Joining bay window boards

[niall Y]

Hi All,
The idea of using a solid un-joined MDF to cut out an L- shaped window board is OK. in theory. The problem, as I see it would the bull-nose moulding to the front of the board, unless, you omit this detail and keep the front square.
The description of the OP's joint as " Mason;s Mitre".is not quite right. With a true Mason's Mitre, both the boards would remain the same width throughout. The boards would then be butted together, and a bull-nose routed along their front face. Where the cutter leaves a radius at the junction of the boards would then be carved with a sharp chisel to square it off to give the appearance of a mitre - so not really a mitre at all. Niall

 

[ObservantGround28]

why not? essentially your not wasting any wood your just cutting it from the edges of the sheet.

I guess you're technically right. In practice, I'd fail miserably.

 

[Bellyboy]

Imagine if someone actually did this...

I use to do this most of the time. Always did a template out of thin hardboard first and then transplanted onto mdf then cut , planed and bull nosed it. If i had a few to do i found i could alter the hard board template by knifing it and adding bits by layering if it was short in places.

 

[Bristol_Rob]

I'd use dowels or dominos for alignment and jointing plates underneath to hold them in place.

https://www.screwfix.com/p/jointing...PpNXdRBz9KEGpuo_vL0aAhKKEALw_wcB&gclsrc=aw.ds

 

[Limey Lurker]

The smaller run of window board is not confined by a wall on the end so it should be easier to get them to mate properly. I would definitely groove along the entire end of the board though as you've suggested. Thanks for the advice!

If you groove the entire end of the board, then why don't you use a spline, instead of biscuits, and get 100% alignment?