Machine Hardware: Optics, Motion and Cooling

Tubes and sources, mirrors and lenses, alignment, belts and steps, water cooling, air assist, extraction and power supplies.

On this page

Laser sources
Mirrors, lens and focusing
Beam alignment
Motion system
Water cooling
Air assist and extraction
Power supplies and electronics
Tube life and spares
FAQ

Laser sources

Source	Wavelength	Typical power	Good at	Notes
CO2 glass tube	10.6 µm	40 to 150 W	Wood, acrylic, paper, leather, fabric, glass engraving	Cheap; life 1 000 to 3 000 h; needs water cooling; bulky
CO2 RF metal tube	10.6 µm	30 to 400 W	The same, with a finer beam and fast pulsing	Costs more; sealed; life 20 000 h; air or water cooled
Diode (blue)	445 to 455 nm	5 to 40 W optical	Wood, dark acrylic, engraving; thin cuts	Compact, no tube; clear acrylic passes the beam
Fiber	1 064 nm	20 W to 20 kW	Metals (cut and mark)	Efficient; long life; see Industrial Laser Cutting: Metals, Gas and Process
Nd:YAG / UV	1 064 / 355 nm	5 to 100 W	Marking; glass and plastics	Specialist; see Engraving, Marking and Raster Work

The wavelength decides what the beam can do (see How Laser Cutting Works and Laser Types). The wall-plug efficiency decides the electricity and cooling needed: a CO2 tube is about 11 % efficient, a fiber source about 35 %.

Worked example: electricity per watt of light

An 80 W CO2 tube at 11 % efficiency draws 727 W of electrical power from the supply and turns the other 647 W into heat (which the cooling water must carry away).
A 3.0 kW fiber source at 35 % draws 8.6 kW: 2.86 W in for each watt out, against 9.09 W for the CO2 tube.

Mirrors, lens and focusing

A flatbed CO2 laser guides the beam through three mirrors (fixed at the tube, moving with the gantry, and on the head) to a focus lens. Mirrors are silicon, molybdenum or copper, coated for 10.6 µm; the lens is zinc selenide (ZnSe) or germanium, usually 50.8 mm (2 inch) focal length for cutting and 101.6 mm (4 inch) for thick or deep work. Gold-plated mirrors and ZnSe are poisonous powders when broken: never sand them or use glass-cleaning tricks.

Worked example: loss in the optics and the cost of dirt

With 3 mirrors at 98.5 % reflectance and a lens at 98 % transmission, the work gets 80.0 × 0.985³ × 0.98 = 74.9 W (a loss of 6.3 %).
Dirty mirrors reflect less. If each drops to 93 % the work gets only 63.1 W, 84 % of the clean figure, and the dirt absorbs the difference as heat (which can crack the lens). A weak cut is often just dirty optics.
Focus: a beam of 8 mm diameter into a 50.8 mm lens (M² = 1.1) has a spot of 0.094 mm and a depth of focus of 1.20 mm. The 101.6 mm lens gives 0.189 mm and 4.79 mm: a coarser spot with deeper focus for thick material. An expander that widens the beam to 12 mm shrinks the 50.8 mm spot to 0.063 mm.

How the focused beam narrows to a waist and widens again (see the basics page).

Beam alignment

Sequence: align the first mirror so that the beam hits the center of the second at the near and far ends of the travel; then the second to the third; then center the beam in the nozzle.
Test with tape: a piece of masking tape over each mirror aperture, a brief low-power pulse, and the burn spots show where the beam lands. Spots that move as the gantry moves are an alignment error.
The long arm magnifies errors: a tilt of 0.5 mrad at the first mirror moves the beam by 0.4 mm over an 800 mm path to the far mirror.
Do it with the beam on low power, with eye protection, and the lid interlock respected (see Laser Safety, Fire and Fumes).

Motion system

A typical machine moves the head on a gantry with stepper motors and toothed belts (the cheaper machines), or servo motors with rack and pinion or ball screws (industrial machines). The theory is in Motion Control and Actuators.

Worked example: steps per millimeter, speed and acceleration

A 200-step motor at 1/16 microstepping with a 20-tooth pulley on a 2 mm pitch belt: 200 × 16 ÷ (20 × 2) = 80 steps per mm, a step of 12.5 µm. (This is the number to enter as $100 in GRBL; see Files, Software and Toolpaths.)
At 400 mm/s the controller must send 32 000 steps per second (32 kHz): within the range of a typical controller.
At an acceleration of 3 000 mm/s² the head takes 0.13 s and 26.7 mm to reach 400 mm/s. A shape smaller than this never reaches the set speed, which is why small detail is slow (see Power, Speed, Focus and Assist Gas).
Limits of the cheap design: belts stretch and teeth skip when the acceleration is too high; the stepper loses steps silently (there is no feedback), so a skipped step shifts the whole job. Check by returning to the home position and measuring.

Limit switches and homing give the machine its zero. A switch that fails lets the head crash into the frame.
Z axis: a motorized bed (or head) sets the focus distance; some machines have auto-focus with a probe.
Belt tension and bearings: a loose belt shows as ghosting in engraving (see Engraving, Marking and Raster Work); dry rails jam and stall.

Water cooling

A CO2 glass tube turns about 89 % of its electrical input into heat. The water must carry it away or the tube overheats, the power drops and the glass can crack. The temperature rise of the water is ΔT = heat ÷ (density × specific heat × flow).

ΔT = P_heat ÷ (ρ · c · Q)

The water temperature rise against flow for three tube powers.

Worked example: flow, tank and chiller

The heat taken from the circuit is about 8 times the optical power: 80 W × 8 = 640 W (close to the 647 W found above).
At 3 liters per minute the water rises by 640 ÷ (1 000 × 4 186 × 5.0 × 10⁻⁵) = 3.1 K. For a limit of 5 K the flow must be at least 1.8 L/min. (3 L/min = 5.0 × 10⁻⁵ m³/s.)
A bucket is not enough. A 20 L tank without a chiller warms by 5 K in 654 s (10.9 minutes) at 640 W, and it keeps rising; a chiller (or a large tank and radiator) must remove the heat. Size the chiller at about 800 W of cooling capacity (25 % margin).
Keep the water between 20 and 25 °C. Colder water than the air can make dew on the tube, and the tube loses power when hot. Use distilled or deionized water with an algae inhibitor (tap water leaves scale and conducts), and a flow switch that stops the laser if the pump fails.

Air assist and extraction

Air assist blows through the nozzle to keep smoke and flame off the lens and to clear the kerf. Use clean, dry air (an aquarium pump is weak; a small compressor is better) and check the lens for oil.
Extraction removes smoke and fumes from the cabinet and sends them outdoors or through a filter (see Laser Safety, Fire and Fumes).

Worked example: sizing the extraction fan

The cabinet is 0.70 × 0.50 × 0.25 m = 0.088 m³. A 150 m³/h fan changes the air in 2.1 s.
Air must flow into the cabinet through the gaps to stop smoke leaking out: through a total gap area of 0.010 m² the inflow is 150 ÷ 3 600 ÷ 0.010 = 4.2 m/s. Seal the unwanted gaps to raise this.
In a 100 mm duct the air speed is 5.3 m/s: a quiet, free-flowing speed (bends, long runs and filters cut the real flow a lot, so choose a fan with margin).

Power supplies and electronics

Laser power supply (LPSU): a high-voltage unit that drives the tube; it takes a PWM signal from the controller to set the power. It must match the tube’s rating. The output is lethal: never open the unit or touch the tube’s terminals while it is powered.
Controller: reads the file, drives the steppers and sets the laser power (GRBL, Ruida, Trocen, Smoothieboard).
Interlocks and switches: lid switches, emergency stop, water-flow switch, key switch.
Grounding: the frame and the supply need a good protective earth; the high-voltage return goes to the laser supply’s own terminal.

Worked example: the power budget

The 80 W tube needs about 727 W electrical input; with 30 % margin the supply is rated about 945 W.
Add the motion system (60 W), the extraction fan (100 W) and the chiller pump and compressor (150 W): about 1 037 W in total, 4.5 A from a 230 V supply (8.6 A at 120 V). The chiller’s compressor is extra, on its own supply.

Tube life and spares

A CO2 glass tube loses power slowly over thousands of hours, then fails faster; the rated life (about 2 000 h) is at full current. Running at lower current extends life, a reason to match the tube power to the job.
Signs of a worn tube: the power for the same cut keeps rising, the beam color changes, or the discharge flickers.
Spares to keep: a lens, three mirrors, a nozzle, belts, a fuse and a spare water pump are cheaper than a stopped job.

Worked example: tube cost per hour

A $300 tube with a 2 000 h life costs $0.15 per hour of laser time. At 4 hours a day for 250 days (1 000 h a year) it lasts 2.0 years.
If a lower-power setting doubles the life (illustrative, not a rule) the cost falls to $0.075 per hour. The numbers feed the machine-hour rate in Running a Laser Shop: Costs, Maintenance and Troubleshooting.

Laser Cutting: the overview of this guide.
Power, Speed, Focus and Assist Gas: the effect of acceleration and focus on the cut.
Laser Safety, Fire and Fumes: enclosure, interlocks and fume extraction.
Motion Control and Actuators (steppers, belts and acceleration) and Electronics Fundamentals.

FAQ

How much flow does the cooling water need?

Enough to keep the rise across the tube under about 5 K: for an 80 W tube about 1.8 L/min or more, and a chiller or large radiator, because a tank alone warms steadily.

Why is my cut weaker than it used to be?

Clean the mirrors and lens first, then check alignment and focus, then the tube. Dirty optics can lose a large share of the power.

Which lens should I use?

A 50.8 mm lens gives the finest spot for thin material and engraving; 101.6 mm gives deeper focus for thick or uneven material.

Can I use tap water in the cooling circuit?

Distilled or deionized water with an algae inhibitor is better: tap water leaves scale and is conductive.

References

Laser tube and optics makers’ manuals (CO2 glass and RF tubes, ZnSe lenses, mirrors).
Incropera, DeWitt: Fundamentals of Heat and Mass Transfer (specific heat of water and cooling calculations).
IEC 60825-1, Safety of laser products (enclosure and interlock requirements).

Last reviewed: October 2026. Efficiencies, prices and lifetimes are typical figures: check your tube and supplier.