Skip Navigation

Course 726 - Introduction to Machine Guarding

1    2    3    4    5    6    Course Homepage     Final Exam      Contact Instructor     Website Homepage
Safety guides and audits to make your job as a safety professional easier

Methods of Machine Safeguarding - Guards

Introduction

There are many ways to safeguard machines. The type of operation, size or shape of stock, method of handling, physical layout of the work area, type of material, and production requirements or limitations will help to determine the appropriate safeguarding method for the individual machine.

As a general rule, power transmission apparatus is best protected by fixed guards that enclose the danger areas. For hazards at the point of operation, where moving parts actually perform work on stock, several kinds of safeguarding may be possible. One must always choose the most effective and practical means available.

Five General Classifications of Safeguards

We can group safeguards under five general classifications.

  1. Guards
    1. Fixed
    2. Interlocked
    3. Adjustable
    4. Self-adjusting
  2. Devices
    1. Presence Sensing
      1. Photoelectrical (optical)
      2. Radiofrequency (capacitance)
      3. Electromechanical
    2. Pullback
    3. Restraint
    4. Safety Controls
      1. Safety trip control
        1. Pressure-sensitive body bar
        2. Safety tripod
        3. Safety tripwire cable
      2. Two-hand control
      3. Two-hand trip
    5. Gates
      1. Interlocked
      2. Other
  3. Location/Distance
  4. Potential Feeding and Ejection Methods to Improve Safety for the Operator
    1. Automatic feed
    2. Semi-automatic feed
    3. Automatic ejection
    4. Semi-automatic ejection
    5. Robot
  5. Miscellaneous Aids
    1. Awareness barriers
    2. Miscellaneous protective shields
    3. Hand-feeding tools and holding fixtures

Guards

Guards are barriers which prevent access to danger areas. There are four general types of guards:

Fixed Guards

As its name implies, a fixed guard is a permanent part of the machine. It is not dependent upon moving parts to perform its intended function. It may be constructed of sheet metal, screen, wire cloth, bars, plastic, or any other material that is substantial enough to withstand whatever impact it may receive and to endure prolonged use. This guard is usually preferable to all other types because of its relative simplicity and permanence.

Examples of fixed guards

A fixed guard on a power press that completely encloses the point of operation.
A fixed guard on a power press that completely encloses the point of operation. The stock is fed through the side of the guard into the die area, with the scrap stock exiting on the opposite side.
A fixed guard enclosing a belt and pulley system.
A fixed guard enclosing a belt and pulley system. The inspection panel allowing inspection of the system without exposure to the point of operation.
A fixed guard on a power press that completely encloses the point of operation.
A fixed enclosure guards are shown on a bandsaw. These guards protect the operator from the turning wheels and moving saw blade. Normally, the only time for the guards to be opened or removed would be for a blade change or maintenance.

Interlocked Guards

Interlocked barrier guard
Interlocked Barrier Guard: In this picture, the guard cannot be raised while the machine is running, nor can the machine be restarted with the guard in the raised position.

When this type of guard is opened or removed, the tripping mechanism and/or power automatically shuts off or disengages, and the machine cannot cycle or be started until the guard is back in place.

An interlocked guard may use electrical, mechanical, hydraulic, or pneumatic power or any combination of these. Interlocks should not prevent "inching" by remote control if required. Replacing the guard should not automatically restart the machine. To be effective, all movable guards should be interlocked to prevent occupational hazards.

Adjustable Guards

Adjustable guards are useful because they allow flexibility in accommodating various sizes of stock.

Examples of adjustable guards

Adjustable Guard
Adjustable Guard Example
Adjustable Guard
Adjustable Guard Example: This figure shows an adjustable enclosure guard on a bandsaw.

Self-Adjusting Guards

The openings of these barriers are determined by the movement of the stock. As the operator moves the stock into the danger area, the guard is pushed away, providing an opening which is only large enough to admit the stock. After the stock is removed, the guard returns to the rest position. This guard protects the operator by placing a barrier between the danger area and the operator. The guards may be constructed of plastic, metal, or other substantial material. Self-adjusting guards offer different degrees of protection.

The self-adjusting guard protects the operator by placing a barrier between the danger area and the operator.
The self-adjusting guard protects the operator by placing a barrier between the danger area and the operator. As the blade is pulled across the stock, the guard moves up, staying in contact with the stock.
Self-Adjusting Guard on a Jointer
Self-Adjusting Guard on a Jointer: This guard is moved from the cutting head by the stock. After the stock is removed, the guard will return, under spring tension, to the rest position.

Videos

Instructions

Before beginning this quiz, we highly recommend you review the module material. This quiz is designed to allow you to self-check your comprehension of the module content, but only focuses on key concepts and ideas.

Read each question carefully. Select the best answer, even if more than one answer seems possible. When done, click on the "Get Quiz Answers" button. If you do not answer all the questions, you will receive an error message.

Good luck!

1. As a general rule, power transmission apparatus is best protected by which of the following?

2. Each of the following is one of the five general methods for safeguarding machinery, EXCEPT.

3. Which of the following is NOT one of the four types of machine guards.

4. When this type of guard is opened or removed, the tripping mechanism and/or power automatically shuts off or disengages, and the machine cannot cycle or be started until the guard is back in place.

5. This guard is usually preferable to all other types because of its relative simplicity and permanence.


Have a great day!

Important! You will receive an "error" message unless all questions are answered.