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I admit it, I’m dumb, but I’m totally confused about mitering crown molding. What’s the purpose of the 22.5º settings on miter saws? In my ignorance I’ve always mitered the stuff by standing it in position between the fence and the bed of the saw and cutting it at 45º. It seems to work fine.
Yesterday I spent quite some time, and several feet of crown molding fooling around on my SCMS with cuts at 22.5º on various axes. No matter how I oriented the stuff, I couldn’t make a useful miter this way. And yesterday, I saw a “helpful hint” sign at Home Depot in the molding aisle which mentioned some other weird angle – 33 point something degrees, if memory serves.
Would someone be kind enough to explain this?
Many thanks.
Replies
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FXDP,
View Image
© 1999-2001
"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it."
Aristotle
*What is the traditional way? I know I'm ignorant here, but when does cutting at 45º and 135º come up in real work, so much so that a special setting appears on saws? And what do you get with 33 point whatever laying the molding flat? I know I'm missing something basic and obvious here. Please bear with me.Is there something wrong with the way I'm making 90º miters -- that is, standing the molding up between the fence and table and cutting at 45º? It seems to work fine.Thanks for the reply, but I'm still puzzled.
*FXDP,
View Image © 1999-2001"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*I didn't mean to imply that there are no 45º miters in real work. I'm just wondering why these settings are always refered to as being for crown molding. It seems they would work whenever a 45º miter is called for, regardless of the material. And I'm still puzzled by the 33 point whatever cut for crown molding laid flat. What does that yield. (By the way, nice looking work!)
*The 33.whaterver number on the miter scale can be combined with a corresponding number on the bevel scale of a compound miter saw to cut certain crown molding while lieing flat on the saw instead of standind up as you mentioned before. Most people I know including myself rarely cut on the flat because you then have to adjust the bevel as well as miter.
*Did you bother to read the instructions that might have come with that scms? All your questions are answered right there. That positive stop has nothing to do with crown. It's a stop like the 90 and 45. There are probably a few others on the guide. Again, your manual book should explain this. If you got it used, locate a cust. service rep and get a reprint. They really do include those things for a reason. It'll explain cutting on the flat. You should get a hold of a table of settings for angles other than 90 also. A must if cutting on the flat. Best of luck.
*The 31&5/8 (miter) and the 33&7/8 (angle) refers to the settings on a compound miter box or sawbuck to cut standard 52 degree x 38 degree crown molding.That is, flat, rather than backwards and upsidedown.As Joseph tried to explain, 22.5 degrees is for splitting a 45 degree angle.......just as 45 degrees splits 90.The stops saves us (and our eyes) time.As Calvin pointed out, read your manual or get a book, or better yet, work with a Master......
*F...Cut a piece of crown your 45 degree way...then lay it flat and adjust the saw to fit the cut...you will see the saw line up on the goofy degree marks. It's just a way to cut super wide crown these days.near the stream,ajAnd like others have said...I just cut it upsidedown and backwards on the fence like you do.
*If you can stand the crown up then do so! But if you have 8" crown to install then the 12" Dewalt won't do it. Then you need the odd angles 'cause you have to lay it down and hope you only have 90 degree corners to work on. Buy extra to fiddle with to get it right.
*Those goofy settings as AJ appropriately called them are all a result of somebody having calculated tricky dihedral angles, which is the angle formed at the intersection of two planes. The dihedral angle of crown moulding springing from the wall at 52° is 112.27°, therefore to mitre the joint line on outside corners (and get a line to cut to with a coping saw for back cutting inside corners,) half that number = 56.135°. Subtract 56.135° from 90° = 33.865°. My saw has a wee mark on the bevel gauge at just under 34°. The mitre angle required for a moulding rising at an angle of 52° from the wall is 57.82°, which results in 31.62° when subtracted from 90°. Most people just find it easier to remove all the calculations and simply rear the stuff up in the saw as they've described, and you've probably been doing. I seldom install crown moulding in rooms, but as a furniture maker I come across similar necessary techniques, and if I can find a simple no maths method, I'll go for it too!!The simple no maths methods quite often don't work for me. I'm sometimes asked to make up oddball things like a truncated pyramid, perhaps as a display base for a piece of sculpture. I've been asked, and made polyhedra that have an odd number of sloping sides, say 3, 5, or 7. At the high end furniture level, the old mastic, or caulk gun trick to fill any gaps in mitred corners normally doesn't go down a treat with clients. Take a simple example as below. Say the sides of the pyramid depicted form an angle of 60° to the baseline. The dihedral angle- b intersection of the planes - as indicated by the arrow pointing from the top point to the corner of the base is 104.48°, and the b true angle of the edges of the triangular pieces b to the b base line as viewed from a point perpendicular to the face is 63.43°. On a table saw (preferably one with a European style sliding cross cut table) to mitre the dihedral angle I'd tilt the blade over to half the dihedral angle, i.e., 52.24° to the saws table- the bevel cut- and set the mitre gauge to cut the true angle of the sides edges to 26.57°. There is a set routine to cutting such parts on a table saw involving flipping the pieces that will form the triangular pyramid sides top to bottom against the mitre gauge, with a resetting of the mitre gauge to the second 26.57° setting available on it, but final cuts are made with the base of the triangle against the mitre fence. All of this has probably just confused the hell out of you, but I thought I'd throw it in to the discussion anyway. Sliante, RJ.
*Sliante,
View Image © 1999-2001"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Interesting Joe that as usual there is more than one way to skin the proverbial cat. Personally I want to know what angle the slopes 'rise' at from the 'baseline' before I get into calculating dihedral angles and their related ilk, which is somewhat bass 'ackwards to your information needs, but results in the same thing really. For instance I want to know what angle cornice (US crown) mouldings rise either from the wall, or from the ceiling before I start inputting figures into my calculator. Actually, nowadays it's an Excel spreadsheet set up for an infinite number of sides, but I can print out the common ones up to 11 sides. I have no Excel skills, but I have friends that do have them, and I tell them what I want to know, and they set it up for me!The information at your website as linked by you earlier is excellent by the by. I haven't looked closely due to lack of time but have you tackled raking mouldings into horizontal mouldings of the same profile, as per applications in house gable ends, cathedral ceilings, and perhaps in furniture cornice mouldings, and other related applications? Sliante, RJ.
*Sgian,
View Image © 1999-2001"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Joe, Let's see if I can explain myself, which wouldn't surprise me if I can't! All I need to know when calculating my earlier described dihedral angles, and 'true' angles is how many sides are required, and how tall the polyhedran is, because from that I can draw a section through one of the sloping side which tells me axactly what angle the side rises from the baseline. If I know this I can do the sums. Let's take that simple (four sided) pyramid I gave as an example. It doesn't matter whether the base length of each side is 300 mm long, or 3 metres long- whatever those measurements are in feet and/or inches. If each side leans inwards at 60° to the base line, then the dihedral angle is b always 104.48°, and the 'true' angle of the edges of each side of the pyramid to the base line is b always 63.43°.Similarly, a five sided pyramid, or more accurately, polyhedran, that has sides leaning in from the baseline at the same 60° results in a b dihedral angle of 118.80°, and my described b 'true' angles of 70.04°. Another example, a seven sided polyhedran leaning inwards at 60° to the baseline results in a b dihedral, 135.86°b 'true angle, 76.46°.The respective degrees that apply to a particular configuration never vary, and ascertaining the slope from the baseline is what determines that precise relationship. As before, I'm not sure I've made much sense in trying to explain myself, and for me, being a very poor mathemetician, a lot of it is pure 'gut' feeling about what seems right, but I suspect with your ability with geometry, trig. and the like, you'll start pounding some numbers to see what I'm whittering on about. The example in your photographs is a little more complex, and I'm not 100% sure without doing the exercise for real, but I i think I could probably work out all the pertinent angles that you had to cut using my method. Sliante, RJ.
*There are two types of crown molding. One has a 45 degree angle on top and bottom bevel, and the other has a 52 degree top, and 38 degree bottom. In order to get the 52 degree and the 38 degree to sit with the bevels flat on the wall/ceiling, you have to cut the oddball angles that are marked on your saw (with the trim flat, of course) Otherwise, the miter may be a perfect fit, but the bevels on the top and bottom of the crown molding ain't sitting flat on the wall/ceiling.Of course, with all the wavy walls I have to deal with, whatever works to make the molding look good is what I end up doing.James DuHamel
*Sgian,
View Image © 1999-2001"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Joe, It seems from reading what you say that we approach these problems from different angles, pun intended, but end up with the same thing. You said "That base length and height may not be the height or base length you want or need." I understand that to mean that you change one or the other, or perhaps both to suit your needs for the job in hand, and recalculate the various requisite angles, readjusting your saw settings accordingly. This sounds like what I do. The more I think about it, the more I'm convinced that we are on the same page but approaching from a different set of thought processes. For instance, I've yet to incorporate into my thinking something that readily makes sense of US carpentry terms such as a 4/12 rise in a roof. I can understand that terminology if I think about it a bit, but to me the important measure has always been the angle something forms to a baseline or some other convenient reference, whether it be a curved Chinese Chippendale style bonnet atop a piece of furniture, or a hipped roof, the latter being something I've never made. I suspect this difference in thinking has much to do with my training as a furniture maker in the UK rather than as a joiner or carpenter in the US. I also, as an example of difference in approach, have no ability to use a framing square, which I've heard is a tool that works rather neatly in Imperial measure, but is a dead loss in the metric system that I have used for decades. Sliante, RJ.
*Sgian,
View Image © 1999-2001"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
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I admit it, Im dumb, but Im totally confused about mitering crown molding. Whats the purpose of the 22.5º settings on miter saws? In my ignorance Ive always mitered the stuff by standing it in position between the fence and the bed of the saw and cutting it at 45º. It seems to work fine.
Yesterday I spent quite some time, and several feet of crown molding fooling around on my SCMS with cuts at 22.5º on various axes. No matter how I oriented the stuff, I couldnt make a useful miter this way. And yesterday, I saw a helpful hint sign at Home Depot in the molding aisle which mentioned some other weird angle 33 point something degrees, if memory serves.
Would someone be kind enough to explain this?
Many thanks.