from cutting material and I can't reduce the height since it'll affect focus (my bed is not adjustable)

How could the beam be in the centre of the lens at both the shortest and longest ditance ? It could be anywhere,and only at one place right?
also by changing the mirror can't I control where the laser beam falls? I mean by adjusting 3rd mirror could I make the beam to fall the centre of lens?

Edited 1 time(s). Last edit at 04/29/2016 03:04AM by athul.

@falwty99

In the first picture laser falls at the centre of 3rd mirror and falls at the centre of lens too.

In the second picture laser falls at the top of 3rd mirror, mirror is not adjusted and laser falls the corner of lens.

in the 3rd picture fig1 ,laser falls the top of 3rd mirror and it's adjusted so that laser falls at the centre of lens when the adjustable head is at max length and in fig b, head is adjusted so that lens is now closer to 3rd mirror and with out any new adjustment laser falls at the corner of the lens not at the centre.

Quote
falwty99
If you have a head with adjustable length the beam should be in the centre of the lens at both the shortest and the longest distance. That is what is important. Adjust the third mirror so this happens.

So how colud I adjust the mirror so that beam would be centre of lens at both max and min lenght?

Edited 1 time(s). Last edit at 04/29/2016 03:37AM by athul.

You are on the right track, absolutely. Here is what I do.
Remove the lens. Adjust to shortest length. Put a paper at then end of the now open tube. Pulse the laser.
Then do the same with the head at its longest distance. When the laser dots are in the middle of the tube in
both the upper and lower position - then its good. Put lens in, adjust focus and run the laser.
The beam is perpendicular to lens and in the middle.

Edited 2 time(s). Last edit at 04/29/2016 07:36AM by falwty99.

Quote
falwty99
You are on the right track, absolutely. Here is what I do.
Remove the lens. Adjust to shortest length. Put a paper at then end of the now open tube. Pulse the laser.
Then do the same with the head at its longest distance. When the laser dots are in the middle of the tube in
both the upper and lower position - then its good. Put lens in, adjust focus and run the laser.
The beam is perpendicular to lens and in the middle.

May be I am wrong here, but one doubt, How can the laser beam strike at the exact centre of lens at both shortest and longest distance if doesn't strike at the centre of 3rd lens.?

If the laser falls at the centre of lens at the shortest distance ( 3rd mirror in default position -no screw adjustments ) then by adjusting screws or without any adjustments on 3rd mirror I could strike laser at the exact spot (centre) when head is at the longest distance and for that to work laser should strike at the centre of 3rd mirror (by default 3rd mirror is at 45 degree, so it will deflect incident beam to 90, and I think without any adjustment laser will be perpendicular and it would strike the centre of lens at both shortest and longest distance ).

What if laser falls not at the centre of 3rd mirror, it will be deflected at 90 degree but wouldn't fall on the centre of lens (say lens at shortest distance ), and by adjusting the screws on 3rd mirror I can make it fall on the centre of lens (but deflection here will not be 90 degree ), but when I move the lens to its longest distance obviously beam would not stay at the centre , it will at some other spot. By adjusting screw even if I make the spot centre, It won't be in the same place when lens move to the shortest distance. simply I can make the laser fall at the same spot at both distances, but it won't be at the centre of the lens.

This is my conclusion,
1. For the beam to strike at the same spot (shortest and longest distance ) it should be perpendicular to bed.
2. If it strikes at the centre of 3rd mirror then beam would strike at the centre of lens at both distances.

3. If it strikes any place other that centre of 3rd mirror, the postion of beam on lens will vary accordingly, and by adjusting screw I could make it fall at the centre of lens , but only at one postion.


Correct me if I'm wrong , Please..

Edited 2 time(s). Last edit at 05/02/2016 02:20AM by athul.