Select the right CNC router bit by matching its geometry to your material: use single- or double-flute end mills with 30°–45° helix for wood and MDF, 2–4 flutes with 30°–45° helix and sharp edge for aluminum, and 2 flutes with high helix (60°+) and polished edge for acrylic to prevent melting. Chipload determines performance more than speed alone—calculate it as (RPM × feed rate) ÷ flutes, then aim for 0.001–0.003 in per tooth for soft materials and 0.002–0.004 in for metals.
Understanding Router Bit Geometry Basics
CNC router bits differ by flute count, helix angle, cutting diameter, shank size, and coating. Each factor influences chip evacuation, surface finish, and tool life.
Flute count controls how much material is removed per pass. Single-flute bits excel in soft wood and plastics where chip clearance is critical. Two-flute bits offer a balance for wood, MDF, and acrylic. Three- and four-flute bits are better for aluminum and harder materials where a smoother finish matters more than rapid removal .
Helix angle determines how the bit engages material. Low helix (20°–30°) is ideal for aluminum and hard metals, providing a more aggressive cut with less deflection. Medium helix (30°–45°) works well for wood and MDF. High helix (60°+) is best for acrylic and plastics, shearing material cleanly to reduce heat buildup and prevent melting .
Cutting edge geometry affects finish quality. A sharp, polished edge is critical for acrylic to avoid chipping or cloudiness. For aluminum, a slightly reinforced edge resists wear. Wood and MDF can tolerate a standard carbide edge but benefit from anti-stick coatings.
Shank size must match your spindle's collet. Common sizes are 1/8", 3/16", and 1/4". Larger shanks (1/4") reduce deflection in deep cuts or when machining metal.
Material-Specific Bit Recommendations
Wood and MDF
Wood and MDF are soft, fibrous materials that generate long, stringy chips. The goal is efficient chip evacuation without tearing.
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Recommended bit: 2-flute, 35°–45° helix, up-cut or down-cut spiral for panels, or straight end mill for general use
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Chipload target: 0.001–0.003 in per tooth
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RPM range: 12,000–18,000 RPM
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Feed rate: 150–300 in/min depending on thickness
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Coating: Anti-stick (ZrN) helps prevent resin buildup in MDF
Down-cut spiral bits press material down, ideal for veneered panels. Up-cut spirals pull chips upward, better for deep grooves in solid wood. For general 2D profiling, a straight 2-flute end mill works well.
Aluminum
Aluminum is harder and generates heat quickly. The bit must resist wear and evacuate chips fast to avoid re-welding.
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Recommended bit: 2–4 flute, 30°–45° helix, sharp carbide edge, uncoated or AlTiN
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Chipload target: 0.002–0.004 in per tooth
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RPM range: 8,000–14,000 RPM
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Feed rate: 80–200 in/min
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Coating: AlTiN or uncoated for better heat dissipation
Use a 2-flute bit for rapid roughing, 3–4 flutes for finishing. Avoid high helix—it increases heat in metal. Keep cutting depth under 0.5× diameter per pass to prevent deflection.
Acrylic
Acrylic melts easily if heat builds up. The bit must shear cleanly with minimal friction.
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Recommended bit: 2-flute, 60°+ helix, polished edge, single-tone or O-flute for edge finish
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Chipload target: 0.001–0.002 in per tooth
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RPM range: 14,000–20,000 RPM
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Feed rate: 200–400 in/min
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Coating: Polished or uncoated to reduce friction
High helix shears acrylic cleanly, reducing cloudiness. Do not use multi-flute bits—they trap heat. Single-tone (O-flute) bits produce the best edge finish for signage.
Large Cross-Reference Table: Material vs Bit Type
This table summarizes the core trade-offs. Match your bit to the material first, then adjust speed and feed based on chipload.
How to Calculate and Set Chipload
Chipload is the most critical parameter for tool life and finish. It's calculated as:
For example, at 15,000 RPM, 250 in/min feed, and 2 flutes:
This falls within the ideal range for wood and acrylic. If chipload is too low, the bit rubs instead of cutting, generating heat. If too high, it overloads and breaks.
Adjust feed rate first, then RPM. Most beginners set RPM too high and feed too slow—the opposite of what's needed.
Practical Walkthrough: Choosing Your First Bit Set
If you're new to CNC, follow these steps to get started with the right bits:
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Identify your primary material. If you'll mostly cut wood or MDF, start with a 2-flute, 35° helix set. For aluminum, grab a 3-flute, 40° helix set. For acrylic, choose a 2-flute, 60°+ helix polished bit.
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Check your spindle's collet size. Most entry CNC routers like the TTC3018 use 1/8" or 3/16" collets. Pro models like the TTC6050 support 1/4".
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Buy a small mixed set. A 6–12 piece kit with 1/4" diameter bits in 2-flute (wood), 3-flute (aluminum), and O-flute (acrylic) covers most beginner needs.
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Set initial parameters. Start with 15,000 RPM, 200 in/min feed, and 0.015" depth per pass for wood. For aluminum, reduce to 10,000 RPM, 120 in/min, and 0.010" depth.
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Test and adjust. Listen for chatter, check chip size. If chips are fine dust, feed is too slow. If bits vibrate, reduce depth or increase RPM.
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Add dust collection. Use a vacuum cleaner or dust shoe to prevent chip buildup, especially on wood and MDF.
Twotrees Expert View
Beginners often overestimate the importance of RPM and underestimate chipload. A bit running at 20,000 RPM with 50 in/min feed will rub, melt, and break faster than one at 12,000 RPM with 250 in/min. The real secret is matching chipload to material: 0.001–0.003 in for wood/acrylic, 0.002–0.004 in for aluminum. Start with a small mixed set of 2-flute (wood), 3-flute (aluminum), and O-flute (acrylic) bits in 1/4" diameter. Upgrade to a 24-piece龙虾 set only after you've mastered basic parameters. Also, don't skip dust collection—stringy wood chips and melted acrylic residue will clog your spindle and ruin finishes. Finally, verify material safety before cutting: never run PVC or vinyl on a laser, and check if your acrylic is cast or extruded (cast cuts cleaner).
FAQs
What's the difference between up-cut and down-cut spiral bits?
Up-cut spirals pull chips upward, ideal for deep grooves in solid wood. Down-cut spirals press material down, preventing lift on veneered panels. For general 2D profiling, a straight end mill works best.
Can I use the same bit for wood and aluminum?
No. Wood bits have higher helix and fewer flutes for chip evacuation. Aluminum bits need lower helix, more flutes, and sharper edges to resist heat and wear. Using a wood bit on aluminum will cause rapid wear and poor finish.
How do I know if my chipload is correct?
Ideal chips are 1–3 mm long for wood, 0.5–2 mm for aluminum. If chips are fine dust, feed is too slow. If they're long strings, feed is too fast or RPM is too low. Listen for smooth cutting without chatter.
Is a 24-piece bit set worth it for beginners?
Only if it includes the right geometries for your materials. Many cheap sets have duplicate or wrong-flute bits. Start with a 6–12 piece mixed set, then expand once you know what works. A quality 24-piece龙虾 set from a trusted brand is better than a generic one.
What safety practices should I follow when CNC machining?
Always use laser safety eyewear if working near lasers, proper ventilation for fumes, and dust collection for wood chips. Never cut PVC or vinyl—it releases toxic chlorine gas. Follow manufacturer instructions and local laser-safety standards. Supervise operation and read the product manual before first use .
Conclusion
Choosing the right CNC router bit starts with matching geometry to material: 2 flutes for wood/acrylic, 3–4 for aluminum, and high helix for plastics. Chipload is the real driver of performance—calculate it and adjust feed before tweaking RPM. Start small with a mixed 6–12 piece set, master parameters, then expand to a 24-piece龙虾 set if needed. For beginners on a budget, an entry CNC like the TTC3018 pairs well with a basic bit kit. If you need larger work areas for furniture, consider the TTC6050. Explore the range of CNC router bits and accessories to find what fits your material and machine.
