[Kevan]

I hadn't considered it but never say never. 

There's a couple of tweaks I'd like to do, one of which is fit a 'magnet joint' to the other end of the slider plate so it can be used either way round and therefore fresh sections of the wet'n'dry paper.

Also the roller washers will be modified to sit just over the top edge of the slider plate to prevent it lifting, they will also be eccentric so you can set the roller as close to the slider as you wish.