Some people don't like my method, some don't like the small blocks, but I'll pass this on to you anyway.
Instead of just a series of short blocks attached to the wall at intervals, I like to rip 2 x 4's (sometimes 2 x 6's) and run them the whole length.
Of course (considering typical 52/38 crown molding) the 38 degree rip is no problem. You just set the saw to 38 degrees. But the 52 degree will present a challenge. The trick is to spend a few minutes making a jig to add 7 degrees to a 45 cut.
Basically, this is just a 7 degree wedge cut out of the long side of a 2 x 4. Mine is about 18" long, and is glued to an 18" x 6" scrap of VT laminate with an 18" x 1/2" strip of hardwood along the loose edge. Yours will likely vary in both length and width to fit your table saw.
Took about ten minutes to make, and I've used it for years.
- You tilt your blade to 45.
- Set the jig next to the blade.
- Place the saw fence on top of the VT, with the back side of the fence right up against the hardwood strip.
- Lock down the fence... My fence fits pretty tight to the table surface, so it holds the VT snug. If yours doesn't, you may need to use regular thickness laminate. The thing is you want the fence to hold the jig in place so it won't slide.
- Then just run your 2 x through, and you have a 52 degree rip down the length.
Of course you will vary the width of your 2 x, depending upon the size of the molding you're installing. The tip here is to make the long side of your 2 x about 1/4" shorter than the back side of the molding.
This keeps the 2 x just shy of the back of the molding when it's up on the wall, allowing for a little adjustment in tilt, and it also keeps the 2 x from bulging the molding out anywhere.
I like this setup for two reasons.
One, I don't have to make certain each and every small backer block is well nailed to either a stud or a rafter/truss (sometimes they are not in the same place, leaving either the top or the bottom of the backer block floating)
Secondly, the obvious... I can nail the molding absolutely anywhere I choose, without having to be sure to hit a small block that I usually can't see, and perhaps forgot to mark on both the wall and the ceiling.
The jig may sound like a hassle to make, but it is no harder than the jig you made for your upside down cuts.
***********************************
The drawings below show a very clear picture of how this method gives you solid mounting on both the wall and the ceiling while, as a bonus, giving you a "clipped" 90 degree corner at the wall/ceiling intersection. And, unlike the 45 degree rips I used to make, this one gives you the same angle the crown molding will assume.... just in case you need to add some glue behind the crown to cheat a little. There is a parallel surface running the full length of the molding, and glue will join the two anywhere you choose. (For instance, at a scarf joint? :thumbsup: )
**********************
The last pic shows a Backer ripped from a 2 x 6 for larger Crown Molding. (And, of course, this could be ripped from any size 2 x you choose, depending upon how large your crown is.)