Butting two cornices together in a corner

The wiggle room on the left dust cover allows us to draw the two pieces together so no light peeps through the jointRight side board butts tightly against the dust cover of the left side board

  When we are making a corner cornice where two boards come together and wrap around the corner with no returns the most effective joint will not allow any light to peep through.  If the measurements from the corner to as far out as you want the cornice to go are 125″ on the left side and 72″ on the right side we will make the top board (dust cover) 124 1/4″ because it fits inside the left return which is 1/2″ wide plywood and we want a little wiggle room (1/4″) on the right end.  The dust cover on the right side board is the same size as the face board minus 1/2″ because it fits inside the right return.  How do we figure the size of the face boards?  If you look at the photos you will see that the right side board butts up against the dust cover  of the left side board.  Let’s say we have 6″ returns so our dust cover board is 5 1/2″ wide.  If the customer wants the right side cornice to extend 72″ from the corner we would make the face board 72″-5 1/2″ = 66 1/2″.  The face board on the left  side will but up against the finished face of the right side which is 6″ deep.  With the left side measure 125″ from corner to outside left return we will make the face board 125″-6″= 119″.  Notice from the photos there is about 1/4″ between the inside end of the left side dust cover and the wall at the corner.  This is the ‘wiggle room’ we need so the joint is nice and tight.

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