How flexible should my prints be?

I have read that 2mm is a good thickness, but even that has an unexpected softness. I have had my machine since last week and even the build pads on my workbench have not gone hard. Over here in England we say, sun, what sun? Should I be setting up a UV lightbox to assist the curing? I wondered if the UV boxes they use to harden nail varnish would do, although they have a 3 minute timer. I do not think there is anything wrong with the machine because I am getting crisp detail. Roger