by dirktheeng » Sat Oct 29, 2011 5:45 pm
There are 2 things going on here, I think.
1) the laser beam naturally cuts in a V shape with the widest part at the top.... this is unavoidable, but can be minimized to a certain extent by making sure you only put in the minimum amount of power to make the cut
2) bart is correct, no matter where the beam hits the lens (if the optics are perfect) it should make it go through the focal point. However, if it is off center it will come in at an angle.
Consider the flolowing 2 beam paths... the top one the light goes directly into the center of the lens, the second comes in off to the side
_____|_____
|
|
.
_________|_
/
/
.
Granted, this is a gross oversimplification, but you can see that this can affect the angles of your side cuts. If the system is aligned correctly, the cut angles should be the same on the +x and -x side as well as on the y's. They will never be perfectly square to the edge, but both should be at the same angle tilting into the piece. Also, x's and y's may not have the exact same angle as the end grain cuts differently than long grain.
So in the regard of making sure the ends are near to square, it is important to not use any more power than you need, to find the right focus, and to try to get that beam in the middle.
Oh also, I just thought of something else... you should take your lense out and make sure the mirror is actually directing your beam in as near of a perpendicular course as possible. I did this with my red laser when I did the primary alignment. Mine was WAY off. This will aslo affect (probably more than getting it into the center of the lense). I had to rotate the head and shim one side to get it right.