Ovality is a term to used to measure "out of roundness". Ovality designates how close to a perfect circle a bar is at the point being measured. Of all the machines in the process the grinder has the largest impact on ovality.
The grinder fine tunes the product but the turning machine has to get it right first. The pre-straightening machine is also important as the straighter the bar going into the turner the more consistent the roundness and finish coming out.
In the peeling process, the bar moves horizontally thru the turner while carbide cutting tools rotate around the bar on a spindle peeling the bar which leaves a spiral mark which in the industry are called barber poles. The tools in the peeler, peels the rusty surface from the bar similar to the way a knife is used to peel an apple. When there is no overlap the bar receives one wrap or one peel per inch of length. Two wraps per inch gives a rounder better finished bar than one wrap. The more the wraps the better the quality of the bar produced. One has to decrease the thru put speed to get more wraps which means the cost of production increases. There is an obvious trade of between quality and production costs in both the turning machine and the grinder. A commodity bar will have the least number of wraps possible whereas, a custom-engineered bar will have the optimum number of wraps.
If the grinder takes one pass to remove a certain amount of material the finish will not be as good as if it takes two passes. The amount of reduction in a grinder is a function of the grit in the grinding wheel. The rougher the grit, the more the reduction, but the rougher the finish. All things being equal the more the passes in the grinder the better the finish and the better the ovality.