7 DFM Tips for Your Next Precision Machining Project

In the precision machining world, there’s a notable gap between what’s designable and what’s manufacturable. 

Engineers may design a part that looks great in 3D model or print form but introduces significant challenges when it hits the shop floor. As a result, they'll face high costs and long lead times—or, in the worst-case scenario, a no-quote. 

At All Metals Fabricating, we're CNC machining experts with a department dedicated to design and engineering. We review all prints through the lens of Design for Manufacturing (DFM) before beginning a project to help our customers save time and money. 

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7 DFM Tips for CNC Precision Machining

DFM is the practice of optimizing part designs for easier manufacturing. The easier a part is to manufacture, the more likely it is that machinists can run it efficiently and without issues. Consider these tips when designing your next CNC machined part: 

1. Provide as much information as possible

When submitting an RFQ for precision machining, more information is always better. We encourage customers to include: 

• 3D model in STEP format. For the fastest quoting, upload a 3D model in addition to drawings. A 3D model reduces programming time, as we can immediately determine whether we’ll need to recreate a new design file before manufacturing. 

• Mating information. If the part is going to mate with another part, that’s helpful for your manufacturer to know. We can take certain precautions during machining to ensure you get the right fit for mating parts.

• Critical call-outs. Be sure to indicate which specifications or features are absolutely critical to the part’s functionality.

• Test fixtures. If the part has a test fixture it needs to fit into, give us that information up front. We can make a test fixture in our shop or use one that you provide. 

• End use. Knowing how the part will be used helps inform finishing methods and material selection. It also tell us which quality inspection processes to use to meet your requirements. 

2. Pay attention to depth

A good rule of thumb when designing a hole in a part is to ensure the depth doesn't exceed 6x the diameter. This best practice ensures tooling can reach the hole at standard speeds. 

The deeper the hole, the slower machining equipment needs to run to avoid tool breakage. Slowing down the machining process can significantly affect both cost and lead times.

Here are similar considerations to keep in mind when designing cavities and pockets: 

• Cavities. Cavities deeper than 3” are manufacturable but will add cost to the project due to custom tooling requirements. 

• Pockets. The deeper the pocket, the bigger the corner radius should be. Pockets should not exceed standard end mill lengths unless necessary. (Contact us to find out what our standard end mill lengths are.)

3. Avoid square corners

Square corners on interior pockets are difficult to machine due to tooling constraints. We encourage customers to avoid designing square corners on pockets and on the shoulders of turned parts.

Instead, add a radius. But remember: the smaller the radius, the smaller the tooling required to machine it. It’s best to design radii to accommodate the standard tooling sizes of 0.10”, 0.015”, and 0.03” to avoid the risk of tool breakage and optimize machining time.

4. Design thick-walled parts

Thinner parts take longer to set up and run, so we advise customers to design walls no thinner than necessary. 

When we run thin-walled parts, we have to slow down the RPMs on the equipment and feed the material slowly; otherwise, there’s a risk of shattering the material. Again, this slowing down can drive up cost and lead time.

5. Loosen non-critical tolerances 

 If a specific feature has a tolerance requirement tighter than the standard +/- 0.005”, be sure to call it out. Keep in mind, however, that tight tolerances aren’t always required—and the looser the tolerance, the faster the part will run. 

Recently, a customer sent us a prototype design with tight tolerances throughout. We collaborated with them and identified opportunities to loosen some tolerances for non-critical features, saving them time and money on their prototype. 

6. Select materials strategically 

Choosing the most readily available material ensures a faster turnaround. But even for common materials like stainless steel, certain grades are more manufacturable than others.  

For example, many customers assume 303 stainless steel and 304 stainless can be used interchangeably. However, 303 stainless is much easier to machine, so if that’s an option, we recommend it for precision machining projects. 

If you’re unsure which type of material would be best for your project from a manufacturability standpoint, ask our team, and we’ll happily work with you on material selection. 

7. Say “yes” to simple parts 

The risk of variability from one part to the next increases with the number of setups a part requires because each setup introduces the possibility of human error. 

To mitigate that risk, we encourage our customers to design the simplest parts possible to meet their needs. Simple parts require fewer setups, resulting in better costs, shorter lead times, and more consistent results. 

A quality precision machine shop makes CNC machining seem easy, no matter how complex the process is behind the scenes. At All Metals Fabricating, we’re glad to help you design and manufacture the parts you need. Our team of engineers and machinists can collaborate with you from vision through production, ensuring your design is manufacturable from the start. 

We’d love the opportunity to serve you and become your trusted manufacturing partner. Request a quote to start working with us today.