CNC Machining Design Considerations

CNC machining involves using a high-speed rotating cutting tool to remove material from a solid block in order to produce the required part according to the blueprint. Among them, the tool plays a crucial role in CNC machining as it directly contacts the part and removes the excess material to obtain the desired part.

CNC machining involves using a high-speed rotating cutting tool to remove material from a solid block in order to produce the required part according to the blueprint. Among them, the tool plays a crucial role in CNC machining as it directly contacts the part and removes the excess material to obtain the desired part.

The CNC milling cutter has a cylindrical shape. When cutting the inner wall, a radius will appear on the vertical angle. Small tools can achieve multiple cuts at a lower speed to obtain a smaller radius, which will result in more time and higher costs.

Therefore, when you design the parts made through CNC processing, it is best to increase the depth radius of the cavity and use a similar radius for the inner edge. If you do not provide a 2D drawing specifically indicating that the corners at right angles need to be chamfered, our company will process all the inner corner straight angles according to the following rules with the minimum R value:

Assuming the tool diameter is ∮D mm, the maximum depth of the inner cavity is H mm, and the minimum inner R mm is R. The formula is R = (H/10) + 0.5. ∮D = H/5. For example: if the inner cavity depth is 30 mm, the minimum inner R can be processed to R3.5 mm = (30/10) + 0.5. The corresponding tool is ∮6 = 30/5. Currently, we can achieve the minimum inner R of R0.5 with a depth of ≤ 3 mm. The smaller the inner R, the smaller the tool required, and the processing cost will be higher.

The platform suggests that, if possible, the R angle should be as large as possible!

If you require the workpiece to retain right angles, please provide a 2D drawing file with the relevant annotations. If this requires spark machine discharge for chamfering (chamfering involves CNC machining of the copper core first and then discharge machining on the spark machine, which is more costly), or if you need to change the workpiece structure to make R-shaped corners with clearance, and have CNC directly machine it, the cost will be lower. If both sides of the workpiece are through holes, they can be cut and machined for chamfering on the online cutting machine, which is more costly.

⭐ To reduce communication costs and avoid processing errors, it is recommended that when designing, the threads should be sized according to the standard drilling inner diameter and rolled outer diameter, and the thread parameters should be fully described. When placing orders, try to include both the internal and external threaded parts in the same order for processing.

⭐ Each engineer may draw 3D diagrams with different thread bottom hole diameters. For example, the standard diameter of the bottom hole for M3x0.5 is ∮2.5 (as shown in the figure). During programming, directly program the bottom hole with a diameter of ∮2.5 to drill the bottom hole, and then use an automatic thread machine to thread. If the bottom hole is drawn as ∮3, the bottom hole processing will be too large and cannot be threaded (some can be remedied by fitting a thread sleeve);

⭐ Special threads require providing physical samples for compatibility;

⭐ Tight thread connections occur in the first few threads. Sometimes, a very long thread length is not necessary. Long thread holes may require special tools and will require more processing time and costs. The thread length is recommended to be no more than 3 times the hole diameter. When the thread hole is a blind hole, it is recommended to leave at least half of the hole diameter without a thread at the bottom of the hole.

Processing deep cavities will significantly affect the cost of CNC parts, as it requires removing a large amount of material and takes an extremely long time. The cutting length of CNC tools is limited, and the best processing effect is achieved when the cutting depth reaches 2-3 times the diameter of the tool. For example, a ø12 milling cutter can safely cut a cavity up to 25mm deep.

Cutting deeper cavities (5 times or more of the tool diameter) will cause problems such as tool sagging, tool skewing, difficult chip removal, and tool breakage. Therefore, special tools or multi-axis CNC systems are required. Additionally, when cutting cavities, the tool must be tilted to the correct cutting depth, and a smooth entry requires sufficient space.

Limiting the depth of all cavities to 5 times their length (i.e., the maximum size on the XY plane) can achieve the minimum processing cost.

Thin-walled processing requires multiple passes with low cutting depth, which is prone to vibration and leads to deformation or fracture. Therefore, thin-walled parts are difficult to be precisely processed and the processing time will increase.

The wall thickness of metal parts is preferably designed to be 0.8mm or more (the minimum can be 0.5mm), and the minimum wall thickness of plastic parts should be 1.5mm or more (the minimum can be 1mm).

The stricter the tolerance, the higher the processing cost will be, as it increases the processing and quality inspection time.

If the specific tolerance is not marked on the part drawing, the processing will be carried out according to the standard tolerance (±0.1mm or higher). If there are special processing requirements for tolerance, please provide 2D drawings and mark them accordingly.

2D drawings are the best way to convey certain aspects of the design. They clearly indicate tolerances, surface roughness, assembly methods, key inspections, and quality control for these key features. This provides a reference for selecting the best processing method and process route, and the cost will also be lower.

For threaded holes and depth of dimensions, they also need to be marked simultaneously.

Engineering review drawings will also compare 3D and 2D drawings. If there are conflicts, timely communication and feedback can be provided.