When you’re cutting firewood with a circular saw (or a specialized firewood‐cutting table saw), selecting the right blade can make the job faster, safer and give you longer blade life. In metric terms, here are the key factors to consider:
1. Diameter & Arbor Size
- Blade diameter (D): Must exactly match your saw’s capacity. Common firewood‐cutting blades Start at 250mm and can go up to 900mm. Larger ones can be specially made.
- Arbor bore (d): The hole in the center—often 25.4 mm, 30 mm or 32 mm. If your arbor is 30 mm, don’t fit a blade with a 25.4 mm bore unless you use a proper steel reducer ring.
2. Plate Thickness & Kerf Width
- Plate (body) thickness: Typically 1.8 mm to 3.2 mm. Thicker plates (≥ 2.8 mm) resist bending when pushing heavy logs; thinner plates (≈ 2 mm) remove less wood, reducing effort and waste.
- Kerf (cut width): Often 2.4 mm to 3.5 mm. A thin‑kerf blade (≤ 2.8 mm) is gentler on lower‑power saws and wastes less wood, but draws more power under load. A standard kerf (≈ 3.2 mm) offers the best stiffness for ripping dense hardwood.
3. Tooth Count & Pitch
- Number of teeth (z): Firewood splitting is a ripping operation along the grain, so blades with fewer teeth—commonly 14 to 24—are ideal.
- Tooth pitch (p): The centre‑to‑centre distance between teeth. For a 14‑tooth blade of 300 mm, p ≈ (π·D) / z ≈ (3.14·300 mm) / 14 ≈ 67 mm. In practice, look for “ripping” blades with tooth spacing ≥ 10 mm (“4 tpi” in imperial, ≈ 6.35 mm pitch) which give large gullets to clear chips quickly.
4. Tooth Geometry & Hook Angle
- Hook (or rake) angle (α): Ripping blades often have a positive hook of +10° to +15°. This aggressively pulls the lumber into the blade, speeding up feed—ideal for softer logs. If you’re cutting frozen or very dense hardwood, a milder hook (+5°) gives more control.
- Tooth shape: “Flat‑top” (FT) or “Alternate Top Bevel” (ATB) both work, but FT grind excels at fast, straight rip cuts in firewood; ATB gives slightly cleaner edges (not vital for logs).
5. Material & Coating
- Plate material: High‑tension spring steel resists bending at high RPMs—look for blades labelled “HT” or “Surfacing grade.”
- Carbide tips: Tungsten carbide‑tipped teeth last much longer on abrasive bark and dirt.
- Coating: A PTFE or paint finish helps pitch and sap slide off, reducing gumming and corrosion.
6. Maximum RPM & Saw Compatibility
- Blades are stamped with a maximum safe speed (e.g. 6 000 RPM). Your saw’s no‑load speed must not exceed this. If your saw spins at 5 000 RPM, and the blade rating is 6 000 RPM, you’re within safe limits. Never fit a blade rated for 4 500 RPM onto a 5 000 RPM motor.
7. Application & Feed Method
- Cross‑cut vs. rip: Always choose a blade specifically labelled “ripping” or “firewood” rather than a general multipurpose blade—this ensures tooth design and gullet size suit longitudinal grain cutting.
- Feed rate: Allow the blade to pull the wood at a steady pace. For a 300 mm, 18‑tooth ripping blade at 4 000 RPM, aim for ~2–3 m/min feed—adjust based on motor load and chip ejection.
8. Maintenance & Safety
- Sharpening: With large gullets and FT grind you can resharpen less often—ideally when tooth height wears down by 0.5 mm.
- Cleaning: After every few cords, remove pitch with a commercial blade cleaner to maintain sharpness.
- Safety guards & push blocks: Always use the guard and employ push sticks or blocks when cutting smaller offcuts.
By matching
diameter,
arbor,
kerf,
tooth count,
hook angle and
material to your saw’s characteristics and the nature of firewood (soft vs. hard, frozen vs. green), you’ll maximize cutting speed, minimize waste and extend blade life—all measured in clear metric specifications for perfect compatibility.
