New app puts several machining calculations in the palm of your hand.

With applications such as the “Machinist Buddy” (now available for Android devices), machinists no longer need to take copies of tables to their machines or scrawl calculations on a notepad.

The free version of the app has a number of useful tools for anyone working in a machining environment and is designed with seven main areas—milling, turning, threading, business, geometry, utilities and reference. Your current area will be underlined with a thick blue line, as shown in Figure 1.

Keep in mind that unlike the “Machining Mate” (see review), this app will not perform metric calculations. And like many apps, the free version will display advertising—unless you purchase the app for $2.19.

### Milling Calculators

Figure 2. Machinist Buddy milling menu.

The milling functions include the following calculators: revolutions per minute (RPM), surface feet per minute, feed per tooth, metal removal rate, RPM with carbide tooling, RPM with high-speed steel (HSS) and inches per minute feedrate, as shown in Figure 2.

To return from a calculator to the home screen, select the Machinist Buddy icon found in the upper left-hand corner of the screen. To return to the previous screen, select the home button . Unfortunately, its position is not in the same location within each calculator. All of the calculators—although useful—are only available in imperial units and not in metric. In addition, when working with a tablet, not all calculator screens will rotate their orientation, thereby forcing users to reorient the screen themselves.

The RPM, surface feet per minute, feed per tooth and inches per minute milling feedrate calculators are all accurate and equivalent to their Machinist Mate counterparts.

Figure 3. Metal removal rate calculator.

The metal removal rate calculator (see Figure 3)—although potentially a useful feature—attempts to adjust the calculated value based on the temperature in the shop but does not allow you to select different materials. This would be a great feature if it just assumed room temperature and ignored thermal expansion.

The RPM calculators for carbide and HSS tools—although accurate—are limited in that they only work for six materials: aluminum, brass/bronze soft, bronze high tensile strength, copper/copper alloys, free-machining stainless steel and titanium alloys. In addition, they may not use your desired cutting speed. These two calculators are also somewhat redundant because the RPM (general) calculator will already calculate all of the required speeds.

### Turning Calculators

The turning functions include calculators for RPM, feed per revolution, inches per minute feedrate, metal removal rate, advance per revolution, RPM with carbide tooling and RPM with HSS tools.

Figure 4. Turning RPM calculator.

A few of these, including the metal removal rate, RPM with carbide tooling and RPM with HSS tool calculators, have the same drawbacks as the milling versions.

In addition, the revolutions per minute calculator (see Figure 4)—although accurate—should be reworded for two reasons: On a lathe, the diameter of the workpiece is used to calculate the RPM, and the tool diameter is only used when making a hole on the center of the part’s end face.

### Tapping Calculators

Figure 5. Tap drill size calculator.

There are three threading-related calculators: mill tapping rate, tap drill size and percent of full thread. All of these function properly and provide accurate results; however, the tap drill size calculator is poorly named, as it does not calculate a tap drill size. Instead, it calculates the correct feed per revolution for threading on a lathe. For example, if you need to thread a part with 20 threads per inch, the calculator will return a feed rate of 0.05 inches per revolution (see Figure 5).

### Geometry Calculators

The nine geometry calculators include radius of arc length, area of parallelogram, volume of cube, volume of cylinder, area of trapezoid, area of triangle, surface area of ball, volume of a ball and volume of a cone. All of these accurately calculate the desired feature.

### Utilities Calculators/Tables/Reminders

Figure 6. The X/Y coordinates of seven holes on a 3.5-inch bolt hole circle centered at X2.0 Y1.0 with an angle to the first hole of 15 degrees.

This section includes many useful and time-saving calculators, including sine bar stack, oblique triangles, G/M codes, conversions, Cartesian bolt hole and the machinist notepad (a simple note storage).

The Cartesian bolt hole calculator (see Figure 6) will quickly generate the X/Y hole center coordinates. For example, if coordinates were required for seven holes on a 3.5-inch bolt hole circle with; 1) the bolt hole circle centered at X2.0 Y1.0 and 2) the first hole located 15 degrees above the horizontal axis. Enter the values as shown in Figure 6, press the Calculate button and the locations will be displayed.

Figure 6. The X/Y coordinates of seven holes on a 3.5-inch bolt hole circle centered at X2.0 Y1.0 with an angle to the first hole of 15 degrees.

**Reference Tables/Charts**

Lastly, this application contains 10 handy reference tables, charts and diagrams, including an end mill diagram, manual mill diagram, manual lathe diagram, drill point diagram, thread spec diagram, tap drill chart and HSS drill speeds chart, as well as insert grade comparison charts and Morse and Jacob’s taper charts. The insert grade comparison will allow you to determine what grade of carbide from one manufacturer is equivalent to another.

Overall, as a free calculator, there are many helpful items, provided you are aware of its limitations.

For more information, check out the Machinist Buddy app on Google Play.