Originally Posted by Cartierusm  I thought with VMC you use a fancy, and expensive, fixture holder and it helps set the tool in the mount exactly at the same length? So if you break something you reset it and the tool is perfect? |
Not exactly; the length of the tool has to be measured somewhere.
In a big operation with a proper toolcrib you may have a tool pre-setter which measures the distance from the tool tip to the gauge line on the holder; It is impossible to install the tool at a specific distance accurately enough so it is measured afterwards. Then this measured distance is used to set the offset for that tool in the machine without needing to actually measure it in the machine.
When the tools are not prepared beforehand and measured in a presetter the tool offsets have to be determined with reference to some point in the machine. You can do it almost anyplace but it is probably more convenient to have a fixed reference point as has been discussed.