b'\x1b\x1a\x19 \x1f\x18\x1d\x17\x16Ask the Grinding DocINDICATING PLATED WHEELSD ear Doc: We grind hardened steel with platedquickly. situation is unavoidable because you always CBN wheels. When a wheel reaches the end of itsThis life, sometimes only half of it is worn while the otherhave some runout after mounting. If runout is excessive, half appears untouched. Is our supplier selling wheelsa wheel may bang for a long time before wearing away to us that arent round? enough so the entire circumference of the wheel is in TheDocreplies:Probablynot.Yourelikelythe grinding zone. You might reach the end of life for mounting the wheels eccentrically, and they die beforethe portion of the wheel circumference thats in the being broken in fully. action before the other portion even gets a chance to On all grinding wheels, the bore diameter is largergrind. For large-grit wheels, this scenario is unlikely as than the spindle shaft diameter. When mounted, theretheres a lot of radial wear during their lifetimes. For is play between the shaft and bore, which causes runout. small-grit wheels, there is less wear, and using only half a wheel is a bigger risk.Whats the solution? Get a piece of wood, a rubber mallet and a dial gauge. Then, mount the gauge on the machined metal rim that is on most plated wheels. Next, mark the runout high point and tap the mallet, with the wood acting as a cushion, to tap away the runout.It usually takes me 30 taps before the runout is reasonable, but you might achieve this with significantly fewer taps.Its tough to say how much runout is acceptable. Ive seen people get it as low as 2 to 3 m (0.00008" to 0.00012"), and Ive seen people tap like mad for 30 minutes J. Badger only to get it to 15 m (0.00059"). It dependsA lot of play between a grinding wheel and shaft can result in using only half a wheel. on your tolerances, the age of a machine, the condition of a shaft and how talented If you dress a wheel, this runout isnt a problem.you are. Regardless, lower is better.Dressing knocks off the high points, creating a wheelThis philosophy is also true with rotary diamond shape concentric to the axis of rotation. dressing tools. Actually, its even more important in that But plated wheels arent dressed. Therefore, thecase because those tools can be on grinding wheels high point on a freshly mounted eccentric wheel bangsfor years and can take months to finally wear away for against a workpiece. Gradually, more and more of thefull-circumference contact.wheel circumference acts on the workpiece until theTry it. You might find that your wheel life suddenly entire wheel circumference is being used. (See thedoubled or more.CTEfigure.)Ive had customers argue that they have perfect tolerances and, accordingly, no runout. Dont buy it.about the authorAll wheels and shafts are required to have some play.Jeffrey Badger, Ph.D., is an indepen-An H6 tolerance on a 37.5 mm (1.48") bore is +0/-16dent grinding consultant. His three-m (0.0006"). When a wheel is mounted poorly, thats atday High Intensity Grinding Course will least 16 m of runout. Add to that the out-of-tolerancebe held June 8-10 in Amsterdam. For state of a beat-up shaft, and runout can increasemore information, visit www.TheGrindingDoc.com.22MAY 2020GrindingDoc.indd 22 4/17/20 4:12 PM'