Out of Roundness on Cold Finished Steel Products
Let us first understand that it is not sufficient just to measure the diameter of the shaft in different places with a micrometer, with the difference in readings representing out of roundness. There will be consequences to this; the most being it can affect the fit between components (ie: a bearing on a shaft). To accomplish accurate out of roundness readings, the v-block is the most widely affordable and accepted for shop purposes. This technique is done by placing the shaft in a v-block, then rotating it while in contact with a dial indicator. Understand that this three point method is influenced by the number of lobes and the angle of the v-block.
Methods of Measuring
Since we know the angle of the v-block will influence the out of roundness readings, Northlake keeps multiple v-blocks on hand for checking the different diameters of shafting we produce. To check out of roundness using v-blocks there are two methods. The first method is to place the bar stock in two v-blocks which will usually be at an even distance from center. While rotating the piece it will move the dial indicator. Be careful on this method as you are only using two supports, and with long length + small diameter bars, you will get a wobble. The second method, and preferred by Northlake, is to invert the v-block and mount the dial indicator on top (see picture). As a result, this is more efficient and we can check material in process to make adjustments as needed.
Causes and Solutions
Now that we know how to check roundness, lets look at the causes. The material in hot roll form will be the first indicator to out of roundness. Here at Northlake, we work diligently with our suppliers to get the best product available for production. Next we look at what’s going on in process with our centerless grinders. If we happen to incur out of roundness, this will generally point to several machine issues that require attention. Some examples include the angle of the regulating wheel, proper coolant flow & level, grinding wheel composition vs. material being processed. Another very important factor is the height and top angle of the work rest blade. This helps with rounding a shaft. Work rest blades set slightly above center will help out of roundness issues (too much and you might cause chatter). Consequently, work rest blades set below center could cause out of roundness.
In conclusion, there are many factors that require attention. Northlake has the experience and knowledge necessary to accomplish a superior product above the rest. Feel free to contact our sales department with any questions you might have at (P) 888-278-4682.