What is a DTI good for?
There are many times when you want to know if two points are on the same axis. For example, when truing a vise, you want to know when the right top corner of the fixed jaw is at the same Y-axis location as the left top corner. When these corners are at the same Y value, the vise is parallel to the X-axis. In a similar fashion you can verify that your spindle is perpendicular to the Z-axis. Used in conjunction with a DRO, the DTI can tell you when you have precisely touched down on a surface. Then the DRO tells you the distance. You can trust the DTI when it reads zero. These DTIs are also used to measure runout. The DTI is brought up to the side of a cylinder that can rotate. The DTI is then zeroed. As the cylinder is turned, you watch the DTI for a maximum positive and a maximum negative reading. This maximum swing is the Total Indicated Runout (TIR) and tells you how far off the center of the cylinder is from the center of rotation. If the cylinder is held in a 4-jaw chuck, it is a s
