siliconchip.com.au Australia’s electronics magazine July 2019 73
centre of the first mirror, which was no
surprise, since it is close to the end of
the laser tube.
Proceeding to the second mirror,
we found that the beam was strik-
ing a little low. We adjusted this by
turning fine-pitched screws on the
back of the first mirror, changing its
angle to aim it towards the centre
of the second mirror. A fraction of a
turn was all that was needed to cor-
rect the aim.
Repeating with the paper on the
third mirror, we found that this was a
little low too, so a similar adjustment
was performed on the second mirror.
The alignment test is repeated with
the carriage in all four corners of the
laser cutter bed, to ensure that the re-
sults are uniform. We found only a
tiny amount of variation, so the beam
alignment was complete.
Testing
While checking the mirrors, we took
the opportunity to clean them using ac-
etone and a lint-free cloth. The cloth
was dirty afterwards, so a clean was
undoubtedly due.
The laser beam focusing is dictated
by the distance between the beam and
the bed; it should not have changed,
but we decided to check it anyway.
We performed a ‘ramp test’ by
placing a piece of acrylic on the bed,
propped up at one end so that the cut-
ting depth changes along the piece.
We ran a cut, and the results showed
that the focus was fine, as the cut was
cleanest close to the bed.
We followed by running a job, and
all seemed to be in order. By this time,
we had quite a backlog of orders for
case pieces, so we had to run the laser
cutter continuously for several hours.
Disaster strikes
While setting up for one of these
jobs, one of the hinges that holds the
lid on snapped, leaving the lid hang-
ing by the remaining hinge and the
gas struts.
The lid had been getting quite hard
to close, and appeared to have shift-
ed, but now it was impossible to close
as the gas struts were pushing the lid
against the remaining hinge, threaten-
ing to break it too.
Due to the safety interlock, the la-
ser will not operate unless the lid is
closed, so this had to be fixed before
we could continue.
Fortunately, Bunnings has an ex-
tensive range of hinges. Thus we did
not have to wait weeks to get the laser
cutter going again.
We took the broken hinge to the
closest store and compared it to the
hinges there, and found one that was
a similar size and had a similar hole
spacing at one end.
We removed the gas struts, as they
pushed the lid around awkwardly, and
in any case, it made it easier to work
on the lid by detaching it entirely from
the laser cutter.
Although the holes on the new hing-
es were in slightly different locations,by enlarging two holes on each and
drilling six new holes in the lid, we
got them to fit.
These hinges are a different style
than the old ones and don’t sit flush
when fully open. So we inserted some
spacers under them, to ensure that the
laser protection switch would engage
with the lid closed (the laser is disa-
bled when you open the lid).
The new hinges work even better
than the old hinges, with the lid not
jamming so much and we were back
up and running again less than a day
later. SCDuring calibration, a small
piece of paper was placed
over the mirror in the optical
path, to help centre the beam.Air bubbles appeared in the
outflow pipe of the laser when
the cooling system was refilled.
These went away after running
the water pump for some time.