I am a complete and utter novice when it comes to woodwork (this is in fact my first ever project) so there may be an obvious solution to this, but:
I'm building a TV lift cabinet. I started with the shell of an old oak & hardboard unit. I stripped everything out (shelves, screws & nails, drawers, plinth) and added a lot of pine and MDF to drastically strengthen it and support the TV lift mechanism. This all works, but the TV lift needs another ~100mm of clearance at the top.
I was going to use the same sturdy pine I've been using for supports (47mm x 100mm), however I'm not confident that I could do a decent mitre join to get a perfect 90° (and I'm not sure how to join mitre joins either), and they're too thick to do a dovetail join. They also need to be reasonably sturdy; although they're not structural, they do need to support a 20mm hardwood top (either sapele, walnut or oak).
I'm also not sure how best to attach this wooden rectangle (assuming that's the best solution) to my 'structural top' - this is a sheet of 19mm MDF with a hole cut into the middle for the TV to pop up through. For reference:
I've debated using wood screws up from underneath (although this will be tricky in a couple of spots), and/or glue, but I've not had much luck with No More Nails, and as I said it does need to support a hardwood top (with will be 1240mm x 480mm).
Any suggestions would be gratefully received - I've been winging it thus far.