Head scratcher - alignment issue?

[Chuck Stone]

I had to pull the tube again to replace resistors. No biggie, I'm getting to
be a pro at that. I thought I had aligned everything afterwards, but I'm
noticing that the engraving is much lighter at the top of the table as
compared to the bottom. The first 6 inches or so are very light.
I re-aligned and still have the problem. Ran some tests to confirm.

Then I noticed that I'm getting a stray reflection coming off of the last
mirror (in the lens housing) that I can't figure out. After about 5-5 inches
of travel along the X axis, the red dot starts reflecting back toward the
3rd mirror and hits one of the belt clamps. I can see it because I replaced
one of the clamps with one I made, and it's a lighter color. This may have
been happening for a while, but not seen on the black clamp.

I'm assuming that since the red dot and laser beam line up, that the beam
is probably going back and hitting the clamp, too. (could that be why the
last one failed?)

But bow does the light bounce back off of a mirror aimed 45° away? I've
checked the mirror for cracks, nothing I can see even under strong light
and magnification. I wondered if a crack in the lens might reflect back
into the mirror, but don't see a problem there either.

I'm scratching my head here.. figured the gurus of SMC might have an idea..

[Doug Griffith]

Scratching my head with you. Does the design of the head allow you to rotate the mirror 90 or 180 degrees? You might want to try it to see if this still happens.

[Chuck Stone]

Hi Doug.. it will let me rotate the mirror (which I've done) and still keep the same alignment.
I understand a mirror reflecting back 180°, but not not off of a 45° angle.. not unless it was
a beam splitter. (which this ain't!)

[Doug Griffith]

Sounds like it's acting like an infinity mirror. A small amount of light bouncing back through the lens. The "observer" being the bracket. Just a guess.

http://prettyawfulthings.files.wordpress.com/2013/10/fq0toizhkvljxm2-large.jpg

[Chuck Stone]

Yeah.. that makes sense. I'm starting to wonder if there's a crack somewhere inside
the last mirror that I can't see. I have a couple of old hard drives, going to try and
cut one of the plates for a mirror and see if that changes anything.
now.. where did I put my coring bits?

[Chris DeGerolamo]

keep us posted if'uns you figure it out.

[Kev Williams]

My guess is the beam is heading towards the lens at a bad angle, and is ending up near the side of the lens barrel-- if you have a metal sleeve that's holding the lens in place like I have, the beam could reflect off the flat metal edge of the sleeve, straight back to the mirror. This alignment wouldn't work well for engraving either!

288285

[Chuck Stone]

Kev.. I was hoping I had done something dumb like that (still a possibility)
but the beam SEEMS to be centered. Looks like it hits the center of the lens.
But it *is* reflecting back off of the lens, not the mirror. Good call!

Alignment may not be as good as I thought. Now that it is getting darker, I
see a secondary red dot about 3/4" to the 6:00 position of the bright red dot.
When I move the carriage forward, it moves to about 1/2" to the 8:00 position
of the red dot. I hate trying to align alone..

[Dave Gabry]

Any chance the reflection is off the white base plate under the lens rather than from the lens itself?
Dave

[Chuck Stone]

Well..there's no base plate under my lens, so it was coming off the glass. But it's all
about the same thing.. it was alignment. It still isn't perfect, but I might need to wait
till I have another body here. My knees are killing me and parts of the alignment go
better with a second person to act as your eyes and handle the keyboard.
But I just cut a sheet of 21 parts with 6 tiny little cutouts in each one. Usually I have
to go back and poke them out with something sharp, sometimes re-cut lines with
an x-acto. But this time I lifted the parts out and all 126 little cutouts were sitting
on the table in neat little rows...
(sigh) life is good..

[Chuck Stone]

so nice to send a sheet to be cut, pick up your parts and all the little
pieces stay behind. I havent' seen that in ages.