Chapter 25 Flashcards
Twist drill
Most drilling done with this. Had two cutting edges or lips. Common drill geometry. Cutting action happens inside the workpiece.
For actions that take place at point of drill:
1 a small hole is formed by the web, chips are not cut here. 2 chips are formed by the rotating lips. 3 chips are removed from the hole by the screw action fo the helical flutes. 4 the drill is guided by lands or margins that run against the walls of the hole.
Drilling
Process creates two chips.
V Speed
In surface feed per minute. This is the cutting speed at the outer corner of the cutting lip.
Twist drills have what parts
The body, the point, and the shank.
Body of twist drill
Contains two or more spiral or helical grooves called flutes, separated by lands.
Lands on drill
To reduce friction, each land is reduced in diameter, leaving a narrow margin of full diameter and a cutting edge.
Flutes of drill
Serve as channels through which the chips are withdrawn from the hole and coolant gets to the cutting edges.
Helix angle
The principal take angles behind the cutting edges are formed by relation of flute helix angle to the work.
Take angle of drill
Varies along the cutting edges. Being negative close to the point and equal to the helix angle out at the lip.
Dubbing
Can change the rake angle adjacent to the cutting edge by a special grinding procedure.
Cone shaped point
Contains the cutting edges and the various clearance angles. Come able affects the direction of flow of the chips across the tool face.
Drill produces what
A thrust force, T, and a torque, M. drill torque increases with feed and drill diameter, while the thirst force is influenced greatly by the web design.
Web
Web is between the flutes and forms a metal column or backbone.
Straight line chiseled end
If a conical point is ground on the drill, the intersection of the web and the cone produces this.
Chisel point
Form a high negative rake angle, resulting in high thrust forces and excessive heat. Drill failure occurs both at the center and the outer tips rconsequently.
Straight line chiseled point does what
Had the tendency to walk along the surface, moving the drill away. This will require additional supporting operations like center drilling, burr removal, and tool change, which increase time and reduces productivity.
Straight shank drills
Size uo to 3/8 diameter and must be held in drill chuck.
Taper shanks
Available on larger drills and common on drills above 1 in. Morse tapers used on these drills.held in a female taper in the end of the machine tool spindle. Taper assured that the drill is being accurately centered.
Tang
Is at the end of the taper shank and fits loosely into a slot ah the end of the tapered hole in the spindle.
Drift
The drill maybe be loosened for removal by driving a metal wedge called a drift through a holder in the side of the spindle.
TiN coasting does what
Greatly increases drilling performance. Increase tools life by 200 to 1000 percent,
Depth of the hole drilled
The depth of the hole to be drilled. Dived by the diameter of the drill is the depth to diameter ratio.
Deep hold drills/hu drills
Are used when deep holes are to be drilled.
When starting to drill a hole
It can reflect rathe readily because if the walking action of the chisel point.
Center drill
To ensure that a hole is started accurately use this.
Special drill holders
Available that permit drills to be held with only a very short length protruding.
Chuck
Straight shank drills must be held in a. Chuck. Chucks are adjustable and have steel fingers.
Chucks with chuck keys
Required that the machine spindle be stopped in order to change a drill.
Quick change chucks
Each drill is fastened in a round college that can be inserted into the chuck hole while it is turning by raising and lowering a ring on the chuck body.
Keyless chucks
Have limited gripping strength
Jigs
Work that is to be drilled is held in a vise or in jigs.
Drill press
Consists of a base, a column that supports a power thread, a spindle, and a work table.
Power bead
Obtains mot for diving the spindle
Spindle
The spindle is fed by hand using a capstan wheel. Contains. Hole with a Morse taper in its lower end for which taper shank drills or dill chucks can be inserted.
Drilling machines classified as
Bench, upright with single spindle, turret or NC turret, gang, multi spindle, deep hole, and trasnfer
Sensitive drilling machines
Smaller, plain, bench type machines with more accurate spindles.used for tool and die work and filling small holes.
Gang drilling machines
Often used when several opérateurs must be done on a single part. This consists of several independent columns and share a single table, the part can be slide into position for the other operation.
Turret type upright drilling machines
Used in marge work pieces that cannot be easily handled manually.spindle can be quickly positioned.
Plain radial drilling machines
Provide only a vertical spindle motion
Semi universal machines
The spindle head can be pivoted at an angle to a vertical plane
Universal machines
The radial arm is rotated about a horizontal axis to permit drilling at any angle.
Radial drilling machines
Designated by the radius of the largest disk in which a center hole can be drilled
Multiple spindle drilling machines
Mass production machines with many spindles.
Cutting fluids
Fluid should be applied copiously.
Counterboring
Provides an enlarged cylindrical hole with a flat bottom so that a bolt head will have a smooth bearing surface. Two or more diameters can be produced in a single counter boring operation.
Countersinking
Makes a beveled section at the end of a filler hole to provide a proper seat for a flat head screw or Rivet.
Spot facing
Done to provide a smooth bearing area on an otherwise fought surface at the opening of a hole and normal to its axis.
Reaming
Removed a small amount of material from the surface of holes.
Purposes of reaming
To bring holes to an size and to improve the finish of the existing hole. Multi edge cutting tools used.
Hand reamerd
Inteneded to be turned by hand and to remove only a few thousandths of an inch of metal.
Machine or cutting reamerd
Used for various machine tools at slow speeds.
Rose chucking reamerd
Found cylindrical and have no relief behind the outer edges of the teeth
Flutes chucking reamerd
Have relief behind teeth edges. Can cut on all portions of teeth. Their flutes are intended for light finishing cuts.
Shell reamerd
Used for larger sizes in order to save cutting tool material. Only the shell is subjected to wear and need to be replaced.
Expansion reamerd
Can be adjusted over a few thousandths of an inch to compensate for west to permit variation in bold size. Available in hand and machine types.
Adjustable reamerd
Have cutting edges in the form of blades that are locked in the body. Blades can be adjusted over a greater range. The blades cna be replaced
Taper reamerd
Are used for finishing holes to an exact taper.
Roughing reamer
Had nicks along the cutting edges to break up the heavy chips that result ad a cylindrical hole is cute to a taper
Finishing reamer
Had smooth cutting edges
Solid type reamerd recommended for
Material that is hard, or if you need to a fairly large hole.
Reamer speed
Two thirds that of drilling, for close tolerance, speeds should be lower
Reamers p.2
Fluids should be used as drills are, and they must be held securely.
