Rx for MACHINING WOOD Gene Wengert & Bobby Ammerman
PROGRAM TOPICS 1. The Wood Part of Machining 2. Knife geometry 3. Effects of Feed Rates 4. Planer Machine Design Features 5. Sawtooth Angles 6. Sanding and Sandpaper 7. Machining Defects 8. Special Concerns
THE WOOD PART OF MACHINING
Wood machining is actually breaking of the wood. So wood strength is a key.
ALL ABOUT WOOD SOFTWOODS
SOFTWOODS Earlywood Center of tree End grain Latewood Vertical in tree Radial or quartersawn face Flat or tangential grain Spruce
ANALOGY: a handful of miniature soda straws Consider this analogy for * moisture movementy * gluing *machining * finishing
CELLS Facts * Cells are very small- -1/8 long * The heavier the wood, the smaller the cell opening and thicker the wall.
SOFTWOODS Earlywood Center of tree End grain Latewood Vertical in tree Radial or quartersawn face Flat or tangential grain Spruce
Wood machining is actually breaking of the wood. So wood strength is a key.
Consider - - Depth of cut Feed speed Knife sharpness
SOFTWOODS Earlywood Center of tree End grain Latewood Vertical in tree Radial or quartersawn face Flat or tangential grain Spruce
SPECIAL WOOD Compression Wood Tension Wood Juvenile Wood
COMPRESSION WOOD
TENSION WOOD Tension wood is weak and shrinks lengthwise
TENSION WOOD Tension wood blotchy staining
SAP & HEART JUVENILE WOOD-- 15 rings about Sapwood is open. Heartwood (used to be sapwood) is often closed. Juvenile wood is weak, shrinks lengthwise
Mature wood Juvenile
STRESS
Growth Stress RESOURCE ISSUES
Drying Stress (also called casehardening) causes IMMEDIATE - - Cupping when machining - - Side-bend when ripping
BACTERIAL INFECTION
BACTERIAL INFECTION * In living tree, but does not kill the tree * Anaerobic (no air) * Enters through roots * Moves 1 to 1-1/2 per year * Wet soils; older trees; bottom of butt log
BACTERIAL INFECTION * Secrete enzyme that destroys and weakens wood (causes shake, surface checking, honeycomb) * Creates fatty acids that turn rancid
BACTERIAL INFECTION What this means is * Shake (or wind shake) * Smelly wood * Very high initial MCs; longer drying time * Wet pockets in dry wood; delayed shrinkage * Checks, honeycomb and splits much more likely when drying * Planer splitting
Bacteria
BRASH WOOD
BRASH WOOD Slow growth causes weak, brash wood
MOISTURE CONTENT Lower MC means stronger wood
If over-dried, the wood can become brittle. Avoid under 10% MC for softwoods. Avoid under 6% for hardwoods.
MOISTURE
Hotter drying temperatures (over 160 F) worsen machining quality.
ANGLES to eye CIRCULAR SAW
Poor Side Dressing MACHINING
MACHINING Saw Tooth Design Flat-Top Grind (FTG)--miniature chisels; ripping Alternate-Top Bevel (ATB)--ripping or crosscutting
MACHINING ATB & Raker (ATB & R)-- Triple-Chip (TC or TCG)--particleboard
MACHINING HOOK More hook means more aggressive; pulling into the wood - ripping: 15 to 20 degrees - crosscutting: 10-15 degrees - radial arm: 0 to -5
MACHINING HOOK - crosscutting: 10-15 degrees - ripping: 15 to 20 degrees
MACHINING HOOK - radial arm: 0 to -8 degrees - compound miter: 0 to -5 degrees
MACHINING HOOK - SkilSaw: +10 degrees
MACHINING BEST CIRCULAR SAW Crosscutting solid wood and cutting plywood 10 diameter ATB with 40 to 80 teeth 12 diameter ATB with 50 to 90 teeth Ripping solid wood 10 ATB with 40 teeth; 12 with 50 teeth 10 FTG with 20 to 30 teeth; 12 with 30 to 40 teeth Cutting Composite Materials 10 TC with 80 teeth 12 TC with 90 or more teeth You get what you pay for
MACHINING DEFINITIONS
MACHINING BAND SAWS * Blade width --narrow turns corners (3/4 can cut nine inch diameter and 3/16 can cut about a dime size) --narrow best for resawing (narrow blade moves backward and not sideways) * Blade thickness (gauge) --thicker means more tension and straighter cuts --thicker means larger band wheels; check saw mfr. specs. --thicker means more sawdust * Set * Cleaning
* Cleaning MACHINING BAND SAW FACTORS * Blade width * Blade thickness * Tooth design * TPI * Tooth shape and angles * Set
SPECIAL CONCERNS End grain Casehardening & Growth Stress Weakened Wood Delayed Warp Delayed Checking
QUESTIONS