MACHINING Copyright Goodheart-Willcox Co., Inc. Chapter 26 Milling Machines 453 End mills may be mounted in spring collets, adapt- ers, shell end mill holders, or stub arbors, depending upon the type of work to be done. See Figure 26-26. Spring collets accommodate straight shank end mills and drills. Some collets must be fitted in a collet holder. 26.4.4 Care of Arbors To maintain precision and accuracy during the machining operation, care must be taken to prevent damage to the cut- ter holding and driving devices. Follow these guidelines: • Keep the arbor taper and the spindle taper free of nicks. Wipe them with a clean, soft cloth before using. • Clean and lubricate the bearing sleeve and arbor support bearing before use. • Clean the spacing collars before slipping them on the arbor. A chip between spacers can cause cutter runout, making it difficult to make an accurate cut, Figure 26-27.7 7 • Store arbors separately and in a vertical position. • Never loosen or tighten an arbor nut unless the arbor support is locked in place, because this could spring the arbor and it will not run true. A B B C D E Collet Collet holder Cap nut Wrench to tighten shell mill on holder (not drawn to scale) Arbor screw ot Pilot diameter Stub arbor b Spacers Arbor nut Goodheart-Willcox Publisher Figure 26-26. Mounting devices. A—Spring collet (R-8) taper type. B—Collet chuck and collet. C—Adapter used with taper shank cutting tools. D—Shell end mill holder (R-8 taper). E—Stub arbor (R-8 taper). Goodheart-Willcox Publisher Figure 26-27. The arbor will spring out of true if chips get between the collars. This drawing greatly exaggerates the situation.