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 Basic or Semiprecision Layout Unit 20

20-2 Objectives Lay out a workpiece to an accuracy of ±.007 in. Lay out straight lines using the combination square and surface gage Lay out hole centers, arcs, and circles

20-3 Basic or Semiprecision Layout Requires use of basic tools (Unit 19) –Dividers, trammels, scribers, calipers, squares Keep simple as possible to save time Accuracy of layout will affect accuracy of finished workpiece Layout different for each workpiece, but certain procedures should be followed in any layout Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

20-4 To Lay Out Hole Locations, Slots, and Radii 1.Study workpiece and select proper stock Sample workpiece for example of basic layout procedures

Cut off stock, allowing enough material to square ends if required 3.Remove all burrs 4.Clean surface thoroughly and apply layout dye 5.Place suitable angle plate on surface plate 6.Clamp work to angle plate with finished edge of part against surface plate or on a parallel Leave one angle protruding beyond workpiece

With surface gage set to proper height, scribe center line for full length of work 8.Using centerline as reference, set surface gage for each horizontal line and scribe center lines for all hole and radii locations 9.With work still clamped to angle plate, turn angle plate 90º and scribe baseline at bottom of workpiece 10.Using baseline as reference line, locate and scribe other centerlines for each hole or arc

Locate starting points for angular layout Note: All measurements for any location must be taken from baseline or finished edge 12.Remove workpiece from angle plate 13.Carefully prick-punch center of all hole or radii locations 14.Using divider set, scribe all circles and arcs Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Scribe any lines required to connect arcs or circles 12.Draw in angular lines Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

20-9 To Lay Out a Casting Having a Cored Hole Foundry molds casting that requires hole, core used to produce rough hole –Core often shifts out of place and hole off center –Hole machined concentric with outside of casting Procedure to lay out hole location: 1.Grind scale off surface to be laid out 2.Tap tightly fitting wooden piece into cast hole

Coat surface to be laid out and wooden piece with solution of slaked lime and alcohol or layout dye 4.With hermaphrodite calipers, scribe four arcs using outside diameter of shoulder as reference surface 5.Using the intersection of these arcs as center, scribe circle of required diameter on casting (concentric with outside of casting) 6.Prick-punch layout line at about eight equidistant points around layout circle

20-11 Keyseat Recessed groove cut in a shaft and into which a key is fitted to prevent a mating part (pulley or gear) from turning on shaft Layout requires much care –Particularly if mating parts must maintain certain relative position

20-12 Procedure To Lay Out a Keyseat in a Shaft 1.Apply layout dye to end of shaft and to area where keyseat is to be laid out 2.Mount workpiece in a V-block 3.Set surface gage scriber to center of shaft 4.Scribe line across end and continue it along shaft to keyseat location 5.Rotate workpiece in V-block and mark length and position of keyseat on the shaft

Set dividers to half the width of keyseat, and scribe circle at each end of layout 7.Using keyseat rule and scriber, connect the circles with line on either side of the centerline and tangent to circles Circle may be connected using surface gage 8.Prick-punch keyseat layout and center- punch centers of the circles 9.If necessary to drill holes at end of keyseat, set up shaft by aligning end layout line in vertical position with square