DRILL GEOMETRY
Lip angle/ Tip Angle/ Point Angle
Land / Margin: It maintains the alignment of the drill so that hole is straight and to the right (correct) size.
Helix angle: Angle formed b/w a plane containing drill axis and the leading edge of land. Based on the value of the angle the drills can be classified as
1) Slow spiral series: 12o to 22o - Used for brass, bronze, CI that produce broken chips (brittle materials). They provide less lifting power, but are stronger, used for
shallow holes. Also used in horizontal applications where drill is not rotating.
2) Regular spiral series: 28oto 32o - most widely used 3) Fast/High spiral series: 34 o to 38o – Used for softer ferrous and non-ferrous materials producing long string like chips (ductile materials). They provide great lifting power, but are weak, used for deep holes.
Lip angle: Angle formed b/w the cutting edges (lips).
Smaller point angles results in lower effective rake. Effect of change in effective rake is negligible on drill performance.
Smaller the point angle, longer the lip length. Smaller point angles generate wider and thin chips. Higher point angles generate narrow and thick chips. Higher point angle increases the cutting efficiency of the drill because most materials are cut efficiently in the form of thick chips.
Longer lip lengths reduce load per unit length of the lip and helps in resisting the wear caused by abrasive action during machining of metals like C.I.
1) M.S. 1180 (< 180 HB) 2) Steel 1180 (180 - 280 HB)
3) Steel 1350 - 140o(280 – 380 HB) 4) Grey C.I. 900 (< 180 HB)
5) Grey C.I. 1180 (180 - 280 HB) 6) Chilled C.I. 1350 – 1400(> 350 HB) 7) Aluminum 118
0
8) Copper 1180 9) Bronze 1180
10)Brass 1110
Clearance / Lip relief Angle:
Angle formed b/w flank and a plane normal to drill axis at the
tip of the drill. Large angles (80 –120) are used for ductile matls. to compensate elastic recovery. Small angles (60 –80) are used for brittle matls.
OPERATIONS OPERATIONS
1) Drilling – Process of making hole in solid body.
2) Boring – Enlarging a hole completely with an adjustable tool with only one cutting edge.
3) Counter boring - Enlarging one end of the hole to form a square shoulder with srcinal hole to avoid projections in assemblies.
4) Counter sinking - Making a cone shaped enlargement to provide a recess for a screw head.
5) Reaming – Sizing and finishing a small unhardened hole.
a) b) c)
a) Straight flute reamer is used for through holes in materials that do not form chips like C.I, Bronze, Brass. They form fine powder that will fall by gravity.
b) Left hand spiral flute reamer is used for through holes in other materials and is very effective as they push the chips out of the through hole.
c) Right hand spiral flute reamer is used for blind holes as they pull the chips out of them.
Chucking (M/c) Reamer
M/c Reamers
Manual Reamer & Wrench
d) Rose reamers are primarily used for roughing prior to final reaming. The cylindrical part of the reamer has no cutting edges, but merely grooves cut for the full length of the reamer body, providing a way for the chips
to escape and a channel for lubricant to reach the cutting edges. To prevent binding they have a slight back taper. The cutting edges at the end are ground to a 45
0
bevel.
e) Shell reamers are similar to cutting portion of a chucking reamer. They are supplied without a shank and has a hole through the center. A arbor is used in conjunction with the shell reamer, the slots in the reamer engage lugs on the arbor for driving power.
6) Lapping – Sizing and finishing a hole already hardened.
7)Tapping–Process of making internal threads in small holes.
8) Spot facing – Process of smoothing and squaring the surface around the hole or seat for a nut (or) head of a screw for burr removal.
Machine Tap with holder Manual Tap
Spot facing tools with pilot
Centre Drill used for making a centre impression on surface for locating the drill point, locating the lathe & Grinding centres.
Burr formation
during drilling
9) Trepanning – Operation of producing a hole by removing metal along the circumference of a hollow cutting tool. Used for producing large holes in plates.
Video 9,10,11
TIME ESTIMATION
MILLING MILLING
INTRODUCTION:
A milling machine is a machine tool that removes metal as the work is fed against a rotating multi point cutter. The cutter
rotates at a high speed, and because of the multiple cutting edges it removes the metal at a very fast rate.
The first milling machine came into existence in about 1770 and was of French srcin.
TYPES TYPES
1. Column & knee type: Most commonly used for general shop work. The ta ble is mounted on the kn ee casting, which in-turn is mounted on the vertical slides of the main column. The knee is vertically adjustable on the column, so that the table can be moved up and down to accommodate work of various heights. The table can be moved longitudinally and cross wise on the knee
casting. Classification of this type is based on methods of supplying power to the table, diff. movement of the table and diff. axis of rotation of the main spindle.
(a) Hand milling machine Feeding is done by hand and used for light and simple operations like slots, grooves, keyways. This is available in both horizontal & vertical models Table movements are as above.
(b) Plain milling
Table can be fed as above.
Video 1,2
(c)Universal milling machine This is also a horizontal type milling m/c. In addition to 3 movements in plain milling machine the table has a fourth movement i.e. it is fed at an angle to milling cutter. This enable it to perform helical milling. This machine can produce spur, spiral, bevel gears, twist drills, reamers, milling cutters etc.
(d)Omniversal
milling machine
This is a horizontal type milling m/c. The extra fifth movement is the table can be tilted in vertical plane by providing aswivel arrangement
at the knee. This enables milling in any plane. Taper spiral groves in reamers, bevel gears etc can be done.
(e) Vertical milling machine Here the position of the spindle is vertical and
┴
to the work table. The spindle head is clamped to the vertical column and can be swiveled at an angle . Also the spindle head can be adjusted up / down relative to work. The table movements are same as plain milling machine.Video 3,4
2. Plano Miller:
It resembles a planer. It is having multiple spindle heads both in vertical and horizontal planes. It has a cross rail which can be raised or lowered along with cutters. Hence no. of work surfaces can be machined simultaneously, thereby reducing production time. In a plano miller, the table has
feed movement instead of reciprocation. Hence the table movement here is much slower than planning machine.
Video 5
3. Rotary table Machine A modification of vertical milling machine adopted for machining flat surfaces. A No. of work pieces can be mounted on a circular table which rotates about vertical axis.
The face milling cutters can be mounted on two (or) more vertical spindles and can be set at diff.
heights relative to work so that when one cutter is roughing the other is finishing them. Continuous loading and unloading of work pieces can be done by the operator
while milling is in progress.
4.Planetary milling machine: Here the work is held stationary while the revolving cutter / cutters move in a machine is particularly adopted for milling internal / external threads of different pitches.
Video 6,7
5. Pantograph milling machine It can duplicate a job by using a pantograph mechanism which permits the size o
the work piece reproduced to be smaller than, equal to or greater than the size of a template or model used for this purpose. A pantograph is a mechanism that is generally
constructed of fou r bars or links joined in the fo rm of parallelogram. Pantograph machines are available in 2D or
3D models. 2-D models are used for engraving letters or other designs, 3-D models are used for copying any shape and contour of the work piece. The tracing stylus is moved manually on the contour of the model to be duplicated and the milling cutter mounted on the spindle moves in a similar path on the work piece, reproducing the shape of the model.
Video 8
SPECIFICATIONS SPECIFICATIONS
1. The maximum length of longitudinal, cross and verti cal travel of the table.
2. No. of spindle speeds,
3. No. of table speeds and feeds 4. Floor space required
5. Net weight required
6. Spindle nose taper (for vertical milling machine spindle) and taper on horizontal milling machine arbors