Rough boring is primarily focused on metal removal and preparing the hole for finishing. Roughing machining is performed to open up an existing hole made by methods such as pre-machining, casting or forging. Rough boring tools can be configured for productive-, step- and single-edge boring.
Productive boring is the basic set-up for most boring applications and is the best choice for highest productivity.
It involves two or three cutting edges and is employed for roughing operations of holes with tolerances of IT9 or larger, where metal removal rate is the first priority. Feed rate is obtained by multiplying the feed for each insert by the number of inserts (fn = fz × z).
A step-boring tool has the inserts set at different axial heights and diameters. This method is used when a large radial depth of cut is required or to get improved chip control in long-chipping materials, since the chips can be divided into smaller and easily handled chips. The number of tools and tool changes might be reduced when step boring.
The feed rate and produced surface finish is the same as if only one insert were used (fn = fz). The hole tolerance produced is IT9 or greater.
Single-edge boring is performed when using only one cutting edge. It can be beneficial in materials where chip control is demanding (e.g long-chipping materials), or when machine tool power is limited (fn = fz).
Choice of inserts for rough boring
Carefully select insert style, entering (lead) angle, geometry and grade to achieve good chip control and machining performance.
Positive or negative insert style
Negative inserts: Choose negative inserts in stable conditions for better insert economy and in tough applications that require strong inserts and improved process security.
Positive inserts: It is an advantage to use positive inserts in rough boring, as they produce lower cutting forces compared to negative inserts. A small nose angle and small nose radius also contribute to keeping the cutting forces down.
Entering/lead angle for rough boring
The entering angle (lead angle) of boring tools affects the direction and magnitude of axial and radial forces. A large entering angle (small lead angle) produces a high axial force, while a small entering angle (large lead angle) results in a high radial cutting force.
90° entering angle (0° lead angle)
First choice for general operations, step boring and shoulder operations.
84°/75° entering angle (6°/25° lead angle)
For interrupted cuts, sand inclusions, stack boring etc. Through holes only.
95° entering angle (-5° lead angle)
For high feeds or improved surface finish, with wiper inserts in stable conditions.
Boring insert geometry and grade
Component material, type of operation and machining conditions define what insert geometry and grade to use. For boring, turning inserts are used. Find out more about how to choose the correct turning insert.
- Choose a roughing geometry for large cutting depths
- Choose a medium geometry for smaller cutting depths or to achieve improved chip breaking
- A large insert nose radius (RE) will improve process security and enable higher feed, but might generate vibration. The recommended starting nose radius is 0.08 mm (0.031 inch)