Couple of Basic questions on Hole-making operations

[Haroon1]

To improve my knowledge.. These are not homework questions :)

1. How does 'Trepanning' work and where is it used in the manufacturing industry?

2. What is the need for a 'Lip Relief Angle' in drills?

3. If 15-20 deg helix angle drills are called 'low helix angle' and 35-40 deg are called high, then what about 20-35 deg drills, are these classified as well?

4. What is the 'web size' of a drill?

5. Carbide drills are coated with Titanium Nitride (TiN). is there a particular reason for this?

6. In brazed carbide tipped drills, Tungsten carbide inserts are brazed onto the steel body of a drill. why this particular material?

7. Please explain the 'True Rake Angle' of a boring operation tool. HOW is it a function of side, back rake and lead angle? Also Id be grateful to find a diagram of these?

 

[Haroon1]

What, no one??

 

[Skrambles]

1. Trepanning is a method of creating a hole by cutting a groove in the form of a circle and then removing the center in one piece. This method is more economical for large diameter holes than conventional drilling.

2. The Lip Relief Angle ensures that only the cutting edge is contacting the material, without it there would be more friction and wear on the tool.

3. All drills or other tools with spiral flutes have a helix angle, so I don't know what you mean by "helix angle drill." A tool with a lower helix angle will have more flutes or threads per unit of length than one with a higher helix angle.

4. The web is the central part of the drill and is measured as the distance between the bottom of one flute to the bottom of the flute on the opposite side. Smaller webs leave more room in the flutes to carry away chips, but make the drill less sturdy.

5. TiN is only one of several coatings available for carbide tools. The coatings improve tool performance and allow them to be run at higher cutting speeds.

6. Carbide is relatively hard compared to steel and other metals, so it holds an edge longer and can be used on hardened metals that steel tools cannot be used on. But because of this hardness carbide tools are more expensive to produce and more brittle than steel tools. By using carbide inserts on a steel tool you get the benefits of both materials.

7. The true rake angle is the angle the chips slide along the tool after being cut from the workpiece. Changing the relief angles on the tool affects the way the chips come off the piece, thereby changing the true rake angle.

If you're looking for a good reference I have to suggest Machinery's Handbook because that's where I found most of these answers. It has lots of definitions, diagrams, and tables that can come in handy around the shop.