Category: Machine Shop

With Mirror 1 and Mirror 2 aligned, the next step is positioning the laser head to put the beamline at the center of both the aperture and Mirror 3 inside:

Raising the laser tube by 5 mm put the head’s Z axis screws in the middle of their slots. This had the additional benefit of letting me rotate the head slightly around the X axis to make it perpendicular with the bed, thus fixing its mysterious from-the-factory misalignment.

Centering the beamline horizontally required a few iterations of Mirror 2’s position along the Y axis, but eventually produced this result:

Those are five manual pulses with the head at the corners and center of the platform. I put the 3M target on the mirror rotated 90° from the proper orientation with the stretched scale aligned vertically and parallel to the slightly oval beam mark.

The F target shows the beam position inside the head just above the focus lens:

The little target in the middle gets centered on the nozzle by feel and shows the beam position within a 2 mm circle. The initial position was off against the side of the nozzle, but slight twiddling of the Mirror 3 screws centered it.

I centered the lower F target at the beam position using the red dot aiming pointer, then pulsed the laser to put a pinhole almost exactly at the graticule center. The larger scorch shows the beam size with the platform lowered 10 mm from the focus level. The Z axis leadscrews are not particularly precise and the platform moves by about a millimeter in X and Y as they rotate, so that’s about as good as it gets.

After all that, the laser behaves at least as well as it ever did and I feel better about having the beamline actually travel along the center of the optical path.

Now, back to cutting out interesting shapes …

With Mirror 1 moved 10 mm to the right (as seen from the front of the cabinet), Mirror 2 must move 5 mm to fix the problem that started this whole thing and put the beam in the center of the mirror:

This puts the bracket holding Mirror 2 closer to the center of its x axis adjustment range:

Remember, the flange is fixed to the gantry and the bolts move with the mirror mounting bracket.

Raising the laser tube by 5 mm requires Mirror 2 to go upward by a bit to put the beam at the center:

The least awful way to make simultaneous X and Z axis adjustments seems to be by feel. Tighten the screws just enough to prevent the bracket from moving easily, then slide it while aligning the top edge with respect to the flange on the gantry.

When it feels about right, stick a target to the aperture, fire a pulse, check the results, and iterate until it is actually right.

The two screws holding the mirror mount to the bracket sit in slots allowing some adjustment in the Y axis, as well as a slight amount of rotation. AFAICT, the mount was rotated enough that the test pulses passed through the center of the aperture, but hit the mirror off-center as shown in the top picture. I aligned the aperture parallel with gantry, which should put the holder at 45° to the beamline, and hoped for the best.

With the pulse mostly centered, twiddle Mirror 1’s alignment to make the beam parallel to the Y axis, which eventually produced these results, with each target getting a pulse at each end of the Y axis travel:

Not perfect, but much better than where it started.

Raising the laser tube 5 mm required nothing more than cutting and inserting 5 mm spacers and finding slightly longer M4 screws:

I used an ancient adjustable inside caliper to put the tube the same distance from and aligned parallel to the partition.

Sliding the tube an inch to the left provided enough space to drill & tap two new holes for the Mirror 1 mount to move the beamline 10 mm along the X axis:

I briefly considered crunching rivnuts in there, but the mirror mount expects to sit flat on the floor with no room for rivnuts. So it goes.

Although Mirror 1’s mount has some vertical adjustment, the central stem was already close to its maximum extension, so I cut a 5 mm plywood pad to raise the base:

Despite what the lighting suggests, it’s concave. The image was clean and contrasty enough to just trace into vectors with LightBurn, then Fire The Laser to cut the spacer:

If you’re wondering how that worked with the tube jacked up, Mirror 1 sitting on the scanner, and the beamline in disarray, there’s considerable benefit in doing things out of the obvious narrative sequence.

Reassemble the mirror, square the entrance aperture to the partition, fire a couple of test shots to center the mirror on the beamline:

And that part’s done.

Although the most recent mirror alignment exercise put the laser beam parallel to the axes and centered in the aperture perpendicular to the beam, a target directly on Mirror 2 showed the beam was badly off-center:

Because that target is sitting flat on the mirror, the beam appears wider than it is tall. The horizontal graticule divisions are 1.4 mm apart to allow direct measurements: the spot is really circular and 3 mm in diameter.

Poking around inside the cabinet reminded me that all of the mirrors sat with their adjustments jammed at one end of their range, rather than being more-or-less centered.

Mirror 2, in particular, was up against all three limits. The slots behind these two screws allow the mount to slide along the X axis:

Seen from the front of the cabinet, those same two screws set the mirror position in the Z axis:

As you may imagine, using those two screws to secure the mirror at a specific location in both X and Z at the same time is … challenging.

The two screws directly under the mirror set its position along the Y axis and allow a slight rotation around Z to fine-tune the alignment of the perpendicular aperture used for mirror alignment; unlike the other two axes, the mirror wasn’t jammed against the end of the slots.

Moving the laser beam horizontally toward the center of Mirror 2 requires one or more of:

• Moving Mirror 2 farther away from the center of the cabinet, but it is already at that end of the X axis slots above
• Moving the laser tube toward the back of the cabinet, which also requires moving Mirror 1, which is almost at the end of its adjustment range.
• Moving Mirror 1 closer to the laser tube, which its adjustment slots do not permit

Mirror 1 sits on a pedestal with a slotted base allowing adjustments along the Y axis:

The pedestal could move a few millimeters to the rear, but the screw on the far side is even closer to its limit.

Moving the laser beam spot upward on the mirror requires:

• Lowering the mirror, which is obviously impossible given the position of the Z axis slots around the adjusting screws
• Raising the laser tube

Mirror 3, inside the laser head on the gantry, was also sitting at the lowest possible point in its adjustment range:

All of which suggested I should resign myself to adjusting the beamline:

• Raise the laser tube by 5 mm
• Move Mirror 1 closer to the laser tube by about 10 mm

Raising the tube gets both Mirror 2 and Mirror 3 off their Z axis adjustment limit, but requires raising Mirror 1.

Moving Mirror 1 gets Mirror 2 off its X axis adjustment limit.

Nothing changes the position of Mirror 2 on its Y axis screws, but that adjustment will help fine-tune the beamline into Mirror 3.

So I cut some 5 mm plywood spacers and nerved myself.