# Workholding Technology Pt. 4: Locating of Workpieces with External Forces Applied

Introduction

Another important consideration to take into account when trying to locate work pieces is the role external forces will play in the process. Depending on the machining process that the work piece will be subjected to, there may be different setups that would be required to hold it securely. For example a drilling operation will create different forces on a workpiece compared to a milling operation.   As such the forces that a work piece will be subjected to need to be analyzed so that the proper locating techniques can be used to avoid:

• Damage to the workpiece due to being incorrectly secured
• Damage to the tool
• The operator being harmed during the process
• Machining inaccuracies due to the part having shifted or moved unexpectedly during the operation

We can use the example of a typical drilling operation to understand the effects of a good and bad practice when it comes to locating work pieces subjected to external forces.  The drilling process produces two types of forces; rotational forces known as torque and a plunging force as the drill bit sinks through the part. Figure 1 shows a setup where the radial forces have not been accounted for. In this setup as the drill is lowered it would cause the work piece to spin. This may cause the work piece to fracture or result in the hole being misaligned. The proper way to secure the piece is seen in Figure 2. The optimum design for this kind of work would also include a clamping force to stop the part from moving when the plunging and removing the drill bit.

Left: Correctly Placed Locators; Right: Incorrectly Placed Locators

When considering forces we need to account for the magnitude of the force along with its direction. Simple calculations can be used to estimate these forces so as to ensure the locating features are able to withstand these forces. Rotational forces such as torque on the work piece can be calculated using the formula laid out below.

Locating methods to avoid deformation

As seen in the previous example, locating efforts usually involve applying a force onto the work piece so as to hold it down securely to avoid movement.  The action of applying this force to secure the part can have unintended consequences if done incorrectly as it can lead to part deformation.

The reason these deformations happen can be boiled down to a simple principle. They usually occur in situations where the binding force experienced by the part due to being secured is greater than the force required to deform a part. Reducing the clamping force may seem as a logical way to avoid this problem but many machining operations require parts to be clamped with forces larger than what it would take to deform the part because of safety reasons.

When designing locating fixtures with the intent to take deformations into account we need to consider what force is needed to cause part deformation, where the clamping force is being applied, and what changes can negate the force imbalance. A simple example of deformation from clamping can be seen in Figure 3. In Figure 3(a) we can see the clamping or “fixturing” force may cause the part to deform. A simple solution to this would be to add supports as seen in figure 3(b) – negating the clamping force.

An example of handling deformations caused by clamping forces

As we are trying to remove the chances of deformation occurring in our workpieces we also have to understand what the tolerances are on our finished parts. Some parts may have a loose enough tolerance where small deformations may not affect the integrity of the part or its function. In such situations we can avoid overdesigning to help with cost savings.

Conclusion

Proper locating methods are necessary to efficiently and consistently manufacture components. It is also important to consider every variable to ensure one does not introduce supplemental complications. With the final blog on the basics of locating and fixture design, you are now prepared to tackle your own design.

• ### Workholding Technology Pt. 4: Locating of Workpieces with External Forces Applied

Introduction Another important consideration to take into account when trying to locate work pieces is the role external forces will play ...
• ### Workholding Technology Pt. 3: Locating with the Intention of Avoiding Burrs

Introduction One of the problems faced when locating on jigs and fixtures is the presence of burrs and foreign material on ...
• ### Workholding Technology Pt. 2: Locating Basics

Introduction One of the most common ways of workholding is by location with reference to an external surface. This is also ...
• ### Work Holding Technology Pt. 1: Introduction to Work Holding

Introduction Continual advancements in the fields of mechanization and automation have led to large strides forward for the manufacturing industry. Various ...
• ### E2E Video: Locating Pins Pt. 4 – Alignment Concerns

When working with and designing jigs or fixtures with locating pins, proper alignment is crucial to ensuring smooth operation and repeatable ...
• ### E2E Video: Locating Pins Pt. 2 – Types of Locating

In our second Locating Pins episode in the Engineer to Engineer Series, locating pins are used in workholding fixtures and jigs to secure workpieces during ...
• ### Mastering Ball Screws Pt. 2: Ball Screw Preloads

Preloading is used to increase the feed accuracy and rigidity of ball screws. Why is this necessary? In many applications utilizing ball ...
• ### Mastering Ball Screws Pt. 1: Steel Ball Recirculation System and Characteristics

Ball screws are one of the many components seen throughout factory automation applications. Using the same concept seen with a bolt ...
• ### An Introduction to Aluminum Extrusion and Profiles

The aluminum extrusion (also known by ‘aluminum frames’) forming process is a bulk plastic deformation process. First, a billet of aluminum ...
• ### How GD&T Form Tolerances Affect Hole and Shaft Fits

The relatively new and sometimes confusing world of Geometric Dimensioning and Tolerancing (GD&T) opens up a whole new world of ways ...
• ### Workholding Technology Pt. 4: Locating of Workpieces with External Forces Applied

Introduction Another important consideration to take into account when trying to locate work pieces is the role external forces will play ...
• ### Workholding Technology Pt. 3: Locating with the Intention of Avoiding Burrs

Introduction One of the problems faced when locating on jigs and fixtures is the presence of burrs and foreign material on ...
• ### Compressed Air Systems: Pipe Diameter Sizing

Diameter for factory-wide air distribution plumbing is sized with increased future demands in anticipation. Additionally, the pipes accumulate scales and specks ...
• ### Compressed Air Systems: Distribution Plumbing Design

On factory floors, compressed air is often perceived as free, therefore, compressed air plumbing design may be somewhat neglected. However, the ...
• ### MechMinutes Video: Intro to Linear Motion Part 3

INTRO TO LINEAR GUIDES – ACCURACY GRADES #3 | MECH MINUTES | MISUMI USA In today’s session of “Mech Minutes”, we ...
• ### It’s Spring Time Part 4: Energy Absorption, Natural Frequency, and The Surging Phenomenon

In our last post on the spring series, we examine energy absorption, natural frequency, and the surging phenomenon. When you apply ...
• ### It’s Spring Time Part 3: Load-Deflection Relationships

We’ve been introduced to materials and characteristics of springs. Let’s dive into helical springs more deeply specifically compression and extension springs. ...
• ### It’s Spring Time Part 2: Types of Springs

As we have been introduced to springs, as promised, it is time to dive into the types of spring shapes and ...

1. ### Workholding: Locating While Avoiding Burrs | MISUMI USA Blog

September 6, 2016 at 2:11 pm

[…] Part 4 of our Workholding Technology series, we will examine the considerations needed for locating of workpieces with external forces […]