newbie basic miter question


I have an inexpensive ryobi miter saw that I bought just to do straight chopping when I was making a lot of crates. I just butted the cleats, and didn't really bother with miters. The saw table will rotate 45 deg. in either direction, but the blade tilts 45 deg. in only one direction (meaning it's not a so-called compound miter saw I guess?)
I would like to do some baseboard molding. Nothing fancy, just 45 deg. angles inside and outside.
So say, looking from the top down, the inside angle is going to look like this /_________\ where the back edge line to the wall is exactly six feet.
With one outside angle, it looks like this /___________/ where the back edge point to front edge point is also six feet, and so on.
How do I apply the 1 to 1 square root formula (1.414) to a baseboard that is, say 3 1/4 tall by 1 1/4 thick, to give me the exact over or under six foot measurement at the angle? Or should I just be using some kind of folding bevel or miter tool? Something cheap I can get at the BORG? If so, what?
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First, you don't miter the inside corner, just the outside corners. You want to cope the inside corners Here is an article on installing moldings: http://doityourself.com/info/h2molding.htm

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When making a 45 degree cut, the longer edge will extend 1.414 * Thickness / 2 further than the short edge. In your drawing, the short side was 6 feet long. There are two 45 degree cuts, adding 1.414 * 1.25 / 2 = 0.884 inches to each end, so the total length ends up being 6' 1.77" on the outside.
The much easier way to do this is to cut one side at 45 degrees and just mark exactly 6' on the back of the board (or better yet, hold the board up to the wall and mark the length EXACTLY). Then cut from the front side being very conservative and leaving yourself some extra length. Then flip the board over and see how close you got to the pencil line. Flip it back to the front side and cut off a little more. Repeat until you get to the exact correct length on the back.
Also, assuming you have a 10" miter saw (and it IS compound if the blade bevels, even in only one direction), you should be able to stand the molding up on edge and, therefore, only have to rotate the table, not change the bevel. You should always keep the front side of the molding facing outwards (towards you), since there will likely be some chipout on the back. If you'd prefer to keep the board flat and tilt the blade to 45 degrees, you should make all of your cuts with the outside facing up, again to isolate chipout to the back side.
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WRONG. When making a 45-degree cut, the longer edge is longer than the shorter edge by exacly the thickness of the board. In his drawing with two 45 degree cuts on a 1.25" board 6' long, the total length will be 6' + (2 * 1.25) 74.5" on the outside.
--
Regards,
Doug Miller (alphageek at milmac dot com)
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Yes; I feel like an idiot (Luckily, not a first for me). I apparently needed some coffee.
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