- -  AGRICULTURE CORE CURRICULUM  - -

(CLF2000) Advanced Core Cluster: AGRICULTURAL MECHANICS

   (CLF2100) Unit Title: TOOL USE AND MAINTENANCE AND SHOP SAFETY

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   (CLF2106) Topic: GRINDER AND WHEEL             Time         Year(s)
                      SELECTION                   2 Hours     1 / 2 / 3 / 4
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          Topic Objectives: Upon completion of this lesson, the students
                             wil be able to:
 
          Learning Outcome #:

               (E-2) - Sharpen selected cutting tools correctly, including 
                       chisels, screwdrivers, twist drills, blades, hoes, 
                       axes, knives, scissors, and shears.

          Special Materials and Equipment: A variety of grinder wheels of 
                       different sizes and grits; examples of different 
                       grinders, both hand and bench grinders; different 
                       types of metals and tools that should be used with 
                       each type of grinding wheel would also be useful.

          References: Burke, Stanley R., & Wakeman, T. J. (1990). MODERN
                         AGRICULTURAL MECHANICS (2nd ed.). Danville, IL:
                         Interstate Publishers.
                       Cooper, Elmer L. (1987). AGRICULTURAL MECHANICS:
                         FUNDAMENTALS AND APPLICATIONS. Albany, NY: Delmar
                         Publishers.

          Evaluation: Quiz administered by the instructor. 


TOPIC PRESENTATION: Grinder and Wheel Selection

A. Introduction

   1. A grinder wheel is a wheel made of abrasive grit that is bonded 
       together with a special material to hold the wheel together at high 
       RPMs. Consideration should be given to grinder size, wheel size, and 
       material to be ground when selecting a grinder wheel. 

   2. Grinder wheels are sized according to a variety of factors:

       a. Diameter - The diameter of a wheel to be selected is determined by 
           the size of the grinder it is to be used on. Common grinding 
           wheel diameters include 5," 6," 7," 8," 10," and 12" sizes.

       b. Width - Grinder wheels come in a variety of widths depending on 
           the grinder size and application.
       c. Grit Number - The grit is determined by the size of the pore space 
           between abrasive particles that make up the wheel. The grit 
           number is determined by the material that is to be ground by the 
           wheel. The smaller the grit number, the coarser or rougher the
           surface of the wheel. Grit numbers range from the number 8, which 
           is very coarse, all the way up through 240, which is very fine.

       d. Arbor Hole Size - The arbor hole is the hole in the center of the
           wheel that allows the wheel to be mounted on the grinder axle, or 
           arbor. This hole size is determined by the diameter of the arbor 
           on the grinder to be used. The wheel must fit properly or it may 
           spin out of round and may shatter when used.

       e. Bond - The bond is determined by the material used to hold the 
           abrasives together. The types of bonds commonly used are: 
           vitrified (V), silicate (S), resinold (B), rubber (R), and metal 
           (E). Most wheels are held together with a vitrified bond. 
           Fine-edged tools are sharpened on wheels that are made of silicate 
           bonds. Rubber and resinold bonds are used in making disk grinding 
           wheels and cut-off disks. Metal bond is used for making diamond 
           grinding wheels because it is the strongest.

B. Dressing the Grinder Wheel

   1. The purpose of dressing the grinder wheel is to insure that it rotates 
       true, is free of grooves on the wheel face, and that the spaces 
       between the abrasive particles do not load up with particles of 
       the material being ground.

   2. The dressing tool is a device that removes some of the abrasive 
       particles on the face of the wheel to expose the fresh abrasives 
       below. It is also used to remove grooves and foreign particles 
       from the abrasive surface.

   3. Squaring the wheel is important to insure that the wheel spins true.
       The face of the wheel must be square to the sides after dressing the 
       wheel. This is checked with a square. 

   4. Trueing the wheel is done while the wheel is being dressed so that 
       the wheel is balanced and does not vibrate excessively. If the wheel 
       is not trued, the high speed at which it turns may break the wheel 
       apart.
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         ACTIVITY:
         1. Form a small groove in the face of the grinder wheel to 
             show the students what true is, and then, using a wheel 
             dresser, demonstrate how to properly dress the wheel 
             including removing the groove, squaring the wheel, and 
             checking for true.

         2. Give examples of different tools that need to be sharpened 
             and have the students select the appropriate grinder wheel 
             for the job.
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7/10/91 DLF/RRE/tf


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