1. Precision Layout
Unit 21

2. Objectives Make a precision layout using the Vernier height gage
Use the Woodworth Coordinate Factors and Angles tables to calculate equidistant hole locations
Make precision layouts using the sine bar and gage blocks

3. Precision Layout
Accuracy of finished workpiece generally determined by accuracy of layout
To make precision layout, must be able to
Read and understand drawings
Select and use proper layout tools for job
Accurately transfer measurements from drawing to workpiece
Check all layout work against sizes on drawings after completing layout

4. Accuracy in Precision Layouts
Vernier height gage used when layout lines must be accurate to within .001 in. (0.02 mm)
Hole locations
Use reference surfaces (two machined edges)
X and Y coordinates
Layout calculated using trigonometry
Can use Woodworth Coordinate Factors and Angles tables (See Appendix of Tables in text)

5. Vernier Height Gage
Used to measure vertical distances to ±.001 in. accuracy
Main parts
Base
Beam
Vernier slide
Scriber
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6. Example for Unit
For the description of a precision layout, the following job has been given:
It is required to lay out the position of five equally spaced holes on a 5 in. diameter circle located in the center of a 7 in. square steel plate.

7. Procedure to Make a Precision Layout Using a Vernier Height Gage
Refer to drawing of required workpiece
Remove all burrs from workpiece
Apply layout dye to surface and mount it on an angle plate
Clean surface of layout table, angle plate, and base of height gage
Mount offset scriber on vernier slide and clamp it in position

8. Check reading on vernier scale.
Move vernier slide and scriber down until scriber touches top of surface plate
Check reading on vernier scale.
Zero mark on vernier should align exactly with zero graduation on beam
Refer to Coordinate Factors and Angles tables in appendix for coordinates for five equidistant holes
Calculate location of all five holes

9. 7 5 1 4 5 7 3 2
.750 diameter: 5 holes equally spaced

10. Example of the calculation of one of the holes in the plate
Example of the calculation of one of the holes in the plate. The other four would be similarly calculated.
Hole 1
Horizontal distance from left-hand edge Y
= (diameter of circle x factor for A)
= (5 x ) =
= 1.122
Vertical distance from upper edge X
= (diameter x factor for B)
= (5 x ) =
= 2.727

11. Place edge Y on layout table surface
Set height gage to and scribe a line by drawing the scriber across the face of the workpiece at the location for hole 1
Set height gage to each of the other settings and scribe the lines. x y
1.122
3.500
4.969
5.878
2.031

12. Rotate angle plate and work 90º and place edge X on layout table
Set vernier height gage to 2.727
Scribe the intersecting lines at the centers of holes 1 and 4.
Set height gage to 5.523
Scribe intersecting lines for centers of holes 2 and 3
Set height gage to and scribe the intersecting line for hole 5

13. Set dividers to .375 in. and scribe five .750 in. circles
Remove workpiece from angle plate and place it on bench with layout surface up
Using sharp prick punch and magnifying glass, carefully mark centers of holes at intersecting lines
Set dividers to .375 in. and scribe five .750 in. circles
Carefully prick-punch circumference of circle for permanency
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14. More Accurate Layout
May use sine bar, gage blocks and height gage to accurately establish hole locations and X and Y axes
Use of coordinates preferred to locate hole centers
Work can be set up on jig borer or vertical mill using coordinates to position holes for machining

15. Check drawing for required dimensions
Procedure To Make Precision Layout Using a Sine Bar, Gage Blocks, and a Vernier Height Gage
Check drawing for required dimensions
machine and grind plate square to size in x in
Clean surface and coat with layout dye
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16. Set work on edge on a surface plate and clamp it to an angle plate
Using vernier height gage, scribe centerlines for hole A
Calculate the position of hole B as follows:
Length of side X Length of side Y
X = cos 30º Y = sin 30º
= x = x .500
= in = in.
These measurements are the position of the center of hole B to the right and above centerline for hole A

17. 3.557
0.000 A
1.813 B Y
3.000 X
2.750
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18. Using vernier height gage, mark off centerline for hole B
Vertical centerline located
Horizontal centerline at –
Remove workpiece from angle plate
Carefully prick-punch intersection of centerlines of these holes using sharp punch and magnifying glass
Lay out the 15º angle at corner of plate, calculate buildup for 15º using 5 in sine bar
Buildup = 5 sin 15º = 5 x =

19. Place buildup under one end of sine bar (on surface plate)
Place workpiece, angled edge up, on sine bar and clamp to angle plate
Calculate length DF
tan 15º =
DF = x 2.750
= .7368
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20. Calculate length DE.
To scribe line accurately at 15º, need to fine vertical distance below D (length DE) DF previously found to be equal to in.
DE = cos 15º x DF
= x .737
= .7118
= .712 in.
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21. Set scriber on vernier height gage to uppermost corner of plate
Lower scriber .712 in. and scribe line GF
This will locate point G at position in. from side of plate
Remove workpiece from angle plate
Lightly prick-punch layout line using magnifying glass and sharp prick punch