Table 16-2.--Constant Values for Locating Center of Flange
SOLUTION:
Boltholes
1. Draw a circle with the specified pitch diameter.
From A, at any convenient angle to the pitch diameter
Boltholes
Constant
(AB), draw a line of indefinite length (AC). Adjust the
dividers at any convenient setting and step off nine
3.........
.
.
..
0.866
spaces along line AC. Draw line B9.
4.........
.
.
..
0.7071
2. From points 1, 2, 3, 4, 5, 6, 7, and 8, construct
5.........
.
.
..
0.5 878
lines parallel to B9, which intersect line AB. This
6.........
.
.
..
0.5
procedure divides line AB into nine equal parts. The
same principle can be used to divide a line of a specified
7.........
.
.
..
0.4338
length into any number of equal parts.
8.........
.
.
..
0.3827
3. With distance AB as a radius, scribe arcs from
9.........
.
.
..
0.342
A and B, establishing point D. From D, draw a line that
10 . . . . . . . . .
.
.
..
0.309
passes through 2 (on line AB) to the circumference at
11 . . . . . . . . .
.
.
..
0.2817
E. Distance AE is the pitch chord and the length of arc
12 . . . . . . . . .
.
.
..
0.2588
AE is equal to one-ninth of the pitch circle.
13 . . . . . . . . .
.
.
..
0.2394
The principles illustrated in figure 16-7 and
14 . . . . . . . . .
.
.
..
0.2225
discussed in problem III may be used to lay out a flange
15 . . . . . . . . .
.
.
..
0.2079
with any number of holes. The division of line AC is
the variable of the layout. Just set the dividers to a
16 . . . . . . . . .
.
.
..
0.195
convenient distance and step off spaces equal to the
17 . . . . . . . . .
.
.
..
0.184
number of boltholes desired. If you want 13 boltholes,
18 . . . . . . . . .
.
.
..
0.1736
divide line AC into 13 equal spaces. The second space
19 . . . . . . . . .
.
.
..
0.1645
point (2 in fig. 16-7) is al ways used for the construction
20 . . . . . . . . .
.
.
..
0.1564
of line D2'E and the location of point E. If a pitch circle
is difficult to divide into the required number of spaces,
this method can be used to advantage. However, it is a
lengthy construction. The layouts for five- and
seven-hole flanges are easier to develop and have
diameter of 10 inches. From the table, select the
greater accuracy.
constant value for an 1 l-hole flange. The pitch diameter
Developments for four-, six-, eight-, and ten-hole
(10 inches) multiplied by the constant (0.28 17) equals
flanges are relatively simple. To determine the length of
the length of the pitch chord (2.817). Set your dividers
the pitch chord for a four-hole flange, construct two
to measure 2.817 inches, from point to point. Now step
bisectors that intersect at 90-degree angles. For six-hole
off the circumference of the pitch circle to locate the
flanges, the radius of the pitch circle is equal to the
centers of the flange boltholes.
length of the pitch chord. Step off that distance on the
You will find the mathematical method using table
pitch circle to lay out the flange boltholes. For eight- or
16-2 to be a rapid and convenient way to lay out flange
ten-hole flanges, bisect the pitch chords of the four- or
five-hole layouts.
boltholes. However, you should also be able to use the
geometric construction method. You will not always
The exact distance to set dividers for a certain
have a table of constant values available, and some
number of holes on a specified pitch circle can be
problems are not easily solved by the simple
constant value for the desired number of boltholes must
be known. The diameter of the pitch circle multiplied
Boltholes are not the only holes you will have to lay
by the constant value equals the length of the pitch
out. At times, pipe will pass through decks and
chord. The constant value for a specified number of
bulkheads at an angle other than 90. When this
holes is given in table 16-2.
happens, you will need to develop an ellipse. This can
Here is an example of the use of table 16-2. Assume
be done in several ways; however, problem IV
that you need a flange with 11 boltholes and a pitch
illustrates the geometric development.
16-8