b'\x1b\x1a\x19 \x1f\x18\x1d\x17\x16Ask the Grinding DocUP-GRINDING VS. DOWN-GRINDINGBy Jeffrey Badger between up-grinding (also calledIn your situation, however, your anti-directional) and down-grindingworkpiece is moving almost as fast D ear Doc: I took your course, and(also called unidirectional). Heresas your wheel, 31.4 m/s versus 42.4 you said that in 99% of grindingwhy. m/s. (See the figure.) Remember, we operations theres no significant dif- Imagine youre a single grit oncare about the relative speed, or the ference between up-grinding andthe wheel. As the wheel plungesspeed differential. If youre going down-grinding. But I think that ourinto the workpiece, you will carveanti-directionally, the speed differ-case falls in that 1%. Due to centrif- out a chip. If the wheel is movingential is 73.8 m/s (42.4 + 31.4). If uni-ugal expansion, we have to cylindri- fast, you will carve out a thin chip. Ifdirectionally, its 11 m/s (42.4 - 31.4). cal-plunge-grind our workpiece atthe wheel is moving slowly, you willThats a huge difference. If youre the speed it runs in its actual appli- carve out a thicker chip. grinding unidirectionally, thats akin cation, which is 3,000 rpm. Our ma- What we care about is how fastto grinding with a wheel speed of 11 chine is set up to go unidirectional.the wheel is moving relative to them/s. Thats lowand will give you Will that be a problem? Our work- workpiece. In the vast majority oflarger chip thickness, more wheel piece is 200 mm in diameter, andcases, the wheel is moving so muchwear and a rougher surface finish. If our wheel is 450 mm in diameterfaster than the workpiece (say, 500you go anti-directionally, thats akin running at 1,800 rpm. times faster) that we just ignore theto grinding with a wheel speed of The Doc replies: Yes, this wouldvelocity of the workpiece. Theoreti- 73.8 m/s. That gives a smaller chip be one of the rare cases in whichcally, we are in error. But an error ofthickness and (usually but not al-therewillbeabigdifference0.2% is trivial, and we ignore it. ways) less wheel wear, more heat In most cases, the difference between up-grinding and down-grinding is trivial. But if your workpiece surface velocity is very high, you may have to think harder about whether to go with up-grinding or down-grinding.J. Badger16SEPTEMBER 2022 GrindingDoc.indd 16 8/16/22 11:36 AM'