CHAPTER XIV.

=MEASURING MACHINES, TOOLS AND DEVICES.=

=Standards of Measurements=, in various countries 341 Use of, by sight and by the sense of feeling 341 Variations in standard gauges 341 The necessity for accurate standards 341 The Rogers Bond standard measuring machine 342 Details of construction of 343, 344 The principle of construction of 344 The methods of using 345 The Whitworth measuring machine 345 The Betts Machine Company's measuring machine 346 Professor Sweet's measuring machine 347 Measuring machine for sheet metal 348 =Circle=, division of the 348 Troughton's method of dividing the circle 348, 349 Ramsden's dividing engine 349 The construction of 350, 351 Pratt and Whitney's dividing device 352 Practical application of 353 Index wheel, method of originating, by R. Hoe & Co. 353 Application of the index wheel (Hoe & Co.'s system) 353 =Classification= of the measuring tools used by workmen 354 =Micrometer Caliper= and its principle of construction 354, 355 =Gauges.= Standard plug and collar gauges 356 Methods of comparing standard plug and collar gauges 356 The effects of variations of temperature upon standard gauges 356 Plug and collar gauges for taper work 357 The Baldwin standards for taper bolts 359 Workmen's gauges for lathe work 359 =Calipers=, outside, the various forms of 360 Inside calipers 360 Calipers with locking devices 360 Spring calipers 360 The methods of holding and using 361, 362 Keyway calipers 363 The advantages of calipers 363 =Fitting.= The four kinds of fit in machine work 363 The influence of the diameter of the work in limiting the application of standard gauges 363 The wear of tools and its influence upon the application of the standard gauge system 364 The influence of the smoothness of the surface upon the allowance to be made for drilling or hydraulic fits 365 Examples of allowance for hydraulic fits 365 Parallel holes and taper plugs for hydraulic fits 365 =Fitting.= Practicable methods of testing the fit of axle brasses forced in by hydraulic pressure 366 Shrinkage or contraction fits 366 Allowances for 366 Gauge for 367 The shrinkage system at the Royal Gun Factory at Woolwich 367 Experiments by Thomas Wrightson upon the shrinkage of iron under repeated heatings and coolings 368 to 374 Shrinking work, to refit it 374, 375