CNC Offsets 210 Welcome to the Tooling University. This course is designed to be used in conjunction with the online version of this class. The online version can be found at http://www.toolingu.com. We offer high quality web -based e -learning that focuses on today's industrial manufacturing training needs. We deliver superior training content over the Internet using text, photos, video, audio, and illustrations. Our courses contain "roll -up -your -sleeves" content that offers real -world solutions on subjects such as Metal Cutting, Workholding, Materials, and CNC with much more to follow. Today's businesses face the challenge of maintaining a trained workforce. Companies must locate apprenticeship programs, cover travel and lodging expenses, and disrupt operations to cover training needs. Our web -based training offers low -cost, all -access courses and services to maximize your training initiatives. Class Outline
Class Outline Objectives The Purpose of Offsets Machine and Program Zero for Turning Offsets for the Turning Center Workshift Offsets Using a Reference Tool Geometry Offsets Wear Offsets Offset Features for Turning Machine and Program Zero for Milling Offsets for the Machining Center Workshift Offsets Tool Length Offsets Tool Length Offset Methods Cutter Radius Compensation Offset Features for Milling Recognizing Tool Wear Summary Lesson: 1/18 Objectives l Describe the role of offsets. l Distinguish between machine and program zero on the turning center. l Identify offsets for the turning center. l Define workshift offset for the turning center. l Describe the use of a reference tool. l Define geometry offset for the turning center. l Identify wear offsets for the turning center. l Describe the toolset probe. l Describe the use of tool nose radius compensation. l Distinguish between machine and program zero on the machining center. l Define offsets for the machining center. l Define workshift offset for the machining center. l Define tool length offset for the machining center. l Identify how to determine tool length offsets. l Define cutter radius compensation. l Describe wear offsets for the machining center. l Identify the importance of tool wear. Figure 1. CNC machines require offsets to accurately position cutting tools.
Lesson: 1/18 Objectives l Describe the role of offsets. l Distinguish between machine and program zero on the turning center. l Identify offsets for the turning center. l Define workshift offset for the turning center. l Describe the use of a reference tool. l Define geometry offset for the turning center. l Identify wear offsets for the turning center. l Describe the toolset probe. l Describe the use of tool nose radius compensation. l Distinguish between machine and program zero on the machining center. l Define offsets for the machining center. l Define workshift offset for the machining center. l Define tool length offset for the machining center. l Identify how to determine tool length offsets. l Define cutter radius compensation. l Describe wear offsets for the machining center. l Identify the importance of tool wear. Figure 1. CNC machines require offsets to accurately position cutting tools. Figure 2. Offsets compensate for various tool lengths and diameters. Figure 3. Turning centers may have a toolset probe for recording offsets.
Lesson: 2/18 The Purpose of Offsets Turning centers and machining centers can rapidly perform a series of metal cutting operations using multiple tools. Figures 1 and 2 illustrate tool positions on these productive machines. Manufacturers use these machines because their rigidity and numerically controlled tools create parts with excellent precision. However, the precision of a CNC machine depends upon the proper referencing of the cutting tool and the workpiece. A key responsibility of the operator is to make sure that every cutting tool is accurately positioned during machining. Operators store a series of offsets to accurately reference the cutting edge of each tool loaded in the machine. Figure 3 shows a series of offsets on the CRT. This class will teach you how offsets are used by first examining the turning center and then addressing offsets for the machining center. Figure 1. The turning center's turret positions the cutting tool, and the chuck holds the part. Figure 2. The machining center spindle positions the cutting tool above the worktable. Figure 3. A list of offsets on a turning center CRT.
Lesson: 3/18 Machine and Program Zero for Turning CNC offsets are essentially the stored numerical values that accurately shift each tool from machine zero to program zero. Every CNC turning center has a built-in machine zero, which acts as the origin for all machine coordinates. You may also see machine zero referred to as the home position. The manufacturer sets this position, and it cannot be changed by the operator or programmer. Machine zero is typically located at the farthest position from the spindle along the Xaxis and Z-axis. Figure 1 shows this position. Before the operator runs a program for the first time, he or she must set program zero. You may also see this position referred to as work zero or part zero. Program zero acts as the origin for tool positions contained in the part program. Each part program requires a zero position selected by the programmer. Most shops place program zero on the spindle centerline at the front of the part, as shown in Figure 2. Figure 1. Machine zero is farthest from the spindle along both axes. Figure 2. Program zero is typically located at the front of the part on the spindle centerline. Lesson: 4/18 Offsets for the Turning Center The two axes that require offsets are the Z-axis and X-axis. As you can see in Figure 1, the Zaxis runs through the centerline of the spindle. The X-axis is perpendicular to the Z-axis and defines tool distance from the centerline of the part. The following offsets are used to position tools from machine zero to program zero along both axes: l Workshift offsets adjust the entire turret along the Z-axis from home position. A workshift offset affects every tool in the turret. l Geometry offsets adjust cutting tools along both the X-axis and Z-axis. A geometry offset affects only one cutting tool.
Lesson: 3/18 Machine and Program Zero for Turning CNC offsets are essentially the stored numerical values that accurately shift each tool from machine zero to program zero. Every CNC turning center has a built-in machine zero, which acts as the origin for all machine coordinates. You may also see machine zero referred to as the home position. The manufacturer sets this position, and it cannot be changed by the operator or programmer. Machine zero is typically located at the farthest position from the spindle along the Xaxis and Z-axis. Figure 1 shows this position. Before the operator runs a program for the first time, he or she must set program zero. You may also see this position referred to as work zero or part zero. Program zero acts as the origin for tool positions contained in the part program. Each part program requires a zero position selected by the programmer. Most shops place program zero on the spindle centerline at the front of the part, as shown in Figure 2. Figure 1. Machine zero is farthest from the spindle along both axes. Figure 2. Program zero is typically located at the front of the part on the spindle centerline. Lesson: 4/18 Offsets for the Turning Center The two axes that require offsets are the Z-axis and X-axis. As you can see in Figure 1, the Zaxis runs through the centerline of the spindle. The X-axis is perpendicular to the Z-axis and defines tool distance from the centerline of the part. The following offsets are used to position tools from machine zero to program zero along both axes: l Workshift offsets adjust the entire turret along the Z-axis from home position. A workshift offset affects every tool in the turret. l Geometry offsets adjust cutting tools along both the X-axis and Z-axis. A geometry offset affects only one cutting tool.
Lesson: 4/18 Offsets for the Turning Center The two axes that require offsets are the Z-axis and X-axis. As you can see in Figure 1, the Zaxis runs through the centerline of the spindle. The X-axis is perpendicular to the Z-axis and defines tool distance from the centerline of the part. The following offsets are used to position tools from machine zero to program zero along both axes: l l l Workshift offsets adjust the entire turret along the Z-axis from home position. A workshift offset affects every tool in the turret. Geometry offsets adjust cutting tools along both the X-axis and Z-axis. A geometry offset affects only one cutting tool. Wear offsets adjust cutting tools by very small distances along both axes. They are used to correct variations in part size. Offsets move the machine components to program zero in increasingly smaller increments that build upon one another, as shown in Figure 2. They make sure each tool is positioned where it is supposed to be throughout the part program. Figure 1. Offsets reposition the turret along both X- and Z-axes. Figure 2. Each offset moves the turret in incrementally smaller distances. Lesson: 5/18 Workshift Offsets The first major offset on the turning center is the workshift offset. To cut a part held in the chuck, the operator must shift the reference point of the turret from the machine zero to program zero. The operator manually moves the turret and then records this position in the controls. Figure 1 illustrates this offset distance. A workshift offset is only necessary for distances along the Z-axis. For the turning center, there is Copyright 2015 Tooling U, X-axis LLC. Allbecause Rights Reserved. no workshift offset in the the X-axis position of program zero is typically located on the spindle centerline. The accuracy built into these machines ensures that the centerline of every part will be in the same position.
Lesson: 5/18 Workshift Offsets The first major offset on the turning center is the workshift offset. To cut a part held in the chuck, the operator must shift the reference point of the turret from the machine zero to program zero. The operator manually moves the turret and then records this position in the controls. Figure 1 illustrates this offset distance. A workshift offset is only necessary for distances along the Z-axis. For the turning center, there is no workshift offset in the X-axis because the X-axis position of program zero is typically located on the spindle centerline. The accuracy built into these machines ensures that the centerline of every part will be in the same position. Operators can store multiple workshift offsets by using G codes, which commonly include G54 through G59. If the operator changes jobs but keeps the same tooling in the turret, he or she will adjust only the workshift offset to reposition the turret in the Z-axis. Figure 1. The workshift offset shifts the turret from machine zero along the Z-axis. Lesson: 6/18 Using a Reference Tool A popular technique for using offsets with the turning center is to determine a reference tool. The reference tool sets the starting place for all the other geometry offsets of other tools. The most common reference tool is an 80 diamond insert because it is almost always on the turret for turning and facing operations. Figure 1 shows this insert in its holder. To use a reference tool, the operator will first take a facing cut on the part. This establishes the reference point of the tool at program zero in the Z-axis. This distance from machine zero to program zero along the Z-axis is stored as the workshift offset. The reference tool requires no further offsets in the Z-axis. This is important because the other tools in the turret will be shifted in the Z-axis based on their relationship to this reference tool point. As long as the tooling in the turret stays the same, the operator can merely change the workshift offset to accommodate the sizes of different parts. Figure 1. An 80 insert is frequently the reference tool.
Lesson: 6/18 Using a Reference Tool A popular technique for using offsets with the turning center is to determine a reference tool. The reference tool sets the starting place for all the other geometry offsets of other tools. The most common reference tool is an 80 diamond insert because it is almost always on the turret for turning and facing operations. Figure 1 shows this insert in its holder. To use a reference tool, the operator will first take a facing cut on the part. This establishes the reference point of the tool at program zero in the Z-axis. This distance from machine zero to program zero along the Z-axis is stored as the workshift offset. The reference tool requires no further offsets in the Z-axis. This is important because the other tools in the turret will be shifted in the Z-axis based on their relationship to this reference tool point. As long as the tooling in the turret stays the same, the operator can merely change the workshift offset to accommodate the sizes of different parts. Figure 1. An 80 insert is frequently the reference tool. Lesson: 7/18 Geometry Offsets The workshift offset shifts the entire turret, which affects every tool within it. However, turning inserts, boring bars, and drills all have their own distinct lengths and orientations. Geometry offsets shift the turret to account for each tool s unique dimensions. The geometry offset for each tool shifts the turret in both the X-axis and Z-axis, as shown in Figure 1. A Z-axis geometry offset adjusts the turret from the workshift offset location for each tool. The X-axis geometry offset adjusts the turret from the spindle centerline. The operator simply touches off every tool against finished part surfaces and stores the Z-axis and X-axis geometry offsets. Remember, the reference tool already has its Z-axis position stored as the workshift offset; however, it still requires an X-axis geometry offset. Consider the boring bar in Figure 2. Both the reference tool and boring bar share the same workshift offset. However, each cutting edge has a different orientation in the turret. Geometry offsets shift each tool to place the cutting edge in the same correct position. Figure 1. Each tool requires a geometry offset for both X- and Z-axes.
Lesson: 7/18 Geometry Offsets The workshift offset shifts the entire turret, which affects every tool within it. However, turning inserts, boring bars, and drills all have their own distinct lengths and orientations. Geometry offsets shift the turret to account for each tool s unique dimensions. The geometry offset for each tool shifts the turret in both the X-axis and Z-axis, as shown in Figure 1. A Z-axis geometry offset adjusts the turret from the workshift offset location for each tool. The X-axis geometry offset adjusts the turret from the spindle centerline. The operator simply touches off every tool against finished part surfaces and stores the Z-axis and X-axis geometry offsets. Remember, the reference tool already has its Z-axis position stored as the workshift offset; however, it still requires an X-axis geometry offset. Consider the boring bar in Figure 2. Both the reference tool and boring bar share the same workshift offset. However, each cutting edge has a different orientation in the turret. Geometry offsets shift each tool to place the cutting edge in the same correct position. Figure 1. Each tool requires a geometry offset for both X- and Z-axes. Figure 2. This boring bar is positioned perpendicular to the reference tool in the turret. Lesson: 8/18 Wear Offsets The operator must determine the workshift offset for a specific part and geometry offsets for each tool before the first run of the program. However, an operator may discover that the dimensions of the part are slightly undersized or inaccurate after machining. The operator can then use wear offsets to make slight adjustments and bring the part within the correct tolerance. Like geometry offsets, wear offsets shift the tool in both the X-axis and Z-axis, as shown in Figure 1. However, the distances stored as an offset may be only a few thousandths of an inch along each axis. Each cutting tool has its own wear offset. Cutting forces, part deflection, tool wear, etc. can potentially cause slight changes to tool location and variations in measurements. Wear offsets act as the minor adjustments that compensate for these variables.
Lesson: 8/18 Wear Offsets The operator must determine the workshift offset for a specific part and geometry offsets for each tool before the first run of the program. However, an operator may discover that the dimensions of the part are slightly undersized or inaccurate after machining. The operator can then use wear offsets to make slight adjustments and bring the part within the correct tolerance. Like geometry offsets, wear offsets shift the tool in both the X-axis and Z-axis, as shown in Figure 1. However, the distances stored as an offset may be only a few thousandths of an inch along each axis. Each cutting tool has its own wear offset. Cutting forces, part deflection, tool wear, etc. can potentially cause slight changes to tool location and variations in measurements. Wear offsets act as the minor adjustments that compensate for these variables. Figure 1. Wear offsets compensate for tool wear in both axes. Lesson: 9/18 Offset Features for Turning Depending on the machine, you may find turning centers with additional features that simplify the setting of offsets. For example, Figure 1 shows a machine equipped with a toolset probe. This probe is a device that swings into position in front of the spindle. The operator touches the tool tip on the probe and automatically records the tool position. This saves valuable time during tool setup. Another important feature is tool nose radius compensation. As you can see in Figure 2, most turning inserts have a slight radius at the tip. This nose radius helps to improve finish and reduce chatter. For linear turning and facing operations, the nose radius has no affect on part size. However, a nose radius will slightly affect part size during contouring and chamfering operations, as shown in Figure 3. Operators can enter the appropriate nose radius of the insert in the geometry offset table, and the CNC controls will automatically adjust tool position accordingly. Nose radius compensation is most important for finishing operations. Figure 1. The toolset probe records geometry offsets for both axes.
Lesson: 9/18 Offset Features for Turning Depending on the machine, you may find turning centers with additional features that simplify the setting of offsets. For example, Figure 1 shows a machine equipped with a toolset probe. This probe is a device that swings into position in front of the spindle. The operator touches the tool tip on the probe and automatically records the tool position. This saves valuable time during tool setup. Another important feature is tool nose radius compensation. As you can see in Figure 2, most turning inserts have a slight radius at the tip. This nose radius helps to improve finish and reduce chatter. For linear turning and facing operations, the nose radius has no affect on part size. However, a nose radius will slightly affect part size during contouring and chamfering operations, as shown in Figure 3. Operators can enter the appropriate nose radius of the insert in the geometry offset table, and the CNC controls will automatically adjust tool position accordingly. Nose radius compensation is most important for finishing operations. Figure 1. The toolset probe records geometry offsets for both axes. Figure 2. The nose radius alters the actual tip of the tool. Figure 3. Without nose radius compensation, chamfering leaves excess material.
Figure 3. Without nose radius compensation, chamfering leaves excess material. Lesson: 10/18 Machine and Program Zero for Milling Like the turning center, the machining center uses and stores various groups of offsets. Both machines require offsets to calculate tool position from machine zero to program zero. However, the types of offsets used are distinctly different due to the layout of each machine. As you can see in Figure 1, the machining center also has a machine zero position. This position is typically located at the farthest point of positive travel along all three axes. However, some manufacturers will locate machine zero at another corner of the worktable. Machine zero cannot be changed by the programmer. Every workpiece requires its own unique program zero. For most operations, program zero is located in a corner of the part, as shown in Figure 2. This helps the operator to locate the zero position once the part is loaded in the fixture. Figure 1. Machine zero is positioned away from the worktable. Figure 2. Program zero is typically located at a part corner. Lesson: 11/18 Offsets for the Machining Center Unlike the turning center, the vertical machining center has three axes of motion, as shown in Figure 1. The X-axis describes left and right motion of the tool. The Y-axis indicates motion toward and away from the operator. The Z-axis describes vertical motion parallel to the spindle. As you can see in Figure 2, machining centers require their own unique categories of offsets:
Lesson: 10/18 Machine and Program Zero for Milling Like the turning center, the machining center uses and stores various groups of offsets. Both machines require offsets to calculate tool position from machine zero to program zero. However, the types of offsets used are distinctly different due to the layout of each machine. As you can see in Figure 1, the machining center also has a machine zero position. This position is typically located at the farthest point of positive travel along all three axes. However, some manufacturers will locate machine zero at another corner of the worktable. Machine zero cannot be changed by the programmer. Every workpiece requires its own unique program zero. For most operations, program zero is located in a corner of the part, as shown in Figure 2. This helps the operator to locate the zero position once the part is loaded in the fixture. Figure 1. Machine zero is positioned away from the worktable. Figure 2. Program zero is typically located at a part corner. Lesson: 11/18 Offsets for the Machining Center Unlike the turning center, the vertical machining center has three axes of motion, as shown in Figure 1. The X-axis describes left and right motion of the tool. The Y-axis indicates motion toward and away from the operator. The Z-axis describes vertical motion parallel to the spindle. As you can see in Figure 2, machining centers require their own unique categories of offsets: l Workshift offsets reposition the spindle in all three axes. This offset affects the location of every tool loaded in the machine. l Tool length offsets compensate for varying tool lengths in the Z-axis. Each tool has its own
Lesson: 11/18 Offsets for the Machining Center Unlike the turning center, the vertical machining center has three axes of motion, as shown in Figure 1. The X-axis describes left and right motion of the tool. The Y-axis indicates motion toward and away from the operator. The Z-axis describes vertical motion parallel to the spindle. As you can see in Figure 2, machining centers require their own unique categories of offsets: l l l Workshift offsets reposition the spindle in all three axes. This offset affects the location of every tool loaded in the machine. Tool length offsets compensate for varying tool lengths in the Z-axis. Each tool has its own offset. Cutter radius compensation (CRC) adjusts for varying tool diameters. CRC is only necessary for tools that travel in the X- and Y-axes. Though these offset categories differ from the offsets used for turning, the main purpose is still to accurately shift the tool reference point from machine zero to program zero. Figure 1. Machining centers require tool motion along the X -, Y-, and Z-axes. Figure 2. Each offset repositions the tool in the spindle. Lesson: 12/18 Workshift Offsets Like the turning offsets, a workshift offset affects the position of every tool held in the machining center. For milling, you may also see this offset referred to as a fixture offset. The operator only needs to set workshift offsets in the X-axis and Y-axis once for a particular part, as shown in Figure 1. Because every tool shares the same spindle, the location of the tool center will always be the same in these horizontal axes. Consequently, the same workshift offset applies for every tool in the toolchanger. The operator uses an edge finder to determine the workshift offsets for a part. Figure 2 illustrates this device. The edge finder has an eccentric knob that pops out of position once it detects the
Lesson: 12/18 Workshift Offsets Like the turning offsets, a workshift offset affects the position of every tool held in the machining center. For milling, you may also see this offset referred to as a fixture offset. The operator only needs to set workshift offsets in the X-axis and Y-axis once for a particular part, as shown in Figure 1. Because every tool shares the same spindle, the location of the tool center will always be the same in these horizontal axes. Consequently, the same workshift offset applies for every tool in the toolchanger. The operator uses an edge finder to determine the workshift offsets for a part. Figure 2 illustrates this device. The edge finder has an eccentric knob that pops out of position once it detects the location of an edge. By touching off the edge finder on two sides, the operator can enter these values to shift the workshift offset to the corner of the part. Figure 1. Both the X-axis and Y-axis require a workshift offset. Figure 2. An edge finder loaded in the spindle. Lesson: 13/18 Tool Length Offsets Almost every part program records the path of a tool according to its centerline. Every cutting tool in the toolchanger shares the same spindle, and consequently the same centerline as well. However, cutting tools will inevitably vary in length, as shown in Figure 1. As you can see in Figure 2, this affects the position of the tool tip in the Z-axis. Operators use tool length offsets to compensate for varying tool lengths along the Z-axis. Figure 3 illustrates what would happen if you did not compensate for varying tool lengths. Like the geometry offsets for turning, each tool requires its own tool length offset. This type of offset typically shifts the tool tip from the position recorded in the workshift offset. However, tool length offsets can be calculated in a variety of ways. Various manufacturers may use different methods to
Lesson: 13/18 Tool Length Offsets Almost every part program records the path of a tool according to its centerline. Every cutting tool in the toolchanger shares the same spindle, and consequently the same centerline as well. However, cutting tools will inevitably vary in length, as shown in Figure 1. As you can see in Figure 2, this affects the position of the tool tip in the Z-axis. Operators use tool length offsets to compensate for varying tool lengths along the Z-axis. Figure 3 illustrates what would happen if you did not compensate for varying tool lengths. Like the geometry offsets for turning, each tool requires its own tool length offset. This type of offset typically shifts the tool tip from the position recorded in the workshift offset. However, tool length offsets can be calculated in a variety of ways. Various manufacturers may use different methods to compensate for tool length, depending on the convention of the shop. Figure 1. Tools inevitably vary in length. Figure 2. Tool length offsets reposition the spindle in the Z-axis. Figure 3. Operators use tool length offsets to get from A to C, without tool breakage (B).
Lesson: 14/18 Tool Length Offset Methods The measuring of various tool lengths can be done either on or off the machine. Every toolholder has an imaginary gage line. This line matches the bottom surface of the machine spindle. The length of the tool is calculated from the tool tip to the gage line. When measuring tool lengths off the machine, the operator places the tool and its toolholder into a special fixture that matches the taper of the spindle. Figure 1 shows this fixture. You can see in Figure 2 that there is often a small space between the gage line and the flange of the toolholder. The operator then enters the measurement taken from the fixture. To measure lengths of tools loaded on the machine, the operator touches off each tool against a fixed machine component, such as the worktable. The operator normally uses either a piece of paper or a 1-2-3 block to avoid damaging components. A 1-2-3 block is shown in Figure 3. He or she then records the position in the tool length offset table, adjusting for the height of the paper or block. This process is then repeated for each tool. Figure 1. A fixture used to measure tool lengths off the machine. Figure 2. A gage line on the toolholder marks where the spindle surface is located.
where the spindle surface is located. Figure 3. A 1-2-3 block is 1 inch thick, 2 inches tall, and 3 inches wide. Lesson: 15/18 Cutter Radius Compensation Most part programs calculate the path of a tool according to its centerline. For tools that travel only vertically on the Z-axis, no additional offsets are required. The reamer and drill shown in Figure 1 are programmed to the center tool tip. Only one tool diameter will match the hole-making operation. The situation is different for tools that travel along the X-axis and Y-axis. This is especially the case with end mills, which cut with the outer edge. End mills are used to machine pockets, slots, and contour shapes. For these operations, tool diameter affects the dimensions of the part. Programmers use cutter radius compensation (CRC) to adjust for variations in tool diameter. CRC shifts the cutting tool in a direction perpendicular to its programmed path, as shown in Figure 2. This type of offset enables end mills with two different diameters to perform the same milling operation. The operator must input the tool radius or diameter for each tool in the offset table. Figure 1. Tools that travel only vertically are programmed to their tool tip. Figure 2. End mills require CRC to compensate for tool diameters. Lesson: 16/18
Lesson: 15/18 Cutter Radius Compensation Most part programs calculate the path of a tool according to its centerline. For tools that travel only vertically on the Z-axis, no additional offsets are required. The reamer and drill shown in Figure 1 are programmed to the center tool tip. Only one tool diameter will match the hole-making operation. The situation is different for tools that travel along the X-axis and Y-axis. This is especially the case with end mills, which cut with the outer edge. End mills are used to machine pockets, slots, and contour shapes. For these operations, tool diameter affects the dimensions of the part. Programmers use cutter radius compensation (CRC) to adjust for variations in tool diameter. CRC shifts the cutting tool in a direction perpendicular to its programmed path, as shown in Figure 2. This type of offset enables end mills with two different diameters to perform the same milling operation. The operator must input the tool radius or diameter for each tool in the offset table. Figure 1. Tools that travel only vertically are programmed to their tool tip. Figure 2. End mills require CRC to compensate for tool diameters. Lesson: 16/18 Offset Features for Milling Manufacturers are adding features to machining centers that make offsets easier to use. For example, newer machines are available with wear offsets similar to the type used for turning. Older machines may require an operator to account for wear by adjusting CRC or tool length offsets instead. Traditionally, CRC can adjust for wear in the X-axis and Y-axis, and tool length offsets can account for wear in the Z-axis. Nowadays, the wear offsets available on newer machines enable operators to better track tool wear when changing tools. Figure 1 shows wear offsets on the CRT. Newer machines are also available with semi-automatic tool compensation. This feature allows an operator to touch off a tool and use the button in Figure 2 to automatically enter the tool length offset into the controls. This process saves time during setup. Other machines are also equipped with a toolset probe similar to those found on the turning center. Figure 1. This machine is equipped with wear offsets.
Lesson: 16/18 Offset Features for Milling Manufacturers are adding features to machining centers that make offsets easier to use. For example, newer machines are available with wear offsets similar to the type used for turning. Older machines may require an operator to account for wear by adjusting CRC or tool length offsets instead. Traditionally, CRC can adjust for wear in the X-axis and Y-axis, and tool length offsets can account for wear in the Z-axis. Nowadays, the wear offsets available on newer machines enable operators to better track tool wear when changing tools. Figure 1 shows wear offsets on the CRT. Newer machines are also available with semi-automatic tool compensation. This feature allows an operator to touch off a tool and use the button in Figure 2 to automatically enter the tool length offset into the controls. This process saves time during setup. Other machines are also equipped with a toolset probe similar to those found on the turning center. Figure 1. This machine is equipped with wear offsets. Figure 2. Semi-automatic tool compensation reduces setup time by quickly storing offsets. Lesson: 17/18 Recognizing Tool Wear The adjustment of the various offsets is a normal part of the machine operator s job. Whether the machine is a turning center or machining center, it will require a calculation of the workshift offset and geometry offsets or tool length offsets for every part setup. After the first part has been run, the operator must keep an eye on tool wear and make the necessary adjustments. As a tool wears, slight changes in part dimensions will appear. Figure 1 shows an operator checking part dimensions with a measuring instrument. Poor surface finish, increased horsepower, and inconsistent part sizes are all signs that an insert needs to be changed. Keep in mind that every shop has its own system for setting offsets. In addition, machine manufacturers differ in their methods for storing offsets in the machine.
Lesson: 17/18 Recognizing Tool Wear The adjustment of the various offsets is a normal part of the machine operator s job. Whether the machine is a turning center or machining center, it will require a calculation of the workshift offset and geometry offsets or tool length offsets for every part setup. After the first part has been run, the operator must keep an eye on tool wear and make the necessary adjustments. As a tool wears, slight changes in part dimensions will appear. Figure 1 shows an operator checking part dimensions with a measuring instrument. Poor surface finish, increased horsepower, and inconsistent part sizes are all signs that an insert needs to be changed. Keep in mind that every shop has its own system for setting offsets. In addition, machine manufacturers differ in their methods for storing offsets in the machine. Figure 1. An operator using a micrometer to check part dimensions. Lesson: 18/18 Summary The precision of a CNC machine depends upon the proper referencing of the cutting tool and the workpiece. Operators will store a series of offsets to accurately reference the cutting edge of each tool loaded in the machine. Program zero acts as the origin for tool positions contained in the part program. For the turning center, the workshift offset adjusts the turret along the Z-axis. Each tool has a geometry offset that adjusts along the X-axis and Z-axis. Wear offsets make subtle adjustments to account for the wear a tool experiences through use. Nose radius compensation is important during finishing operations. Offsets are determined with respect to a reference tool. On the machining center, the workshift offset adjusts the spindle in three axes to a place closer to the workpiece. Each tool has a tool length offset to adjust for its unique length in the Z-axis. For tools that travel in the X- and Y-axes, the cutter radius compensation accounts for a tool s diameter. Figure 1. Offsets for the turning center.
Lesson: 18/18 Summary The precision of a CNC machine depends upon the proper referencing of the cutting tool and the workpiece. Operators will store a series of offsets to accurately reference the cutting edge of each tool loaded in the machine. Program zero acts as the origin for tool positions contained in the part program. For the turning center, the workshift offset adjusts the turret along the Z-axis. Each tool has a geometry offset that adjusts along the X-axis and Z-axis. Wear offsets make subtle adjustments to account for the wear a tool experiences through use. Nose radius compensation is important during finishing operations. Offsets are determined with respect to a reference tool. On the machining center, the workshift offset adjusts the spindle in three axes to a place closer to the workpiece. Each tool has a tool length offset to adjust for its unique length in the Z-axis. For tools that travel in the X- and Y-axes, the cutter radius compensation accounts for a tool s diameter. Figure 1. Offsets for the turning center. Figure 2. Offsets for the machining center. Class Vocabulary Term Definition 1-2-3 Block A precise metal block with dimensions measuring one, two, and three inches long respectively. Chamfering Machining an angled edge around the end of a cylindrical workpiece. Contour A curved surface or dimension that is cut into a workpiece. Contouring Tool movement along two or more axes at the same time that creates a curved surface. Cutter Radius Compensation An offset used on the machining center that accounts for variations in tool diameter. CRC is only necessary for tools that continuously cut along a horizontal plane.
Class Vocabulary Term Definition 1-2-3 Block A precise metal block with dimensions measuring one, two, and three inches long respectively. Chamfering Machining an angled edge around the end of a cylindrical workpiece. Contour Contouring Cutter Radius Compensation Edge Finder Flange G Code A curved surface or dimension that is cut into a workpiece. Tool movement along two or more axes at the same time that creates a curved surface. An offset used on the machining center that accounts for variations in tool diameter. CRC is only necessary for tools that continuously cut along a horizontal plane. A device used on a machining center to locate the exact position of a part edge along the X-axis or Yaxis. A ring or collar surrounding the toolholder that allows the tool to be grasped by the toolchanger. A programming code that determines the type of operation performed on the machine. Gage Line The imaginary line marking the portion of the toolholder that matches the bottom edge of the machine spindle. Geometry Offset An offset used on a turning center to account for the setup and geometry of a specific tool held in the turret. Each tool requires its own geometry offset. Machine Zero The position located at the farthest possible distance in a positive direction along the machine axes. This position is permanently set for each particular CNC machine. Machining Center A sophisticated CNC machine that can perform milling, drilling, tapping, and boring operations at the same location with a variety of tools. Offset A numerical value stored in the CNC controls that repositions machine components. Offsets are used to adjust for variations in tool geometry, part size, tool wear, etc. Origin The central point in a coordinate system. The origin has a numerical value of zero. Pocket Program Zero Reference Tool Referencing Slot Taper An interior recess that is cut into the surface of a workpiece. The position that acts as the origin for the part program of a particular workpiece. This position is unique to each workpiece design, and it is selected by the part programmer. The tool in the turret to which all the other tools are compared when setting geometry offsets. The reference tool does not require a geometry offset because its exact location is already stored as the workshift offset. Locating a tool, workpiece, or machine component in a known position. A narrow channel cut into the surface of a workpiece. A shape with a gradually decreasing diameter, similar to the shape of a cone. Tool Length Offset An offset used on the machining center that accounts for variations in tool length along the Z-axis. Each tool requires its own offset, which is measured from the tip of the tool to the gage line. Tool Nose Radius Compensation An offset feature used on a turning center that slightly shifts the toolpath for the rounded tip of an insert during contouring, chamfering, and other multi-axis operations. Toolset Probe A device on a turning center that swings into position and acts as a point for touching off tools to quickly calculate their geometry offsets. Toolset probes help to reduce setup time. Touches Off To determine the exact location of a tool tip by touching it against an object with a known Copyright 2015 Tooling U, LLC. All Rights measurement. Reserved. Turning Center A sophisticated CNC machine that specializes in turning, boring, drilling, and threading operations, all at
quickly calculate their geometry offsets. Toolset probes help to reduce setup time. Touches Off Turning Center Wear Offset Workshift Offset To determine the exact location of a tool tip by touching it against an object with a known measurement. A sophisticated CNC machine that specializes in turning, boring, drilling, and threading operations, all at the same location. An offset used on a turning center and some machining centers that allows for the slight adjustment of tool tip location. Wear offsets account for part deflection, tool wear, etc. An offset used to adjust the location of every tool loaded in the machine. Workshift offsets change the position of the turret on a turning center and the spindle on a machining center. X-Axis For turning, the linear axis describing turret motion toward and away from the spindle centerline. For milling, the linear axis describing the horizontal left and right motion of the cutting tool or worktable. Y-Axis The linear axis that describes horizontal tool motion on the machining center toward and away from the operator. Z-Axis The linear axis that describes motions along a line parallel to the spindle.