Fixture Design Basics 210
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Class Outline
Class Outline
Objectives
Design Criteria for Fixtures
The Base Plate
Supporting Principles
Support Components
Locating Principles
Locating Components
Clamping Principles
Clamping Components
Power Clamping
Standard Workholding Components
Tolerance Considerations
Lot Size
Nonproductive Time
Summary
Lesson: 1/15
Objectives
l Describe the design criteria for a workholding device.
l Describe the base plate.
l Identify the principles of support.
l Describe support on a plate fixture.
l Describe locating on a plate fixture.
l Describe locating components.
l Describe clamping on a plate fixture.
l Describe clamping components.
l Describe power clamping.
l Identify the benefits of standard workholding components.
l Identify the required tolerance in a workholding device.
l Describe the impact of lot size on fixture design.
l Describe nonproductive time.
Figure 1. Base plates are made of steel or
lightweight aluminum and function as the
foundation of the fixture.
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Figure 2. Supports and locating pins are
essential components in a customized fixture.
Lesson: 1/15
Objectives
l Describe the design criteria for a workholding device.
l Describe the base plate.
l Identify the principles of support.
l Describe support on a plate fixture.
l Describe locating on a plate fixture.
l Describe locating components.
l Describe clamping on a plate fixture.
l Describe clamping components.
l Describe power clamping.
l Identify the benefits of standard workholding components.
l Identify the required tolerance in a workholding device.
l Describe the impact of lot size on fixture design.
l Describe nonproductive time.
Figure 1. Base plates are made of steel or
lightweight aluminum and function as the
foundation of the fixture.
Figure 2. Supports and locating pins are
essential components in a customized fixture.
Figure 3. Clamps secure the workpiece on the
workholding device.
Lesson: 2/15
Design Criteria for Fixtures
© 2015 device
Tooling U,
Allthat
Rights
Reserved. a relationship between the workpiece and the
ACopyright
workholding
is LLC.
a tool
establishes
machine tool. Every workholding device is designed to securely support, locate, and hold the
workpiece as it sustains machining forces, as shown in Figure 1. However, many variables affect the
Lesson: 2/15
Design Criteria for Fixtures
A workholding device is a tool that establishes a relationship between the workpiece and the
machine tool. Every workholding device is designed to securely support, locate, and hold the
workpiece as it sustains machining forces, as shown in Figure 1. However, many variables affect the
design of an effective customized fixture for any given machining operation.
The responsibility of the designer is to create a fixture that is sturdy, easy to use, and inexpensive.
An effective fixture also reduces nonproductive time spent on tasks other than machining. In small
shops, the designer may also be the person who builds the fixture. However, larger shops often
employ individuals that are solely responsible for the design of the fixture. The designer plays a
crucial role in maintaining quality while increasing production.
This class will walk you through the construction of the plate fixture shown in Figure 2 to teach you
fundamental workholding design principles.
Figure 1. Machining forces impact workholding
design.
Figure 2. A simple plate fixture.
Lesson: 3/15
The Base Plate
Consider the workpiece shown in Figure 1 in its fixture. This workpiece requires drilling and other
operations to create several holes in an aluminum plate that is approximately 19 in. (48.3 cm) wide,
9 in. (22.9 cm) high, and 1/8 in. (0.318 cm) thick. What is the most effective workholding design
for this workpiece?
In this case, an effective workholding device is a plate fixture. The design of a plate fixture begins
with the selection of a base plate, shown in Figure 2, which acts as the tool body containing all the
workholding components. The designer must choose the appropriate thickness and material for the
base plate.
Severe machining operations require strong base plates. For example, a milling operation may
require a tool steel plate with a 3/4 in. (1.9 cm) or 1 in. (2.54 cm) thickness. However, drilling
typically generates less cutting forces. In this example, the designer selected a 3/4 in. thick
aluminum
Aluminum
reduce the weight of the fixture. Because of the size of
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2015plate.
Tooling
U, LLC. Allmaterials
Rights Reserved.
the workpiece, a larger base plate is required. Since there is no machining on the right half of the
part, the base plate does not need to be as large as the workpiece.
Figure 1. The finished part, still in the fixture.
Lesson: 3/15
The Base Plate
Consider the workpiece shown in Figure 1 in its fixture. This workpiece requires drilling and other
operations to create several holes in an aluminum plate that is approximately 19 in. (48.3 cm) wide,
9 in. (22.9 cm) high, and 1/8 in. (0.318 cm) thick. What is the most effective workholding design
for this workpiece?
In this case, an effective workholding device is a plate fixture. The design of a plate fixture begins
with the selection of a base plate, shown in Figure 2, which acts as the tool body containing all the
workholding components. The designer must choose the appropriate thickness and material for the
base plate.
Severe machining operations require strong base plates. For example, a milling operation may
require a tool steel plate with a 3/4 in. (1.9 cm) or 1 in. (2.54 cm) thickness. However, drilling
typically generates less cutting forces. In this example, the designer selected a 3/4 in. thick
aluminum base plate. Aluminum materials reduce the weight of the fixture. Because of the size of
the workpiece, a larger base plate is required. Since there is no machining on the right half of the
part, the base plate does not need to be as large as the workpiece.
Figure 1. The finished part, still in the fixture.
Figure 2. The base plate is the tool body,
which contains all the workholding
components.
Lesson: 4/15
Supporting Principles
After the base plate is selected, the designer must choose the appropriate components for
supporting the workpiece. Besides size and shape, the material of the workpiece will greatly affect
workholding design. A workpiece made of aluminum or other soft material will generate less cutting
forces. However, softer materials may distort and bend, especially while cutting features such as
those shown in Figures 1 and 2. Extra support may be necessary to prevent this distortion during
machining.
With high-carbon steels, tool steels, or other harder materials, the designer must anticipate greater
cutting forces. Harder materials experience less distortion. However, supporting components must
be able to resist these increased cutting forces. Supports must also be able to withstand the wear
encountered by the loading and unloading of parts. Regardless of the material, the workpiece must
always be supported near the location of the machining.
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Figure 1. Thin and flexible materials may
require extra support in the fixture to prevent
Lesson: 4/15
Supporting Principles
After the base plate is selected, the designer must choose the appropriate components for
supporting the workpiece. Besides size and shape, the material of the workpiece will greatly affect
workholding design. A workpiece made of aluminum or other soft material will generate less cutting
forces. However, softer materials may distort and bend, especially while cutting features such as
those shown in Figures 1 and 2. Extra support may be necessary to prevent this distortion during
machining.
With high-carbon steels, tool steels, or other harder materials, the designer must anticipate greater
cutting forces. Harder materials experience less distortion. However, supporting components must
be able to resist these increased cutting forces. Supports must also be able to withstand the wear
encountered by the loading and unloading of parts. Regardless of the material, the workpiece must
always be supported near the location of the machining.
Figure 1. Thin and flexible materials may
require extra support in the fixture to prevent
distortion.
Figure 2. The holes and notch need support to
prevent distortion.
Lesson: 5/15
Support Components
With the design of any plate fixture, you must choose components that are both accurate and
replaceable. For example, for the sample fixture in Figure 1, the designer placed rest buttons
between the small drilled holes around the large hole, as well as among the set of three holes along
the top. Figure 2 shows the supports added to the base plate.
These supports, like the component in Figure 3, are ground to precise tolerances within 0.0005 in.
(0.013 mm). They can also be easily replaced if they wear out over time. Rest buttons provide
clearance underneath the workpiece for chip and coolant removal, which is especially important for
drilling operations.
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In theory, a designer needs only three contact points to support a workpiece. In fact, supporting is
the first step in the 3-2-1 method. However, this particular workpiece is only 1/8 in. (0.318 cm)
thick, and machining may distort the metal. By using multiple supports underneath the larger hole,
Lesson: 5/15
Support Components
With the design of any plate fixture, you must choose components that are both accurate and
replaceable. For example, for the sample fixture in Figure 1, the designer placed rest buttons
between the small drilled holes around the large hole, as well as among the set of three holes along
the top. Figure 2 shows the supports added to the base plate.
These supports, like the component in Figure 3, are ground to precise tolerances within 0.0005 in.
(0.013 mm). They can also be easily replaced if they wear out over time. Rest buttons provide
clearance underneath the workpiece for chip and coolant removal, which is especially important for
drilling operations.
In theory, a designer needs only three contact points to support a workpiece. In fact, supporting is
the first step in the 3-2-1 method. However, this particular workpiece is only 1/8 in. (0.318 cm)
thick, and machining may distort the metal. By using multiple supports underneath the larger hole,
the designer helps prevent this distortion. Additional supports away from the machining areas will
help stabilize the large piece and provide spots for clamping.
Figure 1. The completed workpiece, still loaded
in the fixture.
Figure 2. Supports are placed next to the
machining locations.
Figure 3. Supports can be replaced as they
wear out over time.
Lesson: 6/15
Locating Principles
After
the workpiece
is supported,
the next
task is locating. A designer essentially has the option
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U, LLC. All Rights
Reserved.
of internal locating or external locating.
Lesson: 6/15
Locating Principles
After the workpiece is supported, the next task is locating. A designer essentially has the option
of internal locating or external locating.
One of the most effective methods is to locate the part by using two machined internal holes, as
shown in Figure 1. A round internal locating pin and a relieved pin are all that is necessary to
precisely locate a part. This method is ideal if a workpiece contains holes. Even if the workpiece
does not require holes, the designer may choose to add them anyway. Internal locating may help to
improve accuracy and reduce setup time.
If internal holes are not feasible, the designer can locate the part externally using the 3-2-1
method, as demonstrated in Figure 2. Regardless of the locating method, machined surfaces are
always preferable as a locating point on the workpiece.
Figure 1. Two holes can accurately locate a
part.
Figure 2. External location requires location on
several surfaces.
Lesson: 7/15
Locating Components
For the sample fixture in Figure 1, the original workpiece is simply a flat piece of metal.
Consequently, the fixture must locate the part by using external surfaces. The designer chose to
locate the workpiece by adding two small locating pins at the top and a single pin on the left next
to the large hole in the workpiece, as shown in Figure 2.
According to the 3-2-1 method, the workpiece must be supported by at least three points from
below. The rest buttons accomplish this task. The workpiece must also be located along an axis by
two points, which is satisfied by the two locating pins at the top and right. Finally, the workpiece
must be located along an axis perpendicular to the previous axis by a single point. The pin at the
left next to the circle of supports performs this final requirement.
Because drilling generates primary cutting forces down toward the thin aluminum sheet, only a
moderate amount of force will be driven into the pins. These small locating pins are sufficient for
proper location.
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Figure 1. The completed workpiece, still loaded
in the fixture.
Lesson: 7/15
Locating Components
For the sample fixture in Figure 1, the original workpiece is simply a flat piece of metal.
Consequently, the fixture must locate the part by using external surfaces. The designer chose to
locate the workpiece by adding two small locating pins at the top and a single pin on the left next
to the large hole in the workpiece, as shown in Figure 2.
According to the 3-2-1 method, the workpiece must be supported by at least three points from
below. The rest buttons accomplish this task. The workpiece must also be located along an axis by
two points, which is satisfied by the two locating pins at the top and right. Finally, the workpiece
must be located along an axis perpendicular to the previous axis by a single point. The pin at the
left next to the circle of supports performs this final requirement.
Because drilling generates primary cutting forces down toward the thin aluminum sheet, only a
moderate amount of force will be driven into the pins. These small locating pins are sufficient for
proper location.
Figure 1. The completed workpiece, still loaded
in the fixture.
Figure 2. Three pins keep the part from sliding
off the supports.
Lesson: 8/15
Clamping Principles
After the part is located, it must be securely held in place by clamping. A variety of clamps are
made for different workpiece materials and their machining operations. In general, a fixture should
be designed with clamps that offer plenty of clearance and a low profile. This is particularly true for
milling operations. Clamps should not get in the way of tools during machining.
With harder materials, the designer should expect increased cutting forces. Consequently,
stronger, sturdier clamps will be required. However, with softer workpiece materials, excessive
clamping forces may harm the workpiece surface. Smaller clamps will be sufficient.
Most importantly, clamps should always be positioned over a locator or support. As shown in
Figures 1 and 2, this type of placement avoids any potential distortion of the workpiece during
machining.
Figure 1. If clamps are not positioned over a
locator or support, workpiece distortion can
occur.
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Lesson: 8/15
Clamping Principles
After the part is located, it must be securely held in place by clamping. A variety of clamps are
made for different workpiece materials and their machining operations. In general, a fixture should
be designed with clamps that offer plenty of clearance and a low profile. This is particularly true for
milling operations. Clamps should not get in the way of tools during machining.
With harder materials, the designer should expect increased cutting forces. Consequently,
stronger, sturdier clamps will be required. However, with softer workpiece materials, excessive
clamping forces may harm the workpiece surface. Smaller clamps will be sufficient.
Most importantly, clamps should always be positioned over a locator or support. As shown in
Figures 1 and 2, this type of placement avoids any potential distortion of the workpiece during
machining.
Figure 1. If clamps are not positioned over a
locator or support, workpiece distortion can
occur.
Figure 2. Clamps should be placed over
supports.
Lesson: 9/15
Clamping Components
Once again, consider the sample fixture in Figure 1. The designer selected five strap clamps
positioned around the outside of the workpiece. As you can see in Figure 2, every strap clamp has
a method of support below it. Because the workpiece is relatively large and thin, the extra clamps
are necessary to eliminate possible vibration. Lastly, strap clamps should be positioned so that the
maximum reach is exactly where the clamping force is supposed to be. There should be no need for
an operator to guess or estimate clamp placement.
Notice that the designer chose strap clamps instead of toggle clamps. For this particular
workpiece, strap clamps offer greater freedom in moving the clamp out of the way. Toggle clamps,
like the one in Figure 3, are limited by a small clamping range, and there is always a risk that a
clamp may be dislodged by heavy machining.
When clearance is a concern, low profile clamps, such as toe clamps, can secure the part while
staying out of the way of tools. For the sample fixture, the part is too thin to use toe clamps
successfully.
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Figure 1. The completed workpiece, still loaded
in the fixture.
Lesson: 9/15
Clamping Components
Once again, consider the sample fixture in Figure 1. The designer selected five strap clamps
positioned around the outside of the workpiece. As you can see in Figure 2, every strap clamp has
a method of support below it. Because the workpiece is relatively large and thin, the extra clamps
are necessary to eliminate possible vibration. Lastly, strap clamps should be positioned so that the
maximum reach is exactly where the clamping force is supposed to be. There should be no need for
an operator to guess or estimate clamp placement.
Notice that the designer chose strap clamps instead of toggle clamps. For this particular
workpiece, strap clamps offer greater freedom in moving the clamp out of the way. Toggle clamps,
like the one in Figure 3, are limited by a small clamping range, and there is always a risk that a
clamp may be dislodged by heavy machining.
When clearance is a concern, low profile clamps, such as toe clamps, can secure the part while
staying out of the way of tools. For the sample fixture, the part is too thin to use toe clamps
successfully.
Figure 1. The completed workpiece, still loaded
in the fixture.
Figure 2. Strap clamps secure the workpiece.
Figure 3. Toggle clamps are limited by a small
clamping range, and there is always a risk that
the clamp may be dislodged by heavy
machining.
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Lesson: 10/15
Power Clamping
For any workholding assignment, the designer has numerous tools and components available.
Every workholding device must accurately support, locate, and hold the workpiece. However, the
task of the designer is to develop a fixture that is cost efficient as well.
A sample fixture of this class contains clamps that are manually tightened by turning a knob. These
clamps are both effective and relatively inexpensive. However, manual clamps may increase the time
required to load and unload a workpiece. This introduces a labor cost.
Another option for the designer is power clamping. If power clamps such as the system in Figure
1 are used, the operator can clamp the workpiece with a flick of a switch. Because they are driven
by hydraulic power or pneumatic power, the clamping force is always the same and is evenly
distributed to all the clamps. Most importantly, the time required for securing parts is greatly
reduced. Unfortunately, power clamping is more expensive.
So, which clamping method is best? Both methods sufficiently hold the workpiece. The best choice
depends upon the lot size and other factors. More expensive workholding components must be
justified by improved cost savings over time.
Figure 1. Pneumatic clamping can reduce setup
time while consistently clamping parts.
Lesson: 11/15
Standard Workholding Components
An effective way to reduce the cost of a workholding device is to use standard components
whenever possible. The fixture in Figure 1 consists of various standard components. Tool designers
rarely machine a fixture from scratch because it is simply not a cost-effective alternative. Instead,
designers can choose numerous standard components that are assembled into a customized
workholding design:
l
l
l
Base plate components are made of steel or lightweight aluminum. They function as the
foundation of the fixture.
Rest buttons and locating pins are hardened for wear resistance. They support and locate
the part on the tool body.
Strap clamps, toggle clamps, and other standardized clamping devices are used to hold the
part in place.
By using standardized components, like the base plate and the rest button shown in Figures 2 and
3, designers can save time and reduce costs. Most importantly, these devices already adhere to
very tight tolerances, some as strict as ±0.0005 in. (±0.013 mm).
Figure 1. A fixture can be constructed from
standard components.
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Figure 2. Base plates are made of steel or
lightweight aluminum and provide the
Lesson: 11/15
Standard Workholding Components
An effective way to reduce the cost of a workholding device is to use standard components
whenever possible. The fixture in Figure 1 consists of various standard components. Tool designers
rarely machine a fixture from scratch because it is simply not a cost-effective alternative. Instead,
designers can choose numerous standard components that are assembled into a customized
workholding design:
l
l
l
Base plate components are made of steel or lightweight aluminum. They function as the
foundation of the fixture.
Rest buttons and locating pins are hardened for wear resistance. They support and locate
the part on the tool body.
Strap clamps, toggle clamps, and other standardized clamping devices are used to hold the
part in place.
By using standardized components, like the base plate and the rest button shown in Figures 2 and
3, designers can save time and reduce costs. Most importantly, these devices already adhere to
very tight tolerances, some as strict as ±0.0005 in. (±0.013 mm).
Figure 1. A fixture can be constructed from
standard components.
Figure 2. Base plates are made of steel or
lightweight aluminum and provide the
foundation for the fixture.
Figure 3. Standard components are made to
withstand wear.
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Lesson: 12/15
Lesson: 12/15
Tolerance Considerations
Every workpiece has specified tolerances. As you can see in Figure 1, not all tolerances of a
workpiece are the same. The designer of the workpiece selects the tolerances necessary to make
sure the part functions as expected.
Ideally, the same fixture can be designed to hold the part during multiple operations. Every time
you load and unload a part, you potentially introduce inaccuracies into part dimensions. If a fixture
can hold a part during multiple operations, the result is greater accuracy.
Workpiece tolerances affect the required tolerances of the fixture. Also, tighter tolerances cost
more to produce. Generally, the workholding device should have a tolerance no greater than 50%
of the expected workpiece tolerance. Inspection fixtures are typically 10% of the expected
workpiece tolerance. Consequently, an expensive workpiece with tight tolerances requires an
expensive fixture with even tighter tolerances.
Figure 1. Different dimensions have different
tolerance requirements.
Lesson: 13/15
Lot Size
A key consideration during the design of a workholding device is the expected lot size. The number
of parts that will be made affects the choice of the best workholding setup.
Dedicated fixtures can be expensive to make. The cost of the fixture is spread out over its useful
lifespan. If only a small handful of parts needs to be made, an expensive fixture is probably not the
best choice. It would be better to use a standard workholding device, such as a vise, to save
money.
However, imagine that you must design a fixture that will be used to make 5000 parts. A dedicated
fixture may cost more, but this cost is spread out much farther. If this fixture cuts down on setup
time, it will likely save money in the long run compared to other setup options.
What exactly is a large lot size? It depends on the part. If it takes two minutes to machine a part,
200 parts may be a small lot size. However, if each part requires 30 minutes of machining, 200
parts is a significant lot size. The example part shown in Figure 1 is infrequently made in small
batches of a few dozen. This is a relatively small lot size that does not call for expensive
components.
Lesson: 14/15
Nonproductive Time
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Modern manufacturing is a race to produce the greatest number of high quality parts in the least
amount of time. As time increases, the cost of the part increases as well. As you might imagine, the
workholding setup plays a key role in reducing the time it takes to make a part.
Figure 1. The finished workpiece, still loaded in
its fixture.
Lesson: 13/15
Lot Size
A key consideration during the design of a workholding device is the expected lot size. The number
of parts that will be made affects the choice of the best workholding setup.
Dedicated fixtures can be expensive to make. The cost of the fixture is spread out over its useful
lifespan. If only a small handful of parts needs to be made, an expensive fixture is probably not the
best choice. It would be better to use a standard workholding device, such as a vise, to save
money.
However, imagine that you must design a fixture that will be used to make 5000 parts. A dedicated
fixture may cost more, but this cost is spread out much farther. If this fixture cuts down on setup
time, it will likely save money in the long run compared to other setup options.
What exactly is a large lot size? It depends on the part. If it takes two minutes to machine a part,
200 parts may be a small lot size. However, if each part requires 30 minutes of machining, 200
parts is a significant lot size. The example part shown in Figure 1 is infrequently made in small
batches of a few dozen. This is a relatively small lot size that does not call for expensive
components.
Figure 1. The finished workpiece, still loaded in
its fixture.
Lesson: 14/15
Nonproductive Time
Modern manufacturing is a race to produce the greatest number of high quality parts in the least
amount of time. As time increases, the cost of the part increases as well. As you might imagine, the
workholding setup plays a key role in reducing the time it takes to make a part.
An effective fixture can reduce nonproductive time. A fixture effectively secures more parts with
fewer clamps. Nonproductive time includes setup time spent setting up the fixture, calculating tool
offsets, and other tasks required to make the first good part. However, nonproductive time also
includes more general tasks such as loading and unloading the part, part checking, tool changes,
etc.
A basic truism of the shop is that if you are not producing chips, you are not making money. An
effective workholding setup reduces the amount of nonproductive time and helps keep a machine
running.
Figure 1. Nonproductive time is reduced by
using one clamp on two parts.
Lesson: 15/15
Summary
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The responsibility of the tool designer is to create a fixture that is sturdy, easy to use, and
inexpensive. The design of the plate fixture begins with the selection of a base plate, which acts as
the tool body containing all the workholding components. Besides size and shape, the material of
Lesson: 14/15
Nonproductive Time
Modern manufacturing is a race to produce the greatest number of high quality parts in the least
amount of time. As time increases, the cost of the part increases as well. As you might imagine, the
workholding setup plays a key role in reducing the time it takes to make a part.
An effective fixture can reduce nonproductive time. A fixture effectively secures more parts with
fewer clamps. Nonproductive time includes setup time spent setting up the fixture, calculating tool
offsets, and other tasks required to make the first good part. However, nonproductive time also
includes more general tasks such as loading and unloading the part, part checking, tool changes,
etc.
A basic truism of the shop is that if you are not producing chips, you are not making money. An
effective workholding setup reduces the amount of nonproductive time and helps keep a machine
running.
Figure 1. Nonproductive time is reduced by
using one clamp on two parts.
Lesson: 15/15
Summary
The responsibility of the tool designer is to create a fixture that is sturdy, easy to use, and
inexpensive. The design of the plate fixture begins with the selection of a base plate, which acts as
the tool body containing all the workholding components. Besides size and shape, the material of
the workpiece and the operations performed greatly affect workholder design.
First, supporting components are used to resist cutting forces and sustain wear. Second, locating
pins are strategically placed to prevent the workpiece from sliding. Finally, clamping prevents the
workpiece from lifting off the supports and out of the fixture. Clamps should be secured over
supports to prevent distortion of the workpiece.
These workholding steps are often best accomplished with the use of standard components.
Workholding components are generally hardened to resist wear and ground to precise dimensions.
An effective fixture can also be an opportunity to reduce nonproductive time and increase overall
efficiency.
Figure 1. The workpiece, still in its fixture.
Figure 2. The assembled fixture.
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Lesson: 15/15
Summary
The responsibility of the tool designer is to create a fixture that is sturdy, easy to use, and
inexpensive. The design of the plate fixture begins with the selection of a base plate, which acts as
the tool body containing all the workholding components. Besides size and shape, the material of
the workpiece and the operations performed greatly affect workholder design.
First, supporting components are used to resist cutting forces and sustain wear. Second, locating
pins are strategically placed to prevent the workpiece from sliding. Finally, clamping prevents the
workpiece from lifting off the supports and out of the fixture. Clamps should be secured over
supports to prevent distortion of the workpiece.
These workholding steps are often best accomplished with the use of standard components.
Workholding components are generally hardened to resist wear and ground to precise dimensions.
An effective fixture can also be an opportunity to reduce nonproductive time and increase overall
efficiency.
Figure 1. The workpiece, still in its fixture.
Figure 2. The assembled fixture.
Class Vocabulary
Term
Definition
3-2-1 Method
Base Plate
An effective method for locating a rectangular workpiece. Three datum points support the workpiece, two datum
points locate a flat workpiece surface, and a single datum point locates a second surface perpedicular to the previous
surface.
A precisely ground plate that acts as the foundation of a fixture. Various components, such as locators and clamps,
are fastened to the base plate.
Clamping
The appropriate forces used to hold a workpiece against the locators during the machining operation.
External Locating
The use of external surfaces to locate a workpiece. The 3-2-1 method is an external locating method.
Fixture
A customized workholding device used on machine tools to position and hold a part during various machining
operations. A fixture is built to hold a specific part design.
Ground
Machined with an abrasive to achieve highly accurate measurements.
Hydraulic Power
Power created by water or fluid pressure.
Inspection
A fixture
usedReserved.
to hold a workpiece while it is being examined. Inspections usually involve comparing workpieces with
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desired measurements for accuracy.
Internal Locating
The use of internal surfaces to locate a workpiece. The most common internal locating method is the use of a round
Class Vocabulary
Term
Definition
3-2-1 Method
Base Plate
An effective method for locating a rectangular workpiece. Three datum points support the workpiece, two datum
points locate a flat workpiece surface, and a single datum point locates a second surface perpedicular to the previous
surface.
A precisely ground plate that acts as the foundation of a fixture. Various components, such as locators and clamps,
are fastened to the base plate.
Clamping
The appropriate forces used to hold a workpiece against the locators during the machining operation.
External Locating
The use of external surfaces to locate a workpiece. The 3-2-1 method is an external locating method.
Fixture
A customized workholding device used on machine tools to position and hold a part during various machining
operations. A fixture is built to hold a specific part design.
Ground
Machined with an abrasive to achieve highly accurate measurements.
Hydraulic Power
Power created by water or fluid pressure.
Inspection Fixture
A fixture used to hold a workpiece while it is being examined. Inspections usually involve comparing workpieces with
desired measurements for accuracy.
Internal Locating
The use of internal surfaces to locate a workpiece. The most common internal locating method is the use of a round
and relieved pin to locate two machined holes.
Locating
The accurate positioning of the workpiece in a horizontal plane to establish a relationship between the workpiece and
cutting tool.
Locating Pin
Lot Size
Nonproductive Time
Plate Fixture
Pneumatic Power
Power Clamping
An assembled locating device that can be used to locate either an outside workpiece surface or an interior hole.
Locating pins are available in numerous shapes and sizes.
The number of parts created during the use of a particular tooling setup.
Time that is spent without the machine in operation producing chips. Nonproductive time includes setup time,
changing of parts, equipment failure, etc.
A fixture consisting of assembled components such as a base plate, locating pins, rest buttons, clamps, etc.
Power created by air pressure.
A clamping system that converts hydraulic or pneumatic power into mechanical clamping forces.
Relieved Pin
A locating pin with a diamond-shaped head that is used to position a workpiece in only two opposite directions.
Relieved locators are most often used with an internal locating pin.
Rest Button
A short locating pin that is used to both support and locate a workpiece.
Setup Time
Strap Clamp
Supporting
Toe Clamp
Toggle Clamp
Tolerance
Time that is spent setting up the fixture, calculating tool offsets, and performing all the necessary tasks to produce
the first accurate part.
A type of clamp that reaches over the workpiece to hold it in place. Strap clamps are often used when extra
toughness is required.
The process of locating from underneath the workpiece. Supports generally restrict motion down along the Z -axis.
A type of low-profile clamp with a serrated surface that reaches forward and down to grip the workpiece on its edge.
A type of clamp that operates on a pivot and lever system. Toggle clamps have a limited clamping range.
An unwanted but acceptable deviation from the specified dimension.
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ToolTooling
Steel U, LLC.
A specialized
of alloy steel that has excellent strength, toughness, and wear resistance. Tool steels are used in
cutting tools, punches, and other industrial tooling.
Tolerance
An unwanted but acceptable deviation from the specified dimension.
Tool Steel
A specialized type of alloy steel that has excellent strength, toughness, and wear resistance. Tool steels are used in
cutting tools, punches, and other industrial tooling.
Workholding Device
A device used to support, locate, and hold a workpiece during machining. The workholding device accurately
references the tool performing the operation on the part being held.
Copyright © 2015 Tooling U, LLC. All Rights Reserved.