If you are running at 18000 RPM using a 25mm cutter with two flutes, and a recommended chip load of 0.1 mm/tooth:Feed = 2 x 0.1 x 18000 = 3600 mm per minIf the RPM were increased to 24000 RPM the new feed rate would work out to be:Feed = 2 x 0.1 x 24000 = 4800 mm per min

Slabmilling diagram

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Wu, Mingzhou, Guangpeng Zhang, Tianle Wang, and Rui Wang. 2023. "Milling Force Modeling Methods for Slot Milling Cutters" Machines 11, no. 10: 922. https://doi.org/10.3390/machines11100922

Facemilling diagram

Wu, Mingzhou, Guangpeng Zhang, Tianle Wang, and Rui Wang. 2023. "Milling Force Modeling Methods for Slot Milling Cutters" Machines 11, no. 10: 922. https://doi.org/10.3390/machines11100922

Once you have determined what feed and speed to start with, there are other factors to be taken into consideration. The next thing to be considered is the direction of the cut, which is the direction the cutter is fed into the material. Conventional milling or cutting forward is the most commonly used method.  With this method, the work is fed against the rotation direction of the cutter. The other method is climb milling or cutting reverse. For this machining method, the workpiece and the machine must be rigid. When machining non-ferrous materials, climb milling should be used to achieve a good finish.

Wu M, Zhang G, Wang T, Wang R. Milling Force Modeling Methods for Slot Milling Cutters. Machines. 2023; 11(10):922. https://doi.org/10.3390/machines11100922

Endmilling diagram

For most material that you will be cutting on a CNC router you will typically set the RPM between 12000 and 24000, and adjust your feed rate to obtain the required results. The speeds and feeds chosen can be affected by the power of the spindle being used. Higher power spindles will produce more torque thus allowing the machine to run at a variety of RPM’s (torque drops off as the RPM is reduced).

Abstract: The slot milling cutter is primarily used for machining the tongue and groove of the steam turbine rotor, which is a critical operation in the manufacturing process of the steam turbine rotor. It is challenging to predict the milling force of a groove milling cutter due to variations in rake, rake angles and cutting speeds of the main cutting edge. Firstly, based on a limited amount of experimental data on turning, we have developed an equivalent turning force model that takes into account the impact of the rounded cutting edge radius, the tool’s tip radius and the feed rate on tool’s geometric angle. It provides a more accurate frontal angle for the identification method of the Johnson–Cook material constitutive equation. Secondly, the physical parameters, such as shear stress, shear strain and strain rate on the main shear plane, are calculated through the analysis of experimental data and application of the orthogonal cutting theory. Thirdly, the range of initial constitutive parameters of the material was determined through the split Hopkinson pressure bar (SHPB) test. The objective function was defined as the minimum error between the theoretical and experimental values. The optimal values of the Johnson–Cook constitutive equation parameters A, B, C, n and m are obtained through a global search using a genetic algorithm. Finally, the shear stress is determined by the governing equations of deformation, temperature and material. The axial force, torque and bending moment of each micro-segment are calculated and summed using the unit cutting force vector of each micro-segment. As a result, a milling force prediction model for slot milling cutters is established, and its validity is verified through experiments. Keywords: milling force model; orthogonal cutting force model; unit cutting force; groove milling cutter

These often provide a good starting point but can usually be further improved through a small amount of trial and error. Most machine controllers allow you to adjust the feed rate while a program is running and by listening to the sound the cutter makes this can be a good way of optimizing the parameters.Feed rate is calculated using the following equation:

Slot millingoperation

- Forget that doing some test cuts on a spare piece of material is a good way of checking settings before running your main program

Wu, M.; Zhang, G.; Wang, T.; Wang, R. Milling Force Modeling Methods for Slot Milling Cutters. Machines 2023, 11, 922. https://doi.org/10.3390/machines11100922

Another factor is depth of cut. Depth of cut will affect edge finish as well as tool life. You will have to adjust your depth to achieve the desired results depending on the type of material and size of the cutter. Usually, a depth of cut that equals the radius of the cutter is a good starting point when cutting non-ferrous metals.

One thing to remember is to make chips, not dust. Chips will help by removing the heat produced in the cutting process thus increasing tool life and improving edge quality. Feeds and speeds are usually all set in the programming software that is used to create the machine program. There are many resources available to help determine suitable settings for particular material/router bit combinations.

Slot millingtool

When calculating the feed rate for any material the chip load is therefore one of the most important factors to be taken into account because the chip load determines the amount of material that each tooth will remove, plus the load that each tooth will have to take. Another factor that affects chip load is the diameter of the cutter. A larger cutter will be able to handle a larger chip load.

When material is machined the cutter must revolve at a specific RPM and feed at a specific feed rate to achieve the proper Chip load. There are also several factors to be considered when choosing the proper RPM and feed rate.

Slot millingmachine

Even though there are formulas for calculating feed rates you will find that the optimum feed rate will be determined from experience. You will typically start off with the calculated feed rate. Under ideal conditions, it is usually suggested that the actual feed rate be set to approximately one-half the calculated amount and gradually increased to the capacity of the machine and the finish desired.

Wu M, Zhang G, Wang T, Wang R. Milling Force Modeling Methods for Slot Milling Cutters. Machines. 2023; 11(10):922. https://doi.org/10.3390/machines11100922

T-slotmillingoperation

Based on this equation, as RPM increases, the feed rate will also increase if all other settings remain the same. If the number of cutting edges changes, however, the feed rate will either increase or decrease depending on whether the number goes up or down. The same applies to chip load if the recommended chip load is 0.1 mm/tooth the RPM, feed or number of cutting edges may go up or down to maintain the required chip load. Therefore if the chip load remains the same, and the feed rate increases, either the RPM and or number of cutting edges must increase to maintain the recommended chip load.

N = number of cutting edges (flutes)T = chip load (chip per tooth) is the amount of material, which should be removed by each tooth of the cutter as it rotates and advances into the work (mm per tooth)Z = RPM, the speed at which the cutter revolves in the spindle (Revolutions per minute)We will now break down the relationship between the Feed rates, number of cutting edges, chip load and RPM. For most materials, there is a recommended chip load.

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Sidemilling diagram

The feed rate used depends upon a variety of factors, including power and rigidity of the machine, rigidity of part hold-down, spindle horsepower, depth and width of cut, sharpness of cutting tool, design and type of cutter, and the material being cut.

- Cut too deep in a single pass. Sometimes it can be more efficient to use a higher feed rate and two or more passes rather than a single cut at a low feed rate

To obtain the optimum Chip load, you must consider these variables, along with the machine and materials you intend to cut. This will help you find the best feed rate and RPM for any given tool and material.

Wu, M.; Zhang, G.; Wang, T.; Wang, R. Milling Force Modeling Methods for Slot Milling Cutters. Machines 2023, 11, 922. https://doi.org/10.3390/machines11100922

Therefore depending on the diameter of the tool, if the RPM and number of cutter edges stay the same chip load will increase with a larger diameter cutter, thus the feed rate will also increase. When machining softer materials or using a stubby router bit the chip load can be increased. If an extra long router bit is being used, the chip load should be decreased.

Feature papers are submitted upon individual invitation or recommendation by the scientific editors and must receive positive feedback from the reviewers.