CNC machining efficiency refers to the output, measured by the number of parts produced, in a given period. The higher the output, the higher the efficiency, and vice versa. Multiple factors, such as the cutting tool or the structure holding the workpiece, directly influence CNC machining efficiency, making the role of custom tools and accessories clear.
This article explores the reasons for customizing CNC tools and accessories, their benefits and drawbacks, and key considerations when designing them for optimal performance. Read on to learn how to integrate your newly produced CNC custom tools into your CNC machining operations, too.
Table of Contents
Reasons for Customizing CNC Custom Tools and Accessories
You can design and machine or order custom CNC tools for several reasons. These include:
- Unavailability of a standard tool or accessory for the machining job at hand: Custom tools are optimized for specific machining operations and geometries. For instance, you might need a reamer with specific diameter and tolerance requirements that are not readily available.
- To substitute multiple different cutting tools with one CNC custom tool
- To enhance parameters such as the tool life, material removal rate (MRR), coolant delivery, and chip removal. Analysis has shown that customizing tooling to increase the tool life by 50% lowers the total cost per part by about 1-2%. Similarly, creating a CNC custom tool with a 20% higher MRR could reduce the total cost per part by 15%. It’s important to note that tools with higher MRR are generally more expensive to produce or purchase than those with lower MRR.
- Mass production of unique parts: CNC custom tools offer an ideal solution when standard tools and workholders cannot be used for bulk machining. Custom CNC tools and accessories are common in the automobile industry, where manufacturers regularly design and manufacture new engines with unique parts from previous models. This uniqueness usually calls for the production of new workholders, such as the tombstone-type CNC fixture for machining engine heads (shown below). Because of the associated cost, CNC custom tools and accessories make financial sense in mass production.
Illustration of a Tombstone Workholder (source)
Role of CNC Custom Tools and Accessories in Enhancing CNC Efficiency
These reasons point to CNC custom tools enhancing CNC efficiency. For instance, tool changing cycle time as well as part-to-part and new setup turnaround time are known to impact efficiency in CNC machining operations. You could create a custom workholding and toolholding accessory that simplifies the mounting and dismounting of tools and workpieces.
In this scenario, you could substantially boost the efficiency by reducing the tool changing cycle time and part-to-part or new setup turnaround time. Similarly, creating a custom tool that performs tasks requiring multiple tools eliminates the need for tool changes, further boosting CNC efficiency.
Additionally, when you look at CNC custom tools and accessories through the lens of a manufacturing company that produces parts in bulk, it is easy to see how these tools and accessories boost efficiency. The enhanced CNC efficiency again lies in the fact that the CNC custom tools and accessories reduce the time it would otherwise take to machine parts. These time savings accumulate significantly during mass production, leading to cost reductions.
Custom Tools for CNC Machines
It’s important not to confuse cutting tools with machine tools. Machine tools are responsible for moving cutting tools along a path prescribed by the CNC program. Machine tools move simultaneously along multiple axes, enabling the repeatable production of complex parts with consistent quality. Some of the components of the machine tool structure include the spindle, axis drive, automatic tool change (ATC) system, coolant system, and pallets. Cutting tools, on the other hand, are responsible for removing material from the workpiece through various machining processes.
Classification of CNC Cutting Tools
CNC custom tools, as well as standard CNC tools, are broadly classified into two:
- Single-point tools: These tools have one active cutting edge. These tools are typically used for turning and boring.
- Multipoint/multifunctional/multitasking tools: These tools have multiple active cutting edges and are used for milling, special-purpose tooling, and drilling. A single multipoint tool can machine several features or create multi-step holes.
CNC tools can also be classified based on other criteria, including clamping method, geometry, and cutting-edge material.
Types of CNC Cutting Tools
There are numerous types of CNC cutting tools:
1. Turning Tools
Turning tools are either single-point cutting tools or tools with only one active cutting surface. They are used in lathes or machining centers. Turning tools include form tools, thread-turning tools, and grooving and cutoff tools.
Form tools are fed perpendicular to the surface of the workpiece, cutting a particular profile on a rotating part or workpiece. The profiles can be conical, concave, convex, ball, or chamfered, depending on the shape of the tools. Form tools use a single plunge cut to make this cut. Grooving and cutoff tools use inserts that create grooves inside the workpieces such that the tools are surrounded on three sides by the workpiece.
2. Drilling Tools
Drilling tools, which are end-cutting tools, use their leading edge to remove material. The drilling tools also feature one or more helical or straight flutes (grooves that line the outer edge of the tool) to remove the cut material (chips) from the drilled hole.
3. Milling Tools
Milling tools have multiple cutting edges and remove material through rotary action. There are different types of milling cutters, namely face milling cutters, slot milling cutters, end milling cutters, and rotary milling cutters, each suited for a specific operation. For instance, face milling cutters create flat surfaces, while slot milling cutters are used for side and face milling, as well as slotting and grooving. Additionally, end milling cutters create two working surfaces simultaneously, with rotary milling cutters used to enhance productivity.
4. Boring Tools
Boring tools act on the internal surfaces of parts in turning or machining centers. They create and enlarge holes, improving the accuracy of the internal dimensions. Two types of boring tools exist: single-point boring tools and multipoint boring tools. Single-point boring tools are essentially long boring bars with small diameters and an insert mounted at a single point. For this reason, they have the least rigidity of all cutting tools. On the other hand, multipoint boring tools feature multiple inserts mounted on opposite sides or at different points along the longitudinal edge of the boring bar.
5. Deburring Tools
Deburring tools are designed to remove burrs. Burrs are unwanted material projections that occur after machining. The burrs are caused by plastic deformation during machining. There are various deburring methods, including abrasive-jet/water-jet deburring, barrel tumbling, centrifugal barrel tumbling, ultrasonic deburring, chemical deburring, electropolishing, sanding, brushing, ice-blasting, mechanical deburring, electrochemical deburring, and more. Tools for deburring holes can include chamfering tools that chamfer the exit or entrance of holes.
6. Reamers
Reamers are used to enlarge holes and improve their precision and finish. This means reamers are deployed after a drilling, boring, or milling operation. There are several types of reamers: adjustable/expansion reamers, single- and multi-diameter reamers, straight and tapered reamers, and single- and multi-flute reamers.
7. Threading Tools
As the name suggests, threading tools cut screw threads. There are various types of threading tools: cut taps, thread chasers, thread mills, roll form taps, thread turning inserts, and dies.
8. Grinding Wheels
Grinding wheels are made of abrasives bonded together using a bond material. In this case, the bond material acts as a toolholder (more on this below). Grinding wheels rotate against the surface of a part to remove material.
9. Microsizing Tools
Microsizing tools have a fixed diameter and operate using a single stroke. These microsizing tools are used to adjust the internal diameter, roundness, surface roughness, and positional tolerances of bores.
10. Honing Tools
Honing tools are made up of abrasive stones held in the tool body and expand repeatedly to exert pressure on the bore wall. These honing tools are passed through the bore in a multi-stroke movement. Like microsizing tools, honing tools are used to correct the internal diameter, roundness/shape, surface roughness, and positional tolerances of bores.
11. Burnishing Tools
There are two types of burnishing tools – ball and roller. These tools are rotated against a workpiece’s internal or external surfaces to improve their surface strength and surface finish.
Producing CNC Custom Tools
With CNC custom tools, you can design and machine them in-house if your workshop has the expertise and machines. Alternatively, you can hire specialists to create custom tools for you. A simple online search of companies that design and produce CNC custom tools presents numerous results for you to choose from.
Custom Accessories for CNC Machines
Today, there are several service providers and precision instrument companies that let you order custom accessories. Such companies walk with you throughout the journey, consulting you as they develop designs that best suit your workholding and toolholding needs. If you possess the necessary skills, you can design and machine custom accessories yourself based on your prevailing requirements.
Like standard CNC accessories, custom CNC accessories come in various designs, shapes, and sizes, but can be broadly categorized into four types:
- Workholders/Fixtures
- Toolholders/adapters
- Toolholder accessories
- Measuring tools
Toolholders
Toolholders hold cutting tools in the machine spindle. Types of toolholders include:
- Tool Chucks: These toolholders clamp tools with cylindrical cross sections. Examples of tool chucks include collet chucks (precision and standard), hydraulic chucks, shrink-fit chucks, drill chucks, milling chucks, Weldon-type chucks, and Clarkson-type chucks
- Arbors: arbors act as the interface between the cutting tool and the drive spindle of the CNC machine. They facilitate rapid tool changes and accurate machining.
- Adapters: adapters are designed to adapt the shank of a cutting tool with the machine taper (discussed below), enabling you to use a toolholder of a particular size in a machine with a larger spindle holder. Adapters can also be considered toolholder accessories if used to adapt the toolholder with the machine taper.
- Reduction sleeves: Reduced sleeves connect a larger toolholder to a smaller spindle holder. Essentially, they are the opposite of adapters.
Fixtures
Also known as fixtures, workholding devices or workholders are generally used to clamp, secure, locate, and support parts and workpieces. Fixtures that have a built-in feature for guiding/controlling the lateral movement of the tool are known as jogs. Workholders consist of several elements, including the supporting structure, clamps, and locators. These elements hold the workpiece in position, ensuring that the cutting and clamping forces do not affect the specified tolerances. Workholders can be broadly categorized into:
- General-purpose fixtures, which are designed to hold any workpiece regardless of geometry
- Dedicated/custom fixtures, which are meant for specific machining operations or particular workpiece geometry
Under the two categories mentioned, we have the following types of workholders, including:
- Workpiece chucks, e.g., lathe chucks
- Standard clamps
- Vises
- Universal indexing heads
- Sine and angle plates
- Live and dead centers, which hold or support workpieces in lathe machines
This article will focus on custom fixtures, which are primarily used in unique production settings. For instance, if machining loads primarily come from one direction, a custom fixture can be designed to provide enhanced support in that direction. This also applies to situations where the part to be machined has a unique geometry that general-purpose fixtures cannot accommodate.
Dedicated fixtures are usually made from casting or tooling plates. However, they are usually more expensive, more complex, and often have longer construction lead times. For these reasons, dedicated fixtures are preferred in high-volume production as they more than pay for themselves.
Tool and Toolholder Accessories
Tool and toolholder accessories are detachable components that, when attached to tools or toolholders, enhance
Examples of toolholder accessories include:
- Spacers
- Sleeves, sockets, and bushings
- Pull studs
Measuring Tools
There are various types of measuring tools, including dial gauges, testers (e.g., hardness testers), calipers, micrometers, and probing tools. While it may be illogical to customize standardized measuring tools like digital micrometers, dial gauges, and calipers, you can work with experts in precision measurement to order some custom measurement systems for CNC machine tools.
For instance, you can work with Renishaw, which offers expert advice and design services for anyone looking for custom probes or tool-setting solutions. The company has a custom products team that designs and makes high-quality measuring tools at competitive prices and with fast delivery times. Additionally, Renishaw supports the installation process regardless of whether you are working with a new or old CNC machine.
Benefits and Drawbacks of Custom Tools and Accessories
Benefits of Custom Tools and Accessories
The advantages of custom tools and accessories include:
- Improved productivity because the custom tools are optimized for operations that other standard tools are not and, thus, improve the MRR, leading to faster machining operations
- Reduces the setup and processing times, as the custom tools are designed to be easy to mount and dismount
- Better machining performance because with custom tooling, you can select materials with the best mechanical, thermal, and chemical properties that have a high MRR and can support high cutting speeds without being susceptible to shocks or stresses
Disadvantages of Custom Tools and Accessories
The drawbacks of custom tools and accessories are:
- Custom tools and accessories require a long lead time, as they need to be designed, prototyped, tested, and manufactured
- They can be more costly per item than mass-produced tools and accessories, especially in cases where they are not manufactured
- It can be difficult to find a supplier/company with the necessary expertise to design and produce a custom tool and accessory
Designing Custom Tools and Accessories
Design of Custom Tools
As with all other cutting tools, the design of custom cutting tools significantly impacts machining performance. Well-designed tools produce parts and features of consistent quality and have long, predictable useful lives. On the contrary, poorly designed tools may wear or chip easily, rapidly, and unpredictably. These tools often need frequent replacement, which increases costs. They also affect productivity and reduce the quality of parts. This means that tooling significantly impacts the productivity and economics of a machining operation.
Material for CNC Custom Tools
Another consideration you should make during the design phase is the choice of cutting-tool materials and their properties. Ideally, you should choose materials with the following characteristics:
- Enhanced penetration hardness at high temperatures to resist abrasive wear
- Elevated deformation resistance to avoid deformation or collapse of the edge under stresses caused by chip formation
- High thermal conductivity to reduce the temperatures near the edge of the cutting tool
- Low friction vis-à-vis the work material to prevent built-up edge (BUE)
- High thermal shock resistance to prevent tool breakage when cutting is periodically stopped
- Low chemical affinity to resist chemical wear
- High fatigue resistance to enable continuous machining
- Elevated stiffness to ensure continued accuracy and precision
- High fracture toughness to prevent the edge from breaking or chipping
CNC custom tools can be made from materials such as carbides (e.g., tungsten carbide), polycrystalline materials (e.g., polycrystalline diamond and cubic boron nitride), ceramics, cermets (composites of metal and ceramic), steels, high-speed steels (HSS), and superabrasives.
You can also consider coating the tools made using HSS, tungsten carbide, and ceramics to increase the allowable cutting speeds and enhance the tool life. Some of the conventional coating materials include aluminum oxide, titanium nitride, titanium carbide, boron carbide, hafnium nitride, chromium nitride, titanium diboride, titanium aluminum nitride, and titanium carbo-nitride.
Design of Custom Accessories
The design of custom accessories takes multiple factors and parameters into consideration. After all, these components are subjected to considerable amounts of forces, stresses, temperatures, and more that may affect performance. As shown in the image below, several factors can influence the design of a custom fixture.
Factors Affecting Design of Custom Fixtures
Similarly, custom toolholders and toolholder-spindle interfaces should be properly engineered to ensure high performance and throughput. After all, a particular toolholder and/or toolholder interface is only effective if used for the application it was initially designed. Put simply, all toolholders and/or toolholder interfaces are not to be universally deployed in all types of machining. They must first meet the performance requirements to be fit for purpose and for the best results.
Poorly engineered toolholder interfaces result in reduced accuracy, shorter tool life, diminished rigidity, and lower repeatability. This is because the toolholder may wear out at its interface with the spindle if it improperly fits the opening or is out of tolerance.
Thus, when designing a toolholder and the toolholder-spindle interface, you should consider structural and dynamic characteristics such as cost, chemical and thermal behavior and stability, maintenance requirements, ease of mounting and dismounting, manufacturing tolerances, radial and axial positioning accuracy and repeatability, force transmission capabilities (based on cutting forces and torque), and clamping forces.
The other factors/characteristics you should consider are fatigue life and durability, momentum and torque characteristics, connection rigidity, sensitivity to corrosion and contamination, ability to transmit coolant, safety, retention force requirements, storage and handling cycles, time on the machine, tool weight and capacity, and much more. Additionally, you must decide whether the body of the toolholder should be one solid piece or a modular design that uses a mechanical connection.
Integration of Custom Tools into CNC Operations
Designing custom CNC tools is only the first step. You must undertake additional software-based steps to integrate them into a particular CNC operation. Normally, whenever you want to produce a part of an existing 3D model, you first have to import it into computer-aided machining (CAM) software. Besides importing, you have to provide information such as the machine, cutting tools, and machining parameters to be used. The CAM software then liaises with a software called a post-processor to produce machine-specific instructions.
The cutting tools are usually stored in a tool library. The tool library is a database of tools that can be updated by adding new tools or editing tool settings. So, if you want to use a new tool that is not among the options in the tool library, you must update the database. This process applies to custom tools as well. And many CAM software products do, in fact, let you add custom tools to the library. To add a CNC custom tool to the CAM software’s tool library, follow the following general steps:
- Open the tool library
- Click the “Add” button or “Plus”) icon
- Enter the name of the custom tool
- Select the type of custom tool
- Input the custom tool’s dimensions, cutting speeds, and feeds
- Save the tool information
Now that the custom tool is part of the tool library, you can generate the CNC program. It is worth noting that while creating this program, the post-processor considers the information you will have specified while adding your custom tool. As such, the program will be customized for your tool, preventing unforeseen issues like collisions or unsupported feed rates and cutting speeds that may lead to tool breakage.
Conclusion
CNC custom tools and accessories are quite common in the machining practice. They are preferred when standard tools for a particular job are inefficient or unavailable. Alternatively, they are chosen when you want to increase productivity or use tools that are optimized to enhance certain parameters. However, custom CNC tools are more expensive than standard tools. Their use, therefore, makes the most sense in mass manufacturing operations. When it comes to designing and producing custom tools and accessories, you can opt to do everything in-house or outsource that service to specialist companies. And once you have created the CNC custom tools and want to integrate them into your machining operations, you should remember to add them to your CAM software’s tool library.
