Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint to accompany Krar Gill Smid Technology of Machine Tools 6 th Edition Metal-Cutting Saws Section 9

35-2 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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint to accompany Krar Gill Smid Technology of Machine Tools 6 th Edition Types of Metal Saws Unit 35

35-4 Objectives Name five types of cutting-off machines and state the advantage of each Select the proper blade to use for cutting various cross sections Install a saw band on a horizontal bandsaw Use a bandsaw to cut off work to an accurate length

35-5 Methods of Cutting Off Material Five most common methods of cutting off material –Hacksawing –Bandsawing –Abrasive cutting –Cold sawing –Friction sawing

35-6 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

35-7 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

35-8 Abrasive Cutoff Saw Cuts by means of thin, abrasive wheel revolving at high speed 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

35-9 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

35-10 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

35-11 Horizontal Bandsaw Parts Frame - hinged at motor end with two pulley wheels over which continuous blade passes Step Pulleys - Used to vary speed of blade Roller guide brackets - Provide rigidity for section of blade Blade tension handle - Used to adjust tension on saw blade Vise - Mounted on table, adjusted to hold work

35-12 Saw Blades Commonly made of high-speed tungsten and high-speed molybdenum steel –Hardened completely for power hacksaw –Flexible blades on bandsaws have teeth hardened Manufactured in various degrees of coarseness, ranging from 4-14 pitch –10-pitch blade used for general-purpose sawing –Always select saw blade as coarse as possible Always have two teeth of blade in contact with work at all times

35-13 Installing a Blade Make sure teeth are pointing in direction of saw travel or toward motor end of machine Adjust blade tension to prevent blade from twisting or wandering during cut Rotate work ½ turn in vise, if need to replace blade before cut finished –Prevent new blade from jamming

35-14 Procedure for Installing a Saw Blade 1.Loosen blade tension handle 2.Move adjustable pulley wheel forward slightly 3.Mount new saw band over two pulleys Check that saw teeth pointing toward motor end of machine

Place saw blade between rollers of guide brackets 5.Tighten blade tension handle only enough to hold blade on pulleys 6.Start and quickly stop machine to make saw blade revolve turn or two Will seat blade on pulley 7.Tighten blade tension handle tightly as possible with one hand

35-16 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

35-17 To Saw Work to Length 1.Check solid vise jaw with square 2.Place material in vise, supporting long pieces with floor stand 3.Lower saw blade until it just clears work Engage ratchet lever or close hydraulic valve to keep position 4.Adjust roller guide brackets until they just clear both sides of material to be cut 5.Hold steel rule against edge of saw blade and move material until correct length

Always allow.060 in. for each 1 in. of thickness longer than required to compensate for any saw run-out 7.Tighten vise and recheck length from blade to end of material 8.Raise saw frame slightly, release ratchet lever or open hydraulic valve, and start machine 9.Lower blade slowly until just touches work 10.When cut completed, machine will shut off

35-19 Sawing Hints 1.Never attempt to mount, measure, or remove work unless saw is stopped 2.Guard long material at both ends to prevent anyone from coming in contact with it 3.Use cutting fluid whenever possible to help prolong life of saw blade

When sawing thin pieces, hold material flat in vise to prevent saw teeth from stripping 5.Use caution when applying extra force to saw frame Generally causes work to be cut out of square 6.Set stop gage when several pieces of same length are required 7.Place short piece of same thickness in opposite end of vise when holding short work