TWIST DRILL : TWIST DRILL LEARNING OUTCOMEIDENTIFY AND STATE THE PURPOSE OF DIFF. TYPE OF TWIST DRILL.IDENTIFY THE VARIOUS FEATURES OF A TWIST DRILL.MEASURE DRILL FOR SIZE. CALCULATION OF R.P.M : LEARNING OUTCOMEIDENTIFY AND STATE THE PURPOSE OF DIFF. TYPE OF TWIST DRILL.IDENTIFY THE VARIOUS FEATURES OF A TWIST DRILL.MEASURE DRILL FOR SIZE. CALCULATION OF R.P.M Slide 3: A TWIST DRILL is an end-cutting tool used to produce a hole in a piece of metal or others materials. The most common drill manufactured has two cutting edges (lips) and two straight or helical flutes which provide the cutting edges, admit cutting fluid, and allow the chips to escape during the drilling operation. Twist Drills : Twist Drills Most Twist Drills are made of either Carbon Steel or High Speed Steel, usually marked on the Drill “Shank” (carbon steel) or (HS or HSS) for High Speed Steel.
The Twist Drill consists of three main sections; the Shank, the Body, and the Point. Shank: The Shank end of the Drill fits into the chuck of an electric drill or drill press. The drill size is usually stamped on the Shank.
Body: The Body section of the Twist Drill consists of the flutes, the margin and the web.
Web: The Web is that thin part that runs from the shank to the point of the drill. It separates the flutes. TYPES OF DRILLS : TYPES OF DRILLS CARBON STEEL DRILLS-GENERALLY USED IN A HOBBY SHOP
AND NOT RECOMMENDED FOR MACHINE SHOP WORK
SINCE THE CUTTING EDGE TEND TO WEAR DOWN
QUICKLY. Slide 6: HIGH-SPEED STEEL DRILLS-COMMONLY USED IN MACHINE SHOP WORK
BECAUSE THEY CAN OPERATED AS TWICE AS THE SPEED
OF CARBON STEEL DRILLS AND THE CUTTING EDGES
CAN WITHSTAND MORE HEAT AND WEAR. Slide 7: CEMENTED-CARBIDE DRILLS used to drill hard materials and they are capable of withstanding higher heat. Slide 8: LOW HELIX-DRILL – developed primarily to drill brass and thin materials. Because of its design, the low helix drill can remove the large volume of chips formed by high rates of penetration when it is used on machines such as turret lathes and screw machines. Slide 9: HIGH-HELIX DRILL – is used to drill deep holes in low tensile strength materials, such as aluminum, copper, die-cast materials and plastic. Chips from these materials tend to jam in the flutes, however the wide polished flutes and the high helix help to clear the chips and prevent jamming. Slide 10: CORE DRILL – is used to punch hole, have three or four flutes, and greater accuracy with respect to hole size and location. The primary use of this drill is to enlarge cored holes in casting. Slide 11: COOLANT HOLE DRILL (OIL HOLE DRILL) – has two holes running through the lands from the shank to the cutting pint of the drill. During use, the coolant is forced under high pressure through the holes in the lands. To the critical machining area (the chisel edge and pint), serves as a lubricant and coolant – is generally used in screw-machine and turret lathe production work. Slide 12: STRAIGHT FLUTE DRILL – designed to produce short chips and is recommended for drilling brass, sheet metal work and nonferrous materials Slide 13: Flutes: large spiral grooves on each side of the drill body that runs from the shank to the point to form the cutting edges (lips). They also allow the chips to escape during the drilling process and permit lubricant to reach the drill point. Margin: that narrow raised section that extends along the entire length of the flutes. It determines the full diameter of the Twist Drill. If the size of the drill is to be checked with a micrometer, the measurement must be taken on the margins. Body Clearance: the cut portion between the margin and flutes. This clearance reduces the friction between the drill and the edge of the hole while the drill is turning. Slide 14: The Point: the entire cone shape section which forms the cutting edges of the drill. Each cutting edge is sharpened to form an angle of 59° with the drill center line. Together, these angles form the included angle of 118° which is recommended for the general purpose. Lip Clearance: the relief ground on the point from the cutting edge (lip) back to the heel. Lip Clearance allows the cutting edge of the drill to enter the material being drilled without interference. The amount of clearance angle determines how deep the lip will cut into the metal. The average lip clearance angle for a Twist Drill is 12 – 15 degrees. The Clearance angle should be decreased for hard materials and may increase for softer materials. When sharpening a drill bit, always grind from the lip to the heel. Slide 15: Fraction, Number and Letter Drill Sizes ? Twist Drill sizes are designated under four systems; Fractional, number, letter, and metric.
The Fractional Drill sizes range from 1/64 inch to 1 inch and over.
Numerical drill sizes, corresponding to wire gauge (the larger the number, the smaller the drill). Example: Starting with a # 80 drill and a #1 drill.
Drill size is designed by letter range from letter “A” (measures .234 inch) to letter “Z” (measures .431 inch).
The metric sizes range from 0.4mm (measures .015 inch) to 50mm (measures 1.968 inch). Slide 16: MEASURING THE SIZE OF A DRILL
In order to produce a hole to the required size, it is important that the correct size drill is used. It is a good practice to always check a drill for size before using it by two methods. With a drill gage and with a micrometers by taken measurements across the margin of the drill. Slide 17: CUTTING SPEED
Cutting speed may be defined as the distance in either surface feet or surface meters that a point on the circumference of the drill travels in a 1 minute.
CALCULATION FOR R.P.M.
The number of revolutions necessary to produce the desired cutting speed is called revolutions per minute (r/min).
To find the number of revolutions per minute at which a drill press spindle must be set to obtain a certain cutting speed, the following must be known:
The recommended cutting speed of the materials to be drilled.
The type of materials from which the drill is made.
The diameter of the drill. Slide 18: CUTTING SPEED THE SPEED OF A TWIST DRILL IS GENERALLY REFERRED TO AS
CUTTING SPEED,SURFACE SPEED,OR PERIPHERAL SPEED..IT IS
THE DISTANCE THAT A POINT ON THE CIRCUMFERENCE OF A
DRILL WILL TRAVEL IN A MINUTE. ECONOMICAL DRILLING SPEED DEPENDS ON MANY VARIABLES THE TYPE AND HARDNESS OF THE MATERIAL.
THE DIAMETER AND THE MATERIAL OF THE DRILL.
THE DEPTH OF THE HOLE.
THE TYPE AND CONDITION OF THE DRILL PRESS.
THE EFFICIENCY OF THE CUTTING FLUID EMPLOYED.
THE ACCURACY AND QUALITY OF THE HOLE REQUIRED
THE RIGIDITY OF THE WORK SETUP. Slide 19: REVOLUTIONS PER MINUTE THE NUMBER OF REVOLUTIONS OF THE DRILL NECESSARY TO ATTAIN
THE PROPER CUTTING SPEED FOR THE METAL BEING MACHINE. TO DETERMINE THE CORRECT NUMBER OF R/MIN OF A DRILL
PRESS SPINDLE FOR A GIVEN SIZE DRILL,THE FOLLOWING
SHOULD BE KNOWN:
THE TYPE OF MATERIAL TO BE DRILLED.
THE RECOMMENDED CUTTING SPEED OF THE MATERIAL.
THE TYPE OF MATERIAL FROM WHICH THE DRILL IS MADE. Slide 20: FORMULA (INCH) R/MIN = CS(FEET PER MINUTE)X 12
pD (drill circumference in inches) Where: CS= THE RECOMMENDED CUTTING SPEED IN FEET PER MINUTE
FOR THE MATERIAL BEING DRILLED.
D= THE DIAMETER OF THE DRILL BEING USED. NOTE : THE CS WILL VARY DEPENDING ON THE MATERIAL FROM WHICH
THE DRILL IS MADE. SINCE NOT ALL MACHINES CAN BE SET TO THE EXACT CALCULATED
SPEED ,p(3.1416) IS DIVIDED INTO 12 TO ARRIVE AT A SIMPLIFIED
FORMULA,WHICH IS ACCURATE ENOUGH FOR MOST DRILLING
OPERATIONS. Slide 21: SIMPLIFIED FORMULA(INCH) R/MIN = CS X 4
CALCULATE THE R/MIN REQUIRED TO DRILL A ½ IN. HOLE IN CAST
IRON(CS 80) WITH A HIGH SPEED STEEL DRILL.
D = 80 X 4
= 640 Slide 22: FORMULA(METRIC)
pD (mm) IT IS NECESSARY TO CONVERT THE METERS IN THE NUMERATOR
TO MM SO THAT BOTH PARTS OF THE EQUATION ARE IN THE SAME
UNIT.TO ACCOMPLISH THIS,MULTIPLY THE CS IN METERS PER MINUTE
BY 1000 TO BRING IT TO MM PER MINUTE. R/MIN= CSX1000
pD NOT ALL MACHINES HAVE A VARIBLE SPEED DRIVE AND THEREFORE
CANNOT BE SET TO THE EXACT CALCULATED SPEED.BY DIVIDING
?3.1416 INTO 1000, A SIMPLIFIED FORMULA IS DERIVED THAT IS
ACCURATE ENOUGH FOR MOST DRILLING OPERATIONS. R/MIN= CS X 320
D Slide 23: EXAMPLE
CALCULATE THE R/MIN REQUIRED TO DRILL A
15-MM HOLE IN TOOL STEEL(CS 18) USING A
HIGH-SPEED STEEL DRILL.
= 384 Slide 24: STEEL
STEEL CS FOR HSS For More Information visit the site Below: : For More Information visit the site Below: http://www.jjjtrain.com/vms/cutting_tools_twist_drill.html#top