Range of Usefulness

While in many shops the grinding machine is used only as a finishing tool on parts which require a special surface, or in which greater accuracy is required than is readily reached by the other machine tools, in modern work shops it is one of the large production factors. The work which comes to the grinding machine has usually been rough turned to an approximate diameter, but in many instances it has been found that the grinding machine will completely finish the piece of work from the rough stock at a lesser labor cost, doing its own roughing and finishing. This is especially true when long slender shafts are produced. Automobile crank shafts, for example, are commonly ground from the rough.

Fig. 325. Example of Steady Rests as Employed by Norton Grinding Company Courtesy of Norton Grinding Company, Worcester, Massachusetts

Fig. 325. Example of Steady Rests as Employed by Norton Grinding Company Courtesy of Norton Grinding Company, Worcester, Massachusetts.

Cylindrical Grinding

Producing cylinders of revolution is one of the more common uses to which grinding machines are put. This is usually accomplished by traversing a rotating abrasive wheel in contact with the rotating piece of work, as in Fig. 325. In this operation the rotating wheel can be made to feed along the length of the work by giving the work table a traversing motion along the bed of the machine. Some of the things to be noted in this machine are: (a) Its large wheel spindle with generous journals making it possible to use abrasive wheels large in diameter with broad faces; (b) the abrasive wheel bearing stand giving large spindle bearings and great rigidity; (c) a heavy traversing table with large bearing area upon the bed; (d) the work-supporting rests; and (e) the general massiveness of construction.

Fig. 326. Traverse Markings on Piece of Ground Work

Fig. 326. Traverse Markings on Piece of Ground Work.

Wheel Speed

The peripheral or surface speed of the abrasive wheel is usually held pretty closely to 5500 linear feet per minute. While in some cases a wheel speed of 6500 feet per minute or as

Table XI. Revolutions Per Minute For Various Sizes Of Grinding Wheels To Give Peripheral Speed In Feet Per Minute

Diameter of Wheel

IN INCHE3

4000

4500

r,ooo

5500

0000

G500

1

15,279

17,200

19,099

21,000

22,918

24,850

2

7,639

8,590

9,549

10,500

11,459

12,420

3

5,093

5,725

6,366

7,000

7,639

8,270

4

3,820

4,295

4,775

5,250

5,730

6,205

5

3,056

3,440

3,820

4,200

4,584

4,970

6

2,546

2,865

3,183

3,500

3,820

4,140

7

2,183

2,455

2,728

3,000

3,274

3,550

8

1,910

2,150

2,387

2,635

2,865

3,100

10

1,528

1,720

1,910

2,100

2,292

2,485

12

1,273

1,543

1,592

1,750

1,910

2,070

14

1,091

1,228

1,364

1,500

1,637

1,773

16

955

1,075

1,194

1,314

1,432

1,552

18

849

957

1,061

1,167

1,273

1,380

20

764

860

955

1,050

1,146

1,241

22

694

782

868

952

1,042

1,128

24

637

716

796

876

955

1,035

26

586

661

733

809

879

955

28

546

614

683

749

819

887

30

509

573

637

700

764

827

32

477

537

596

657

716

776

34

449

506

561

618

674

730

36

424

477

531

534

637

689

38

402

453

503

553

603

653

40

382

430

478

525

573

621

42

364

409

455

500

546

591

44

347

391

434

477

521

564

46

332

374

415

456

498

539

48

318

358

397

438

477

517

50

306

344

383

420

459

497

52

294

331

369

404

441

487

54

283

318

354

389

425

459

56

273

307

341

366

410

443

58

264

296

330

354

396

428

60

255

277

319

350

383

414

low as 4500 feet per minute may give good results, wheel speed does not in general practice vary much from the 5500 feet given. Table XI gives wheel speeds used in good practice.