Dimensioning Rolling Offsets

Figure 13-25 identifies the six measurements required to dimension a rolling offset. There are four length dimensions and two angular dimensions. When a rolling offset is part of a configuration similar to that shown in Figure 13-28, the lengths of the sides of triangle 3 are applied to the dimensions of the isometric box (see Figure 13-25). Notice the SA of triangle 3 in Figure 13-28 is equal to the RUN of the box, the ROLL of the box is equal to the SO of triangle 3, and angle X of triangle 3 is the same as the horizontal angle (HOR°).

Isometric Piping Drawing Rolling Offsets
Figure 13-27. Isometric of rolling offset.
Rolling Offset Pictures

The RISE is determined by subtracting the lower plane elevation from the upper plane elevation. Rolling offsets are typically fabricated using 45° elbows; therefore, the vertical angle will be 45°. Notice the dimension labeled TRAVEL in Figure 13-25. It establishes the true length of the pipe from the upper plane to lower plane across the box. This length is the most difficult to calculate. The values used to determine its length depend on how the pipe enters and exits the isometric box. Figure 13-29 shows the two examples of the ways pipes enter and exit the isometric box.

In example A, the pipe enters and exits the isometric box in the vertical plane. Example B shows the pipe to enter and exit the box in the horizontal plane. When a pipe enters and exits in the vertical direction, a 45° angle is formed between the TRAVEL and a dashed line drawn diagonally across the bottom of the box (hypotenuse of triangle 3). When a pipe enters and exits in the horizontal direction, a 45° angle is formed between the TRAVEL and the RUN of the box. Depending on the type, vertical or horizontal, two different 45° right triangles will be formed. The TRAVEL of the pipe becomes the hypotenuse for either triangle. When solving a right triangle whose angle is 45°, the SA and SO will always be equal. As you can see in example A, the length of the dashed line is equal to the RISE of the box, and in example B, the dashed line drawn diagonally across the end of the

Piping System

box is equal to the RUN of the box. Once the SA and SO lengths of the 45° right triangle are known, Pythagorean's theorem can be used to easily solve the TRAVEL dimension of the pipe. Since 45° is a commonly used angle, Figure 13-18 can also be used.

The chart in Figure 13-30 converts inches into decimals. Multiplication and division of fractions is simplified using decimal equivalents. This chart is extremely helpful when performing mathematical calculations on a calculator that is limited to decimal input only.

Pythagorean Theorem Rolling Offsets

\

DECIMALS OF

A FOOT

/

DECIMALS OF AN

s

0"

1"

2"

3"

4"

5"

6"

r

8"

9"

10"

11"

12"

A® /

INCH

.0000

.0833

.1667

.2500

.3333

.4176

.5000

.5833

.6667

.7500

.8333

.9167

----

1/16"

.0052

.0085

.1719

.2552

.3385

.4219

.5052

.5885

.6719

.7552

.8385

.9219

1/16"

.0625

1/8"

.0104

.0937

.1771

.2604

.3437

.4271

.5104

.5937

.6771

.7604

.8437

.9271

1/ar

.1250

3/16"

.0156

.0990

.1823

.2656

.3490

.4323

.5156

.5990

.6823

.7656

.8490

.9323

3/16"

.1875

1/4"

.0208

.1042

.1875

.2708

.3542

.4375

.5208

.6042

.6875

.7708

.8542

.9375

1/4"

.2500

5/16"

.0260

.1093

.1927

.2760

.3594

.4427

.5260

.6094

.6927

.7760

.8594

.9427

5/16"

.3125

3/8"

.0312

.1146

.1979

.2812

.3646

.4479

.5312

.6146

.6979

.7812

.8646

.9479

3/8"

.3750

7/16T

.0365

.1198

.2031

.2865

.3698

.4531

.5365

.6198

.7031

.7865

.8698

.9531

7/16"

.4375

1/2"

.0417

.1250

.2083

.2917

.3750

.4583

.5417

.6250

.7083

.7917

.8750

.9583

1/2"

.5000

9/16"

.0468

.1302

.2135

.2969

.3802

.4635

.5469

.6302

.7135

.7969

.8802

.9635

9/16"

.5625

5/8"

.0521

.1354

.2187

.3021

.3854

.4687

.5521

.6354

.7187

.8021

.8854

.9687

5/8"

.6250

11/16"

.0573

.1406

.2240

.3073

.3906

.4740

.5573

.6406

.7240

.8073

.8906

.9740

11/16"

.6875

3/4"

.0625

.1458

.2292

.3125

.3958

.4792

.5625

.6458

.7292

.8125

.8958

.9792

3/4"

.7500

13/1 (f

.0677

.1510

.2344

.3177

.4010

.4844

.5677

.6510

.7344

.8177

.9010

.9844

13/16"

.8125

7/8r

.0729

.1562

.2396

.3239

.4062

.4896

.5729

.6564

.7396

.8229

.9062

.9896

7/8"

.8750

15/16"

.0781

.1615

.2448

.3281

.4115

.4948

.5781

.6615

.7448

.8281

.9115

.9948

15/16T

.9375

Figure 13-30. Inch to decimal conversion chart.

226 Pipe Drafting and Design 1. What is an isometric?

CHAPTER 13 REVIEW QUIZ

2. Which three dimensions found in orthographic views are required when drawing an isometric?

3. What is material take-off?

4. T F Pipe 14" and above is drawn double line on an isometric.

5. T F Multiple pipes are drawn on a single sheet of isometric grid vellum.

6. T F All isometrics are drawn to scale to show exact size and pound rating.

7. T F Lengths of pipe should be drawn proportionally on an isometric.

8. T F Symbols should be drawn different sizes to reflect a change in pipe size.

9. What is the preferred direction to draw the north arrow on an isometric?

10. What are placed on isometrics to define the pipe's exact routing through a facility?

11. How are isometric offsets formed?

12. To establish proper visual orientation, the indication of_or_angles are included on all isometric offsets.

13. State Pythagorean's theorem. _

14. What are the names of the three sides of a right triangle?

15. Name the six dimensions required on a rolling offset box.

+3 -1

Responses

  • dahlak
    How to find rolling angle of piping iso?
    2 years ago
  • feorie
    How to find rolling offset in isometric drawing?
    2 years ago
  • jessica anderson
    How to check vertical rolling in isometric drawing?
    2 years ago
  • Rosamunda
    How to find rolling from iso metric drawing?
    2 years ago
  • Frida
    How to find the vertical and horizontal rolling in piping?
    2 years ago
  • Phyllis
    How many types of rolling in piping drawing..?
    2 years ago
  • lisa holzman
    What is definition of pipe rolling in iso drawing?
    2 years ago
  • mildred
    How to calculate a pipe size in an iso drawing?
    2 years ago
  • fatima
    How to calculate the rolling angle in an isometric drawing?
    2 years ago
  • Michela
    How to calculate pipe isometric drawing scale?
    2 years ago
  • tricia
    How to fiend rolling in piping isomatric?
    2 years ago
  • fredrik
    How can understand rolling scale in iso pipe drawing?
    2 years ago
  • alvisa
    How to calculate offset in piping isometrics?
    2 years ago
  • karen
    How many types of rollings are in piping?
    2 years ago
  • Negisti
    How to calculate boxes from a roll?
    2 years ago
  • Sarah
    How to read piping isometric drawing box?
    2 years ago

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