Custom Carbide-Tipped Form Drill Bit for Brass Bearing Cage Ball Pockets

Aoshiji® developed a custom carbide-tipped form drill bit for machining spherical ball pockets in a machined brass bearing cage.

The finished cage pocket required a diameter of Ø60.8 mm with a full ball-radius profile of R30.4 mm, together with a 2 mm × 45° entrance chamfer. The specified surface-finish range was Ra 0.8–1.6 µm.

The machining requirement was considerably more difficult than simply producing a large hole.

The customer needed the tool to solve five problems at the same time:

Reliable centering of a ball-end cutting profile
Direct drilling without a separate spotting or centering operation
Formation of the R30.4 spherical pocket and 45° entrance chamfer with one tool
Light, pliable and easily removable burrs instead of hard burrs
A clean pocket wall without scratches while maintaining the specified surface finish

The previous tooling process could not reliably produce the feature to the customer’s production requirements.

Aoshiji® therefore developed a drawing-specific carbide-tipped form drill bit with proprietary center-cutting geometry, controlled cutting-edge preparation and an integrated chamfer section.

The resulting tool allowed the customer to drill the bearing cage pocket directly, generate the spherical form and entrance chamfer in the same tool cycle, maintain the required surface quality and produce burrs that were considerably easier for operators to remove.

The tool was used on a machining center with a BT40 setup and an MT4 Morse taper shank.

Exact cutting speed and spindle-speed data are intentionally not disclosed because they form part of the application-specific process data developed for this project.

For a broader explanation of carbide-tipped and brazed carbide tool construction, see our main product guide: Custom Carbide-Tipped Cutting Tools.

Table of Contents

01 Application Results at a Glance
02 Brass Bearing Cage Ball Pocket Geometry
03 Why a Ball-End Cage Pocket Is Difficult to Drill
04 Challenge 1 — Centering Without a Spot Drill
05 Challenge 2 — R30.4 Ball Profile and 45° Chamfer in One Tool
06 Challenge 3 — Producing Light, Easily Removable Burrs
07 Challenge 4 — Preventing Pocket-Wall Scratches
08 Carbide-Tipped Form Drill Bit Construction
09 Cutting-Edge Preparation and Chip Control
10 BT40 Machining Center and MT4 Tool Setup
11 Previous Machining Problem vs Aoshiji Solution
12 Production Results
13 Why Burr Quality Matters as Much as Tool Life
14 Suitable Applications
15 Information Required for a Custom Form Drill Review
16 Frequently Asked Questions
17 Machining Tool Video
18 Request an Engineering Review

19 Related Technical Pages

Custom Carbide-Tipped Tools

Carbide-Tipped Cutting Tools Overview

Carbide-Tipped Form Milling Cutters

Carbide-Tipped Counterbore Tools

Side and Face Milling Cutters

Carbide-Tipped Turning Tools

Carbide-Tipped Reamers

Carbide-Tipped Drill Bits

Custom Carbide Form Tools

Carbide-Tipped Tools vs Solid Carbide and Indexable Tools

Case Study :

Carbide-Tipped Form Milling Cutter

Carbide-Tipped Form Counterbore

Carbide-Tipped Step Reamers

carbide-tipped staggered-tooth side and face milling cutter

Carbide-Tipped Milling Cutter

PCD REAMER:

PCD Reamer Basics

PCD-Tipped Reamers

01 Application Results at a Glance

Item	Project Data
Component	Machined bearing cage / bearing retainer
Workpiece material	Brass
Machined feature	Spherical ball pocket
Pocket diameter	Ø60.8 mm
Pocket radius	R30.4 mm
Entrance chamfer	2 mm × 45°
Surface finish	Ra 0.8–1.6 µm
Tool type	Custom carbide-tipped form drill bit
Cutting profile	Ball-end / ball-nose form
Additional feature	Integrated 45° chamfer
Tool construction	Brazed carbide cutting elements on engineered steel body
Machine tool	Machining center
Machine interface	BT40 setup
Tool shank	MT4 Morse taper
Separate spotting operation	Not required with the Aoshiji tool
Burr requirement	Light, pliable and easily removable
Pocket-wall requirement	No unacceptable scratches
Main process objective	Stable one-tool generation of the ball pocket and chamfer
Tool life	Stable long production life achieved
Cutting speed / spindle speed	Proprietary project data — not disclosed

The primary success criterion was not tool life alone.

The customer also needed stable centering, acceptable surface finish, controlled burr formation and a scratch-free pocket surface.

02 Brass Bearing Cage Ball Pocket Geometry

The workpiece was a machined brass bearing cage.

In bearing engineering terminology, the openings that locate and guide rolling elements are commonly described as cage pockets. In this application, the machined feature was a spherical-profile ball pocket.

The finished geometry was:

Pocket diameter: Ø60.8 mm
Ball radius: R30.4 mm
Entrance chamfer: 2 mm × 45°
Surface finish: Ra 0.8–1.6 µm

Because:

Ø60.8 mm = 2 × R30.4 mm

the main cutting section had to generate a complete ball-radius profile.

The feature also required a controlled 45° chamfer at the pocket entrance.

This meant that the tool was not simply a conventional large-diameter drill.

It was a custom carbide-tipped form drill bit designed to generate several connected features from one controlled cutting geometry:

Initial center engagement
Spherical R30.4 form
Ø60.8 maximum pocket diameter
Pocket side surface
Entrance transition
2 mm × 45° chamfer

The relationship between these features had to remain stable throughout production.

03 Why a Ball-End Cage Pocket Is Difficult to Drill

A ball-end or ball-nose form drill creates a very different cutting condition from a conventional pointed twist drill.

The central portion of a normal drill is designed specifically to establish the hole position and begin penetration.

A spherical-profile tool does not naturally have the same pointed geometry.

Without an appropriately engineered center-cutting section, the tool may have difficulty establishing a stable cutting center.

Possible results include:

Wandering at entry
Unstable initial engagement
Radial movement
Vibration
Uneven cutting load
Poor pocket geometry
Surface scratches
Cutting-edge damage

For this reason, a conventional process may use a separate centering or spotting tool before the form tool enters the workpiece.

However, every additional tool introduces another operation, another positioning cycle and another opportunity for accumulated error.

The objective of this project was therefore not merely to manufacture a ball-shaped cutter.

The objective was to develop a form drill that could establish its own cutting center and drill directly into the brass cage.

04 Challenge 1 — Centering Without a Spot Drill

The first engineering problem was the drill center.

The customer’s ball-pocket geometry required a full R30.4 cutting profile, but a conventional ball-end geometry was not sufficiently suitable for stable direct entry.

Aoshiji® therefore developed a proprietary center-cutting geometry for the form drill.

The exact center geometry and grinding parameters are not disclosed.

The design objective was to allow the center section to establish cutting action immediately and keep the tool positioned around the intended axis as the remaining ball-profile edges entered the material.

This eliminated the need for a separate spotting operation in the final process.

Conventional Process Direction

A conventional process may require:

Spot / center drill
↓
Ball-profile drilling tool
↓
Chamfering tool

That creates several separate machining stages.

Aoshiji Process

The custom form drill reduced the process to:

Custom carbide-tipped form drill bit
↓
Direct centering and drilling
↓
R30.4 spherical pocket generation
↓
2 mm × 45° entrance chamfer

The same tool established the pocket and generated the required connected features.

Removing the separate centering operation also reduced one tool change and one positioning cycle.

05 Challenge 2 — R30.4 Ball Profile and 45° Chamfer in One Tool

The second problem was integrating the entrance chamfer into the form drill.

The customer required:

Ball pocket: Ø60.8 mm / R30.4 mm
Entrance chamfer: 2 mm × 45°

The spherical cutting section and the chamfering section could not be treated as two unrelated geometries.

If the chamfer section entered the material with excessive or unstable cutting load, it could generate vibration.

That vibration could affect:

The spherical pocket surface
Pocket-wall finish
Chamfer appearance
Pocket diameter
Tool stability
Cutting-edge life

The chamfer cutting section therefore received application-specific geometry and edge preparation.

The objective was to allow the chamfer to enter progressively while the primary form section remained stable.

This enabled the R30.4 pocket and 45° entrance chamfer to be completed with the same form drill bit.

The customer did not need a separate chamfering tool after the pocket was drilled.

This is particularly valuable for drawing-specific bearing cage pockets because the relationship between the pocket and entrance chamfer is generated from the same tool axis.

06 Challenge 3 — Producing Light, Easily Removable Burrs

Burr formation was one of the most important requirements in this project.

The customer did not simply request “no burrs.”

The practical requirement was that any remaining burr should be:

Light
Thin
Pliable
Easy for the operator to remove
Unlikely to damage the machined pocket during subsequent handling

Hard, rigid burrs were unacceptable.

A hard burr can make manual deburring more difficult and increases the risk that the operator will apply excessive force during removal.

For a precision bearing cage pocket, aggressive secondary deburring can damage:

The pocket edge
The machined wall
The entrance chamfer
Surface finish
Local dimensional accuracy

Aoshiji® therefore applied controlled edge preparation to both the spherical cutting section and the peripheral cutting edges.

The exact preparation method is proprietary.

The objective was not simply to make the cutting edges as sharp as possible.

Instead, the cutting edges had to balance:

Clean cutting
+
Stable edge strength
+
Controlled chip formation
+
Controlled burr formation

The resulting chips and residual burrs were easier for the production operator to handle.

This became one of the most important improvements of the new tool.

07 Challenge 4 — Preventing Pocket-Wall Scratches

The customer also specified that the machined pocket wall could not contain unacceptable scratches.

This requirement is especially important when machining a form pocket because chips are generated along a wide curved cutting profile.

If chip flow is unstable, a chip can become trapped or dragged between the cutting tool and the freshly machined brass surface.

Possible results include:

Long scratches
Local scoring
Surface smearing
Secondary rubbing
Deteriorated surface finish
Rejected pockets

The specified surface finish was:

Ra 0.8–1.6 µm

The tool therefore had to control the entire cutting process rather than only final diameter.

Important design priorities included:

Stable initial centering
Balanced engagement of the ball profile
Controlled edge preparation
Predictable chip formation
Sufficient chip-clearance space
Reduced rubbing
Stable chamfer engagement
Controlled tool runout

With the custom tool, the customer was able to produce the required pocket without the unacceptable wall scratching experienced in the previous machining problem.

08 Carbide-Tipped Form Drill Bit Construction

The tool is described on this page primarily as a:

custom carbide-tipped form drill bit

It may also be described technically as a:

brazed carbide form drill

These terms refer to different aspects of the same basic construction.

Carbide-Tipped Form Drill Bit

Carbide-tipped describes the cutting-tool structure.

Carbide is used at the active cutting edges where wear resistance, edge retention and precision grinding are required.

Brazed Carbide Form Drill

Brazed carbide describes the joining method.

The carbide cutting elements are permanently joined to an engineered steel drill body through a controlled brazing process.

For this project, the tool combined:

Carbide cutting elements
Engineered steel body
Ball-end form geometry
Proprietary center-cutting geometry
Integrated 45° chamfer
Special cutting-edge preparation
MT4 Morse taper shank

This construction is particularly practical for a large drawing-specific form drill because the entire long tool body does not need to be manufactured from solid carbide.

09 Cutting-Edge Preparation and Chip Control

The cutting-edge design had to solve several problems simultaneously.

Center Cutting Section

The center section was developed to provide stable direct entry without a separate spot drill.

Ball-Radius Cutting Edges

The ball-profile cutting edges generated the R30.4 spherical feature.

They also had to maintain stable contact as the effective cutting diameter increased from the tool center toward the maximum Ø60.8 mm pocket diameter.

Peripheral Cutting Edges

The outer cutting area influenced:

Maximum pocket diameter
Pocket-wall condition
Burr formation
Chip flow
Surface quality

Chamfer Cutting Section

The 45° cutting section generated the 2 mm entrance chamfer during the same tool cycle.

The cutting load had to transition smoothly into this section without introducing chatter into the finished ball pocket.

Edge Preparation

Different functional areas of the drill do not necessarily require identical edge preparation.

Aoshiji® therefore treated the cutting edges according to their function within the complete form geometry.

The detailed edge-preparation values remain proprietary.

The engineering goal was to achieve:

Reliable self-centering
Controlled cutting resistance
Smooth form generation
Stable pocket-wall finish
Light burr formation
Long cutting-edge life

10 BT40 Machining Center and MT4 Tool Setup

The form drill was used on a machining center with a BT40 machine setup.

The custom drill itself used an:

MT4 Morse taper shank

The production configuration can therefore be summarized as:

Machine:
Machining center

Machine setup:
BT40

Tool shank:
MT4 Morse taper

Workpiece:
Brass bearing cage

Operation:
Direct ball-pocket form drilling + 45° chamfer

The actual cutting speed and spindle speed are not published.

These parameters are part of the application-specific machining data developed for the customer’s component and tool geometry.

They should not be transferred directly to another brass bearing cage without reviewing:

Brass alloy
Pocket geometry
Machining allowance
Tool projection
Machine rigidity
Holder condition
Workpiece clamping
Required surface finish
Burr requirement
Production quantity

11 Previous Machining Problem vs Aoshiji Solution

Machining Requirement	Previous Problem	Aoshiji Solution
Tool centering	Ball-profile tool difficult to center reliably	Proprietary center-cutting geometry
Spot drilling	Additional centering operation normally required	Direct drilling without separate spotting
R30.4 spherical pocket	Difficult to generate stably	Drawing-specific ball-end form geometry
Ø60.8 pocket	Stability required across full form	Controlled profile grinding and tool alignment
2 mm × 45° chamfer	Separate operation or vibration risk	Integrated chamfer cutting section
Burr condition	Hard burrs unacceptable	Edge preparation for light, pliable burr formation
Surface finish	Ra 0.8–1.6 µm required	Controlled cutting geometry and stable engagement
Pocket wall	Scratches not permitted	Improved chip control and reduced rubbing
Tool changes	Multiple tools increase process complexity	One custom combination form drill
Tool life	Stable production life required	Long and stable tool life achieved

The important result was that the tool solved the complete machining problem, not only the nominal pocket dimensions.

12 Production Results

After introducing the custom carbide-tipped form drill bit, the customer was able to machine the brass bearing cage pockets successfully.

The final process achieved the key production objectives:

Direct Drilling

The form drill could enter the workpiece directly.

A separate spotting or centering drill was no longer required.

Stable Spherical Pocket Generation

The tool generated the required:

Ø60.8 mm
R30.4 mm

ball-pocket geometry.

Integrated Chamfer

The same tool produced the:

2 mm × 45°

entrance chamfer.

Required Surface Quality

The machining process achieved the specified:

Ra 0.8–1.6 µm

surface-finish requirement.

Controlled Burr Formation

The remaining burr was light and pliable rather than hard and rigid.

This made subsequent operator handling and deburring easier.

No Unacceptable Pocket-Wall Scratches

The finished pocket wall remained free from the unacceptable scratching that had been a major production concern.

Stable Tool Life

The custom carbide-tipped form drill also achieved long and stable production tool life.

The exact tool-life figure and cutting parameters are not disclosed.

For this project, however, tool life was not the only measure of success.

The more important result was that the customer could finally produce the pocket reliably while meeting the combined requirements for geometry, surface finish, burr condition and wall quality.

13 Why Burr Quality Matters as Much as Tool Life

Tool-life figures are easy to compare.

Burr quality is often more difficult to quantify, but in this bearing cage application it was equally important.

A cutting tool could theoretically achieve long life and still be unacceptable if it generated:

Heavy burrs
Hard rolled-over edges
Scratched pocket walls
Poor chamfer finish
Unstable surface quality

For the customer, a hard burr created a secondary manufacturing problem.

Operators still had to remove the burr after machining.

If excessive force or aggressive deburring was required, the secondary operation could damage a pocket that had already been machined accurately.

The target was therefore not simply:

Long tool life

The target was:

Stable geometry
+
Ra 0.8–1.6 µm finish
+
Scratch-free pocket wall
+
Light removable burr
+
Reliable direct centering
+
Long tool life

This complete-process approach is particularly important for bearing cage and bearing retainer machining.

14 Suitable Applications

A similar custom carbide-tipped form drill bit may be considered when a component requires:

Ball pockets
Spherical-profile pockets
Ball-end holes
Radius-bottom holes
Combined radius and chamfer features
Large formed holes
One-tool drilling and chamfering
Direct drilling without a separate spot drill
Controlled burr formation
High-quality brass machining
Stable pocket-wall surface finish
Drawing-specific form geometry

Potential workpieces include:

Brass bearing cages
Brass bearing retainers
Bronze bearing cages
Copper-alloy bearing components
Ball-bearing cages
Large bearing components
Drawing-specific non-ferrous components

The exact tool geometry must be designed according to the component drawing and actual machining conditions.

15 Information Required for a Custom Form Drill Review

For a custom form drill evaluation and quotation, provide the following information whenever available.

Component Drawing

Complete part drawing
Pocket diameter
Pocket depth
Ball radius
Chamfer dimensions
Entrance geometry
Required transitions
Dimensional tolerances
Position tolerances
Surface-finish requirement

Workpiece

Material specification
Brass or bronze grade
Material hardness if available
Blank condition
Existing pre-machined features
Annual production quantity

Machine and Holder

Machine-tool model
Spindle interface
Toolholder
Available shank interface
Tool projection
Workpiece clamping condition

Existing Process

Current tool drawing
Current tool photographs
Whether a spot drill is currently used
Number of machining operations
Existing burr condition
Surface-finish problem
Scratch or scoring photographs
Current tool life
Current cycle time

Production Requirements

Required burr condition
Required tool life
Required quantity
Regrinding requirement
Retipping requirement
Inspection report if available

For a form drill, the complete finished-pocket drawing is particularly important because the cutting-edge profile must be developed from the required component geometry.

16 Frequently Asked Questions

What is a carbide-tipped form drill bit?

A carbide-tipped form drill bit is a custom drilling tool with profile-ground carbide cutting elements supported by an engineered steel body. The cutting geometry is designed to produce a drawing-specific hole, radius, spherical profile, chamfer or combination of connected features.

What was machined in this bearing cage case study?

The tool machined a spherical ball pocket in a brass bearing cage. The finished pocket diameter was Ø60.8 mm with an R30.4 ball-radius profile and a 2 mm × 45° entrance chamfer.

Why is a ball-end form drill difficult to center?

A ball-end cutting profile does not naturally provide the same pointed centering geometry as a conventional drill. The center section must be engineered specifically to establish stable cutting action and prevent the tool from wandering during entry.

Did this tool require a spot drill first?

No. Aoshiji® developed proprietary center-cutting geometry that allowed the custom form drill bit to enter the brass workpiece directly without a separate spotting or centering operation.

Can the ball pocket and chamfer be machined with one tool?

Yes. In this application, the custom form drill generated the R30.4 spherical pocket and the 2 mm × 45° entrance chamfer during the same tool cycle.

What surface finish was required?

The specified surface-finish range for the machined pocket was Ra 0.8–1.6 µm.

Why was burr control important?

The customer required light, pliable and easily removable burrs. Hard burrs would make secondary deburring more difficult and could increase the risk of damaging the finished pocket surface or edge.

How did Aoshiji control the burr condition?

The spherical cutting edges, peripheral edges and chamfer section received application-specific edge preparation designed to balance cutting sharpness, edge strength, chip formation and burr control. The detailed geometry is proprietary.

Why are scratches a problem in brass bearing cage pockets?

Trapped or recut chips can score a freshly machined surface. For this project, the customer required a clean pocket wall without unacceptable scratches while maintaining the specified Ra 0.8–1.6 µm finish.

Is this a brazed carbide drill?

Yes. The tool can also be described as a brazed carbide form drill because the carbide cutting elements are permanently brazed to an engineered steel tool body. Carbide-tipped describes the tool structure, while brazed carbide describes the joining method.

What spindle speed and cutting speed were used?

The cutting speed and spindle speed are application-specific process data and are not disclosed for this project.

Can this type of drill be used for bronze bearing cages?

A similar tool can be developed for bronze and other copper-alloy bearing components, but carbide grade, center geometry, cutting-edge preparation and machining parameters must be reviewed for the actual material and pocket design.

Can Aoshiji develop the tool from a bearing cage drawing?

Yes. Provide the component drawing, material, pocket diameter, radius, chamfer, tolerance, surface finish, machine interface, current tooling problem and required quantity for engineering review.

What machine and shank were used?

The tool was used on a machining center with a BT40 setup and an MT4 Morse taper shank.

17 Machining Video — Carbide-Tipped Form Drill Bit Cutting a Brass Bearing Cage

The video below shows the actual machining process of an Aoshiji® custom carbide-tipped form drill bit cutting a spherical ball pocket in a brass bearing cage.

The video shows both the custom cutting tool and the workpiece during machining. The carbide-tipped form drill enters the brass cage directly, machines the drawing-specific spherical pocket and completes the integrated 45° entrance chamfer in the same machining cycle.

This application demonstrates several key functions of the tool:

Direct centering without a separate spot-drilling operation
Machining of the Ø60.8 mm / R30.4 spherical cage pocket
Integrated 2 mm × 45° entrance chamfer
Stable cutting during the ball-pocket forming operation
Controlled chip and burr formation
Protection of the machined pocket wall from unacceptable scratching
Stable surface quality in the finished brass bearing cage pocket

The tool uses carbide cutting elements brazed to an engineered steel body and an MT4 Morse taper shank for the BT40 machining-center setup.

The exact cutting speed and spindle speed used in this production application are proprietary process data and are not disclosed.

18 Request an Engineering Review

Request a Custom Carbide-Tipped Form Drill Bit

Aoshiji® Custom Tool supports made-to-drawing carbide-tipped drill bits and brazed carbide form drills for bearing cage, bearing retainer and other drawing-specific hole-making applications.

Engineering review may include: