Twist drill and its nomenclature

• Twist drill

-Twist drills are fluted drills made from a round bar of two material,by forging or milling rough fluted and then twited to a spiral shape .

-These are the most commonly use of. drills

• -Several types of twist drills are :- 

1. Jobber's drill
2. Parallel shankdrill
3. Taper shankdrill
4. Stub drill

 ✓TwistDrill Nomenclature

• Twist drill is the most widely used drilling tool.
• It is made from a round bar of tool material by forging or milling rough fluted and then twisting to a spiral shape.
• These drills are milled to the size, heat treated and the ground to exact size after twisting.

✓Twist drills have two cutting edge with the following advantages:-

1. Two cutting edge are more efficient.
2. Cutting forces are balanced.
3. Cutting fluid is allowed to reach down the hole being machined due to flutes and flutes also help to dispose off the chips.

• Twist drill has three main parts.

1. The point
2. The body
3. The shank.

• The drill is hold and rotated by its shank.

1. The point consists of the cutting elements while the body guides the drill in operation.
2. The body of the drill has two hellical grooves called "flutes " cut into its surface.

• The flutes from the cutting surface and also help in removing chips out of the drilled hole.

✓The description and nomenclature of a twist drill are as follows :-

1. Axis
2. Body
3. Back taper
4. Flutes 
5. Land 
6. Body clearance
7. Margin
8. Drill diameter
9. Clearance diameter
10. Web
11. Point
12. Lips or cutting edge
13. Chisel edges
14. Shank
15. Tang
16. Lip relief or clearance
17. Face 
18. Fland
19. Lip relief Angel
20. Point angle
21. Helix angle
22. Chise edge angl
23. Heel
24. Web thickness
25. Neck

https://photos.app.goo.gl/WKNsqy2S33pP1LJq7https://phtos.app.goo.gl/WKNsqy2S33pP1LJq7

Photo nomenclature of twist drill

1. AXIS :-

• Axis is the longitudinal center line of the drill along which the whole body,neck and shank of the drill are concentric.

2. BODY :-

• The portion of the drill extending from the outer corner of the cutting lips upto the starting of neck or shank is called body of the drill.
• It carries flutes and is always relieved during operation.

(3)  BACK TAPER:-

• Back taper is a slight decrease in the diameter of the drill from the front end to the back in the body of the drill.

(4) FLUTES:-

• Helical grooves cut or formed in the body of the drill to provide cutting edge, to allow chip removal and to allow cutting fluid to reach the cutting edge; The flatted eare called flutes.
• Drills may have two types of flutes; flutes that group from left to right and flutes that go up from right to left.

(5) LAND:-

• It is the peripheral portion of the drill body between adjacent flutes.
• The diameter of the drill is measured across its land.

(6) BODY CLEARANCE :-

. Body clearance is the space provided to eliminate or reduce the friction between the drill and the walls of the hole a and helps in cutting and increasing tool life as well.

(7) MARGIN :-

• The margin is glound to the diameter of the drill.
• The margin keep the drill aligned during the operation.
• Friction losses in drilling depends on the Margins.

(8) Drill diameter :-

• It is the diameter of the drill over the margin or land measured at the point.

(9) Clearance diameter :-

• The diameter over the cutaway portion of the drill lands.

(10) WEB :- 

• The central portion of the drill body that connects the lands and separate the flutes from one another is called WEB.

(11) POINT:-

• The cutting end of a drill formed by the end of the lands and the web which contains dead centre,lips and flanks etc is called POINT.

(12) LIPS or CUTTING EDGE :-

There are so many lips in a drill as the number of flutes and faces.

• In two flutes drill there are two lips.
• For correct drilling both lips should be equal length and equally inclined with the axis of the drill.

(13) CHISEL EDGE :-

• It is the edge at the end of the web formed due to the intersection of flanks.
• It coincides with the axis of the drill.
• It length depends on the drill diameter.

(14) SHANK :-

• Shank is the part of the drill by which it is hold and rotated.
• It may be tappered or parallel.

(15) TANG :- 

• The flatted end of rectangular cross-section of a taper shank which fits a driving slot in a socket in the holding devices is called TANG.

(16) LIP RELIEF  or CLEARANCE  :-

It is the axial relief on the drill point to provide relief near the cutting edge is called Lip Relief.

(17) FACE :-

The curved surface of the flute near the lip o which the cut chips imp

a slide upward is called FACE.

(18) FLAND :- 

It is the surface on a drill point which extends behind the Lip to the following flute.

(19) LIP RELIEF ANGLE :-

It is the axial relief angle at the outer corner of the lip.

• It is formed by the flank and a plane normal to the Drill axis.
• Tha value varies from b