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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
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
SOFTWOODSEarlywood
Center of tree
End grain
Latewood
Vertical in tree
Radial or quartersawn face
Flat or tangential grain
Spruce
SAP & HEART
Sapwood is open.Heartwood (used to be sapwood) is often closed.
Juvenile wood is weak, shrinks lengthwise
JUVENILE WOOD--15 rings about
Drying Stress (also called casehardening) causes IMMEDIATE
- - Cupping when machining
- - Side-bend when ripping
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
If over-dried, the wood can become brittle.
Avoid under 10% MC for softwoods.Avoid under 6% for hardwoods.
MACHININGSaw Tooth Design
Flat-Top Grind (FTG)--miniature chisels; ripping
Alternate-Top Bevel (ATB)--ripping or crosscutting
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
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
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