Machinery's Handbook, 31st Edition
760 Right-Angle Plates Type III, Universal Right-Angle Plate: By far the most versatile and useful right-angle plate in the machine shop is the Type III universal right-angle plate, Fig. 3. The Type III has two outside working surfaces at right angles and all adjacent sides are ground and finished to the same tolerance assigned to the main working surfaces. This provides a full range of positioning capabilities and makes the universal right angle just as accurate on its side as it is resting on its main working surface. All opposite sides are parallel within 0.0002 inch per foot. The universal right angle has a rib located between the ends that is square in configuration and provides support and stability to the main working surfaces while providing additional working surfaces that can be utilized for work support due to the accuracy assigned to the entire plate. The rib is hollowed out to provide good hand grip without sacrificing the stabilizing characteristics. Type IV: Machinist’s Adjustable Angle Plate: The Type IV adjustable angle plate, Fig. 4, is designed to allow rotation of the workpiece through 360 ° . The workpiece support table is adjustable from zero horizontal to 90 ° vertical in 10 ° increments. Basically, the Type IV machinist’s adjustable angle plate consists of a tilting table mounted on a rotary table base. The base has heavy lugs or bolt slots to accommodate mounting the plate on machine tools. The bottom of the base is machined true flat, parallel to the top plate and square to the vertical axis. The base is the true foundation of the plate and must be manufactured to the tightest of tolerances. All accuracies extend from the craftsmanship that is put into the base work of the Type IV plate. The top of the rotary base is graduated in one degree increments for the full 360 ° and is marked at least every 10 ° for a minimum of plus and minus 90 ° from zero (0 ° ). Most plates are marked around the full 360 ° in 10 ° major divisions with 1× minor divisions, permanently engraved or etched on a chrome or brightly finished face for ease of reading and maintenance. The standard rotary accuracy to which all Type IV plates are made is ±2.5 minutes, noncumulative. This tolerance maintains the accuracy ratio necessary to maintain a good measurement assurance level in your quality system. The tilting table consists of two plates joined together at one end by a precision hinge and provided with an adjustable and positive locking mechanism. The bottom plate is attached to the base at the vertical axis. This plate will swivel through 360 ° freely and will also have a positive locking mechanism. The bottom of the plate is marked with a permanent line for accurate positioning in relation to the graduations on the base. The top plate is made in one piece as a casting and has T-slots milled in from the solid plate, as shown in Fig. 4. The top plate is adjustable up to 90 ° and the positive locking mechanism is robust enough to secure the workpiece into position during milling, drilling, or boring operations without movement. The top plate is made with a protractor integrated into the design that is marked from 0 ° (horizontal) to 90 ° (vertical) with major scale indications at every 10 ° . Minor scale graduations may be indicated at 1 ° increments. The noncumulative error between graduations of the protractor is no greater than ±2.5 minutes, which allows for a high level of confidence in the measurements and operations made with this plate.
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B C Fig. 5. Type V, Toolmaker’s Adjustable Knee
Fig. 4. Type IV, Machinist’s Adjustable Angle Plate
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