When you say two ceilings do not have 90 deg. returns I'm assuming you mean that they go up on angle from the horizontal plane.
I have a site that deals with crown mouldings www.installcrown.com to help diy & the pros that don't do this all of the time like I do. Refer to that if you want further advice.
What you need to do is create a transition piece that is shaped like a "pie", that takes to from the spring angle of the crown on the angled ceiling plane. (like the picture below)
Place the crown to the angled ceiling as it sits best seated, typically it won't sit to it's spring angle without ripping the flanges so try to get it so that the top and bottom fits snug with a minimum space.
The corners to the angled ceiling you'll return like a regular 90 corner at a wall (check that with a protractor, so that your miter is 45 or it may be 46 for example)
Now, in a perfect world, the bottom of the return will be level... bzzzz, wrong, typically it will come off the corner on a slight angle... so project that.
Now, place the crown on the angled ceiling at it's spring angle, and project that line down from the bottom of the crown to the intersection of the two lines.
Bisect that. That is will be your transition angle.
The trick here is, that angle is from the ceiling, not the wall like normal crown. So you won't be cutting the crown in position upside down and backwards, but right side up.
Man this is hard to explain... look, I'm doing another one of these on the 4th or 5th of April (I usually get one or two per month) and I'll take some step by step photos and put it on my FAQ page for you.
..and below is a of the pics I got from
of the other crown vaults I've done.
PS> sorry it sounds so difficult, it really isn't... but do get yourself a good protractor to be able to read the angles, for in position I use hte prosite, here is the amazon link:
(I do make a couple of cents on that, but not enough to steer you wrong, I can't do crown without mine)
I hope you can see the full message as I see with the google ads most of the posts are covered up... if you are having any problems just use my crowmn molding forum (don't like to take away from Bob but until this is fixed) use:
for crown questions.
Alter Eagle Construction & Design
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