Twist drill
A twist drill including a cutting tip having a front flank face, a substantially cylindrical tool body extending rearwardly from the cutting tip, and a shank. The tool body includes a rotational axis therethrough and at least one flute formed on an outer peripheral surface thereof and extending to the front flank face. The at least one flute includes a first helical portion opening to the front flank face and a second helical portion extending from the rear end of the first helical portion toward the rear portion of the tool body. The second helical portion twists in a direction opposite of the first helical portion.
1. A twist drill comprising:
a cutting tip including a front flank face, a substantially cylindrical tool body extending rearwardly from the cutting tip, and a shank;
the tool body having a rotational axis therethrough and including at least one flute formed on an outer peripheral surface thereof and extending to the front flank face;
wherein the at least one flute includes a first helical portion opening to the front flank face and a second helical portion extending from the rear end of the first helical portion and a third helical portion extending from the rear of the second helical portion toward the rear portion of the tool body, wherein the second helical portion twists in a direction opposite of the first helical portion and wherein the third helical portion twists in a direction opposite of the second helical portion.
2. The twist drill of claim 1 wherein the first helical portion is positioned in a positive helix.
3. The twist drill of claim 1 wherein the cutting tip is an interchangeable cutting tip.
4. The twist drill of claim 1 wherein the cutting tip includes an S-shaped chisel edge.
5. The twist drill of claim 1 wherein the tool body is made of steel.
6. The twist drill of claim 1 wherein the tool body is made of cemented carbide.
7. The twist drill of claim 1 wherein the tool body includes a pair of helical flutes formed in a peripheral outer surface of the tool body.
8. The twist drill of claim 7 wherein the helix angle of the first helical portion is maintained constant from the cutting tip to the tool body and on a portion of the flutes in the tool body.
9. The twist drill of claim 1 wherein the twist drill includes at least one coolant hole.
10. The twist drill of claim 1 wherein the helix angle of the first helical portion is about 0 to about 40 degrees.
11. The twist drill of claim 10 wherein the helix angle of the first helical portion is about 30 degrees.
12. The twist drill of claim 1 wherein the helix angle of the second helical portion is from about 1 to about 30 degrees.
13. The twist drill of claim 12 wherein the helix angle of the second helical portion is about 3 degrees.
14. The twist drill of claim 1 wherein the third helical portion extends from the rear of the second helical portion to the shank of the drill.
15. The twist drill of claim 1 wherein the helix angle of the third helical portion is constant.
16. The twist drill of claim 1 wherein the helix angle of the third helical portion is from about 0 to about 40 degrees.
17. The twist drill of claim 1 wherein the helix angle of the third helical portion is about 5 degrees.
18. The twist drill of claim 1 wherein the twist drill has web thickness that is constant along the length of the twist drill.
19. The twist drill of claim 1 wherein the twist drill has a web thickness that is tapered along the length of the twist drill.
20. The twist drill of claim 1 wherein the twist drill has a web thickness that varies along the longitudinal length of the twist drill.