Laser Maintenance

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This requires training. The laser is easy to damage. Replacement parts for the laser are expensive and take a while to arrive. Only perform maintenance if you've been shown how to do so and if someone with appropriate authority has said you're allowed to.


Overview

This page describes how the small laser is maintained.

NOTE: There is a logbook tied to the shelf near the small laser. If you notice any problems, please write them down in the book. If you perform maintenance, please write down that you did so and what you did and what the before/after condition of the laser was.

Testing

Paper Burn Test

The most common problems with the laser are poor alignment and poor airflow. A burn test on paper can check for these. The steps are as follows:

  • Open Laser Cut and load the burn test file. There's a copy in the top-level documents folder. NOTE: This must be opened from Laser Cut; clicking on it to open it from Windows Explorer scrambles power and speed settings.
  • Place an ordinary sheet of laser printer paper on the bed and hit Z-datum (yes, we've all forgotten that at one point or another).
  • Set Laser Cut to "immediate" mode, and load the file into the laser's memory.
  • Burn the pattern at 9 positions on the table (corners, edges, and middle). You'll have to move the paper around to do this. I normally burn the pattern into the edges, corners, and middle of the paper so that I can remember which burns were from which locations.
  • Watch the smoke as burning proceeds. It should be drawn quickly towards the vent. If it's drawn slowly, or collects under the glass, there's an airflow problem.
  • Examine the burn patterns. A perfect burn has 3 fully-cut lines, a fourth barely cut (fading at the ends), and a fifth line that's marked near the middle (but not the ends) and that does not cut through the paper.

If the mirrors are misaligned, the pattern will fade out over part of the board (usually one corner). If it's especially bad, the laser might only cut properly in one corner, and be faded everywhere else. If the pattern is consistently poor everywhere, it could be a problem other than alignment.

Burn test file location.
Burn test in progress.
Burn test pattern.

Other Problems

Here are symptoms of a few other problems that occur from time to time with the laser:

  • If circles and other curves have wobbles or notches in them, the laser's XY stage has loose screws. See the appropriate section for maintaining it.
  • If the XY stage homes on startup and then starts grinding into the corner of the machine instead of stopping, one of the microswitches has broken again. Hit the emergency stop button (the big red one) to prevent further damage. The defective switch gets identified and replaced, and the XY stage gets inspected for damage.
  • If someone forgets to hook up the inductive sensor, the optics assembly may strike the aluminum cylinder when performing Z datum. This will throw it out of alignment and may loosen parts of the XY stage. Move the table back down, inspect the XY stage and optics assembly for damage, and perform any needed maintenance on both. And hook the inductive sensor back up. If the table is jammed and can't move down, unscrew the optics assembly to take the pressure off.
  • If smoke seems to be lingering near the optics assembly, it probably means the air hose is kinked again. Hold your hand under the optics head and feel for airflow. If necessary, adjust the plastic tubing that connects to the copper tubing. The plastic tubing is easily kinked, and that's a bad thing (smoke damages the lens in about three different ways).
  • If the laser's air pump seems louder than usual and smoke is lingering near the optics assembly, check to see if the air hose inside and under the machine has come off. This is held on by friction and wishful thinking; it's come off at least once before.
  • If the red laser is in the right place but fades out, check the wiring connecting the laser diode to the system electronics. The solder joints are dodgy; squeezing it with fingers fixed it once before. If problems happen again, it may be time to properly fix them.
  • If the laser cutter is ever strongly jostled, the red laser may go out of alignment (no longer in the same place as the CO2 beam). To test this, put a business card or other piece of thick cardstock in the beam path, close the lid, observe where the red spot is, and hit the "laser" button to fire the CO2 laser briefly. This will burn a hole. If this is not aligned with the red laser, see the appropriate section for fixing this.

Air Filter

There are two things that need to be maintained in the air filter: the furnace filter (which removes smoke) and the activated charcoal (which removes fumes).

  • To inspect the furnace filter, open the latches in the midsection of the filter box, and pull out the filter.
    • This should be vacuumed when it gets too dusty.
    • This should be replaced when it's turned brown (that indicates wood resin or other clogging material).
    • Filters are standard 10"x20"x1" furnace filters, available at Canadian Tire, Home Depot, and so forth. If you use one, please pick up a replacement if possible.
  • FIXME - Charcoal maintenance goes here. I don't know how it's done (CJT).

Optics

FIXME - I'm leaving this section as an outline for now. (CJT)

Mirror Alignment

  • Check alignment before adjusting mirrors. If the laser works, don't fiddle with the optics.
  • Check that the lens mount is in the correct position. If it's mis-mounted, it can block the beam (per below).
    • The most important thing is that it's at the correct angle. The bottom of the assembly (and lens) should be flat with respect to the laser bed.
    • The next most important thing is that it's as far down as possible. The mounting screw is in a slot, so you have a bit of vertical play with the lens assembly; loosen the screw holding the assembly to the XY stage, move the assembly all the way down, make sure it's flat with respect to the bed, tighten the screw, and then check that it's still flat.
  • Check to see if the back mirror is in alignment.
    • Do this by moving the laser from the front of the bed the back of the bed (or vice versa), watching the front mirror (the one on the left side of the XY stage). If the dot crawls across the mirror while doing this, the back mirror is out of alignment. If it does not crawl, it's still in alignment. If the back mirror is ok, leave it alone.
  • When adjusting the back mirror:
    • Move the XY stage to the front of the laser bed (so that you have the longest throw distance between back and front mirrors). This lets you see small angle changes more clearly.
    • Close the lid afterwards. If you forget to do this, it'll slam down a few moments later and potentially throw the red laser alignment off.
    • Do not go near the dichroic mount. Even looking at this funny is risky, and it's a massive pain to realign.
    • Close the lid carefully - if it slams, this may throw the dichroic mount out of alignment (it's held in place by wishful thinking).
    • You're looking for consistency, not centering. The dot should be at the same spot on the front mirror in both positions (XY stage all the way forwards and all the way back).
  • When the beam no longer crawls across the front mirror, check to see if the front mirror is in alignment.
    • Move the XY stage to the middle of the Y range, and then move the laser from the left edge to the right edge of the bed (or vice versa) and watching the mirror inside the lens assembly (or the top surface of the lens). If the dot crawls across the lens's mirror (or the lens) while doing this, the front mirror is out of alignment. If it does not crawl, it's still in alignment.
    • When inspecting the front mirror, also check to see if the beam is obstructed by the optics assembly. If it hits close to the edge of the mirror, the reflected beam may be blocked by the assembly instead of passing through the lens. Look for a red dot on the lens to see if this is happening.
  • When adjusting the front mirror:
    • Move the optics assembly all the way to the right, so that angle changes are visible.
    • After you think you've lined it up, move it back and forth on the X axis to check for crawling and obstruction, per above.
    • If it's impossible to get consistent positioning and an unobstructed, it means the lens mount is in the wrong position (usually too high). Doublecheck that.
  • When alignment is done, do another paper cutting test to confirm that cutting is consistent across the laser bed.

Mirror and Lens Cleaning

Mirrors

The mirrors are ordinary aluminum-on-glass front-surface mirrors. They can be cleaned with just about anything, but alcohol and lens paper work well and are kept on the laser shelf and in the laser supplies drawer respectively.

Lens

The laser lens can be damaged by lots of things (including water and alcohol). It still needs to be cleaned, because if dust collects on it, that dust will heat up and damage the lens. The lens should be cleaned with ACETONE only (anything else will eat the lens and produce poison gas).

Wipe the lens gently. The lens has a delicate anti-reflection coating on it, which will be stripped by rubbing too hard. Be especially careful when wiping off dust, as that can scratch the lens. Do not blow off dust; moisture from your breath, and some propellants from canned air, can react with the lens to degrade it.

Be careful when disassembling the lens assembly. This is greasy, and you don't want grease to contaminate the lens (directly or via transfer from your hands). The lens is also very fragile; disassemble the unit at table height, as a drop of even a few inches may shatter the lens. Be careful when reassembling the lens unit; over-tightening the screws can chip the lens, even with the rubber gasket in place.

(If you're getting the impression that everything can damage the lens, you're right. I'm surprised and impressed that the lens as of this writing has lasted this long.)

Dichroic

The dichroic (beam combining element) shouldn't need to be cleaned; it's in back away from dust. That said, it can be cleaned if necessary.

There are two commonly used materials. If the dichroic is pale yellow, it's made of zinc selenide (the same material as the lens); clean it the same way the lens is cleaned. If the dichroic is dark grey, it's made of germanium; clean it the same way mirrors are cleaned.

As of this writing, the dichroic seems to be germanium, but that type may have been discontinued by the manufacturer. Zinc selenide ones are more common.

Supplies

New lens paper can be mail-ordered from Edmund Optics. Their "commercial grade lens tissue" is fine (any Type 1 Class 1 lens paper/tissue will do).

Note: Edmund Optics ships from the US by UPS. UPS charges an absurd amount to compute brokerage. Edmund Optics will ship by USPS if you ask them to but will charge you a lot to do so. Find a Canadian supplier if possible.

Hardware store acetone is fine. Label the can, and make sure that it's only used for the laser, as contamination will do bad things (grease or plastic deposited on the lens will heat up, damage the lens, and possibly catch fire).

Drug store alcohol for cleaning the mirrors is fine. Get 99% rubbing alcohol if possible. Label this and only use it for the laser, as with acetone.

Aligning the Red Laser

Replacing the Dichroic

Replacing the Tube

FIXME - Tube maintenance goes here. I don't know how it's done. (CJT)

Buying New Optics

The parts that have needed to be replaced in the past are the lens, the dichroic, and the laser tube. Mirrors were also replaced in 2016.

In the past, supplies were ordered from G Weike. The contact person as of 2015 is Lucy Lee (han at wklaser dot com). Their English is spotty; Carl's advice was "take a photo and say, 'I need one of these'.".

Other vendors exist and may be used at the discretion of the person doing the ordering.

Lens

The lens is a ZnSe positive meniscus lens with a diameter of 20mm and a focal length of 50.8mm (2"). It has an anti-reflection coating for CO2 wavelengths (10.6 microns). Replacement lenses cost about $50.

Lens with diameter measurement.
Lens showing positive meniscus profile.

Dichroic

The dichroic is a germanium beam-combiner element with a 20mm diameter and thickness of 2.5mm, with an anti-reflection coating for CO2 wavelengths (10.6 microns). This looks like a grey coin-shaped slab with a yellow coating on it. Grey and opaque means it's germanium; yellow and transparent (the most common type now) means it's ZnSe, which requires more delicate handling.

Vendors do not appear to stock germanium dichroics any more. Flat ZnSe dichroics of the same diameter should be compatible.

Germanium dichroic diameter measurement.
Germanium dichroic thickness measurement.
Mount for the small laser's dichroic.

Mirrors

The mirrors are solid metal, 20mm diameter. These are coin-shaped slabs of metal with one face polished. The sides and back show unpolished metal, not glass.

  • FIXME - Photos go here. If possible, identify the material (possibly nickel- or chrome-plated steel?). (CJT)

Tube

  • FIXME - Tube information goes here. (CJT)

Mechanism

FIXME - Mechanical maintenance goes here. I don't know enough about how the machine is put together to write about it. (CJT).

Electronics

FIXME - Electronics maintenance goes here. I don't know enough about how the machine is put together to write about it. (CJT).

  • The power supply was replaced in 2016. The new supply was this one.
Power Supply Control Signals
Label Function
TH Enable, active-high
TL Enable, active-low
WP Enable, active-low
G Ground
IN Control; analog 0-5V or pwm (both work)
5V 5V output at < 20 mA