The Pocket Guide to Excellent V-Scoring
FAQ # 5 -- What Tolerances Can Be Held?
Good Question! Most modern CNC V-Scoring Machines are designed to hold at least +/-.002" on all dimensions (X, Y and Z). Machine maintenance, condition, age and operator attention/proficiency can effect tolerances as well as drilling, imaging and laminate stability. But, what makes this question so good is that, when the individual board is de-paneled after assembly, what was once the v-groove, becomes a special kind of edge. That edge is illustrated here...
(Cross-section of .062" FR-4 Panel / 30 Degree Score)
"X" = Programmed in Board Size (‘Y’ & ‘Z’ Dimensions +/- .004")
As column "Z" illustrates, the end result is that the individual boards will measure slightly oversized. The amount is dependent on the material type and the web thickness. This phenomenon is a result of a slight unevenness in the edge at the center of the cross-section, where the boards were separated. This oversized condition usually does not present a problem because, unlike a routed edge, a scored edge is relatively "soft", and will yield to pressure when fitted into a frame or case. If an oversize condition will cause a problem, a simple scaling using the chart above, should yield satisfactory results.
"Score to Fab", is a smart time saver too. Parts that do not otherwise require routing for slots, cutouts or chamfers can be v-scored instead of routed. A light pass with sand paper or equivalent on the edges, makes a smooth and serviceable finish that will rival that of a routed edge, while maintaining the programmed specifications, thereby easing the load on your busy fab area.