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CNC Machining Cycle Time Calculation

CNC Machining Cycle Time Calculation

CNC Machining Cycle Time Calculation

When you require unique parts you can’t find elsewhere, CNC machining is a process that can craft precise components for any industry. With our complete manufacturing facility, high-quality materials and customization abilities, American Micro Industries can manufacture parts to match your drawing specifications.

But if you’re working on a machining project on your own, it’s important to know CNC machining cycle time and how to calculate it. Continue reading better understand the necessary calculations and when to use them.

What Is CNC Machining?

CNC machining, or computerized numerical control, is a process where programmed computer software controls the movements of your production equipment. The technology takes a virtual design, often from a CAD program, and transforms it into a physical part made of the specific material you need, such as:

CNC machining replaces manual labor to create precise and unique parts, no matter your industry. Whether you’re in the automotive, aerospace, electronics, military, medical or security sector, CNC machining will likely benefit you. When you demand mass-produced pieces that meet specific requirements, CNC machining can develop and deliver accurate and precise solutions.

What Is CNC Machining Cycle Time?

Understanding CNC machine cycle time will help you estimate machining costs and lower product lead times. How long will the operation take to complete? Does your budget align with the project? Will it be done in time for you or your customer? Knowing machining cycle times can also help you compare two or more different processes that will work best for a project.

The formulas used for calculating machining time are simple to incorporate into your daily operations, and many professionals program their calculators to have the appropriate CNC machining cycle time formula. However, depending on the type of CNC machining, like turning, milling or screw machining, cycle time calculation will differ, making the process a bit challenging. Fortunately, with a simple formula, you can make CNC machining simple.

How to Calculate CNC Machining Time

Similar to calculating other times, the general formula for CNC machining is distance or length divided by rate or speed. When it comes to machining time calculation, the formula is as follows:

  • Machining Time = Length of Cut (mm) / Feed (mm per revolution) x Revolutions Per Minute
  • Revolutions Per Minute = 1,000 x Cutting Speed (mm per minute) / π x Diameter of Rod (mm)

Depending on the project, you may need to replace millimeters with inches.

CNC Machining Time Example

Let’s start with an example in inches with an expected goal of the following:

  • Hole diameter = 1 inch
  • Hole depth = 0.75 inches
  • Approach distance = 0.1 inch
  • Feed = 7 inches / minute

The time needed to drill the hole will result in decimal minutes you need to convert to seconds:

  • Time to Drill Hole = Motion Distance (0.85) / Feed Rate (7) = 0.12143 minutes
  • Seconds = 0.12143 minutes / 0.0166 = 7.2887 seconds

Once you know how long it will take to drill the hole, you will want to determine the feed rate in inches per minute (IPM), which means you have to calculate the spindle RMP and calculate the feed rate in inches per minute, as most handbooks have feed in inches per revolution (IPR). Then, because speed recommendations are often provided in surface per minute (SFM) calculations, you will need the following two formulas to help you finish the calculations:

  • Revolutions Per Minute = 3.82 x SFM / Total Diameter
  • IPM = Revolutions Per Minute x Inches Per Revolution

Depending on the tool, the feed rate may be in “per tooth,” which we will dive into when talking about CNC milling machining time calculation. In that case, the formula would be the following:

  • Inches Per Revolution = IPT x Number of Cutting Edges

It’s simple to apply these formulas to many operations — unless the diameter changes during the machining process. For example, if you’re working on a project that requires multiple passes, the constant surface speed will cause the spindle speed in revolutions per minute to change in relation to the diameter. Therefore, you will need to calculate a new RPM and IPM feed rate for every turning pass.

While that is the general formula, there are differences between milling and turning machine calculations.

CNC Milling Machining Time Calculation

A CNC process called milling creates slots, helical grooves or flat surfaces on vertical, inclined or horizontal planes. In this case, the CNC machining time estimation may use a feed rate that’s per tooth, meaning you need to know the number of flutes, teeth or cutting edges on the specific tool you have.

CNC Milling Machining Time Calculation

When using the original formula for assistance — Machining Time = Length of Cut (mm) / Feed (mm per revolution) x Revolutions Per Minute — the calculation for CNC milling machining time equals Machining Time = Length of Cut (mm) x Number of Passes / Feed (mm per revolution) x Revolutions Per Minute, with the specifications being:

  • Length of Cut (mm) = Tool Approach + Job Length + Tool Over Travel + Compulsory Distance
  • Feed (mm per revolution) = Feed Per Tooth x Number of Teeth
  • Revolutions Per Minute = 1,000 x Cutting Speed / π x Diameter of Rod (mm)

Here, accuracy is key to obtain the best machining time estimate.

CNC Turning Machining Time Calculation

To calculate cycle time for turning, the formula is also based on the original. For example, Machining Time = Length of Cut (mm) / Feed (mm per revolution) x Revolutions Per Minute, with the specifications being:

  • Length = Tool Approach + Job Length + Tool Over Travels x Number of Passes
  • Average Revolutions Per Minute = 1,000 x Cutting Speed / π x Average Diameter of Rod (mm)

The process of turning machining is when a single point tool on a lathe machine creates turned parts. To manufacture rotational — and often complex — shapes, the tool is fed linearly or perpendicular to the rotation axis of the piece, or the tool is on a specified path to create a rotational shape. There are two motions of cutting in the turning process — the primary is the rotation of the workpiece and the secondary is the feed.

Learn More About Our CNC Machining Services

Learn More About Our CNC Machining Services

Driven by quality with a focus on individual pieces made to your specifications, American Micro Industries strives to exceed your expectations. The experts at AMI specialize in manufacturing hard-to-find parts by taking your ideas, drawings and CAD designs into account and helping you identify the appropriate materials to produce and ship products from one location. Here, our professional teams have endless capabilities to help support your growing business.

For more information, request a free quote online or call an American Micro Industries representative at 866-774-9353.