Best Design Tips for CNC Machining Sharp Inside Corners
Apart from material selection, design is one of the most vital factors for determining a parts’ quality and functionality. Product teams must adhere to the principles of design for manufacturability regardless of the production method. This especially applies during the prototyping and design phase of any project. It may, however, be challenging when coming up with parts for CNC machining. CNC machining is often an awesome choice for creating parts with tight tolerances. It is, however, costly to attain sharp internal corners especially the ones at right angles. CNC drilling bits are usually round so trying to machine a 90-degree angle is a bit tricky. Here is an extensive insight into how we machine sharp inside corners.
We refer to the inaccessible corner geometry as a corner radius. The inside corner radii directly affect a part’s machinability. They influence the overall cost and production timelines. Luckily, the product team and designers at Creatingway are adept at navigating this problem. There are a few proper design workarounds for avoiding sharp internal features. If it is an absolute necessity, there are a few manufacturing solutions that we can use.
Below Is What We Use For Your CNC Machining Sharp Inside Corner
How to Avoid Sharp Inside Corners
One of the safest bets in CNC machining of sharp internal corners is to avoid them entirely. Instead, we prefer including radii on all internal edges. We can achieve this by using an end mill with a radius that is slightly smaller than the radius we add to the edge. For instance, in the case of a part with a radius of 0.25” than a 6 mm end mill is the ideal option. This helps the machine run at a proper speed without inducing stress on the tool. Another option is to use a non-standard corner radius. By adding at least 0.02” to 0.05” to an internal corner radius, we give the endmill enough space to turn slightly at the corner. This is especially without adding extra stress to the tool.
An alternate method is to soften the inside corner radii by creating a rounded toolpath using a larger tool. The larger tooling helps create a wider inside corner radii and lowers tool engagement. This helps lower the machining time, cut costs, and produces a smoother surface finish. Ideally, 200% is the perfect tool radius but 150% is adequate enough.
Machining Workarounds for Sharp Corners
If the design must include a sharp inside corner, then there are a few solutions still available. We can opt to leave the inner corner radii intact or reduce their size by using a smaller drill bit. This is a quick cost-effective method that does not complicate the design and makes it tasking to the machine. Notably, this is not a suitable approach for thicker CNC materials.
The most preferred way when keeping sharp corners is to use a bone or dog bone fillet. These fillets are a form of undercuts that extend the corner’s shape beyond the cut area. The drill bit can then make a full rotation and leave the center. It can also back up slightly to create a sharp corner when following the toolpath. T bone fillets are T-shaped with round edges while dog bone fillets closely resemble chew toys.
However, designers must remember to create an entry point for the dog-bot fillet that is 15% to 20% larger than the router bit diameter. If the entry point cannot host a dog-bone fillet, then we can simply include sharp inside corners. This entails manually squaring them off using a chisel, pull saw, and chisel. Shapers, broachers, and EDM machining tools can also help us create sharp corners. However, they tend to be less cost-effective options.
In addition, we can use wire EDM in achieving right angles. However, it will not be a true square corner. The wire only leaves being a tiny radius of 0.005” to 0.006”. This small radius is acceptable. Wire EDM helps in machining sharp corners accurately. It also offers an excellent surface finish. Unfortunately, it is slower compared to CNC cutting tools.
Design for Machinability with Creatingway
For a lot of product teams, coming up with a clean and working part is easy. The more challenging part arises when modifying the design for manufacturability and machinability. It takes plenty of practice to optimize a design for manufacturability. There is also a need for a lot of practice, experience, and technical expertise. This gives rise to query on how we come with a design that gives rise to a functional and beautiful part without raising the CNC machining costs. Designing for machinability gets easier by working with an experienced rapid tooling partner like Creatingway. We have the modern and latest digital design tech at our disposal. Our team of experts and designers is also at hand to aid other product teams with their designs. This is regardless of the shape or the size of the part they wish to machine. We value our esteemed clients and are looking to expand our reach. Contact us now with your inquiry or quote and let’s make new things possible.
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