Although CNC machining is flexible, not every design is feasible. In order to ensure smooth machining, you must be aware of the constraints and restrictions. The two main limitations for CNC design are;
The cutting length of the majority of CNC tools is limited. Additionally, they are all cylindrical in shape and geometry. These cutting tools impart their cylindrical geometry to the workpiece when removing materials from it. Because of this, regardless of the size of the cutting tool, the interior corners of a workpiece always have a radius.
When working on a workpiece with a significant depth-to-width ratio, tool access becomes a significant challenge. This is a problem because CNC machines employ cutting tools that are applied to the workpiece from above to cut.
In other words, it would be difficult to machine a workpiece inaccessible from the top angle. The only exception to this rule occurs during undercut machining for CNC machined parts.
Aligning the features of your part or component to one of the six principal directions is one way to mitigate this tool access challenge. Also, using a five-axis CNC machining with an excellent workpiece holding capacity means tool access is no longer restricted.
In the CNC machining world, no set of standards is generally accepted. This is primarily because the industry and the machines used are always evolving. However, some best practices and recommendations would help ensure your design quality remains top-notch. These recommendations include;
The vertical corner radius should be at least one-third of the cavity depth when creating inner edges. You can use a diameter tool that has the advised cavity depth if you use the indicated corner radii.
Corner radii slightly above the advised value allow you to cut along a circular path as opposed to a 90-degree angle, producing a surface finish with a better level of quality. It is advised to employ a T-bone undercut rather than reducing the corner radius if you require a 90-degree angle instead.
To create holes, machinists may utilize drill bits or end mill equipment. It is best to use standard drill bit sizes, measured in either metric or imperial units, as a guide when determining the diameter of the holes in your design.
Technically, any dimension greater than one millimeter is feasible. Machine operators use reamers and boring equipment to complete holes that need to be within precise tolerances. It is best to utilize a standard diameter for holes that require great accuracy and are smaller than 20 millimeters.
When designing parts for CNC machining, four times the nominal diameter is the maximum proposed depth for any hole, but 40 times this amount is doable. The nominal diameter is typically 10 times the ratio.
The minimal thread size used when developing CNC-machined items is M2, but M6 or above is usually ideal. Machinists can limit the danger of tap breakage by using CNC threading machines to cut threads as small as M6.
The minimum thread length should be 1.5 times the nominal diameter, while the recommended length is three times the normal. For any thread less than M6, you must add an unthreaded length at the bottom of the hole that is 1.5 times the nominal diameter. Threading the hole throughout its length is best for threads larger than M6.
Since end mill tools have a restriction on their cutting length, the industry-recommended cavity depth on any design is four times its width. A lower depth-to-width ratio would result in greater chip evacuation, tool deflection, and vibration.
Does your CNC design require larger depths? One way to solve this challenge is by using a variable cavity depth and a specialized tool.
You may need to mark parts with part numbers or company names. Adding text looks really cool in the custom CNC design, but is time-consuming to process. Electrochemical etching or laser marking is usually better.