Design Tips for Custom CNC Machining Parts

After years of discussion and in-depth conmunication with designers, from the perspective of cost reduction, we sorted out some matters that may be involved in the process of parts processing. We reviewed tens of thousands of CAD files for CNC machined parts each year. Any designer or product development manager who has worked with us for years knows that Modo Rapid not only provide customized CNC machining services, but most importantly, we can provide suggestions and design improvements, which is our added value to customers.

We have the responsibility to communicate those issues to the customer when our expert team see things problematic.
Some parts need to go through both processes, milling and turning to complete, so we sort the order of the processes based on your CAD file what you want and how to machine it.

The corner of CNC machined parts

Rounded corners are better for machining

As we know, very cylindrical parts are suitable for CNC turning process, and very square/orthogonal parts are suitable for milling. As a designer, you have the knowledge of adding fillets to round out your corners. Because when two walls meed, if you visualize it you can see how a round endmill can never create a 100% 90-degree angle.

Can we get a sharp 90-degree angle of a CNC milling part?

Yes, we can get that by square endmill, which are similar with other endmill, however it has a flat, rather than a pointy, lower cutting surface.

If we want to mill out material to create a flat surface, then more machining time must be spent contouring the fillet. Therefore it will make machining times much longer, and more costly, than necessary.

It may be a small design detail, but it has a big impact on your cost of CNC machined part. We will definitely confirm with you again after receiving your drawings.

LxD ratio(depth-to-width ratios)

When we discuss some details about designing for manufacturing, it’s really important to notice the LxD ratio. Each features aspect ratio is critical, as those parts with different ratio will work for you for a long time. Generally speaking, deep holes and pockets should fit for large diameter, and longer standing posts or ribs should be thicker. Therefore, smaller the LxD ratio, the better. However, if there are specific design reasons, LxD ratio is 8:1, we will also help to find a solution.

Complex CNC machined parts

How to make complex parts easy to process and reduce your cost?

Breaking up and then join them together, by bolts, welds, or other methods. It’s practical to simplify a part by breaking it up into two or more components. We would be delighted if you pay attention to tradeoffs between minimizing the number of components and the need to use assembly. Reduce CNC machined part complexity by breaking more complex parts down into several sub-components. So, why not have a try? We, as a professional CNC prototype manufacturer will fully cooperate with you to provide you with a solution.

Wall thickness

As a rule, minimum thickness for walls is 0.794 mm for metals and 1.5 mm for plastics. Some designers need thin walls when they design drone parts or whistles. However, wall thickness is proportional to the stiffness of the material, achievable accuracy will be reduced as inevitable vibrations during machining.

Tolerances of custom part

We need to note that excessive tolerance would increase CNC machining time and cost. If you didn’t mention a specific tolerance, the CNC machine would use its standard tolerance for such dimensions. CNC machines have different tolerance. Only when necessary the tight tolerance should be specified, if you want to save money and time. Maintain homogeneous tolerancing can also reduce the cost and time of CNC machined parts.

Limit thread length

As we know, strong thread connections take place in the first few threads. You can just design sufficiently long thread lengths if you want to improve your design. A thread longer than 3 times the hole diameter is time-consuming.

Hole size

It is common engineering knowledge that standard sized holes are milled using standard drill bit sizes. If you need non-standard holes, the rule of thumb for depth of cavity must be applied, which is the depth must be four times the diameter of the cavity.

Unnecessary text and lettering

Adding text and lettering just for aesthetic features will increase machine time and cost. But if you indeed to do that, we always suggest to do laser carving, and size 20 is recommended. Because size smaller than this are considered small feature which are more difficult and costly to machine.

Adding a radius internal edges

We know that most cutting tools are cylindrical and cannot machine sharp internal edges, so add radii to internal edges in your design is necessary. The best solution is to add a radius of 130% of the milling tool radius. This additional radius will greatly educe stress on the tool and increase cutting speed. And also reduce the cost of your custom CNC machining parts.

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