Upvc Frame Extenders

[oldbutnotdead]

Fitting a window in an hole that is 40mm out of true top to bottom & has an arch at the top.
So, have frame extenders for sides and top- question, should I mitre them where they meet or just butt join?
Q2- what's the best blade for cutting pvc in my mitre saw?
TIA

 

[crank39]

Butt them and it never hurts to seal the joint within with silicone.

For cutting PVC in a mitre saw you want a blade suited for cutting non ferrous metal i.e aluminium, I mention aluminum because that's how they'll be advertised and will have lots of teeth, may possibly also state suitable for PVC, here's an example of the look of the blade you need, note the shape of the teeth, this is the magic bit