Design tips for hobbing cutter starts and flutes
1. Standard criteria for hobbing cutter starts and flutes
| Part NT | Starts | Flutes | Use |
|---|---|---|---|
| 20 and smaller | 1 | 10 ～ 12 | Finish, Preshaving |
| 2 | 12 ～ 14 | Preshaving | |
| Over 21 | 1 | 10 | Finish, Preshaving |
| 2 ～ 3 | 12 ～ 14 | Preshaving | |
| 4 ～ 5 | 14 ～ 17 | Preshaving |
・Formula for advisable design of hobbing cutter starts is "(NT of workpiece / number of starts) ≥ 9"
The appropriate value differs depending on the hobbing machine cutting load and cutting method.
2. Comparison of hobbing cutter design, Starts
Greater starts
| Pros | (1) The machining productivity improves due to the higer table rotation speed |
|---|---|
| (2) The cutter wear resistance improves due to the thicker cutting chips. | |
| Cons | (1) Hobbing accuracy tends to be one rank lower. |
| (2) Chipping is likely to occur. | |
| (3) Tool price is relatively higher |
・In case of increasing the number of starts, make sure that the number of starts x axial feed speed (mm / t.rev.) does not exceed 8.
Fewer starts
| Pros | (1) Better hobbing accuracy (tooth profile, pitch) |
|---|---|
| (2) Better hobbing cutter accuracy | |
| (3) Tool price is relatively lower. | |
| Cons | (1) The machining productivity declines due to the lower table rotation speed. |
| (2) The cutter wear resistance will decline in case the cutting speed increases. |
3. Comparison of hobbing cutter design, Flutes
Greater flutes
| Pros | (1) Hobbing polygonal tooth profile error decreases. |
|---|---|
| (2) Cutting force on hob axis can be slightly reduced which allow the axial feed can be fewer increased. | |
| (3) If the axial feed is the same, the cut part tooth lead accuracy is slightly improved. | |
| Cons | (1) Resharpening stock decreases in case the hob cutter outer diameter doesn't change. |
| (2) Cutter tooth rigidity decreases. | |
| (3) Resharpening cost increases. | |
| (4) Tool price gets higher. |
Fewer flutes
| Pros | (1) Resharpening stock increases in case the hob cutter wear doesn’t change. |
|---|---|
| (2) Chips become thicker and hob wear does not increase, but rather decreases. | |
| Cons | (1) Cutting force on hob axis can be slightly increased which increases cut part tooth lead error. |
| (2) Hobbing polygonal tooth profile error increases. |
