# Tool nose radius compensation for CNC lathes.

In a machine shop, knowledge is often shared sparingly. As the key to success, knowledge is a precious commodity, and those who have it don't often want to give it away. Take the example of tool nose radius compensation. Sure, it's a fairly complex topic. Many companies have CAM systems that calculate tool nose radius compensation automatically. How can you be sure it is right? This first article, in a series of two, takes you through the steps of how to determine the compensation value needed in programming. Next month we discuss how this value is used in programming.

When calculating the compensation use the following

Z axis compensation = nose radius - [nose radius x tan (angle [divided by] 2)]

X axis compensation = 2 [nose radius - (nose radius x tan (45- (angle [divided by] 2))]

two formulas. This example is based on a part angle measured from the horizontal axis.

To find the compensation value, follow these three steps:

#1 Determine the angle of the chamfer.

#2 Determine the size of the nose radius.

#3 Use the values from steps 1 and 2 in the above formulas to determine the compensation values in Z and X.

In this example, the chamfer angle is 37 and the nose radius is 1/32 (0.031). Use the compensation formulas to determine the correct values.

Z axis compensation value = [nose radius - [nose radius x tan (angle [divided by] 2)]

Z comp value = 0.031-[0.031 x tan (37 [divided by] 2)]

Z comp value = 0.0206

Z program value = -0.5846

Use this value in the program

X axis compensation value =

X comp value = 2[0.031-(0.031 x tan(45- (37 + 2))]

X comp value = 0.0311

X value = 0.7189

Use this value in the program
``` The complete program could look like this.
G00 X0.700 Z0.100 (rapid into position)
G01 Z0.000 F0.01 (blend front face)
G01 X0.7189 (X starting diameter)
G01 X1.6000 Z-0.5846 (X & Z angle move)
G01 Z-2. (turn 1.6 diameter)
```

When there are a number of different angles to program, this process can be quite complex. Trying to change the insert mid program is not only time consuming, it increases the chances of making a mistake. The compensation value for each angle must be recalculated to the new nose radius, and the program changed based on the new compensation values,

So how can you use this knowledge? Simple. Use a chart. This solution saves you time and errors, not to mention that it makes you look like an expert. Download a tool nose radius chart from the RTSI website at http://www.cnc-training.com This chart covers the most often-used insert nose radii and angles and is a valuable tool when working with tool nose radius compensation.

Next month we will look at the intricacies of programming with tool nose radius compensation. Using these steps, improves your troubleshooting, programming and overall knowledge. Download the chart and join us next month to discuss programming with tool nose radius compensation.

Steve Rose is a manufacturing consultant and president of Rose Training Systems, Solon, OH, which also offers Internet web site development.