Thursday, May 3, 2012

On Crown Moldings (Part Deux)


Let's dig into ye olde mail bag and see what else we have here.

*sounds of rummaging*

Ah, here's something worthwhile from one of my friends around the North Pole:

Mr. Admin,

Whats with those funny cuts? Can't I just cut 45s on the edges of all four pieces of crown and just slap them up there?

LP, North of Tasker


Hi LP, thanks for listening.  Sure you can cut 45s. You could also fire up your chainsaw, spin around ten times, then run in circles while you cut your house to pieces.  The results would be strikingly similar.

Cutting 45s everywhere will leave big gaps at intersections (rarely is there ever a true 90 degrees in a corner).  Crown profiles are complex, which creates all sorts of opportunities for ugly gaps.  On the other hand, there is a methodology to minimize angle cuts while simultaneously using a person's line of site to minimize the exposure of gaps.  Sounds confusing right? Bear with me.

Cutting crown molding will cause even the most seasoned journeyman a minute of pause.  Its always upsidedown in your saw, the cuts require some scribing or handcutting, and on the last piece in the room... you gotta hit it dead nuts.

So what do I mean "last piece in the room"?  Well, the best way to install crown molding is by the method described here from Fine Homebuilding and describes appropriate usage of three types of cuts: 1) butt 2) Miter and 3) Cope. 

Trimming a room with baseboard and a minimum of perfect cuts. By following the numerical sequence, only pieces 2 and 3 require perfect cuts on both ends. The chance of error is reduced by first coping them and then holding them in place to mark their lengths. The copes are planned so that any cracks will be less obvious to people entering the room.
Line of Sight w/ cutting sequence

Now the above sketch shows baseboard cutting sequence, where the entry door to the room breaks up our last cuts (#8 and #9) above.  When dealing with trim at the ceiling level, you don't have this added luxury of the door breaking your piece.  This means you must cut this thing in one shot:

The last cut for an interior of a small dog house.

Every time you end a piece with Butt joint, you must next do a cope cut to close that intersection.
Now that's a clean line
What's a cope cut? Well you can start the cut a number of different ways.  I prefer setting a fence on  my miter saw and putting me piece of crown upside down in the saw, at the appropriate angle of installation.  In my case, i know the horizontal depth of my crown was 2 1/8", so I set a fence there, and rough cut my piece at 45.

Once my piece is cut to length, I then handsaw with a coping saw to waste the wood behind it.


Back cut with coping saw

I know what you're thinking... that looks like s---, dude.  Well, it doesn't matter.  The goal here is to waste the wood behind it, while keeping the show side impeccable (you will notice a trend with this in carpentry).  That way, the complex contours of your elegant piece of crown behind it can pass through smoothly.  If there's one thing I've learned over the years: good builders know when to be clean, and where to be dirty.

Mock up of the pass through

Here's where that sequence of installation (first picture in post) really comes into play.  With the butt piece on the back wall, look at how the finish is along the appropriate line of site:
Piece #2 intersecting with Piece #1, from "Line of Sight" drawing earlier

When looking along Piece #2, you can see almost no gap at all.  If you install your pieces in the correct order, then people who enter the room will see the exact same thing.

If a coped joint opens up, the crack will be obvious when viewed parallel to the uncoped piece and nearly invisible viewed parallel to the coped piece.
Cartoon depiction of same scenario above

Lets reorient ourselves to the back of the room and take a 90 degree turn and crane our necks upwards:

Not *so* bad
Zooming in:
Oh boy
 
Coped joints: The first piece is butted to the wall. The second piece is mitered as for an inside corner, but the mitered end is cut off where it meets the molding face, leaving a negative of the profile that fits perfectly over the butted piece.
Cartoon depiction of this scenario


But notice, we really had to move up on this thing and take one very specific look at the piece.  Its very unlikely that a person in your room will ever get this specific angle on your crown molding.  And keep in mind, this is also 9 feet up in the air!!


Going back to the typical line of site, you simply cannot see the gap this way
Ahhh. That's better.

LP, I hope this explains how not cutting 45s will actually be easier, and works in your favor to hide any gaps that may arise.  Use these methods described above to get down with the crown!

-Admin

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