Large Glossed Window Frame

You pretty much have it covered there, Mick.

Unless you have the specific tools that can help in these sorts of hellish jobs - detail sander, the wee triangular type, etc - then it's a case of jumping in and removing the really bad stuff first with whatever it takes! The paint-filled grooves - I'd run a Stanley blade down each side and try and cut away a triangular sliver of paint from in there - save you hours of sanding. Then get a former/profile that will fit in that groove and wrap 120 grit around it - work it up and down...

Tackle the really nasty thick paint with whatever comes to hand - nice sharp wood chisels work well - at least until they slip and you bleed.

Be happy to use really coarse grade paper - 80 or possibly even lower - and a block to shift large amounts of thick and bumpy paint. Once it's roughly flattened, move up to finer - 180 will probably be ok to prepare for the undercoat.

One extra thing I'd suggest - once it's all sanded and before you apply the primer on that bare wood, give it a good soaking with a decent wood treatment like 5* from Ronseal(?), especially around the contact points with the glass.

Allow to dry - and then prime and stuff.

 

Oh, and take photos to show yer progress

 

Looks to be a right 'pane' to do!

 

@@@tumbleweed@@@

 

Would just add that after the prep, caulk the section where frame meets sill, wall. work into any gaps/cracks and wipe off excess with a damp rag

Don't be tempted to use too much caulk or use the classic 'damp finger' tool to smooth out

You want to maintain that nice 90 degree angle where 2 surfaces meet and the caulk helps to prevent cracks from forming as it remains slightly flexible. Being acrylic/water based, it's overpaintable with all paint types, as opposed to silicon which can be tricky

A 2 part wood filler such as Ronseal is very good for permanent repairs, sands down to a glass like finish (working through several paper grades) is relatively easy to sand sets in 10-15 mins so no delay in your prep and work flow

 

Yep - getting in to these right angles edges can be a pain, and spookily enough a sanding block with a crisp right-angled corner often ain't good enough.

I have a block which I've planed an edge so's it more acute(?) - chust a wee bit more so - and this gets right in there and crisps up the rounded painty things.

For the decor grooves, I'd try folding a piece of coarseish paper around the blade end of a filling knife, and that'll get in there nicely (after having removed what you can with a blade...)

 

If you need to scrape get a proper carbide bladed scraper like this
http://www.screwfix.com/p/harris-heavy-duty-tungsten-carbide-wood-scraper-9/45940
or the sandvic/bahco ones. If the paint is really thick it's not a bad idea to scrape it off if you can, cos it often chips off after you've painted. Watch out for dust etc, quite likely there's lead-based paint on there.