Machinery's Handbook, 31st Edition
HONING PROCESS 1337 quality of the finish desired. In general, the harder the material to be honed, the lower the speed. Interrupted bores are usually honed at faster speeds than plain bores. Formulas for Rotative Speeds.— Empirical formulas for determining rotative speeds for honing have been developed by the Micromatic Hone Corp. These formulas take into consideration the type of material being honed, its hardness and its surface characteris- tics; the abrasive area; and the type of surface pattern and degree of surface roughness desired. Because of the wide variations in material characteristics, abrasives available, and types of finishes specified, these formulas should be considered as a guide only in determining which of the available speeds (pulley or gear combinations) should be used for any particular application. The formula for rotative speed, S , in surface feet per minute is: S W N K D # # = The formula for rotative speed in revolutions per minute is: W N R R.P.M # = where, K and R are factors taken from the table on the following page, D is the diameter of the bore in inches, W is the width of the abrasive stone or stock in inches, and N is the number of stones. Although the actual speed of the abrasive is the resultant of both the rotative speed and the reciprocation speed, this latter quantity is seldom solved for or used. The reciprocation speed is not determined empirically but by testing under operating conditions. Changing the reciprocation speed affects the dressing action of the abrasive stones, therefore, the reciprocation speed is adjusted to provide for a desired surface finish which is usually a well lubricated bearing surface that will not scuff. Table of Factors for Use in Rotative Speed Formulas
Hardness b Medium
Soft
Hard
Factors
Character of Surface a Base Metal
Material Cast Iron
K
R
K
R
K
R
230 190 300 230 420
110 80 150 110 200 150
420 300 570 420 760 570
80 60
300 230 420 300 570 420
60 50 80 60
Steel
Cast Iron
110 80 150 110
Dressing Surface
Steel
Cast Iron
110 80
Severe Dressing
Steel 300 a The character of the surface is classified according to its effect on the abrasive; Base Metal being a honed, ground or fine bored section that has little dressing action on the grit; Dressing Surface being a rough bored, reamed or broached surface or any surface broken by cross holes or ports; Severe Dressing being a surface interrupted by keyways, undercuts or burrs that dress the stones severely. If over half of the stock is to be removed after the surface is cleaned up, the speed should be computed using the Base Metal factors for K and R . b Hardness designations of soft, medium, and hard cover the following ranges on the Rockwell C hardness scale, respectively: 15 to 45, 45 to 60, and 60 to 70. Abrasive Stones for Honing.— Honing stones consist of aluminum oxide, silicon car bide, CBN or diamond abrasive grits, held together in stick form by a vitrified clay, resi noid or metal bond. CBN metal-bond stones are particularly suitable and widely used for honing. The grain and grade of abrasive to be used in any particular honing operation depend upon the quality of finish desired, the amount of stock to be removed, the material being honed and other factors. The following general rules may be followed in the application of abrasive for honing: 1) Silicon-carbide abrasive is commonly used for honing cast iron, while aluminum-ox- ide abrasive is generally used on steel; 2) The harder the material being honed, the softer the abrasive stick used; 3) A rapid reciprocating speed will tend to make the abrasive cut
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