To set kerf compensation you basically cut a line and measure the kerf width.
You do this for each material / consumable combination you use.
In sheetcam you create a jet tool for each material / consumable / speed combination you use and enter the kerf width for that combination in that tool's settings
Here is a DXF file and explanation on how to set kerf compensation in sheetcam - the file is just a line from (0,0) to (0,2)
basically import the file, create a new jet cutting operation, select the tool that corresponds with the material and consumables you are using, cut the file, measure the kerf, and update the tool kerf width setting
to fine tune kerf compensation very precisely you can cut this interlocking comb shape and adjust kerf compensation to where the male and female parts are exactly the same width
you must flip one of the combs over and compare the fit at the face of the material - the edge and back of the material has a taper - do not include or consider the taper
in the image below the material thickness and edge taper is exaggerated to show how only the face of the two combs fit together when one comb is flipped over - with plasma, typically you end up with parts that are actually slightly larger than the designed shape due to taper as indicated by the lighter colors
if you do not flip one comb over then the edge tapers interfere with and prevent proper engagement
if you wanted two identical combs to fit together including taper you would have to have accurate kerf compensation and then you would have to inset the parts' outlines to the inside by an appropriate amount to eliminate the taper interferance
if one part is not flipped over then the inset distance would have to be greater because there would be more taper interferance - when one part is flipped over they fit tighter together due to their tapers being congruent
in either case - fitting two parts together involves mating inside (concave) curves and corners with outside (convex) curves and corners - and for tight curves and sharp corners no tool can cut all inside and outside curves and corners exactly the same - so tool size (kerf width) must always be considered in designing parts to fit tightly or uniformly together - in this case we are simply gauging how the straight edges fit together - the sharp corners will not actually fit together with full engagement
if you round off the corners and inset the outline to eliminate taper interference then you can test full engagement and axis perpendicularity
blue and purple indicates X and Y axis is perpendicular
red and green indicates X and Y axis is not perpendicular
however it would be better to use large test parts to expose small errors - and you don't need a comb shape to test perpendicularity - a square or rectangle would work better because you could re-use the test material - just always flip one part over to expose the error
