I. Selection of Rough Boring Tools
Rough boring tools aim to achieve a high metal removal rate, their primary function being to enhance work efficiency. As such, they should possess high strength. For holes without stringent precision requirements, rough boring can serve as the final operation.
For holes with high precision requirements, rough boring can remove most of the surplus from the raw holes, improving the precision of the hole size and reducing surface roughness values, thus preparing for semi-finish and finish boring operations.
1. Multi-Edge Boring Tools
To increase bore processing efficiency, it is recommended to use twin-edge boring tools in low to mid-powered machine tools, unstable operations, or for large diameter processing. The two cutting edges of these tools can be pre-adjusted to the size of the hole being machined. The machining precision of twin-edge boring tools can be controlled to an IT9 level.
2. Heavy-Duty Boring Tool
For large-scale, heavy-duty boring operations, one can also opt for a boring tool head equipped with a tool holder and an adjustable extended slide. This setup can accommodate a rough boring head.
3. Step Drill
For holes with larger allowances or when chip control and eccentric hole machining need to be enhanced, a step drill can be selected. By adding different thicknesses of cutter pads between the tool holder slider and the body, the three blades can respectively process three-tiered surfaces with different diameters and depths.
4. Indexable Deep Hole Boring Tool
When machining deep holes with a diameter of over 30mm, it is recommended to use an indexable deep hole boring tool. The geometric angles of the cutting section should be chosen as follows.
1. Front angle γ0, back angle α0, and secondary back angle α0′.
2. The primary relief angle Kr, negative relief angle Kr’, and blade inclination angle λs. The primary relief angle Kr is generally suitable between 45°-65°. When the back cutting amount is large, a higher Kr value is used, and vice versa.
The negative relief angle Kr’ is generally between 3°-5°. Deep hole boring tools do not require smoothing of the cutting edge and blade band. The blade inclination angle λs is generally taken as 0°.
| Angle/Material | General Material | Hardened Steel and High-Strength Steel | Difficult-to-Machine Material |
| Y。 | 0 | 5~-10 | 5-10 |
| α。 | 8-10 | 8-10 | 8-10 |
| α。 | 10-15 | 10-15 | 10-15 |
II. Issues and Measures Related to Rough Boring Cutters
1. Poor Cutting Control
| Reasons | Measures |
| The feed rate is too low. | Increase the feed amount |
| The back cutting amount is too high. | Use a step tool |
2. Tremors and Vibrations
| Reasons | Measures |
| Excessive cutting speed | Reduce cutting speed |
| High length-diameter ratio | Shorten the tool to enhance rigidity. Increase the outer diameter of the handle and extension rod. Substitute with carbide or heavy metal extension rods. |
| Oversized radius of the tool tip arc | Use a blade with a smaller tip radius. |
| Unstable working conditions | Inspect the machine tool spindle for clamping and wear.Make sure all units in the tool assembly are assembled according to the required torque.Check the workpiece for clamping.Ensure rigid clamping is in contact with the spindle surface. |
3. Minor chipping or breakage at the blade edge.
| Reasons | Measures |
| Incorrect selection of cutting tool | Switch to blade materials with better toughness. |
| Severe interrupted cutting | Reduce cutting speed and feed rate. |
| Chip congestion | Inspect the clearance of the rod/hole diameter.Improve chip control and increase feed rate. |
4. The tool life is short.
| Reasons | Measures |
| Incorrect tool selection | Utilize blade materials of higher durability. |
| Excessive cutting speed | Reduce the cutting speed. |
| Minor chipping on the cutting edge of the blade | Inspect the amount of tool wear and feed rate. |
| Insufficient pressure of the cutting fluid | Increase the pressure of the cutting fluid. |
III. Choosing the Right Boring Tool
① Single-edged Boring Tool
When the power of the machine tool is low and there’s a need to reduce cutting force or address vibration issues, a single-edged boring tool is a suitable choice. It can achieve small tolerances, precise roundness, or ideal surface quality.
② Fine-adjustment Boring Tool
In precision boring works, to obtain a high dimensional accuracy for the hole, the tool must be adjusted conveniently and precisely. A fine-adjustment boring tool can precisely adjust the bore size on the machine tool.
③ Floating Boring Tool
For single or small batch production and machining larger diameter holes, a floating boring tool is a fitting choice.
A floating boring tool tip
(Figure 1: Welded type, Figure 2: Mechanical clamp type, Figure 3: Blade edge in arc shape)
④ Vibration-reducing Boring Tool
When tool overhang is five times the diameter of the tool or more, vibration is typically the limiting factor for achieving high production efficiency on the machine tool, necessitating a reduction in cutting speed, feed quantity, and back-off amount.
In such cases, it’s advisable to use a vibration-reducing boring tool. This tool has a vibration reduction system that minimizes vibration, thereby allowing for increased cutting parameters, as well as enabling a more reliable, vibration-free machining process, small tolerances, ideal surface quality, and significant metal removal rate.
IV. Issues and Measures with Fine Boring Tools
1. Tremors and Vibrations
| Reasons | Measures |
| The cutting speed is excessively high. | Reduce cutting speed. |
| The length-to-diameter ratio is too large. | Shorten the tool to improve stiffness.Use a stronger boring tool.Employ carbide or heavy metal long rods. |
| There’s an error in the selection of the cutting tool. | Minimize the tip radius of the cutting blade.Use finely ground blades. |
| Issues are present in the selection of machining allowances. | Alter the pre-machining hole diameter. |
2. Poor Diameter Accuracy and Repeatability
| Reasons | Measures |
| Unstable operating conditions | Ensure rigid clamping in contact with the spindle surface.Inspect the workpiece clamping.Check and confirm all units in the tool assembly are correctly assembled with the proper torque. |
| Uncertain tool replacement | Replace worn and damaged tool holders. |
| Poor spindle stability | Clean the spindle and tool holder.Use sharper, precision-ground blades. |
3. Substandard Roundness
| Reasons | Measures |
| Excessive imbalance in the boring tool | Inspect the spindle runout.Switch to an appropriate boring head.Check the balance ring setting.Reduce the cutting speed. |
| Excessive cutting force | Inspect machining allowance and feed quantity. |
| Insufficient workpiece clamping | Ensure consistency in workpiece clamping. |
| Asymmetry in the workpiece | Lower the cutting force, use fine-ground force bladesIncrease cutting speed, and reduce feed quantity. |
4. Taper Hole Error
| Reason | Measures |
| Premature Failure | Switch to more wear-resistant blade materialAdjust cutting speedIncrease the flow rate of cutting fluid |
