Stecker Machine Blog

How to Choose the Right CNC Machine Tools for Complex Parts

07/02/2019 | Tom Sprang


Today’s world demands the accuracy of CNC machine tools and experienced operators. Of course, machine shops vary in their skill levels and abilities to take on complex parts. So, here are 3 quick signs that a shop lives and breathes complex parts:

  1. Investment in CNC machine tools — Some complex parts’ extremely tight tolerances may require putting money into new CNC machinery. High-end machine shops equip themselves to take on nearly any tolerance level a complex part may require.
  1. Experienced staff — Developing the right process and tool starts upfront with the sales, engineering, quality, and production teams. Look for a shop that’s able to handle complex parts from start to finish (design to assembly) all in-house.
  1. Close relationships with foundries — Work with pros that know castings and have design/build experience. Shops can control quality, reduce timelines, and make changes smoothly, especially prior to production when changes aren’t cost-prohibitive.  

Key Critical Characteristics (KCC) Nail Quality Expectations

The best machine shops can review a print and instantly point out a handful of features that will make or break a part as far as cost-efficiency goes. For these key critical characteristics (KCC), the pressure is on to produce the highest quality work possible … repeatedly, reliably, and robustly for a healthy bottom line. From a $2 part to one that exceeds five figures, proper machining that nails KCCs can eliminate customer complaints, warranty claims, and other points of dissatisfaction.

The Factors That Affect Machine Shop Tool Selection 

PART SIZE — Weight doesn’t determine what CNC machining tool technology is needed; it’s the part’s dimensions. An engine block, a part with high tolerance levels that relies heavily on proper machinability, is large enough to demand specific equipment for machining. On a related note, size alone doesn’t determine a part’s complexity; some smaller parts are extremely challenging, and some large parts are simple.

PART PROCESSING — Consider the number of operations (and order) needed to machine a part: a lathe for turning; a mill for cutting a surface; or even how the part needs to be held to machine certain angles. To increase efficiency, a multitasking machine may be used if it’s cost-effective for the shop to purchase (see “Required Tools” below).

PART TOLERANCE — A shiny, new (and expensive) machine can be purchased to handle nearly any tolerance needed. Yet, the processing of the part (when to perform which features, how to hold the part, which cut to make first) is key to achieving the accuracy that’s demanded with many complex parts. 

MATERIAL — A material’s rigidity determines the spindle speed of the tool and the machine’s needed horsepower. Aluminum can be run faster than iron, for instance.

REQUIRED TOOLS — A complex part may require 100 cutting tools or more in order to process it properly. If that CNC machine center can’t handle the tools needed, that part will be moved to a more capable machine center. The cost of a high-priced, multitask tool is justified by a high quantity of parts that will eventually be made by that tool.

TOOLING UP — Getting a CNC machine prepared for processing a part is critical for a machine shop to be competitive. Performing multiple functions with a single combo tool increases quality and accuracy upon repeat uses. And, only having to use one machine for various functions reduces risks and the possibility of a bur or misalignment. 

CYCLE TIME — An accurate anticipated quoted cycle time generates pinpoint rates that are vital for a machine shop to stay competitive. An experienced design team that knows the capabilities of a machine helps ensure the project is priced correctly. There’s always a goal to reduce cycle times so work can be put into the machine to increase robustness, repeatability, and offload operator processing.

QUANTITY — Depending on the overall lifetime of the project, which could be years, the quantity (perhaps thousands) may justify purchasing a piece of equipment specific to that part. The contract may extend for years with an annual usage, which could make it optimal for robotics instead of heavy labor requirements.

LABOR NEEDS — Quality. Efficiency. Other than safety, those are the most important factors in getting a project through a machine shop. One technician working at one machine is drastically different than moving that part through five different stations and multiple people. And, as difficult as it may be, striving to achieve lean practices is always a goal.

Although “complex” is tricky to define in the machine shop world, it’s easy to see the value of using quality machine tools operated by the right CNC technicians. The tasks many machine shops shy away from are welcomed by some machine shops that simply love the tough stuff, and they prepare themselves for those complex challenges. 

Discover for yourself what makes Stecker tick, and how we embrace the complex part challenges that other shops avoid.


Tom Sprang

About the Author

Tom staffs and develops Stecker Machine's Production team (the shop's largest with over 150 people), including three shifts and two plants. He also leads the tool crib and scheduling as well as transitions new jobs to production by mapping work and identifying/mitigating risks. Tom became familiar with CNC machining at an apprenticeship and ended up working at a SMC competitor for 24 years. He's seen the shop floor, worked as a shift Supervisor, moved to Continuous Improvement, and became Production Manager. Today, Tom is also instrumental in bringing new work into the shop.

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