Machining complex parts is never an easy task. Engineers and manufacturers work with tight tolerances, intricate shapes, and demanding material requirements daily. Many projects fail not because the design is flawed, but because small details—such as hole placement, tool access, or part holding—get overlooked early in the process.
This article was written to help close that gap. It aims to share clear and valuable ideas that simplify, accelerate, and enhance the reliability of machining complex parts. By examining common challenges and providing practical tips, we aim to help engineers, designers, and production teams reduce trial and error, ultimately achieving more stable results.
Now, let’s go through each area step by step and see how innovative design and careful planning can turn complex parts into smooth and successful machining projects.
1. Plan Hole Placement Carefully
When designing parts, consider spacing and depth early in the process. Keep holes away from edges, thin walls, and corners to prevent distortion. Holes placed too close together can remove too much material at once, creating heat and reducing dimensional accuracy.
Grouping holes by size and depth can streamline the production process. It reduces tool changes and maintains consistent machining conditions. For deep holes, step drilling is most effective: start with a smaller pilot hole and gradually enlarge it. This maintains tool stability and ensures better chip removal.
For reference, on-axis holes can typically go as small as 1 mm in diameter. In contrast, side or radial holes should be slightly larger, around 2 mm, to maintain strength and prevent tool deflection. Deep holes should generally stay within six times the hole diameter to avoid instability.
Align holes along common axes whenever possible. This enables the machine to complete multiple holes in a single setup, enhancing accuracy and reducing cycle time. If angled or off-center holes are required, simulate tool paths in 3D to check for clearance issues and prevent collisions.
2. Manage Deep Features with Strategy
Deep features, such as pockets, slots, and cavities, are standard in complex parts, but they require careful planning to machine accurately. Without a proper approach, long tools can bend or vibrate, which affects both accuracy and surface quality. Uneven forces during deep cutting can also create internal stress, leading to warping or deformation after machining.
Use the shortest tool that can reach the required depth. A shorter tool has better stiffness and produces a smoother surface. When deep features are necessary, remove material in several step-down passes instead of cutting the full depth at once. This maintains steady cutting forces and improves tool life.
For design reference, try to keep the depth of a milled slot or pocket within six times its width. Going beyond this ratio often increases the risk of vibration and tool deflection. Leave at least 0.020 in. (0.5 mm) of wall thickness next to the feature to maintain strength and avoid distortion. For external grooves on turned parts, keep the depth under 0.95 in. (24.1 mm) and avoid widths smaller than 0.047 in. (1.2 mm). Following these fundamental limits helps strike a balance between precision and stability.
3. Design Better Threads and Inserts
Start with the correct thread size and fit class for your part. For internal threads, ensure the surrounding wall is thick enough to prevent cracking or distortion during the cutting process. Avoid placing threaded holes too close to edges or thin sections, as this can weaken the part and cause assembly issues.
Choose thread creation methods based on the material. Hard metals often work best with thread milling, which produces clean threads and allows for minor adjustments without requiring a change in tools. Softer metals, such as aluminum, can be tapped efficiently, but good lubrication and chip control are necessary to prevent tearing or galling.
Suppose the part has multiple threaded features; group threads of the same size and type. This reduces the need for tool changes and shortens the cycle time. Using standard thread sizes whenever possible also helps. Custom threads can slow production, make maintenance harder, and increase the risk of errors.
4. Keep Text Simple and Practical
Adding text, logos, or labels to machined parts is common, but it can slow production and increase costs if not designed carefully. Very detailed fonts, deep engravings, or tiny characters can wear tools faster, extend cycle times, and sometimes make markings hard to read. Simple text is easier to machine, produces cleaner results, and avoids unnecessary complications.
Choose clear, easy-to-cut fonts. Sans-serif styles with consistent stroke widths, like Arial or Helvetica, work best for CNC machining. Avoid decorative or cursive fonts, as their thin curves and fine details are difficult for machines to reproduce accurately. Use larger character sizes when possible, especially on small parts where tool access is limited.
Control engraving depth carefully. Shallow text, around 0.2–0.5 mm deep, is usually enough for good visibility. Deep engravings require more passes and increase the risk of tool breakage. If the text is meant for identification rather than function, surface engraving is faster, cleaner, and more consistent than deep cutting.
5. Add Proper Radii to Corners
Design internal corners with radii that match or slightly exceed the cutter’s radius. For instance, if you are using a 6 mm end mill, set the corner radius to at least 3 mm or a bit larger. This allows the tool to move smoothly without leaving uncut material or causing excess stress. Larger radii will also enable you to run at higher feed rates and reduce tool wear.
Avoid very small or inconsistent radii across similar features. Each different size can add programming time and may require separate tools. Using uniform radii wherever possible simplifies setup and improves repeatability. If sharp corners are essential, consider a secondary process like Mecanizado por descarga eléctrica (EDM), which can produce precise edges but adds time and cost.
Radii also improve part strength. Sharp corners act as stress points where cracks can start, especially in load-bearing parts. Adding even a small radius spreads the stress more evenly, enhancing durability and reducing the risk of fatigue failure over time.
6. Think Ahead About Tool Access
Before machining, visualize how the cutting tool will reach each feature to ensure a smooth operation. Every face, pocket, and hole should have a clear path without obstruction. Deep or hidden features may require slight design adjustments, such as widening an angle or shifting a feature, to allow standard tools to fit and operate efficiently.
Avoid designs that force the tool to work at steep angles or in tight spaces for long periods. These conditions increase vibration and tool deflection, which can affect accuracy and surface finish. Instead, break complex features into multiple shallower passes that shorter, more rigid tools can handle easily.
For multi-axis CNC machines, utilize their ability to reposition the part automatically. This improves access from multiple angles and can reduce the number of setups required. Even with 5-axis machining, sharp internal corners or blocked surfaces can limit tool movement, so keeping designs smooth and open helps maintain efficiency and precision.
7. Optimize Fixturing for Stability
Consider how the part will be held before machining starts. Every part requires a stable reference point, or datum, to ensure consistent positioning and alignment. Complex parts may require multiple setups, so include flat, accessible surfaces that can be clamped securely without blocking the tool. Avoid using curved or thin areas for fixturing, as they can bend or deform under pressure.
Distribute clamping forces evenly. Uneven pressure can distort the part, especially in thin-walled sections. Soft jaws, custom fixtures, or vacuum tables are helpful for delicate materials. Modular fixtures work well for prototypes or small batches because they can be adjusted quickly between parts.
For multi-axis machining, plan fixtures that allow access to all critical features. A well-designed fixture reduces the number of repositionings, lowers alignment errors, and shortens cycle times.
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Hola, soy Kevin Lee
Durante los últimos 10 años, he estado inmerso en diversas formas de fabricación de chapa metálica, compartiendo aquí ideas interesantes de mis experiencias en diversos talleres.
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Kevin Lee
Tengo más de diez años de experiencia profesional en la fabricación de chapas metálicas, especializada en corte por láser, plegado, soldadura y técnicas de tratamiento de superficies. Como Director Técnico de Shengen, me comprometo a resolver complejos retos de fabricación y a impulsar la innovación y la calidad en cada proyecto.
