Notes on Machinery’s Handbook
Source: Virtual Machine Shop
Introduction to the Machinery’s Handbook
The Machinery’s Handbook is necessary in any machinist’s toolbox to be referred to on a regular basis. Here is an example of manufacturing a part and the use of the handbook during the machining process.
The Blueprint
Look at this blueprint
The material on the blueprint to be machined is 4130 steel that has been tempered at 800 degrees. Tensile strength needs to be determined to select the appropriate cutting tool. Find the Hardness of the metal, done by a Rockwell C scale tester, to find this information look in the chapter called Properties, Treatment, and Testing of Materials. Look for 4130 steel tempered at 800 degrees, looking at the table, tensile strength is 186,000 Pounds per square inch. (See table 11b page 469) The next thing to do is find the hardness of 4130 on the Rockwell C scale. Note here that the Brinell hardness is 380, to convert Brinell to Rockwell C scale look at in the Hardness Testing section table 1. A 381 Brinell hardness number equals a hardness of 41 RC on the Rockwell C scale. The chose of a cutting tool a coated carbide cutter would be more suitable.
Cutting Speeds and Feeds
Now the machining can begin, at a point, two questions need asking, they are. What should be the feed rate, and RPM for a 3-inch diameter work piece? Look at table 1 in the chapter on Feeds and Speeds in the Machinery’s handbook. See where 4130 under Material AISI/SAE Designation; remember 4130 has Brinell Hardness of 380 BHN that gives a feed rate of .028 per revolution and a speed of 120 feet per minute. Use this formula to determine the correct RPM to use:
RPM= (CSx4)/Dia. or (125x4)/3
RPM= (500)/3
RPM=166
To find feed rate in inches per minute use this formula
Feed=RPM x IPR (inches per revolution)
Feed= 166 x .028 = 4.65 inches per minute.
Finding Major Diameter
Remember the drawing calls for 1-8 UNC-2A thread on this piece. Here is how to go about finding the major diameter, look on table 3 of Unified Screw Threads on page 1744. The class is 2A, the max diameter is .9980 and the minimum diameter is .9930.
Thread Depth and Compound Angle
The material is going to be machined on a conventional engine lathe, next it has to determined how much to feed the material in for a complete thread. Looking back at table 3 in the Unified screw threads chapter to find the pitch diameter, and the table states for a 1-8UNC-2A thread the pitch diameter has to be between .9168 and .91. Take the average value of these two numbers.
(.9168+.91)/2
(1.8268)/2
=.9134
With a major diameter of .990, a feed in rate of, .990-.9134=, .0766 Note here that four things control thread geometry, pitch, major diameter, pitch diameter and tread angle. The minor diameter is a byproduct of these, so a feed of .0776 will produce some minor diameter not shown in table 3.
We are almost ready to machine the thread; however, the compound slide is set to 29 degrees. The question is how many thousands must the compound be moved to achieve the .0766 depth required? To solve a right angle problem, turn to page 91 in the Machinery Handbook, Solution of Right-angled Triangles. The compound slide is set at 29 degrees use the formula:
Side b; angle A
c=b/coos A
Since the distance to dial in is .0766 and the angle of the compound is 29 degrees, .0766 is side b and 29 angles A, use the above formula and plug in the numbers:
c=.0766/cos29
c=.0875
Measuring Over Wires
To measure the thread pitch diameter use three wires, actually these precisely matched ground steel rods fit on the threads as shown on the stretch below.
M
Then a micrometer is used to measure over the wires, with this reading calculations determine the pitch diameter.
From table 3 in the Unified screw threads chapter it states that the pitch diameter has to be between .9168 and .9100. Look at the table on page 1896, Diameters of Wires for Measuring American Standard Threads, of the Machinery’s Handbook for selecting a working diameter of wires for the 1-8 thread. The table states use a wire set of .0700 diameters to .1125 diameters for this thread. This however would take a great deal of calculating to determine what the measurement over wires should be for a given pitch diameter and wire set. Now look on page 1901 of the Machinery’s Handbook, Dimensions over Wires of Given Diameter for Checking Screw Threads of (U.S. Standard) and the V-Form. The table selects a .090 diameter wire, note that this is within the limits of .0700 and .1125. Using all the noted tables a 1-8 thread with a pitch diameter of .9314 will measure from 1.0535 to 1.0806 over three properly placed .090 diameter wires.
Fits
The other callout on the drawing is for a 2.00 Class RC7 fir. Find table 8a American National Standard Running and Sliding Fits page 659 of the Machinery’s Handbook. For a shaft of 2-inch diameter, the tolerance is from -5.8 to -4 thousands of an inch. Therefore, the diameter must be between
2.-.0058=1.9942 minimum
2-.004=1.9960 maximum
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