On Friday 13 April 2007, Abby Katt wrote:
I have one of these laser-center finders - best money I spent in a
long time.
So it struck me too. Having more time than $$$ I just thought I would
see what could happen with trying to make one myself.
They're more than just a laser-pointer (which produces a massive
dot),
Yes, they do, I've done much putzing around with pinhole "lenses" of
various sizes and while they help, they still seem to produce a
huge "dot", well more of an inconsistent sorta kinda blob / smear.
Some of the laser pointers produce a better "dot" than others, but none
I have tried so far (around 5 now) have a seriously good dot.
I'm not complaining about the laser pointers not being perfect, I knew
that going in but it would certainly be nice if this did work out.
One of the problems seems to be getting the pinhole aligned, it looks
like it should be easy and the pinhole arrangement itself should help
(it DOES help), but it isn't working to my satisfaction (yet?).
I'm wondering if the circle I can get easily would do? Alignment is an
issue even with 4 equally spaced set screws around the top and
bottom(ish) of the holder. I've spent a lot of time aligning the
device and I can get it *really* close to concentric at a given
distance but it turns into a circle of light much above and below that.
I'm not sure why, but I suspect alignment issues between the unit
itself and the pinhole "lens". The laser emitter on these cheap(!! :-)
laser pointers is a rectangular SMT device and I would be willing to
bet that these are not exceptionally high quality, possibly emitting
more to the sides than the center. Seems that there are a number of
elements to be aligned: laser diode itself, built in collimating lens
and the pinhole lens.
Short of more sophisticated machining than what I have, once the
batteries go west, you start all over again with the alignment
process :-/.
instead they have a *teensy* little hole at the bottom
through which the laser diffuses. The result is a very, very, small
dot (about 0.1mm or less) - this is usually accurate enough to get
you to close within half of this, as you guage the intensity of the
beam as you jog over the edge of the work. Have a black marker handy
and mark the metal first and the dot is reflected less, and thus
appears much smaller.
That helps here too. I was using a piece of the black 600 grit wet and
dry stuff grit side up for that, for initial alignment stuff, it really
helps. Dykum and just a black marker help a lot too, as you noticed,
just don't cover up the scribed lines :-).
A contact tool may be better for milling, particularly CNC-milling,
as unlike the laser the width of the tool is known - and you could
hook the contact sensor to your CNC system, so the computer can
actually hunt for the edges and set coordinates for you.
But, for a lot of tasks, the laser is more than accurate enough, its
certainly very painless.
From what the one that inspired me site has to say, a couple people
using it were able to consistently(?) get a repeatability of 0.0004.
Not scientific by any means, but that would be more than good enough
for a lot of what I do.
And, the laser makes easy something which is not possible with a
touch-probe: setting the center cutting height of your lathe cutting
tool. Just pop the laser in the head/tailstock and align to the beam.
I really do wonder why I fussed around with that sort of thing for so
long before.. :)
Understand that :-)! I'm sure this is doable and probably even usable
as it sits but there is something there that I haven't nailed down yet
that would simplify this far more than what I am doing now.
While this has been fun, if I was getting minimum wage (less gov
bloodsucking) I would still have been ahead just purchasing one :-).
Still it has been educational and provided for some serious thought in
the matter which is always rewarding if not necessarily successful :).
Someone asked which one, I have found two of them so far, leaning more
toward the first if I decide to just purchase one:
(LMS has these).
Take care, Vikki (Still scratching head).
--
Victoria Welch, WV9K/7
"In these modern times, many men are wounded for not having weapons or
knowledge of their use." -- Achille Marozzo, 1536
