rx for machining wood - forestry.ca.uky.edu
TRANSCRIPT
Rx for MACHINING WOOD
Gene Wengert & Bobby Ammerman
PROGRAM TOPICS
1. The Wood Part of Machining2. Knife geometry3. Effects of Feed Rates4. Planer Machine Design Features5. Sawtooth Angles6. Sanding and Sandpaper7. Machining Defects8. 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
SOFTWOODSEarlywood
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.
SOFTWOODSEarlywood
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
SOFTWOODSEarlywood
Center of tree
End grain
Latewood
Vertical in tree
Radial or quartersawn face
Flat or tangential grain
Spruce
SPECIAL WOOD
Compression WoodTension WoodJuvenile Wood
COMPRESSION WOOD
TENSION WOOD
Tension wood is weak and shrinks lengthwise
TENSION WOOD
Tension wood blotchy staining
SAP & HEART
Sapwood is open.Heartwood (used to be sapwood) is often closed.
Juvenile wood is weak, shrinks lengthwise
JUVENILE WOOD--15 rings about
Juvenile
Mature wood
STRESS
RESOURCE ISSUES
Growth Stress
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 INFECTIONWhat 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
CIRCULAR SAW
to eye
MACHININGPoor Side Dressing
MACHININGSaw Tooth Design
Flat-Top Grind (FTG)--miniature chisels; ripping
Alternate-Top Bevel (ATB)--ripping or crosscutting
MACHININGATB & Raker (ATB & R)--
Triple-Chip (TC or TCG)--particleboard
MACHINING
HOOKMore 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 plywood10” diameter ATB with 40 to 80 teeth12” diameter ATB with 50 to 90 teeth
Ripping solid wood10” ATB with 40 teeth; 12” with 50 teeth
10” FTG with 20 to 30 teeth; 12” with 30 to 40 teeth
Cutting Composite Materials10” 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
MACHININGBAND SAW FACTORS
* Blade width
* Blade thickness
* Tooth design
* TPI
* Tooth shape and angles
* Set
* Cleaning
SPECIAL CONCERNS
End grainCasehardening & Growth Stress
Weakened WoodDelayed Warp
Delayed Checking
QUESTIONS