Knife Template 15–20 mm: Long-Focal (≥100 mm) Process Guide
If you cut knife-template boards (15–20 mm ply or composite), you know the pain: thick stock, lots of glue, and edges that love to scorch. The cure is simple—go deeper on focus, keep the airflow steady, and watch your kerf. This playbook explains why a ≥100 mm lens helps, then walks through real speed targets, airflow/nozzle choices, kerf-width control, a quick two-pass clean-up, and what to tweak when things go wrong.
Why ≥100 mm focal length for 15–20 mm knife templates
At 15–20 mm, a typical 50–63.5 mm lens does not provide enough focal depth to sustain consistent energy delivery across the thickness. The result is:
- Top kerf narrower than bottom (V-shape)
- Lower-side burning & resin charring
- Incomplete cut or crooked wall
Deep focal depth → straighter kerf
A ≥100 mm long-focal lens increases the Rayleigh range and makes energy distribution more uniform through the material. That gives:
- More vertical kerf
- Better dimensional accuracy
- Less over-burn at the bottom
- Higher consistency batch-to-batch
Knife-template material characteristics
Knife-template boards are typically hardwood-ply with resin binders. They have:
- High density → higher heat load
- Glue layers → tough melt; can carbonize
- Vertical heat stacking → bottom more burnt
Cutting quality depends heavily on: focal depth + airflow + nozzle force + multi-pass.
Speed windows (15–20 mm) — from GWEIKE application sheet
Assuming 150 W CO₂ @ ~90% power (best-speed reference):
| Thickness | Power (CO₂) | High speed | Best speed | Lens | Notes |
|---|---|---|---|---|---|
| 15 mm | 150 W | ~6 mm/s | ~4.5 mm/s | ≥100 mm | Good accuracy with small nozzle |
| 18 mm | 150 W | ~4 mm/s | ~2.5 mm/s | ≥100 mm | May require multi-pass |
| 20 mm | 150 W | ~2.5 mm/s | ~1.8 mm/s | ≥100 mm | Strong airflow needed |
Values from GWEIKE table. Adjust ±0.5 mm/s for resin content.
Glue-rich boards → reduce speed by ~10% Dense hardwood layers → add multi-pass cleanup
Airflow & nozzle: why aperture matters
Compared with MDR/acrylic, knife boards produce dense smoke + resin droplets. If not ejected quickly, the resin darkens the wall and widens kerf.
Why smaller nozzle = stronger eject force
The cutting nozzle creates a jet. For the same pressure P:
F = P × A → Smaller A → more force per unit area → deeper penetration
- Small nozzle → concentrated gas → better bottom clearing
- Better clearing → cleaner wall → less charring
- Prevents V-shaped bottom widening
Airflow design tips
- Use small nozzle aperture to maintain thrust
- Keep nozzle-to-surface gap short
- Maintain side-exhaust or under-table breathing
Focal setup — stable straightness
- Lens: ≥100 mm
- Focus depth: ~25–40% into thickness
- Goal: balance energy across full depth
Kerf width control
With proper setup, kerf width for 15–20 mm knife template is typically: ~0.8–1.5 mm.
Kerf depends on:
- Lens focal depth
- Nozzle aperture
- Gas pressure
- Material glue level
- Speed → too slow → burn + widen
For precision parts, use a cleanup pass to narrow wall variation.
Multi-pass method (improve bottom straightness)
- Pass 1: ~90% power @ best-speed → ensure penetration
- Pass 2: 30–50% power @ +10–30% speed → remove resin marks
Multi-pass removes charring and makes kerf cleaner for die-steel insertion.
Standard operating procedure (SOP)
- Clean optics; align nozzle
- Mount ≥100 mm lens
- Set focal depth ~25–40% below surface
- Set speed via table (best-speed first)
- Enable high-pressure + small nozzle
- Ensure under-table ventilation
- Cut → inspect → multi-pass if needed
- Record power / speed / focus offset / nozzle
Troubleshooting
| Symptom | Cause | Fix |
|---|---|---|
| Bottom charred | Focus too high / airflow weak | Deepen focus; smaller nozzle; multi-pass |
| V-shape kerf | Short focal length | Upgrade to ≥100 mm |
| Not cutting through | Speed too high; glue level high | Slow; multi-pass |
| Kerf too wide | Over-burn; over-dwell | Increase speed; multi-pass |
| Smoke stains | Poor extraction | Improve side/under-table suction |
Case: 20 mm knife template @ 150 W
- Lens: 100–125 mm
- Focus: ~6–8 mm below top
- Speed: ~2.0 mm/s (best), ~2.5 mm/s (high)
- Air: high-pressure + small nozzle
- Pass 2: 35% @ ~3 mm/s
- Kerf: ~1.0–1.4 mm
- Result: straight kerf; low charring
Safety notes
- Knife boards release resin fumes → ensure filtration
- Keep enclosure sealed
- Check nozzle pressure regularly
- Dust removal prevents flare
FAQ: Knife-template cutting (15–20 mm)
Why use a ≥100 mm lens?
To maintain uniform energy through thickness → straighter kerf + stable accuracy.
What is the best speed for 15–20 mm?
From GWEIKE data (150 W): 15 mm ~4.5 mm/s → 18 mm ~2.5 mm/s → 20 mm ~1.8 mm/s.
How to prevent bottom charring?
Deepen focus 2–3 mm; use smaller nozzle; increase airflow; multi-pass.
What kerf width can I expect?
~0.8–1.5 mm depending on material + airflow + focal depth.
Do I need multi-pass?
Recommended for 18–20 mm to clean resin and improve kerf.
Which machine fits this workflow?
For CO₂ workflow → M-Series . For metal + composite → GH/GA fiber lines .
