Sawing and Cutoff Machines

11Sawing and Cutoff

Machines

Chapter

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Objectives

• Identify the various types of sawing and cutoff machines

• Select the correct machine for the job to be done• Mount a blade and prepare the machine for use• Position the work for the most efficient cutting• Safely operate sawing and cutoff machines


Metal-Cutting Power Saws• Used to cut the stock to required length• Three principal types

– Reciprocating-type– Band-type– Circular-type


Metal-Cutting Power Saws (Cont.)

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Power Hacksaw• Uses reciprocating motion to move blade across

work, cuts on the backstroke• Positive feed• Definite pressure feed

– Gravity feed

• Feed adjusted to meet varying conditions


Power Hacksaw Accessories• Swivel vise

– Angular cuts made quickly

• Quick-acting vise– Faster manual clamping of the workpiece

• Power stock feed, power clamping of work, automatic cycling– Automate the cutting operation

• High-speed cutting requires use of a coolant


Selecting a Power Hacksaw Blade• Three-tooth rule

– At least three teeth must be in contact with work

• Large sections and soft material– Require a coarse-tooth blade

• Small or thin work and hard material– Use a fine-tooth blade

• Change pressure based on material


Types of Blades• Flexible-back blade

– Safety requirements demand a shatterproof blade– Best for cutting odd-shaped work

• All-hard blade– Used for majority of cutting jobs– Best for straight, accurate cutting

• Made from tungsten and molybdenum steels, tungsten carbide teeth on steel alloy backs

• Follow “rule-of-thumb” when selecting blade


Mounting a Power Hacksaw Blade

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Cutting with a Power Hacksaw• Measure off distance to be cut• Allow ample material for facing if necessary• Mark the stock• Mount work firmly on machine• Use stop gage if several sections are to be cut• Apply ample supply of coolant if the machine has a

built-in coolant system


Power Band Saw• Horizontal band saw

– Referred to as the cutoff machine

• Advantages over power hacksaw– Greater precision– Faster speed– Less waste


Selecting a Band Saw Blade• Made with raker teeth

or wavy teeth• Tooth pattern

determines the efficiency of a blade in various materials– Standard tooth– Skip tooth– Hook tooth



Selecting a Band Saw Blade (Cont.)• Consult blade manufacturer’s chart for proper blade

to use and blade tension• Blade guides should be adjusted to provide

adequate support• Most problems caused by poor machine condition

– Follow maintenance program on a regular basis


Problems When Using Power Hacksaws and Band Saws• Blades breaking

– When dropped on work– Loose blade or excessive feed

• Crooked cutting– Usually result of worn blade– Loose blade or blade rubbing– Excessive blade pressure– Remember to reverse work after replacing blade,

cutting on opposite side


Additional Problems• Blade pin holes breaking out

– Caused by dirty mounting plates or too much tension on blade

– Blade twists and strain, causing pin hole to break out

• Premature blade tooth wear– Insufficient or excessive feed pressure– Lack of coolant or poorly adjusted machine


Additional Problems (Cont.)

• Teeth strip off– Starting cut on sharp

corner– Be sure work is

positioned correctly and clamped securely

– Use proper blade for work



Metal-Cutting Circular Saws• Found in many areas of metalworking• Primarily production machine• Divided into three classifications

– Abrasive cutoff saw– Cold circular saw– Friction saw


Abrasive Cutoff Saw• Cuts material using rapidly revolving, thin abrasive

wheel• Most material can be cut to close tolerances• Special heat-resistant abrasive wheels are available• Two classifications

– Dry– Wet


Cold Circular Saw• Makes use of a circular, toothed blade• Capable of producing very accurate cuts• Large cold circular saws can sever round metal

stock up to 27″ (675 mm) in diameter


Friction Saw• Operates at very high speeds• Actually melts its way through metal• May or may not have teeth

– Teeth used to carry oxygen to cutting area

• Find many applications in steel mills to cut red-hot billets


Power Saw Safety• Never operate while senses are impaired• Get help when lifting, cutting heavy material• Clean oil, grease, and coolant from work area• Remember burrs on cut pieces are sharp• Follow manufacturer’s instructions for tensioning a

blade• Handle blades with extreme care• Mount work solidly before starting cut


Power Saw Safety (Cont.)• Make sure all guards are in place before using• Wear a dust mask and full face shield when

necessary• Avoid standing directly in line with blade• Use brush to clean chips from machine• Keep hand out of way of moving parts• Stop machine before making adjustments• Have any injuries, even minor ones, treated

immediately

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Sawing and Cutoff Machines