Knurling, Grooving, and Form Turning Unit 53

Objectives Set up and use knurling tools to produce diamond-shaped or straight patterns on diameters Cut square, round, and V-shaped grooves on work between centers or in a chuck Machine convex or concave forms on diameters freehand

Knurling, Grooving, and Form Turning Alter either the shape or finish of a round workpiece Normally performed on work mounted in chuck Can also be done on work mounted between lathe centers

Knurling Process if impressing a diamond-shaped or straight-line patter into the surface of the workpiece Improve its appearance Provide better gripping surface Increase workpiece diameter when press fit required

Knurling Diamond- and straight-pattern rolls available in three styles Fine Medium Course Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Knurling Tool Toolpost-type toolholder on which pair of hardened-steel rolls mounted Knurling tool with one set of rolls in self-centering head Knurling tool with three sets of rolls in revolving head Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Universal Knurling Tool System Dovetailed shank and as many as seven interchangeable knurling heads that can produce wide range of knurling patterns Combines in one tool Versatility Rigidity Ease of handling Simplicity

Small Diameter Diamond Cutting Knurling Tool Single Wheel Knurling Head Shoulder Knurling Head Straddle Forming Knurling Head Standard Diamond Knurling Head Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Procedure to Knurl in a Lathe Mount work between centers and mark required length to be knurled If work held in chuck for knurling, right end of work should be supported with revolving tailstock center Set lathe to run at one-quarter speed required for turning Set carriage feed to .015 to .030 in.

Set knurling tool at right angles to workpiece and tighten it securely Set center of floating head of knurling tool even with dead-center point Set knurling tool at right angles to workpiece and tighten it securely Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Start machine and lightly touch rolls against work to check tracking Move knurling tool to end of work so only half the roll face bears against work Force knurling tool into work approximately .025 in. and start lathe OR Start lathe and then force knurling tool into work until diamond pattern come to point

Stop lathe and examine pattern Once pattern correct, engage automatic carriage feed and apply cutting fluid to knurling rolls Knurl to proper length and depth Do not disengage feed until full length has been knurled; otherwise, rings will be formed on knurled pattern If knurling pattern not to point after length has been knurled, reverse lathe feed and take another pass across work

Grooving Square Round V-shaped Done at end of thread to permit full travel of nut up to a shoulder or at edge of shoulder for proper fit Also called recessing, undercutting, or necking Rounded grooves used where there is strain on part Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Procedure to Cut a Groove Grind toolbit to desired size and shape of groove required Lay out location of groove Set lathe to half the speed for turning Mount workpiece in lathe Set toolbit to center height

Locate toolbit on work at position where groove is to be cut Start lathe and feed cutting tool toward work using crossfeed handle until toolbit marks work lightly Hold crossfeed handle in position and set graduated collar to zero Calculate how far crossfeed screw must be turned to cut groove to proper depth Feed toolbit into work slowly using crossfeed handle

Apply cutting fluid to point of cutting tool To ensure cutting tool will not bind in groove, move carriage slightly to left and to right while grooving Should chatter develop, reduce spindle speed Stop lathe and check depth of groove with outside calipers or knife-edge verniers Safety note: Always wear safety goggles when grooving on a lathe

Form Turning Need irregular shapes or contours from workpiece Done on lathe by four methods: Freehand Form-turning tool Spherical tool Hydraulic tracer attachment

Turning a Freehand Form or Radius Presents greatest problem to beginning lathe operator Coordination of both hands is required and practice important in master skill Let's use an example to walk through the steps: Turn a .500 in. radius on the end of a workpiece

Example: Turn a .500 Radius Mount workpiece in chuck and face end With work revolving, mark a line .500 in. from end using a pencil Mount a round-nose turning tool on center Start lathe and adjust toolbit until it touches diameter about .250 in. from end Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Place one hand on crossfeed handle and other on carriage handwheel turn carriage handwheel (not the handle) to feed toolbit slowly toward end of work; at same time, turn crossfeed handle to move tool into work Back toolbit out and move carriage to left Take successive cuts as in step 6 until toolbit starts to cut close to the .500 in. line

Test radius with a .500 in. gage If radius not correct, it may have to be recut Often possible to finish radius to required shape by filing Note: Follow same procedure as in step 6 when cutting internal radii – always start at large diameter Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Form-Turning Tools Used to form smaller radii and contours Lathe toolbit ground to desired radius and used to form contour Also concave radius Eliminates need for checking with gage Leave collar of desired size on workpiece when producing convex radius Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Form-Turning Tools Produce good finish work should be revolved slowly Cutting oil applied as tool fed into work Eliminate chatter during cutting Move cutting tool slightly back and forth (longitudinally)

Procedure for Form Turning Using a Template and Follower Make accurate template to form desired Mount template on bracket fastened to back of lathe Position template lengthwise in relation to workpiece Mount a round-nose cutting tool in toolpost Fasten follower, face must have same form as point of cutting tool, on cross-slide of lathe

Disconnect cross-slide from crossfeed screw Rough-out form on workpiece freehand by keeping follower close to template Final roughing cut .030 in. of template Disconnect cross-slide from crossfeed screw Apply light hand pressure on cross-slide to keep follower in contact with template Engage automatic carriage feed and take finish cut from workpiece, while keeping follower in contact with template

Spherical Tool Can make a perfect spherical ball or spherical cavity to within .0001-in accuracy Consists of dovetailed turret that holds cutting tool and drive mechanism that can be hand fed or power driven Dial microscrew indicates depth of cut and diameter Concave forms can be cut when internal toolholder installed

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

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

Hydraulic Tracer Attachment Used when many duplicate parts having several radii or contours to produce required Incorporates means of moving cross-slide by controlled oil pressure supplied by hydraulic pump Flat template mounted on lathe Stylus bears against template surface and actuates control value regulating flow of oil into cylinder which moves piston and causes toolbit to move in or out

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

Advantages of a Tracer Attachment Intricate forms can be readily produced Various forms, tapers, and shoulders can be produced in one cut Duplicate parts can be produced rapidly and accurately Accuracy and finish of part do not depend on skill of operator

Hints on the Use of a Tracer Attachment Toolbit point and stylus should have same form and radius Radius on toolbit should be smaller than smallest radius on template Stylus must be set to point on template giving smallest diameter of work Centerline of template must be parallel to ways of the lathe

Form of template must be smooth No angle larger than 30º, or equivalent radius, should be incorporated in form of template Duplicate parts produced between centers must be same length and have center holes drilled to same depth Duplicate parts held in chuck should project same distance from chuck jaws Included angle of tool point should be less than smallest angle on template