Hi Chris,
I must admit to not liking Plasticard never much as the blade has a habit of skipping off and spoiling the work , as said by David scoring lightly and many passes works fine, Although I have needle files, it's just as easy to make your own with dowel and abrasive paper and contact adhesive, I use P120 & the finer grade P180 Hermes paper made in Austria from Axminster tools.
This probably explains why I love working with ply down to 1/64th
Are you window frames anodised aluminium of chrome plate on the real boats ??
Snowing quite well this morning in Kent 
Regards Ray
Edited By Ray Wood 2 on 07/02/2021 11:05:04