Calibrating mirrors and lenses - nortd/lasersaur GitHub Wiki

Using a red dot laser pointer

cheap 3d printed solution

http://tvslasercutter.blogspot.com/2015/01/aligning-laser-beam-in-order-to-to.html http://www.thingiverse.com/thing:639069

CO2 & red laser beam combiner

https://groups.google.com/forum/#!msg/lasersaur/e3qxp0fGYKQ/ODp2jYuSlUkJ

Manually

Even though it's possible to get the laser to exit the nozzle everywhere when the laser isn't hitting the center of the mirror...if it's not going vertically down the laser tube (ie if it's not hitting the exact center of the lens) then the laser is hitting the material at an angle and you'll get bevelled cuts...which is "A Very Bad Thing"...so what you're doing right now isn't right and won't work!!

One thing you need to know...when you first align the machine - you may have to physically move the mirrors along the T-slot track to get the POSITION of the mirror right as well as adjusting the ANGLE of the mirror with the little adjustment knobs.

Also, the first time you do it, you may find that you run out of adjustment with the knobs - so you have to physically rotate the entire mirror mount a bit.

Once the mirrors are in the right position, you can tighten them down pretty tight - I didn't need thread-lock, and you can't really use it because you need to subtly adjust the position of the mirror during alignment - which you can't do when they are thread-locked in place! If you get it all right, then take it apart to apply the thread-lock, then it'll be out of alignment again when you reassemble it! So, NO THREAD LOCK!

When you mount the mirrors into the mirror holder, be sure to push them right to the back of the mount before tightening the set screw - getting that wrong may be why you're getting misalignment when you slam the door.

When aligning, it can be hard to figure out whether the problem is due to mirror POSITION or ANGLE. Here is the routine that I figured out...it may not be fast, but you don't have to think too much!

STEP 1: Adjust the mirror ANGLE until the beam hits the exact center of the target when it's as close to the mirror as you can get it. If you run out of adjustment, then you may have to loosen the bolt and physically rotate the entire mount (or, possibly adjust the position of the target).

STEP 2: Move the target maybe 6 inches at a time away from the mirror, re-shooting the laser until you see that the beam now noticeably strays a quarter inch from that perfect center position...or until you reach the far end of the track.

STEP 3: Make small ANGLE adjustments to the mirror until the beam once again hits the exact center of the target. The further you are up the track, the smaller the adjustment you'll need.

STEP 4: Once you've made that adjustment, move the target back up close to the mirror and re-check where the beam hits it ...but DON'T adjust the angle right now!

STEP 5: IF the beam is still perfectly on-target when the target is closest to the mirror and on-target when it's further away - then go back to step #2 and move it even further down the track. Repeat until the alignment is perfect at both ends...then go to step #6.

    OTHERWISE:

    IF the beam is now off-target when the target is closest
    to the mirror that you're adjusting - yet we know that
    it's on-target when it's further away - then you need to
    adjust the POSITION of either the mirror (or possibly
    the target) to get it back to the center.  Unfortunately,
    it's impossible to reposition the mirror mount without
    messing up the angle of it to some small degree...so you
    have to go back to step #1 and do it all over again.

STEP 6: Once you get all the way to the end of the track and the beam is perfectly centered at both ends, then you should be done with that mirror and you can go onto the next one.

Now, even THAT that was an over-simplification!

This is a two dimensional problem. It's possible for the vertical positioning to be wrong in ANGLE and the horizontal to be wrong in positioning...or vice-versa! So you really need to treat the two adjustment problems independently.

When you're working through the algorithm above...you have to think about the vertical error differently from the horizontal.

When you finally have the #2 mirror hitting the X-cart mirror (#3) perfectly, try it at all four corners of the bed.

If it strays off in the front two corners and is good in the back two (or vice-versa), then you didn't quite perfectly adjust the #1 mirror as well as you thought you had...so go back and try again, making much smaller adjustments this time...then RE-DO the #2 mirror again. Neither of these things should happen if you were patient and accurate enough earlier on!

If it strays off in the right two corners and is good on the left two, then you didn't quite perfectly adjust the #2 mirror - so go back and redo that one.

If it strays off in one corner and is right in the other three...then you have "A Big Problem" because it means that your frame is twisted! That's extraordinary bad news! Get out a spirit level and check that all four sides of the frame are perfectly level. Once it's all dead perfect, then you have to go back to adjusting the #1 mirror again.

PLEASE: Don't say "meh...good enough!" at any of these stages. Persist until it's 100% perfect before moving on. Any tiny error will multiply and make life harder later on...so be incredibly patient and very, very picky!

When you are hitting the third mirror, dead center in all four corners of the bed, you're down to adjusting the third mirror, and you're adjusting to get the beam to appear through the center of the nozzle.

You can remove the lens from the tube and put masking tape over the top and adjust the #3 mirror's angle until you're hitting it dead center.

Then remove the entire lens tube and put masking tape over the hole it leaves behind and see where the laser hits that...adjusting the #3 mirror until it hits dead center.

Just like before, if you hit the top of the tube perfectly, but are off-center at the bottom - then the angle of the #3 mirror needs tweaking, but if it's perfect at the bottom and wrong at the top, then the position of the #3 mirror is wrong.

When you think it's perfect, replace the lens and lens tube and put a piece of masking tape over the end of the nozzle. You should get a tiny pin-prick of a hole right in the center of the nozzle in all four corners of the bed.

If it's not dead center, and especially if it's an oval shape or if there are two or more holes(!) then you're not done yet. An oval hole or multiple holes means that the laser is actually hitting the side of the nozzle and bouncing off the side!

When the beam exits the center of the nozzle in all four corners of the bed, you now have to focus the beam. First measure the height of the laser tube to the bed of the lasersaur (the top of the grid if you're using one) in all four corners of the bed. If the distance isn't the same (plus or minus a millimeter) - then loosen the bolts holding that corner of the black frame and lower or raise it until all four corners of the bed are the same distance from the top of the lens tube.

The distance from the underside of the lens to the center of the thickness of the material you're cutting should be about 75mm...it's hard to get it exactly right, so what I do is to make a small SVG file that cuts a 1cm square with an 8mm triangle inside it. I try cutting this on less and less laser power until it won't cut all the way through...then I turn the lens tube one turn clockwise and one turn anticlockwise and try again each way to see if either of them is an improvement. I pick the better of the two, then reduce the laser power a bit more and try again. Gradually, you're getting the focus better and better so you need less and less power to do the work.

Eventually, you'll find that you can't do any better - and then you're done!

This take HOURS the first time you do it. But take your time - and take frequent breaks for bashing your head against a brick wall (it's relaxation compared to adjusting the laser!).

You get better at it with practice - and you shouldn't have to do the entire process more than once in the life of the machine...but quite often you'll need to redo the #2 and/or #3 mirrors (eg if you have to remove one of the Y belts or swap out a mirror or if you move the lasersaur or something).

Refocussing is needed more often...we do it regularly because every time you remove the lens for cleaning (once a day when you're using the lasersaur for 8 hours at a stretch!) you tend to disturb it...so this is a weekly job...or something we do if the machine isn't cutting perfectly despite cleaning the lens and mirrors.