Transcript 11 - Oxford University Press Canada

Chapter
11
Sawing and Cutoff
Machines
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
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Permission granted to reproduce for educational use only.
Metal-Cutting Power Saws
• Used to cut the stock to required length
• Three principal types
– Reciprocating-type
– Band-type
– Circular-type
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Permission granted to reproduce for educational use only.
Metal-Cutting Power Saws (Cont.)
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© Goodheart-Willcox Co., Inc.
Permission granted to reproduce for educational use only.
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
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Permission granted to reproduce for educational use only.
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
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Permission granted to reproduce for educational use only.
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
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Permission granted to reproduce for educational use only.
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
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Permission granted to reproduce for educational use only.
Mounting a Power Hacksaw Blade
Goodheart-Willcox Publisher
© Goodheart-Willcox Co., Inc.
Goodheart-Willcox Publisher
Permission granted to reproduce for educational use only.
Cutting with a Power Hacksaw
•
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•
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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
© Goodheart-Willcox Co., Inc.
Permission granted to reproduce for educational use only.
Power Band Saw
• Horizontal band saw
– Referred to as the cutoff machine
• Advantages over power hacksaw
– Greater precision
– Faster speed
– Less waste
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Permission granted to reproduce for educational use only.
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
Goodheart-Willcox Publisher
© Goodheart-Willcox Co., Inc.
Permission granted to reproduce for educational use only.
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
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Permission granted to reproduce for educational use only.
Problems When Using
Power Hacksaws and Band Saws
• Blades breaking
– When dropped on work
– Loose blade or excessive feed
• Crooked cutting
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–
–
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Usually result of worn blade
Loose blade or blade rubbing
Excessive blade pressure
Remember to reverse work after replacing blade,
cutting on opposite side
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Permission granted to reproduce for educational use only.
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
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Permission granted to reproduce for educational use only.
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
Goodheart-Willcox Publisher
© Goodheart-Willcox Co., Inc.
Permission granted to reproduce for educational use only.
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
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Permission granted to reproduce for educational use only.
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
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Permission granted to reproduce for educational use only.
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
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Permission granted to reproduce for educational use only.
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
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Permission granted to reproduce for educational use only.
Power Saw Safety
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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
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Permission granted to reproduce for educational use only.
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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Permission granted to reproduce for educational use only.