"[news]" wrote in message
...

Hold the coving as if it is already on the ceiling, and then cut!

Did that - joins at the top and bottom but there's a nice 1cm gap in the
middle.

that's because you're doing it wrong !

are you using a standard mite saw ?

I'm using an electric sliding compound mitre saw. There must be some
combination of sloping cut and angle cut that gives the 45 deg needed. Just
haven't found it yet.