TM get on with it. (Although I wouldn't be put out if you just buy the one I made instead
)
Rich nothing to it ..
Pre curve the card before cutting out.( but after marking out the part.)
Plasticard and cardboard have a grain
They'll both flex better in one axis/direction than another. ( grain in a loose sense both )and sand scrap in on direction as well.In the case of plastic you'll get clean shavings in the wrong direction a blade will skid and drag ans make much smaller uneven shavings.
Card the right direction it will sand and cut.the wrong way and the card will bur and occasionally snagg ( especially on thinner widths of card) causing it to fold and bunch. Sanding will causing fluffing and feathering.
The trick is the placement of parts on the card taking the above into account.
Biggest tip is precurve, precurve,precurve,precurve!