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Best Practices: Designing for CNC Drilling

Make the most out of CNC drilling. This guide will help you improve designs.

Precision is paramount in manufacturing.


One of the most common operations, CNC drilling, requires careful design considerations to ensure accuracy and efficiency. In this article, we will explore essential design tips for CNC drilling that can help maximize the drilling process's efficiency, quality, and reliability.


By adhering to these guidelines, you can can ensure smooth operations, avoid potential issues, and achieve desired outcomes in their CNC drilling projects.


What is CNC Drilling?


CNC drilling, short for Computer Numerical Control drilling, is a mechanical process that utilizes automated machinery to precisely create holes in workpieces. drilling machines are programmed to follow specific instructions, guiding the drill bits to penetrate the material at precise locations, depths, and angles.




To optimize the CNC drilling process, designers must consider various factors such as drill entry and exit surfaces, hole straightness, chip clearance, threaded product design, hole shape, and overall part layout. Each of these aspects contributes to the overall success of CNC drilling and influences the final quality and functionality of the workpiece.


Need high-quality CNC machining services? Try MakerVerse for fast lead times.

General Design Tips


1. The drill entry surface should be perpendicular to the drill bit to avoid starting problems and help ensure the hole is in the proper location, like in the photo below.



The exit surface of the drill also should be perpendicular to the axis of the drill to avoid breakage problems as the drill leaves the work, as shown below.


CNC drilling exit surface

2. If the straightness of the finished hole is particularly critical, it is best to avoid interrupted cuts. Some deflection will occur if the drill intersects another opening on one side. Even when straightness is not critical, the center point of the drill must remain in the material throughout the cut to avoid extreme deflection and possible drill breakage.


3. Allow chip clearance with internal threads. Through holes are preferable to blind holes because of more straightforward clearance for tools and chips, especially when secondary operations such as reaming or tapping are required.

4. Shorten your threads. The first four pitchs take most of the load. You can save that space if you don’t have a defined calculated load. If you don’t know the pitch, everything longer then the diameter is unnecessary.


5. The design of threaded products should include a chamfer at the ends of the external threads and a countersink at the ends of the internal threads. These inclined surfaces prevent the formation of finlike threads at the ends, help minimize burrs, and assist the threading tool in cutting or forming the threads.



Designing Holes

6. The bottom shape of blind holes should be that made by a standard drill point, as shown in the image below. When flat-bottom holes are required, allow a standard drill point (118° or 140° with stainless steel).

7. Avoid deep holes (over 8 times diameter) because of chip-clearance problems and possible deviations from straightness. Especial drills on the market can reach 40 times diameter with price tags around 150-400€; avoid them.


8. Avoid designing parts with tiny holes if the small size is unnecessary for your part’s application. This is because small drills are more susceptible to breakage. About 3 mm diameter is a desirable minimum for convenient production.


9. Use rectangular rather than angular coordinates to designate the location of holes on milled parts. They are easier and more foolproof for the machinist to lay out the part or a drill fixture. For turning parts, the center of the part is the natural origin of the measures.


10. Design parts so all holes can be drilled from the smallest number of sides – ideally only one side. This simplifies tooling and minimizes handling time.


11. Standardize the size of holes, fasteners, and other screw threads as much as possible to minimize the number of drill spindles and changes.


12. Leave space for the drilling tool. The manufacturer needs space or access from the top of the closest wall or the clearance between the tool holder and the closest wall. That means to have a 12 mm drill center to the wall or drilled depth, plus wall under 8 times the hole diameter.





13. Avoid intersecting drilled and reamed holes to prevent tool breakage and burr-removal problems.



14. If a blind hole requires reaming, good practice calls for extra drilled depth to provide room for chips. Reamed hole must be design according to the specifications tools manufacturers. The linked table shows you the offset for the reaming.


Getting Started with CNC Drilling


Designing for CNC drilling is a delicate balance between technical know-how and practical application.


By following these general design tips and hole design considerations, you can optimize your manufacturing process, reducing the risk of errors, breakages, and unnecessary costs. Remember that while these tips are guidelines for best practices, each project comes with unique challenges. Strive for standardization but be ready to adapt as required.


Success in CNC drilling is as much about planning and design as it is about execution. If you’re unsure of anything, MakerVerse is here to help. You can upload your designs, get quotes for your parts and work with our experts to help ensure the success of your project. Ready to get started?



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