In CNC machining, many features may look straightforward in a design, but they can dramatically impact manufacturability, driving up costs or rendering a part impossible to produce. Understanding these critical design choices can mean the difference between a fast quote and extensive back-and-forth modifications.
At Approved Machining, our goal is always to help customers save time and money on every project. In this blog, we highlight the eight most common design issues we encounter and offer practical strategies to avoid them and reduce your costs.
Table of Contents
- 1 1. Insufficient Drill Depth
- 2 2. Square Corners in Pockets
- 3 3. Raised Text Instead of Engraved Text
- 4 4. Excessively Thin Walls
- 5
- 6 5. Draft Angles Designed for Molds
- 7 6. Deep Features Near Walls
- 8 7. Small Radii in Deep Pockets
- 9 8. Radiused Areas That Require Blending
- 10 Communicate With Us Early to Ensure Your Success
1. Insufficient Drill Depth
When a tapped hole depth matches a drilled hole depth, chips have no way to evacuate the hole. In these cases, chips can often compact in the hole and break the tap, requiring the part to be scrapped. Designs should extend the drilled hole depth past the required thread depth–for instance, if you require 0.5” of threads, drill the hole about 0.050" beyond your required thread depth.
2. Square Corners in Pockets
CNC machines employ round cutting tools, so creating a perfectly square corner is not possible through standard machining processes. This can be solved by simply adding a radius to any pockets or cutouts with mating edges, which rarely affects part functionality or assembly. Certain processes like EDM can technically create square corners, but they will significantly increase cost and lead time compared to standard CNC milling.
3. Raised Text Instead of Engraved Text
While raised or embossed text may look appealing, it adds significant expense and machining time to your project, especially for small letters. In addition, due to CNC tool radius limitations, raised text requires corner radii that can distort letter shapes and render them difficult to read. Engraved text is faster to produce, more durable, and typically provides better legibility.
4. Excessively Thin Walls
Walls under ⅛” thick can lead to chatter, where a part vibrates during cutting. This can result in poor surface finish, dimensional inaccuracy, or even part failure. Thin sections are also more prone to warping and damage during handling. When possible, simply add thickness to your walls to better withstand the machining process, adding to the longevity of the part and saving on costs.
5. Draft Angles Designed for Molds
When creating machined prototypes of parts intended for eventual injection molding production runs, many engineers include the draft angles that will be required for their final design. However, these angles often complicate the machining process, requiring specialty tooling and adding expense to your project. Unless the draft angles serve a functional purpose in your prototype, we recommend removing them from your design in favor of straight edges during the machining phase. When you move to your final mold design, simply add them to your design once again.
6. Deep Features Near Walls
Placing deep features like holes close to internal walls creates tool clearance challenges. The cutting tool needs adequate space to reach the required depth without striking the side wall or damaging the tooling. Adjust the location of your deep features to allow for greater clearance when needed.
7. Small Radii in Deep Pockets
When designing deep pockets with small corner radii, consider the length-to-diameter ratio of the cutting tool. A general rule is to avoid situations where the cut depth exceeds eight times the tool diameter. Deeper cuts with small tools increase the risk of tool breakage and poor surface finish. By increasing corner radii in deep pockets, your part becomes more easily manufactured and more cost-effective.
8. Radiused Areas That Require Blending
When designing parts with intersecting radiused surfaces, particularly around pocket walls or exterior features, these surfaces will require some form of blending during the machining process. The final appearance may differ slightly from the design due to the limitations of the machining process—if this will be a problem, it’s best to discuss solutions with us upfront.
Communicate With Us Early to Ensure Your Success
While many challenging features can technically be machined, they may significantly increase cost and lead time. By communicating with your machine shop and remaining open to design modifications, you can have more efficient and cost-effective production without any compromise to functionality.
Request a quote from Approved Machining today to start collaborating on your next project!
