GT-500 Field Calculator

🧲 The magnet trick

Carry a magnet in your pocket. It's your first and fastest test.

Magnet sticks strongly: Carbon steel, mild steel, or cast iron. Most forgiving substrates. Go with ferrous metal presets.

Magnet sticks weakly: Likely 400-series stainless (430, 409, 410). Magnetic but still stainless - treat as stainless steel presets.

Magnet does NOT stick: Could be 300-series stainless (304, 316), aluminum, copper, brass, or bronze. Use further tests below to narrow it down.

Galvanized steel: Magnet sticks (it's steel underneath) but the surface looks spangled/crystalline gray. Often has a "grain" pattern in the zinc coating. If it's rusting, the zinc has failed in spots - brown rust bleeding through gray zinc.

🔍 Non-magnetic metals - how to tell them apart

Stainless steel (304/316): Heavy for its size. Silver/gray. Does not corrode normally. Often has a brushed or polished finish. Found in kitchens, food equipment, medical, handrails. Tap it - rings like a bell.

Aluminum: Very lightweight - noticeably lighter than stainless. Silver but duller. Often has white powdery corrosion (not orange rust). Scratches easily with a key. Common on engine parts, wheels, frames, window frames.

Copper: Reddish-brown when clean. Green patina when aged. Heavy. Found in plumbing, electrical, decorative items, roofing.

Brass: Yellow/gold color. Heavier than aluminum. Tarnishes to dark brown, not green like copper. Found in plumbing fittings, doorknobs, musical instruments, shell casings, decorative hardware.

Bronze: Darker than brass, more brown/reddish. Develops green patina over time (like copper). Found in statues, marine hardware, church bells, bearings. Heavier than brass.

🪵 Wood identification basics

Hardwood vs softwood - the fingernail test: Press your fingernail into an inconspicuous spot. Softwoods (pine, cedar, fir) dent easily. Hardwoods (oak, maple, walnut) resist the dent. This matters because softwoods need ~30% less power.

Oak: Visible open grain with prominent pores. Heavy. Light tan to medium brown.

Pine: Light yellow with visible knots and resin pockets. Lightweight. Strong pine smell when heated. ⚠️ Resin flash risk.

Maple: Very tight, closed grain. Light cream/white color. Hard and heavy.

Walnut: Dark chocolate brown with flowing grain. Medium weight. High value - be gentle.

Cherry: Reddish-brown, darkens with age. Fine grain. Medium density.

Cedar: Reddish with aromatic smell. Very lightweight. Softwood - use pine settings.

MDF/Particle board: No visible grain. Uniform color throughout. Edges show compressed fibers/chips. ⚠️ Formaldehyde fumes - PAPR mandatory.

🏗️ Stone, masonry, and brick types

Clay brick (standard red/brown): The most common brick. Fired in a kiln at 1800-2100°F so it's extremely heat resistant. Your laser won't hurt it. Porous surface means paint and soot can soak in deep - may need multiple passes. Very forgiving substrate.

Fire brick (refractory): Used in fireplaces, kilns, furnaces, pizza ovens, chimneys. Rated for 2000°F+. Even more heat resistant than clay brick. You can hit it hard. Common job: removing creosote and soot from fireplace interiors.

Concrete block / CMU: Cinder block, concrete masonry units. Gray, rough, very porous. Made from concrete not clay - absorbs more paint than brick. Treat like concrete for settings. Common on commercial buildings, foundations, retaining walls.

Thin brick veneer / decorative: Thin slices of real brick or manufactured facing. Only 1/2" to 1" thick - less thermal mass than full brick so slightly more careful. Found on interior accent walls, commercial facades, fireplace surrounds.

Pavers (clay or concrete): Driveway, patio, walkway bricks. Can be clay or concrete based. Check by looking at the broken edge - clay is red/orange all the way through, concrete is gray. Use clay brick settings for clay pavers, concrete settings for concrete pavers.

Concrete: Gray, rough, aggregate visible. Very heat-resistant. Your 500W pulsed laser works but is slow on large areas compared to CW systems. Great for targeted work - oil stains, graffiti, rubber marks.

Granite: Speckled appearance with visible crystal grains. Very hard. Extremely forgiving substrate. Go after it.

Marble: Smooth, often veined. Softer than granite. Can glaze (get shiny) if you're too aggressive - use gentle settings with Random pattern.

Sandstone: Grainy, porous, light tan/brown. Soft stone. Gentle approach. Found on older buildings, monuments, natural landscaping.

Limestone: Fine-grained, light colored, often fossil impressions. Soft like marble. Treat the same - gentle approach or you'll damage it.

Slate: Dark gray/black, layered, splits into flat sheets. Dark color absorbs more laser energy than light stone. Start more gentle than you think. Common on roofs, floors, countertops, headstones.

Flagstone: Flat natural stone used in patios and walkways. Can be sandstone, limestone, slate, or quartzite. Identify the stone type first using the descriptions above, then use those settings.

🎨 Paint and coating tips

Dark paint strips fastest. Black, dark blue, dark red all absorb 1064nm laser light aggressively. These need LESS energy than you'd think.

White/silver paint reflects more. Needs 20-30% more energy or slower scan speed than dark paint.

Powder coat is thicker (60-80µm) than spray paint. Needs more passes. Use Line pattern.

Multiple paint layers: Don't try to blast through all layers at once. Remove one layer per pass. Let the surface cool between passes.

Lead paint warning: Pre-1978 buildings and furniture may have lead paint. Laser vaporizes it into lead-containing fumes. Full respiratory protection required. Know your legal obligations.

⚡ Quick parameter logic

Every parameter either concentrates or spreads energy:

More aggressive: Higher power + Lower frequency + Slower scan + Tighter spacing + Shorter pulse width

More gentle: Lower power + Higher frequency + Faster scan + Wider spacing + Longer pulse width

The key formula: Pulse Energy = Power ÷ Frequency. At 500W / 100kHz = 5mJ per pulse (your max hit). At 500W / 1000kHz = 0.5mJ per pulse (10x weaker per hit).

When in doubt: Start at 50% of the preset values, do a test spot, and work UP. It's easier to add power than to fix damage.

Why you need to test

The presets in this app are researched starting points. They will get you close. But every piece of material is a little different. Two sheets of 304 stainless from different mills can react differently. A rusted pipe that sat outside for 5 years is different from one that rusted in 6 months. The contamination thickness, the alloy batch, the surface finish, the age of the coating all play a role.

A quick test on the actual workpiece takes 30 seconds and removes all the guessing. Always test before you commit to a full job.

The quick test (30 seconds)

1. Load the closest preset from the Presets tab. This gives you a researched starting point for that material.

2. Find a hidden spot on the actual workpiece. Back side, bottom edge, inside corner. Somewhere the customer will not see.

3. Fire a short test pass across that spot. Watch what happens and score it:

Score 1-3 = Too weak. The contamination barely reacted. The laser is not delivering enough energy per pulse to break the bond between the contaminant and the base material.

Score 4-6 = Sweet spot. The contamination lifts off cleanly. The surface underneath looks clean and is cool to the touch. No discoloration. This is where you want to be.

Score 7-10 = Too aggressive. The metal is turning yellow, blue, or rainbow colored. The surface feels hot. You might see pitting or roughening. You are putting too much energy into the base material.

How to adjust if you are not in the sweet spot

If your score was 1-3 (too weak), you need MORE energy per pulse. Here is how:

Drop the frequency. This is your first move. Frequency controls how many pulses per second. When you lower it, each pulse gets a bigger share of the total power. Example: going from 400kHz to 200kHz doubles the energy in each pulse. Test again.

If that is still too weak, shorten the pulse width. Pulse width is how long each pulse lasts. Shorter pulse means the same energy gets packed into a shorter burst which makes the peak power higher. Higher peak power is what actually blasts the contaminant off. Example: going from 200ns to 60ns will hit much harder even at the same energy per pulse. Test again.

Last resort: raise the power. This increases the total energy budget. Only do this if frequency and pulse width adjustments did not get you there.

If your score was 7-10 (too aggressive), you need LESS energy per pulse. Here is how:

Raise the frequency. This is your first move. More pulses per second means each pulse gets a smaller share of the total power. Example: going from 200kHz to 400kHz cuts the energy per pulse in half. Test again.

If that is still too hot, lengthen the pulse width. A longer pulse spreads the same energy over more time so the peak power is lower. The hit is softer. Example: going from 60ns to 200ns will be noticeably gentler. Test again.

You can also speed up the scan speed. Faster scan speed means the beam spends less time on each spot. Less time per spot means less total energy delivered to that area. This is a quick way to cool things down without changing the pulse characteristics.

Once you land in the 4-6 range, save those settings to your Recipe Book. That is your proven recipe for this exact material and contaminant. Next time you see the same thing you load it and go.

The full matrix test (when you want to master a substrate)

When you have time and want to fully understand a material, run a matrix test. This is how the professionals do it.

1. Get a test piece of the substrate or use a large hidden area on the workpiece.

2. Hold Power constant. Start at whatever the preset recommends.

3. Pick 4 frequency values spread across a range. Example: 100kHz, 200kHz, 400kHz, 800kHz. These are your rows.

4. Pick 4 pulse width values. Example: 30ns, 60ns, 150ns, 300ns. These are your columns.

5. Test each combination on a small area of the test piece. Score each one 1-10. Take a photo.

6. Look at the scores. The combinations that scored 4-6 are your safe operating window. The fastest cleaning setting in that window is the one with the lowest frequency and shortest pulse width that still scored in range. The gentlest is the highest frequency and longest pulse width that still scored in range.

7. Save all the winners to your Recipe Book. You now have tested, proven settings for this material. That is data you can sell.