CNC machining is an efficient and economical approach to manufacture metal or plastic components that demand cutting or drilling. Over the years, this manufacturing technology has been complemented and significantly enhanced as you can now manufacture it to your design directly via CAD software.
You must get your CAD design right to ensure swift delivery of products to the market while avoiding revisions and re-work. Performing revisions can be problematic when your model lacks optimization for the selected manufacturing process.
Tips to Enhance your CAD Designs for CNC Machining
Here are some tips that can improve your CAD design by making it cost-effective while ensuring compatibility with CNC machining –
Design CNC Machinable Features
Adding unnecessary features complicates the machining process for the CNC machine. If you wish to add features that have little to no effect on the functioning of the part, it is advisable to learn about the machine’s capabilities thoroughly.
For instance, one such feature which CNC mills, lathes, or drills cannot produce is curved holes. If the primary goal of adding such features is merely to complement the aesthetics, it is advisable to scrape it off the list unless you have a highly-capable CNC machine.
Be Accurate with Depth-to-Width Ratios
Massively improve your CAD design by accounting for the depth to width ratio of cavities. Deeper cavities can lead to tool hanging, chip evacuation difficulty, tool deflection, and tool fracture.
Cavities over six times the tool diameter are classified as deep and must have a maximum depth of four times the cavity's width dimensions. For instance, a 15 mm wide cavity must not be over 60 mm deep.
Do Not Excessively Use Tolerances
While maintaining strict tolerances is crucial, it is worth noting that excessive tolerancing would increase machining time and expenses. Different CNC machines offer different tolerance standards, implying that if your dimensions do not have tolerance, the machine would automatically switch to its standard tolerance.
Tight tolerances should only be specified wherever necessary to save time and cost. You must also maintain homogeneous tolerancing to minimize machining time.
Radii When Designing Internal Edges
The machining tool struggles with internal edges owing to its shape since most cutting tools are cylindrical, which renders them unable to create sharp internal edges. Therefore, it is advisable to add radii to the internal edges when designing your CAD file.
Design internal edges that do not overstress the tool beyond its limit. This practice lets you avoid the wear and tear of the CNC machining tool. This feat is achievable by adding a radius of 130 percent of the milling tool radius.
Skip on Redundant Aesthetics
If you are adding aesthetic features and producing parts for visual appeal, consider the amount of material that must get removed, the process involved, and if it is a 5-axis or a 3-axis machining process.
Your CAD design can be significantly improved by raising the production accuracy of essential features over aesthetics since certain post-machining processes can be used for aesthetics.
Refrain from Designing Thin Walls
Studies have demonstrated that wall thickness is proportional to the material's stiffness. This scenario implies that thin walls would negatively affect the stiffness of the material. Reduced material stiffness would also reduce achievable accuracy due to more vibrations during machining. The standard minimum thickness for walls is 1.5 mm for plastics and 0.794 mm for metals.
Do not Design Small Features
Typically, CNC machines have a minimum tool diameter of 2.5mm, implying that any feature smaller than 2.5mm becomes extremely hard to machine. Minuscule features require specialized tools to produce, which increases machining time and expenses. Therefore, too small features must be avoided if not essential.
Refrain from designing small features. Photo by Kumpan Electric on Unsplash.com
Ensure Standard Sizing for Holes
Standard-sized holes get milled by standard drill bit sizes, which helps save machine time and expenses since holes not designed to standard would call for an end mill tool.
With non-standard holes, the rule of thumb for depth of cavity comes into play, which states that the depth should be four times the cavity's diameter.
Check the Threaded Hole Lengths
A massive portion of the strength of a threaded connection happens within the first couple of turns. Since the length of the hole is directly proportional to the time and cost for CNC machining, you must not exceed the thread length beyond what is necessary.
Be sure to keep the threaded hole length to about three times its diameter. This practice must only get overlooked for blind holes that require extra unthreaded length at the bottom.
Avoid Redundant Text and Lettering
When designing parts, avoid unnecessary text since any required lettering can get easily painted on the machined part's surface during finishing. Adding texts during machining increases machine time and expenses.
However, if the design requires text and lettering to be present mandatorily, the following rules are applicable –
- Use engraved texts as it causes less removal of material.
- Use the San Serif font with 20 points if your design software does not have a custom lettering font.
- Stick with size 20 because any number smaller falls under small features, which is tedious and expensive to machine.
The process of CNC manufacturing today involves creating a design of the desired product, which carries certain constraints. However, most people commit errors when working on the CAD design, which degrades the quality and aesthetic of the final part. Getting your CAD design wrong can lead to unnecessary hold-ups and more costs.
However, the CAD designs for CNC machining can be enhanced drastically by following the tips mentioned above. Some useful tips include designing machinable features, avoiding extra-thin walls and minuscule features, refraining from using redundant text, and many more.
About the Author:
Peter Jacobs is the Senior Director of Marketing at CNC Masters. He is actively involved in manufacturing processes and regularly contributes his insights for various blogs in CNC machining, 3D printing, rapid tooling, injection molding, metal casting, and manufacturing in general.