Bandmill Blade Speed, Feed, and Bite per Tooth

Bite per tooth is the number a filer tunes a mill around, and it is the bridge between what the sawyer does and what the saw does. A bandmill with 54 in wheels at 580 rpm runs the band at 8,200 surface ft/min, and on 1.75 in tooth spacing that is 56,226 teeth past the cut every minute. Feeding at 120 ft/min gives 0.0256 in of bite -- comfortably inside the 0.020 to 0.045 in band that suits softwood, with dense hardwood wanting the lower half of it. TOO LITTLE BITE IS NOT THE SAFE SIDE. A tooth taking less than it should is rubbing rather than cutting, which generates heat, work-hardens the tip, and produces the washboard finish that gets blamed on tension. Too much overloads the gullet, and a gullet that fills before it exits the cut packs -- which is what makes a saw dive. THE GULLET IS THE REAL CONSTRAINT, and it is why bite and depth of face cannot be considered separately. At this bite and a 0.100 in kerf each gullet carries 0.0307 cu in through a 12 in face, half of a 0.060 cu in gullet. The same bite in a 30 in cant asks the gullet to carry two and a half times as much, past what it holds: the deepest face this bite supports is 23.4 in. That is the arithmetic behind slowing the feed as the cants get bigger, and it is why a mill running mixed sizes at one feed speed has a saw problem on the big logs only. FOR A FILER THE USEFUL INVERSION is the feed a target bite implies -- 0.030 in wants 141 ft/min here -- because feed is a setting the sawyer can act on directly where blade speed and tooth spacing are not. A kinematic relation between feed, blade speed, and tooth spacing. Gullet capacity is entered rather than derived, because deriving it needs the gullet area and the sawdust bulking factor for the species and moisture. It does not address saw tension, wheel alignment and tracking, tooth geometry, hook and clearance angles, set or swage, blade width and gauge, or strain, all of which affect cutting behaviour at least as much as bite does and none of which is arithmetic. It does not address sawing accuracy or target sizes. Band saws at these speeds are a serious hazard: the saw and mill manufacturers' specifications, a qualified filer, and OSHA govern.

blade speed in surface feet per minute = pi x wheel diameter (in) / 12 x rpm; teeth passing per minute = that speed x 12 / tooth spacing; bite per tooth = feed speed x 12 / teeth per minute; gullet load = bite x kerf x depth of face.

Standard sawfiling kinematics by name, with the 0.020 to 0.045 in softwood bite band as sawfiling practice. The saw and mill manufacturers' specifications, a qualified filer, and OSHA govern.

Kinematics on the mill's own wheel, tooth, and feed figures; no manufacturer speed-and-feed chart is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: wheel_diameter_in, wheel_rpm, tooth_spacing_in, feed_rate_fpm, target_bite_in, kerf_in, depth_of_face_in, gullet_capacity_cuin, blade_speed_sfpm, teeth_per_min, bite_in, feed_for_target_fpm, gullet_load_cuin, max_face_in

• The gullet, not the bite, is the limit the same bite in a face two and a half times as deep asks for two and a half times the gulletsawfiling practice
• Too little bite is not the safe side a rubbing tooth makes heat, dulling, and washboardsawfiling practice
• Feed is the setting a sawyer controls blade speed and tooth spacing are not adjusted between cantsmill practice