stumped! crown moulding calculation

[newman]

the dingo ate him.

[markhoni]

my bet is since he was using a dull blade, that the piece was being pulled out of its nested position by the drag of the teeth.This would cause the edge of the crown that sits against the ceiling to slide toward the back fence as the blade is pulled through the cut. so the start of the cut would be a good miter that would fit to a 90 degree corner, and by the time the blade made it through the end of the cut it would be open in the front.

[markhoni]

I sat the crown on my mitre saw bottom down, bottom up .. every possible combination and I just can't get it to connect at 90 degrees.

Or maybe he just can't get it in his head how to nest the crown properly.

[markhoni]

Actually after reading his original post again, it sounds like the dull blade was pushing the piece sideways away from the blade as he cut, which would form a somewhat concave slice. This would allow the top point of the cut to come together tight, and the bottom to not fit together. or if the crown was rotated to get the top and bottom points to fit, then the center of the cut would be open. It is a lesson that we all should learn that you have to use a very sharp blade on hard woods like maple, or you're going to be fighting your cuts all the way through. I trimmed a house that had hard maple trim throughout. the casing was 4 1/2", very thick, with a bold profile. Base was 7". I got the sharpest blade I could find, and the miters on the casing just would not cut right no matter what I tried. I wound up taking my block plane and sharpening the blade so sharp, it would scare the hairs off the back of my hand, and trued up all the miter cuts. I had to resharpen the blade twice every day because the wood would dull it down that fast. luckily the base board wasn't to bad, and I could cut that without having to touch it up. Later I figured out that if I would have had a SCMS, I could have pushed the miter cuts through the casing instead of having to chop cut it.

[philthegreek]

Whenever I use a new crown profile, the first thing I do is make a nesting jig and test cuts.
Maybe his saw needs to be tuned up. A couple of good bounces in the bed and it's done.

Phil

[tjbnwi]

Probably has a Harbor Freight miter saw;-)

(Phil, I wonder how many will get the joke.

Tom

[newman]

Probably has a Harbor Freight miter saw;-)

(Phil, I wonder how many will get the joke.

Tom

I think Phil's got a couple of those ... :)

[sbebuilders]

It's 3 3/4" rise, 2 3/8" run. Using a Bosch angle finger, spring angle is 150 = 30 degrees. Cabinet is 90 degree angle .. punch it into my Bosch and get the miter/bevel = 26.6/37.8 and I'm off, right?

Has anybody else run into this problem? Any solutions? Am I overlooking something?

Help!!

The miter bevel angle seems to be wrong.

miter/bevel = 26.6/37.8

Shouldn't it be 28.14910° for a 90° corner?
Spring angle should be 32.34744° for 2 3/8 x 3 3/34 inch crown molding.

http://sbebuilders.blogspot.com/2012...ngles-and.html

Sim

JLC-2.jpgJLC-1.jpg