Horizontal Milling Operations Unit 67

Objectives Set a cutter to the proper depth Mill a Flat surface on a workpiece Perform operations such as face, side, straddle, and gang milling

Milling Machine One of most versatile machine tools found in industry Two basic types of milling are: Plain milling Surface cut parallel to periphery of cutter Surfaces may either be flat or formed Face milling Surface cut is at right angles to axis of cutter

Procedure to Set Cutter to the Work Surface Before setting depth of cut, check that work and cutter properly mounted and cutter revolving in proper direction Raise work to within .250 in. of cutter and directly under it Hold long piece of thin paper on surface of work Start cutter rotating

With left hand on elevating screw handle, move work slowly until cutter grips paper Stop spindle Move machine table so cutter just clears end of workpiece Raise knee .002 in. for paper thickness Set graduated collar on elevating screw handle to zero. Move work clear of cutter and raise table to desired depth of cut

Procedure for Milling a Flat Surface Most common operation and generally machined on workpiece with helical milling cutter Remove all burrs from all edges of work with mill file Clean vise and workpiece Align vise to column face of milling machine using dial indicator

Set work in vise using parallels and paper feelers under each corner to make sure that work seated on parallels Tighten vise securely by hand Tap work lightly at four corners with soft-faced hammer until paper feeler are tight Select plain helical cutter wider than work to be machined

Mount cutter on arbor for conventional milling Set proper speed for size of cutter and type of work material Set feed to approximately .003 to .005 in. chip per tooth Start cutter and raise work, using paper feeler between cutter and work Stop spindle when cutter just cuts paper Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Raise knee .002 in for paper thickness Set graduated collar on elevating screw handwheel to zero Move work clear of cutter and set depth of cut using graduated collar For roughing cuts, use depth of not less than .125 in and .010 -.025 in. for finish cut Set table dogs for length of cut Engage feed and cut side 1 Set up and cut remaining sides

Face Milling Process of producing flat vertical surface at right angles to cutter axis Cutters inserted-tooth cutters or shell end mills Face milling cutters made in sizes of 6 in. diameter and over Less than 6 in diameter usually called shell end mills

Procedure for Face Milling When facemilling large surface, use inserted-tooth cutter and mount it into spindle of machine When milling smaller surfaces, face milling cutter should be 1 in. larger than width of workpiece Set speeds and feeds for type of cutter and material being cut

Set up work on milling machine Use cutting fluid if cutter material or work will allow Take large rough cut as possible to bring surface close to within .030 to .060 in. of finish size Set depth of finish cut and machine surface to size After completing operation, clean and store cutter and equipment in proper places

Side Milling Procedure Often used to machine vertical surface on sides or ends of workpiece Set up work in vise and on parallels Tighten vise securely by hand Tap work lightly at four corners with soft-faced hammer until paper feelers are tight between work and parallels Mount side milling cutter

Set proper speed and feed for cutter Start machine and move table until top corner of work touches revolving cutter Set crossfeed graduated collar to zero Move work clear of cutter with handwheel Set required dept of cut with crossfeed handle Lock saddle to prevent movement during cut Take cut across surface

Procedure of Centering a Cutter to Mill a Slot Locate cutter close to center of work Using steel square and rule or gage block, adjust work to center by using crossfeed screw dial Lock saddle to prevent movement during cut Move work clear of cutter and set depth of cut Proceed to cut slot using same methods as for milling flat surface Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Straddle Milling Involves use of two side milling cutters to machine opposite side of workpiece parallel in one cut Cutters separated on arbor by spacers of required length Used for milling square and hexagonal bolt heads Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Points to be Observed When Straddle Milling Select two sharp side milling cutters, preferably staggered-tooth, of suitable size Mount cutters with suitable arbor spacers, as close to column as work will permit Mount arbor support as close to cutters as possible to provide rigidity for cutters Center cutters on workpiece in proper location

Tighten saddle lock to prevent any movement during cut Set cutter to work surface Move table so cutter clears end of work Set depth of cut required and tighten knee clamp Set proper speeds and feeds for cutter size and type of work material; check cutter rotation Use good supply of cutting fluid and complete straddle milling operation in one cut

Gang Milling Fast method of milling used in production work Performed by using two or more cutters on arbor to produce desired shape Diameter and width of each cutter same Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Points to be Observed To Avoid Problems During Gang Milling Operation: Select cutters close to same size and number of teeth to allow maximum speeds and feeds Mount correct cutters on arbor as close to machine column as possible Fasten arbor support close to cutters Set spindle speed to suit largest-diameter cutter Be sure work fastened securely and work-holding devices will not contact cutters Use good flow of cutting fluid

Sawing and Slitting Used for milling narrow slots and for cutting off work Fragile cutting tools because of their thin cross section Break easily To get maximum life from slitting saw, take the following precautions: Never key slitting saw on arbor unless it is mounted in special flanged mounting collar

When selecting slitting saw, choose one with smallest diameter that will permit adequate clearance between arbor collars or supports and holding devices and work Mount saw close to column face and have outer arbor support close to saw Always use sharp cutter Be sure table gibs are drawn up to eliminate play between table and saddle Operate saws at approximately 1/4 to 1/8 feed per tooth When sawing or slitting fairly long or deep slots, climb-mill to prevent cutter from breaking