Using a Test Indicator (2)

WORKSHOP HINTS AND TIPS Using a test indicator (2) By Geometer IN mechanical engineering all and small-end are parallel. On a components and machines drawing, they are two parallel lines. In testing the connecting rod, you have a basis of geometry which put a well-fitting mandrel in each settles the shape and alignment bearing and support the connecting of surfaces. For the most part it rod on a surface plate. Both ends is elementary geometry visible of a mandrel should then give the and tangible, consisting of plane same reading on a test indicator, surfaces, diameters and right- when the connecting rod is lying angles, all of which can be proved horizontally, and when it is standing in straightforward ways with a vertically. If there is an end-to-end difference in the height of a mandrel, test indicator. it is shown by a variation in the But in proving visible features you reading on the test indicator, and often prove those that are invisible you know that the axes are not -except on drawings, where they parallel. (You forcibly true a mal- form the framework as axes and aligned connecting rod through a centre-lines. To ensure accuracy in corrective twist or by applying draughting, axes and centre-lines are pressure opposite the bend.) put in first on drawings. Then you Geometry offers us many oppor- design components, in the flat, tunities for halving errors in seeking around them. When you test three- accuracy, and for doubling the F dimensional components, you prove amplitude of errors the better to find the basic geometry. small ones. An example on the 0 Take as an example a connecting drawing board is the way that you rod on which the axes of big-end check a celluloid square. Holding it to the edge of the T-square, you pencil a vertical line. Then you turn the square over-and any error and for tapping the face of work, is doubled. It is the same when you use a lead or hide hammer. If a test a steel square by scribing lines faceolate wobbles. pack at the low on a straight-edged metal plate. point with paper. To true a button By a similar principle, the flatness C, tap the edge of work with a brass of a lathe faceplate can be verified or aluminium punch-the clamps and the alignment of the cross-slide can set a vertical slide to any angle checked, with a test indicator used just gripping. Then tighten them in a holder on the topslide, as at A. firmly. Turn the faceolate to discover Diagram D illustrates how you wobble and then locate the run-out for a milling operation. The test vertically. Using the cross-slide, run indicator is mounted in a chuck or the test indicator across the near on a driving plate for its plunger to half of the faceplate U. With a bear on the blade of a protractor. long holder, repeat the test on the You can set a vernier protractor to remote half V. a fraction of a degree, and place the If the faceplate has been machined stock to the vertical slide with the on the lathe, an error is concurrent blade across the lathe axis. To hold between the faceplate and the cross- the protractor level, clamp it to an slide for the near half U. And so angle plate. Set the vertical slide the first test reveals nothing unusual. so that the test indicator shows a But on the remote half V. an error steady reading by cross-slide move- runs counter to the one on’the cross- ment X. slide. The second test shows this Two more typical uses of a test clearly. indicator are shown at E and F. To A universal attachment, or a lever set a fly cutter, test over the bar for attachment, equips a test indicator height Y and add the projection of for use in bores and on outside dia- the tool Z. Set a home-made height meters where clamps obstruct direct gauge to Y, and for Z place two access. Examples of use are at B turned rollers under the gauge. To and C (clamps omitted). test concentricity of the pitch circle When work is held in a chuck B, of a gear put a roller in each tooth- its face as well as its bore must be space in turn, and rotate the gear true. Place packing at low jaws; under a test indicator. 9 AUGUST 1962 169 MODEL ENGINEER.

Load more