Practical Treatise on Milling and Milling Machines/Chapter 3

by Brown & Sharpe Mfg. Co.

chapter iii

Erection and Care of Machine

Erection. A machine should be placed upon a level, and, if possible, a solid floor or foundation. If the foundation is not firm, undue vibrations will exist and possibly impair its accuracy and durability. Either stone or concrete makes an excellent foundation for the larger sizes. Neither of these can be used, however, when it is desired to place a machine above the ground floor of a building, and it is best, in this case, to locate it directly over a beam; not in the middle of a bay.

Ordinary wooden shingles are commonly used in leveling a machine. When the exact position has been determined, the fastening screws or bolts should be screwed down until nearly tight. A spirit level should then be used to test the top of the table, both longitudinally and transversely. If the machine is too low at any corner, drive a shingle under the base at this point to bring it up. When the table is found to be level in every direction, the nuts, or bolts, should be brought up solidly. It is well, even after tightening the bolts, to test the surface of the table once more, as this tightening sometimes throws the machine out of level again.

Counter-shaft. Putting up the counter-shaft, when one is employed, is usually the first operation in installing a machine. It is generally placed directly over cone drive machines because of the interference of the driving belt with the upper part of the frame if it is located very far at either side. With constant speed drive machines, it is not necessary to place the counter-shaft directly overhead. It may be placed diagonally as long as the belt does not interfere with the overhanging arm when it is pushed back.

The counter-shaft should be level and accurately aligned paralledl with the main, or driving, shaft. Where the beams are not uniform enough to bring the stringers to which the counter-shaft hangers are attached level, it will be necessary to shim between the feet of the hangers and the stringers to make the shaft level. The holes in the feet of the hangers are usually in the form of slots, which allow the hangers to be slightly adjusted when aligning the counter-shaft with

the driving shaft. In leveling and aligning the counter-shaft, it is the practice to insert the bare shaft in its boxes and take measurements from it. It is afterward removed, the pulleys put on and then replaced in its bearings. When the hangers are securely tightened, the shaft should revolve freely. About an eighth of an inch end play is desirable on a counter-shaft. This can be obtained when placing the hangers.

Fig. 2 The shipper handles are most convenient when they come within easy reach from the left front side of the machine, as this is the position commonly taken by the workman to watch the operation.

Counter-shaft bearings are lubricated in various ways. In our particular type the oil is raised from reservoirs in each hanger by means of rope wicks as shown in Fig. 2.

As a rule it is not necessary to draw off and replace the oil in counter-shaft reservoirs at very frequent intervals if a good machinery oil is used. If the reservoirs are thoroughly cleaned and filled with fresh oil once every year or so they rarely need much attention. It is good practice, however, to put in a little oil every three or four months in order to insure maintaining the proper level.

The arrangement of a three-friction pulley counter-shaft is shown in Fig. 1. Its operation is as follows: A movement of the shipper to the right from the position in which it is shown, causes thimble A to spread the friction levers or engage pulley C. Throwing the shipper to the left until thimble A is about central between uplleys C and E, causes thimble B to spread the friction levers or engage pulley D. A further movement of the shipper to the left allows the levers of pulley D to slip over onto the smaller diameter of thimble B, disengaging the clutch o fthis pulley; at the same time thimble A spreads the levers engaging pulley E.

Diameter of Pulley on Driving Shaft. To find the diameter of pulley required on the driving shaft for driving the counter-shaft at a given speed, multiply the required speed of the countershaft in revolutions per minute by the diameter in inches of the pulley on same, and divide the product by the revolutions per minute of driving shaft. If, for instance, the speed of the main shaft in a shop is 200 R. P. M., and it is required to drive a counter-shaft, having a pulley 14 inches in diameter, 320 R. P. M., the diameter of the main shaft pulley is found as follows:

${320{\text{R. P. M.}}\times 14'' \over 200{\text{R. P. M.}}}=22.4''$, diameter of pulley required on main shaft.

when the counter-shaft has two or more pulleys whose speeds differ, a separate calculation is required for each. And when no counter-shaft is used, the calculation is the same as abovce, except that the required speed and diameter of the machine pulley are substituted for the diameter and speed of the counter-shaft pulley.

Importance of Keeping Machine Clean and Well Oiled. Many workmen fail to appreciate the importance of keeping a machine clean and well oiled, and we cannot emphasize this point too strongly. Proper attention to these details influences the accuracy and efficiency of a milling machine and prolongs its life, while neglect to attent to these matters has ruined many a good machine.

Working parts most exposed to dust, dirt or chips, should be frequently cleaned and oiled. Chips should not be allowed to collect upon the surface of the table until they fall over the sides on to the flat bearings on the top of the knee. Care should also be taken to prevent chips and dirt getting between the knee and column, causing scoring of these flat bearings and throwing the knee out of alignment.

Oil tubes and channels many times become clogged with a gummy substance, due to the accumulation of dirt in the oil, and also to decomposition of the lubricant itself. This can be effectively removed without injury to the bearing surfaces by flushing the tubes and channels with gasoline or naphtha. It is well to do this occasionally to insure free passage of oil to the bearings, for if the bearing surfaces, especially cylindrical ones, run dry, they become roughed up, which necessitates taking them apart, and entails considerable work before they can be made to run satisfactorily again.

A machine that has been in active service for a period of a year or two, should be thoroughly cleaned and inspected. To do this, requires that it be taken apart to some extent, as it is impossible to ascertain the condition of some of the more important bearing surfaces in any other way. Also it is the only way in which one can make sure that some of the oil channels that are not easily accessible are not filled up. Only good mechanics who thoroughly understand the construction of the different parts should be permitted to take apart and reassemble a machine, owing to the liability of parts being put together wrongly and alignments imperfectly made, if the work is intrusted to less responsible persons.

Arbors and collars should be kept clean and care exercised that chips do not get into the hole in the spindle or between collars.

Neatness about a machine is usually the mark of a good workman. By assigning definite places to tools and attachments and returning them immediately after using, he is able to know just where to look for any one whenever he wants it. The time required to replace tools in this way is more than offset by the advantage of being able to readily find them again; besides, the tidiness of a machine materially adds to the appearance of a shop.

It is well to remember when applying oil that ordinary bearings can hold only a few drops at a time and that this amount applied at regular and frequent intervals is far more beneficial than a flood of lubricant at irregular periods. It is a good practice to have one man attend to the oiling daily in shops where the machines are used by different workmen.

Kind of Oil. There are so many good machinery oils upon the market that it is hard to specify any one as the best to use for lubricating a milling machine. Any good coal or mineral oil can be used. Never use an animal oil, as it will gum up the bearing surfaces, oil channels and tubes, and have a tendency to retard rather than render easy the movements of the different parts. It might also be said that in buying machinery oil it is always safest to purchase a lubricant of reliable quality instead of experimenting with the less expensive brands. It is cheaper to buy good oil than to run the risk of damage to bearings from overheating or scoring.

Care of Driving Chain on Motor Driven Machines. The care of the driving chain on motor driven machines is important. It should be kept clean, well lubricated and adjusted. To clean a driving chain, remove it and immerse in a bath of kerosene or gasolene. This will loosen up the gum and dirt, and by working the joints while in the bath, foreign matter will come out. Remove the kerosene or gasoline by soaking the chain in a very hot and fairly strong solution of soda and water. Wipe dry and immerse in a bath of warm and quite thick lubricating oil for several hours. This treatment should be applied about every two or three months. A good quality of lubricant that is free from tendency to gum should be used, and a generous quantity applied daily.

The tension of the chain is usually regulated by the adjusting screws in motor bracket. It should run at a tension tha tmight be termed just a little too slack for a leather belt; that is, a slightly greater sag should be allowed.

Adjustments. As bearing surfaces and parts wear, it becomes necessary from time to time to make adjustments, and at all important points convenient means are provided for doing this. Flat bearings are provided with tapered gibs that are easily adjusted, and cylindrical bearings, like those of the spindle, have ready means of taking up wear. It is essential that any adjustment required be promtly

Fig. 3

made, for otherwise the accuracy of the machine is impaired. Furthermore, parts wear much more rapidly as the lost motion becomes greater. By a little examination and adjustment every now and then, the efficiency of a machine can be maintained and its life indefinitely prolonged.

Before proceeding to adjust or take anything apart, it is a good plan to carefully study the principle of construction. Many times this simple precaution will obviate considerable trouble.

The prevailing practice in designing spindle bearings is to have the front bearing on the spindle tapered and the rear bearing straight. On our machines the front bearing is adjusted by loosening check screw N and tightening nut F, Fig. 3. This draws the spindle back into the box, and as the bearing is tapered, the lost motion is taken up. Should it become necessary, after running a machine for a number of years, to obtain more adjustment in this front box, the spindle can be removed and the washers between the spindle collar and the front of the box can be reduced a little in thickness. The adjusting nut F will then take care of the wear for another long period. Nut K should not be disturbed, as this merely holds the box in place. The rear box is split and fits in a taper hole in the frame. It is adjusted by loosening nut L and tightening nut E.

Explanation of Levers, Hand-wheels, etc., on Brown & Sharpe Constant Speed Drive Milling Machines

1. Friction clutch levers for starting and stopping machine.
2. Power feed trip and reverse lever for longitudinal movement of table.
3. Power feed trip lever for transverse movement of saddle.
4. Power feed trip lever for vertical movement of knee.
5. Knob for fine adjustment of spindle.
6. Table feed disconnecting lever.
7. Hand-wheel for transverse movement of table.
8. Hand-wheel for vertical movement of table.
9. Adjustable dog for controlling length of table movement.
10. Adjustable dog for controlling length of knee traverse.
11. Safety dog for preventing table running too far.
12. Safety dog for preventing knee running too far down.
13. Spindle drive tumbler gear lever.
14. Knob for sliding the tumbler gear.
15. Quill gear adjusting lever.
16. Back gear adjusting lever.
17. Spindle reverse lever.
18. Index plate of spindle speeds.
19. Feed drive tumbler gear lever.
20. Knob for sliding the tumbler gear.
21. Levers for moving change gears.
22. Levers for moving change gears.
23. Index plate of table feeds.
24. Raising block for spiral head.
25. Change gears for spiral head.
26. Table stops for preventing longitudinal table movement.
27. Adjustable centre.
28. Centre Rest.
29. Cutter Driver.
30. Chuck.
31. Drawing-in bolt.
32. Chuck collet.
33. Differential indexing centre.
34. Collet.
35. Index plates.
36. Vise.
37. Rapid index pin lever.
38. Fine feed lever.
39. Transverse and vertical feed locking lever.
40. Safety stop for transverse feed.
41. Adjustable dog for transverse feed.

    

    
    

Hand Milling Machine