The upright drill press is the most common of the variety of  drill presses available.  [Figure 4-42] When using a drill press, the height of the drill press table is  adjusted to accommodate the height of the part to be drilled.  When the height of the part is greater than the distance  between the drill and the table, the table is lowered. When  the height of the part is less than the distance between the  drill and the table, the table is raised. After the table is properly adjusted, the part is placed on the  table and the drill is brought down to aid in positioning the  metal so that the hole to be drilled is directly beneath the point  of the drill. The part is then clamped to the drill press table to  prevent it from slipping during the drilling operation. Parts  not properly clamped may bind on the drill and start spinning,  causing serious cuts on the operator’s arms or body, or loss  of fingers or hands. Always make sure the part to be drilled  is properly clamped to the drill press table before starting  the drilling operation. The degree of accuracy that it is possible to attain when using  the drill press depends to a certain extent on the condition of  the spindle hole, sleeves, and drill shank. Therefore, special  care must be exercised to keep these parts clean and free from  nicks, dents, and warpage. Always be sure that the sleeve is  securely pressed into the spindle hole. Never insert a broken  drill in a sleeve or spindle hole. Be careful never to use the  sleeve-clamping vise to remove a drill since this may cause  the sleeve to warp. The drill speed on a drill press is adjustable. Always select the  optimum drill speed for the material to be drilled. Technically,  the speed of a drill bit means its speed at the circumference,  in surface feet per minute (sfm). The recommended speed for  drilling aluminum alloy is from 200 to 300 sfm, and for mild  steel is 30 to 50 sfm. In practice, this must be converted into  rpm for each size drill. Machinist and mechanic handbooks  Angle adapters can be attached to an electric or pneumatic  drill when the location of the hole is inaccessible to a straight  drill. Angle adapters have an extended shank fastened to  the chuck of the drill. The drill is held in one hand and the  adapter in the other to prevent the adapter from spinning  around the drill chuck. The snake attachment is a flexible extension used for drilling  in places inaccessible to ordinary drills. Available for electric  A straight extension for a drill can be made from an ordinary  piece of drill rod. The drill bit is attached to the drill rod by  shrink fitting, brazing, or silver soldering.  Extension drill bits are widely used for drilling holes in  locations that require reaching through small openings or  past projections. These drill bits, which come in 6- to 12- inch lengths, are high speed with spring-tempered shanks.  Extension drill bits are ground to a special notched point,  which reduces end thrust to a minimum. When using  extension drill bits always: include drill rpm charts or drill rpm may be computed by  use of the formula: Example: At what rpm should a  1 ⁄ 8-inch drill turn to drill  aluminum at 300 sfm? When access to a place where drilling is difficult or  impossible with a straight drill motor, various types of drill  extensions and adapters are used.  CS = The recommended cutting speed in sfm D = The diameter of the drill bit in inches CS × 4  = rpm D Drill Extensions and Adapters  Extension Drill Bits Straight Extension Angle Adapters  Snake Attachment 4-16 Figure 4-42.  Drill press.  3.  Keep the drill bit under control. Extension drills  smaller than  1 ⁄ 4-inch must be supported by a drill  guard made from a piece of tubing or spring to prevent  whipping. 2.  Check the drill bit for straightness. A bent drill bit  makes an oversized hole and may whip, making it  difficult to control. 1.  Select the shortest drill bit that will do the job. It is  easier to control.