On Wed, 20 Aug 2003 18:52:33 -0400, Mike Graham
wrote:

In article m, Ron Coffey wrote:

Take a laser and mount it on the head and after getting it swept in to
perfection turne on the laser and have it pointing to a distant wall in your
shop and made a mark where the point landed. I'm sure the farther the wall
is the more acurate this idea would be.
Crazy enough it might just work.

That is a *wonderful* idea! Just make sure the laser pointer is mounted
really solidly.


One stage further - mount a cheap laser pointer solidly on the
target wall and permanently fix a very small mirror on the mill head
with the mirror aimed to return the laser beam to a target on the wall
close to the laser.

The mirror reflection doubles the angular sensitivity of the
setup and putting the laser on the wall keeps it safely clear of suds
and oil.
Jim


Postscript - for the experimentally minded

If a long throw is inconvenient use both a moving mirror AND a fixed
mirror and set it up so that the beam zig zags between them. Each
reflection doubles the sensitivity so you don't need many reflections.
If you choose an even number of reflections the target finishes up on
the mill head which is a lot more convenient than 8 or 10 feet away.

The quality of the mirrors can affect spot size. With one or two
reflections ordinary vanity mirrors are usually good enough although
you may have to check one or two to select a good one. First surface
optical quality mirrors are not too easy to come by but a pretty
acceptable substitute is a platter rescued from a scrap computer hard
disk. These are amazingly flat and the reflectivity is high enough for
this use. The snag is that it is extremely difficult to cut these to
size without destroying the flatness. A reasonable compromise is to
use a full size platter as the fixed mirror and a selected cut down
vanity mirror on the wheelhead.

The quality of the spot produced by laser pointers is pretty
variable and it pays to check over half a dozen or so to select the
one that produces the best defined long range spot. In this sort of
usage it is the quality of both the laser chip and the built in
collimating lens that determines the long range spot size. Pinholes
will not help.

Most pointers use 3 silver oxide button cells and consume these
at a voracious rate. It pays to replace these by a dummy battery and
run wires to external power. Three AA alkalines are equivalent to 15
sets of AG13 button cells and a lot cheaper. Lasers are pretty fussy
on supply voltage so it's better to avoid rechargeables - three x 1.25
volts is not really enough and four x is too much.

Jim