VARIABLESWHICH AFFECT BANDSAW BLADE LIFE

A practical overview of bandsawing basics

Variable #1The OperatorsThe Operators

Why is the saw operator a variable in bandsaw cutting?

• The operator knows the machine best

• The operator has control over many other variables

Variable #2Number of Teeth in BandNumber of Teeth in Band

Too few teeth . . . tooth straddle, which can cause tooth strippage

Too many teeth . . . loads the gullet, which can cause tooth strippage

The 3Tooth Rule

1 – The tooth cuts a chip which fills the gullet

2 – When the gullet is full, pressure is created

3 – When the pressure is not relieved, the result is a crooked cut, stripped teeth, or both!

Both tooth conditions can create the same result! . . .

Tooth Selection Guidelines:

Minimum 3 teeth in cut Optimum 6-12 teeth in cut Maximum 24 teeth in cut

Variable #3Tooth StyleTooth Style

Skip• 0 degree rake and shallow gullets• Good for cutting large sections of soft, non ferrous metals and wood

Regular • Rake angle of 0 degrees, full round gullets• Used for cutoff and contour cutting - general purpose

Hook • Positive rake angle and deep gullets• Good for cutting non ferrous metals and hard or soft wood

Intenss PRO• Large variable pitch teeth, up to 12 degree positive rake angle• Production cutting, mild to stainless steels

Variable #4Tooth SetTooth Set

Regular Raker Set• One tooth set to the left, one to the right, and a third “raker” tooth, which is 'unset' or straight• Used for general purpose cutoff and contour cutting

Modified Raker Set• Raker teeth are at regular intervals, with multiple set teeth in between (i.e. L-R-L-R-Raker)• Used for cutting a wide variety of shapes and sizes• Allows broader material size variation for varied cutting• General purpose

Wavy Set• Groups of teeth set alternately to the left and right in a wave-like pattern • Reduces strain of individual teeth• Used for cutting thin stock on a variety of shapes

Variable #5Band TensionBand Tension

How do I know what the proper bandsaw blade tension is?

• Measure it . . . With a Starrett Saw Tension Gage

Recommended TensionCarbon blades - 15,000 - 20,000 PSI

Bi-Metal blades thru 1 1/2” - 25,000 - 35,000 PSI

Bi-Metal blades 1 1/2” and wider - 30,000 - 40,000 PSI

As a general rule of thumb, the higher end of the tension range should be used when the guide arms are further apart and the lower end of the range should be used when the guide arms are closer together.

Variable #6Blade SpeedBlade Speed

How does blade speed become a variable? The proper blade speed will affect blade life:

• for tough material, generally slow the blade speed• for softer material, generally increase the blade speed

How do I calculate my blade speed?

1. determine the length of the band saw blade2. mark a spot on the blade (or locate the weld)3. start up the saw4. time one rotation of the blade (in seconds)5. divide the number of seconds for one rotation into 60 seconds6. multiply the result by the length of the blade

* The answer is the Surface Feet Per Minute!

What is a proper break-in? Reduce the normal feed rate by 1/2

Recommended Band Speed in SFPM: 300 250 200 150 100 50 Square inches to cut for break-in: 90 75 60 40 25 10

Variable #7Break-In ProcedureBreak-In Procedure

Remember . . . Proper break-in for your bandsaw blade will greatly improve bandsaw blade cutting life.

Be sure to always take a chip!!

Why? This will 'hone' the teeth of the bandsaw blade and make it last longer.

Think of your band saw teeth as you would a freshly-sharpened pencil . . . the tip is easily broken when you begin to write. A band saw tooth reacts the same way. Band speed is not what breaks down the tooth tip during break-in, the pressure is.

Band Saw Blade Tooth Tips Magnified

ProperBreak-in

ImproperBreak-in

Reduced feedpressure

‘hones’ the cuttingedge of the tooth

Excessive feedpressure ‘breaksdown’ the sharp

tooth edge prematurely

Variable #8Feed RateFeed Rate

Feed rate is measured in Square Inches per Minute (SIM)

How do we determine the proper feed rate?

1. Determine the material that you are cutting2. Decide which band saw blade to use (carbon, bimetal, carbide)3. Consult a feed rate chart for the material being cut, and set the

saw’s feed pressure accordingly

Feed Rate too lightRubs the tooth dull

Feed Rate too heavyPremature tooth wear Recommended Feed Rate

Optimum blade life

Variable #9Blade QualityBlade Quality

There are vast differences in the way bandsaw blades will perform. Bandsaw quality varies widely, depending upon the manufacturer and blade type. The type could be any one of the following:

Carbon Bi-Metal Carbide Tipped

An example of blade type differences are Red Hardness and Shock Resistance:

Shock resistance in a tooth tip is a tradeoff . . . . . . Long wear versus low shock resistance

The relative Red Hardness of tooth tips

Temperature Tolerance Range of Cutting Edges

RcCarbon M-2 M-30

M-42

Carbide Tipped

Resistance to wearResistance to shock

Increase in Rockwell hardness of tooth tip

Shock Resistance vs. Wear Resistance

Shock

Wear

Carbon M-2 M-30 M-42 Carbide Tipped

Variable #10Machine TypeMachine Type

The Machine Type is another variable in bandsaw cutting

Different machine makes and models have different cutting applications

Horsepower ratings can affect the ability to cut some materials

Variable #11WheelsWheels

Proper adjustment of the wheels can create variable blade performance. There are typically two wheels on a bandsaw machine, and they should be checked for proper alignment, bearing condition, and flange condition.

Idler Wheel Drive Wheel

Idler Wheel Alignment

Correct Tracking

Improper Tracking, Slippage Blade Breakage, Flange Wear

Variable #12Machine ConditionMachine Condition

Machine condition, good and bad, can create a high degree of variation in bandsaw cutting productivity and accuracy.

Is the machine OLD?

Is the machine NEW?

Has the machine been well maintained?

Variable #13Proper VisesProper Vises

Why vises? . . . To hold work firmly and accurately.

Proper alignment of the vice will allow square cuts . . .

. . . Improper alignment of the vice will create crooked cuts

Band saw blade squareness also affects the straightness of the cut

Vice Adjustment – Top View

Vice Adjustment – Front View

Band Saw Blade

Machinist’s SquareSaw Bed

Movable Vice

Adjust fixed vice to square with band saw blade

Fixed ViceMachinist’s Square

Movable Vice

Band Saw Blade

Alignment ToolFixed Vice

Band Saw Blade

Machinist’s Square

Band Saw Squareness – End View

Variable #14Guides

Guides should support and align the blade,when properly adjusted they. . .

. . . and reduce vibration

maintain a STRAIGHT

versus a cut . . .

Variable #15Guide ArmsGuide Arms

Guide arms should be as close to the work as possible, and secured firmly

. . .move the adjustable guide arm in!

When the adjustable guide

arm is this far away from the work, the

blade can be damaged . . .

Here’s an example of how properly

adjusted guide arms should look . . . snug

to the work piece

Wrong!

Correct!

Variable #16BrushesBrushes

Brushes aid in the clearing of chips from the gullet of the blade, which helps prevent tooth strippage and leaves smoother cut surfaces

The ends of the brush filaments should just touch the bottom of the deepest gullet

Brushes should not be set so that the brush filaments constantly rub the side of the blade

Band Saw Brushes are very

Important!

Variable #17CoolantCoolant

Should . . .

Wash chips out of the blade’s gulletsCool the tooth tips to reduce heat damageLubricate the cut to reduce heat caused by cutting friction

Coolant . . . to Wash Cool Lubricate

Variable #18Material MachinabilityMaterial Machinability

The “toughness” of metal can vary tool life.Materials can look the same, but vary greatly in it's

machinability.

Most materials have a “machinability rating”, with 100% being “free machining” and anything lower than 100% being more difficult to work

Cold Rolled Stainless Inconel

Variable #19Material HardnessMaterial Hardness

Material Hardness can affect cutting performance . . . the higherthe hardness of the work piece, the more difficult it is to cut

an Rc* of 40 has a machinability rating approaching zero

* Rc is an abbreviation for Rockwell 'C' scale, a measurement used to test the relative hardness of metals

Variable #20Material ShapeMaterial Shape

Structural material and small solids tend to be harder on the

blade

The shape of the work piece can affect cutting performance . . .

Work piece positioning on the saw can affect cutting performance . . .

try to position the material so there is as little cross section dimensional variance as possible across the

blade’s path Multiple “shock” points whencutting structural materials

Variable #21Production RequirementProduction Requirement

What is the customer’s requirement? Is it pieces on the floor?

When making a recommendation, consider whether the blade will face continuous use or intermittent use . . .

Different operating conditions and different expectations will help determine what type of blade is selected

Piece lots?

Short productionruns?

Production cutting – long runs?

VARIABLES . . . A REVIEW The Operators - The largest single variable. The Number of Teeth in the Blade - 3 minimum, 6 - 12 optimum, 24 maximum. Tooth Style - Standard, Skip, Hook, or Variable Pitch. Tooth Set - Regular, Wavy, Alternate, Raker, or Modified Raker. Band Tension - Measured with a Starrett Tension Gage. Band Speed - Start with the manufacturer’s recommendation. Break-In Procedure - Reduce normal feed rate by 1/2. Feed Rate - Set rate by square inches per minute suggested by manufacturer. Band Quality - Carbon vs Bimetal or Carbide Tipped, one brand vs another. Machine Type - Different makes and models, horsepower of motor. Wheels - Check alignment, bearings, flanges. Machine Condition - Old, new, well-maintained. Proper Vises - To hold the work firmly. Guides - Should support the band, roller guides should be adjusted properly. Guide Arms - Should be as close to the work as possible for support. Brushes - Aid in the clearing of chips from the gullet of the band. Coolant - Should wash, cool and lubricate. Material Machinability - The toughness of a metal can reduce tool life. Material Hardness - A Rc of 40 has a machinability approaching 0. Material Shape - Structurals and small solids tend to be harder on the blade. Production Requirement - Continuous vs intermittent use.

Any one variable or any combination of the above variables can affect blade life!