tOAD AND WORKSHOP by HANDYMAN
Page 45
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Grinding Equipment Part 2
nding for accuracy and finish. 21 speed plays an all important though when referring to wheel should be clearly understood that es not mean spindle r.p.m., but ace speed of the wheel. Therefore. ring to wheel speed, think in terms tin. and for external cylindrical t, a surface speed in the range of /min. is a good yardstick. Speeds increased towards 7,000 ft./min.. :peed is reduced for any reason.
it should be remembered that surface speeds below 5.500 will bring about rapid wheel wear. With internal grinding, the surface speed range is wider. varying from 1.500 to 4,000 It./min.
Certain vehicle repairers use surface grinding equipment, and here the best allround results are obtained at around 4,000 ft./min. As an example of surface speed in relation to revolutions per minute. a 4 in. wheel would need 3.820 r.p.m. to give a surface speed of 4.000 ft./min., a 6 in. wheel would need 2.546 r.p.m. and an 8 in. wheel would need 1,910 r.p.m. to give 4.000 ft./min.
A most important factor in grinding is to maintain wheel speed at all costs. no matter what that speed may be, and the motive power should he capable of maintaining that speed during heavy cutting. Any appreciable drop in surface speed and the wheel can be damaged. plus the fact that frequent trueing up is necessary. Also. the work can be glazed badly. creating further difficulties.
As grinding generates heat, it is important that such heat is dissipated quickly, and a lubricant is necessary to maintain a uniform temperature over the work. For this purpose there are coolants from the range of soluble oils. The danger or undercooling is that (unequal expansion will distort the work. As an example. take a heavy vehicle brake camshaft that has had welding attention and is being ground back to standard. If the coolant failed and grinding continued during the shortage, that shaft could bend and be thrown out of parallel with the bush location on the axle. Ample coolant or lubricant is most important.
There is another cause (s1 trouble, and not a little risk where the speed is too high. and this is often the cause of vibration. which can spoil she work. damage the wheel, and in bad cases can start the wheel face disintegrating. Therefore, grinding machines should be securely mounted, and all moving parts maintained al running clearances.
Where equipment is in full-time use, it is wise to fix a set time each week to give the machine service, with special attention to all mounting or fixing nuts. Clean the machine carefully and use an air line to blow the grit olT, rather than paraffin or cleaning fluids in the area of spindle hearings.