Help w/ Compound Mitre

[Greg DeBacker]

I trying to install some crown molding. There will only be outside corners, and all corners are 45 degrees. The crown molding must be installed upside down so that the 38 degree angle is at the top and the 52 degree angle is at the bottom. It has to be installed upside down so the top can span a certain distance out. I am having a heck of a time getting this.

The corner I'm testing on is exactly 45 degrees, left outside corner. The book I'm working with says 33.85 B and 31.62 M. Because I'm installing upside down do these numbers mean anything in my situation? Should I toss them and just figure it out with trial and error? Should I swap the numbers? Is there a formula I could use to figure this out? I've burned through a lot of rough stock and I'm no closer.

Any help is appreciated.

Greg

[Lenny]

. It has to be installed upside

Have you considered building up the moulding with another piece in order to span the area needed. For instance a piece 1/2 " thick by a width that would allow say a 5/8 " exposed area under the crown. You could mill the exposed area with say a 1/2 " cove bit creating a nice "built up" custom moulding. Just a thought.

[The Davenports]

Use those numbers...do'nt swap them, swap the part...if you would normally put the lower edge of the molding to the fence, put the upper edge to the fence instead.

Mike

[Greg DeBacker]

Thanks everyone for the help. I guess it is because I'm a newbie at this but I got very little out of the information given here. Maybe if we try the old "teach a man to fish..." approach. My book also has a chart for compound mitres. I'm sure every one has seen it. The far left column is labled "Pitch Of Side" and starts at 0 degrees and increments 5 degrees until it gets to 90. What exactly is this refering to? What is "Pitch Of Side"?

If I find the 33.85 B and 31.62 M for standard American moulding on the chart it falls somewhere between the 50 and 55 degree "Pitch Of Side". So it would seem this relates to the 52 degree angle of the top of the moulding. So if I flip the moulding over so the 38 degree angle is the to top would I then locate that on the chart and use those numbers. A 38 degree "Pitch Of Side" works out to be a M of 38.20 and a B of 25.79.

Greg

[Greg DeBacker]

The molding is 1X3. I'm restoring an 1895 Victorian home (my home) and the molding goes under the outside window sills. Back in the 40s or

50s some of the ornamental woodwork was removed and cement/asbestos siding was put on. As some would say, the house was "Eisenhowered". Last summer when I removed the cement siding you could see images of what was removed. The outside windows sills were fairly elaborate. They are made up of a total of 7 pieces of wood with 4 compound miters. They didn't mess around back then. When I was under the house working on some plumbing I found a six inch long piece of crown molding that matched the ghost image left behind when they ripped it off 50 years ago. I sent it to the mill to get it reproduced.

In order to span the distance from the backing board to the edge of the under side of the window sill the molding must be installed upside down. This is what has caused me all of the problems. Once I recalculated the bevel and mitre for this it works. The M of 38.20 and a B of 25.79, as I figured out earlier are the magic numbers. That and also the fact that I now know how to position the trim on the saw (thanks to the web site you mentioned) means that the trim fits. I just finished the first window, and it looks pretty damn cool, if I do say so myself.

I have cut some compund mitres by holding the piece at an angle on the chop saw but this cusotm milled redwood is too expensive for my skill level to be trying that for more than 80 cuts.

Greg