Exactly, which is why you practice on a few offcuts. If you've got a kids compass, then you could measure the angle and half it, and there are gadgets that do it for out, but sometimes, a few test custs are the quickest way. You can use any old piece of wood, rather than waste the mouldings.
get it fixed together so its stable and aligned, slap some 2 pack woodfiller in the gappy bits, sand flat and paint. The only thing that will possibly go wrong after that is you will get a hairline crack along the joint.
Had a go fitting the trim and it turned out alright. Both lengths were bowing:
Got the corner joints in:
Panel pinned them in. Then worked at the 2 external corners. I tried to sort the bow by pulling it in with g clamps and adding a mending plate and then sliding the moulding in and panel pinning it down. Of course the bow wasn't sorted and so I had to take off the longer lengths and re-attach to get them flush.
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local