Sawing

Metal-Cutting Saws

Unit 5

Metal-Cutting Saws

First crude saw closely followed origin of stone ax and knife Sharp edges of stones were serrated or toothed Cut by scraping away particles of object

Great improvement followed the appearance of copper, bronze, and ferrous metals

Today steel available for saw blades

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Sawing

A process to cut components, stock, etc.

Process character: Precision: [very low,, very high]; MRR:

low

Sawing

band saw

hand-held circular saw hand-held hacksaw

band saw


circular saw bladewave teeth (for sheet-metal)

right-left teeth (for soft materials)

band saw blade and blade types

raker teeth (for hard, brittle materials)





Sawing

Sawing

band saw


band saw










Types of Metal Saws

Unit 5

Methods of Cutting Off Material

Five most common methods of cutting off material Hacksawing Bandsawing Abrasive cutting Cold sawing Friction sawing

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Power Hacksaw Reciprocating type of

saw Frame and blade

travel back and forth Pressure applied

automatically on forward stroke

Limited use in machine shop work

Usually permanently mounted to floor

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Horizontal Bandsaw Flexible, belt like

"endless", blade that cuts continuously in one direction

Thin, continuous blade travels over rims of two pulley wheels and passes through roller guide brackets ,Support blade and keep it running true

Popular for high production and versatility

Never idle.

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Case study

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Abrasive Cutoff Saw Cuts by means of thin,

abrasive wheel revolving at high speed

Resinoid or rubber bonded wheel is used.

Well suited for cutting most metals and materials such as glass and ceramics

Can cut to close tolerances Can be performed under

dry conditions Use of cutting fluid keeps

work and saw cooler and produces better surface finish

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Cold Circular Cutoff Saw Uses circular blade similar to

one used on wood-cutting table saw

Generally made of chrome-vanadium steel Carbide-tipped blades used

for some applications Suited for cutting aluminum,

brass, copper, machine steel, and stainless steel

Average thickness of cut is 6mm.

Friction Sawing Burning process by which

saw band (with or without) saw teeth, is run at high speeds to burn or melt its way through metal 10,000 to 25,000 sf/min

Cannot be used on solid metal Amount of heat generated

Excellent for cutting structural and honeycombed parts of machine or stainless steel

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Saw BladesCommonly made of high-speed tungsten

and high-speed molybdenum steelHardened completely for power hacksawFlexible blades on bandsaws have teeth

hardenedManufactured in various degrees of

coarseness, ranging from 4-14 pitch10-pitch blade used for general-purpose

sawingAlways select saw blade as coarse as

possibleAlways have two teeth of blade in contact

with work at all times

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Saw Teeth terminology

• In order to produce saw cuts wider than the thickness of saw blade, the tips of the saw teeth are bent sideways.

• These are called “Tooth set”.• It’s purpose is to allow a saw to move freely

in the cut.• 3 types:1.Straight tooth.2.Raker tooth.3.Wave set tooth.

• In Raker set one tooth is unset and then two after it are offset to the right and left respectively.

• This pattern of 3 teeth is repeated.• It is used for heavy work on bar

stock forgings, die blocks etc.

• The straight set is more suitable for non-ferrous metals and non metals.

• In Wave set teeth are offset in groups alternatively from right to left to form a wave pattern.

Tooth FormsPrecision (regular)

Most generally used 0º rake angle, 30º back

clearance Used for fine finish

Claw (hook) Positive rake on cutting

face Faster cutting, longer

lasting than buttressButtress (skip)

Teeth spaced farther apart Tooth angles same as

precision teeth Used on thick work sections

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Sawing Important that correct type and pitch of saw

blade be selected and run at proper speed Blades

Finer tooth when cutting thin cross sections and extra-hard materials

Coarser tooth used for thick cross sections and soft, stringy material

Speed Should suit type and thickness of material Too fast will dull saw teeth quickly

Contour Bandsaw Parts and Accessories

Vertical Bandsaw Latest machine tool to be developed

Early 1930s Widely accepted by industry Fast and economical method of cutting metal

and other materials Continuous cutting action on workpiece

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Advantages of the Vertical Bandsaw

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.


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Bandsaw Common Applications

Notching Sections of metal removed

in one piece

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• Slotting– Quick and accurate without

expensive fixtures


Three-dimensional shaping Simply follow layout lines

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• Radius cutting– Internal or external contours– Internal sections removed

in one pieceCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.


Splitting Accomplished quickly with

minimum waste

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• Angular cutting– Work clamped at any angle– Table may be tilted


Coolants

Power-feed models have cooling system Circulates and discharges coolant against faces

of blade and work

Mist coolant system Uses air to atomize coolant and direct it

(efficient) Recommended for high-speed machining of

nonferrous metals.

Grease-type lubricants and coolants may be applied directly to blade on machines with no system

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Power Feed

Work and table fed toward blade by hydraulic system

Fixed-table machines use gravity to provide steady mechanical feeding pressure Allows operator to use both hands to guide Work forced into blade by cables, pulleys, and

weights Force

Varied up to about 80 lb. (regular 30-40 lbs)

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Pitch Numbers of teeth per standard reference

length Inch standard = No. teeth/inch Metric standard = No. teeth/25 mm

Thickness of material to be cut determines pitch of blade to use Coarse: thick, Fine: thin

Two teeth in contact with work at all times

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Width

Wide blade used for straight, accurate cuts Narrow blades used to cut small radii Radius charts show proper width of blade are

found on all bandsaws Choose widest blade that can cut smallest radius

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Thickness of Blade

Thickness of saw blade Thick blades stronger than thin blades Thickest blade possible should be used for

sawing tough material Standardized according to blade width

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½ in wide are .025 in. thick5/8 in. and ¾ in. wide are .032 in. thick1 in. wide are .035 in. thick

Calculate Lengthof Saw BladePackaged in coils 100 to

150 ft. in lengthCut length required and

weld ends Twice center distance

between each pulley and add it it one pulley's circumference

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CD

Blade length = 2 (CD) + π D D

Documents

Sawing