1. A method of cumulative buffering for surface imaging, the method comprising: representing a workpiece model using a plurality of layer models; displaying a display image of the workpiece model based on a previous update, the previous update comprising a previous display image and one or more previous subtractions made to the previous display image; buffering a display image saved from the previous update; subtracting a model representing a tool from the buffered display image to generate a subtracted display image comprising the one or more previous subtractions and a new subtraction, the new subtraction representing a top surface area of a portion of the buffered display image that is subtracted; displaying the subtracted display image at a fixed angle on the display by subtracting the new subtraction from the buffered display image and drawing a representation of a surface area of the buffered display image located underneath the top surface area without clearing the buffered display image from the display; wherein the subtracted display image comprises a first image portion representing a subtraction made to an upper layer of the plurality of layer models and further comprising a second image portion representing a subtraction made to a lower layer of the plurality of layer models; wherein the first image portion has at least one visual characteristic that is different from a visual characteristic of the second image portion; and saving the subtracted display image as the previous update such that any subsequent subtractions are performed on the subtracted display image.