Parts Undersized

I have a problem with plasma cut parts being undersized. I believe it may be due to the offset I am selecting in Sheetcam. I normally select inside offset so the lead in and lead out occurs on the scrap material and not the part.

Today I cut a sprocket from 1/4" mild steel that also contained an 8"circle cut out of the middle. The sprocket teeth were too small and the hole in the middle was approximately .100" or 2.5 mm too small also. I was able to salvage the part with some grinding and filing.

Is there an explanation of what inside, outside and no offset does? I couldn’t find one. If offset selection isn’t the issue, what could it be?

I’m using a Hypertherm Powermax 65 set at 45 amps with 45 amp nozzle. The kerf used in sheetcam for this tool was .066". 137 volts and 48 ipm.

The offset is a reflection of the plasma torch’s flame width. An inside offset will offset the cut to the inside of the cut so that the edge of the cut will be even with the desired cut location. Similarly an outside offset will do the same thing, just on the opposite side of the desired cut line. A no offset cut will put the center of the plasma kerf right on the desired cut line. In your example of the sprocket, your kerf width setting may be a little too small. Keep in mind that the kerf width will vary depending on the condition of your consumables. Also the teeth should be an outside offset, also keeping the leadin in scrap material.
Hope that makes things a little clearer for ;you, Steve