here is a grinding wheel dressing fixture I machined for a job in the grind shop. its so the guy can redress his grinding wheel by machine not by hand, which is the way he was having to do it before. he could have did it by machine dressing before but he would have had to break his entire setup down to move the regular dressing fixture into place each time he dressed the wheel which is dozens of time through out the job over several days. hand dressing is just what it sounds like. you hold a dressing wheel in your hand and hold it gently against the grinding wheel til you get the desired cleanup on the wheel. the problem is you cant control the bounce from the contact that is happening as you do it. so the end effect is a poor grind finish on a part, or atleast not to spec. this fixture will load between centers just like the part he is grinding does. then he can dress the wheel as often as he wants or needs. if the dressing wheel wears out he just puts a new wheel in the fixture. the fixtures precision is based off the shoulder bolts precision diameter. the bores in the fixture have .0002/.0003 clearence over the bolt dia and the centers machined at each end and within .0002 concintricity to the dia, so its precision. the wheel will wear into round so it does not NEED to be this close BUT the more precision I can make it the less wheel wear will have to occure before the dressing weal will true up and become round. if the dressing wheel spins untrue or out of round as he dresses the grinding wheel is creates the same effect as hand dressing the grinding wheel. so you see what I mean by being precision is better. it will round up much faster then it turn, it will dress the grinding wheel better, hence better finish on the parts. sorry so long, alot of stuff just to grind a wheel.