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Mike,
I wouldnt count on either the top or the bottom to be square. better to measure the height and depth of the crown and clamp a stop fence to the saw table or fence at the proper dimension to keep the crown standing at the correct angle.
to adjust the cut with the crown standing only the miter angle need be adjusted, if cutting flat, the miter and bevel angles must both be adjusted accordingly. if the joint is gapped because the 2 pieces aren’t level but the miter is good, try shimming the one end of the crown off the saw table to match the out of level angle.
CARP.
Replies
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The top of the CM goes against the fence. Preserving the slight closure at the top or base is not that important at the corners and ends. The CM should be able to twist that small amount without any problems.
*Mike, I agree with CARP I have found that by adjusting the miter angle, say 44.5 deg. helps when the gap is at the bottom and vise versa for gaps at the top. I use this technique when I am cutting crown "upside down and backwards". However most of the time I lay it flat on the table since I have a sliding compound miter saw. Here is where both the bevel and miter angle need to be adjusted in order to fine tune the fit on the saw. The same adjustments may also be achieved with a sharp utility knife and rolling the crown slightly. GOOD LUCK , JOE
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Cutting on the flat -- is the miter setting the same as cutting the crown upright, and the bevel equal to half the crown's "spring"? I'd like to start doing it that way, not sure of the geometry.
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Andrew,
In regard to the mitre and bevel angles when cutting on the flat. For 38 degree crown the mitre angle is 31.6 and the bevel is 33.9 . You can usually just estimate the partial degrees if your saw is accurate, and the bottom or top of the crown facing the fence does'nt matter (just make sure you have the angles set in the correct orientation for your intended cut). This sure makes it a lot easier in tight quarters. For other angles and for crowns with springing angles that are not 38 degrees there is an excellent article in one of Finehomebuildings books,(I think it is the finish carpentry series) that gives you the mathimatical formulas for calculating the correct mitre and bevel angles for any springing angle and also any wall angle. All you need is a calculator with a suare root function. Also most sliding saws come with the tables for 38 and 45 degree crowns which seem to comprise most of the crowns that I install. These tables should be somewhere in the back of the owner's manual. At least my Makita has them.
Hope this info helps you out.
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Andrew, I've got the FHB article somewhere, which I would be glad to fax you. It's good.
I've run a lot of crown, and while formulas are helpful aids, no two pieces of crown are the same, ceilings and walls are not 90 deg to each other, and the framers probably refused to put in blocking, so, be prepared for some tweaking.
*Yes, I'm learning the rule that there are no rules. I achieved peace when I started nailing 2x3's ripped diagonally to the top plates so that I could nail the crown silly wherever I needed to (our walls are thick plaster). Also found i could save a lot of tedious guesswork in the corners by buying a small adjustable protractor! The wall/ceiling joint isn't always 90° either...Sawing the crown propped up is probably safer for my limited understanding of geometry right now.Could you give me the FHB cite? I can receive faxes, but it's tricky. :)
*Andrew, try this:View ImageIm sure you've already seen this table, the one at http://www.deltawoodworking.com/table/charts/moulding.html, but I'll throw it up as well.
*Yes, "throw up" is what comes to mind! Does anyone cut on the flat for stain grade work? I'm sure I'd ruin a lot of moldings. I suppose I have a protractor and a programmable HP... Nah, too nerdy, real carpenters just eyeball it, right?Mike, as for your original Question 2, I don't think you use the bevel at all when cutting propped-up crown. Unless you want to backcut a little? The miter should adjust for excess length at the foot or toe.Can anyone explain succinctly why the crown has to be upsidedown? I decided it's not upsidedown at all, rather I'm standing on the wrong side of the saw. A little easier to understand what's going on if you think about it that way.
*Mike,I like to "sneak up on" the miters using short offcuts. This way you can tweak the miter on the shorts, then cut the actual piece for a perfect fit every time. When I'm working alone on crown, I make a couple of floor to ceiling go sticks as slaves to hold up long lengths while I fiddle with the joints.Jon
*I only have a copy of the article, no other info, except for the author, Stephen Nuding, sidebar by Jim Chestnut. I am way too lazy to look through all the indexes. Try ripping 3/4" ply pieces 18" long with the appropriate angles and about an 1/8th narrower than the flat back of the crown. Nail it in the intersection every couple of feet ( on studs and joists or just into the top plates), and behind any joints. A biscuit or two instead of a miter joint at long shots seem to make for a lot less sanding, plus, the pieces do that satisfying pop into place thing, or, they blow the walls apart.Can still fax.
*Succinctly, the bottom is where you measure the length along the wall, and, mark on the piece you're cutting. How else could you see where to whack it?You can go now, your brain is full.Adding the crowning touch,BB
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Mike,
It sounds like you are cutting your crown on a Dewalt 12" compound chop saw using the traditional upside down and backwards technique. A very long article could easily be written to answer your questions.
I set the surface of the crown which will be touching the wall, flat on the fence for a few reasons. It is usually the longer flat, and consequently easier to hold ; it is the one which the designers of the profile have used to determine the projection of the molding (which on custom moldings often projects so far out as to be nearly un-copable before you ever start); and because almost all crown moldings want to be rocked up the wall to fit properly in the corners. This is because ceilings at corners (especially outside walls framed with 2x6's), are always higher than their corresponding straight runs. And this is because there are a number of studs all nailed together, each miniscule difference in length adding to the previous, resulting in taller corners.
While holding the crown with the wall flat against the fence I draw a line on the fence with a pencil. This is my reference, where all the crown would be positioned before cutting, in a perfect world.
On big jobs, I set the miter angle at exactly 45 degrees and make practice copes both lefts and rights, and use these on each corner to prejudge variations.
On outside corners, I leave the first piece to go up (Usually the last piece coped) longer than necessary, and mark the ceiling and wall where the crown sits, then take it down. I then put up the second piece of the outside corner so that the bottom of it intersects the mark where the bottom of the previously fit piece sat, mark its length at the bottom (or short point), mark the long point (from the line on the ceiling), and before taking it down to cut, mark its intersection on the ceiling so you can then mark the long point on the first piece you put up.
The only reason you need the practice pieces is to see if the miter angle of 45 degrees is acceptable. Let's say your eye says that 46 degrees would give you a better fit than your 45 degree practice pieces. Set the miter angle at 46 degrees. Now cut to your marks by rocking the crown whichever way you have to in order to do it, forgetting about your reference line on the fence.
It is much easier to do than to explain how to do. I wrote an article for FHB a number of years ago which has illustrations, but I can't remember what year as my memory cells took a big hit in the 60's, from which recovery has been decidedly sluggish.
If you are working with large crown, you will also find that the "slight back cut" is indeed far too slight, particularly on coped ends. I automatically do a radical top sideectomy with a power plane on the last 6 feet of the coped ends before even getting up on a ladder. It makes scribing the crown to the ceiling much much quicker and easier, and allows you to rock the coped end far more than without doing so.
Forget you ever heard of a bevel angle.
And never ever forget; YOU CAN ALWAYS BLAME THE FRAMER.
*
While you're at it, could you fax me a copy too? (Pretty please) 914 764-9460.
Since wife has decided crown should be in every room, I've become quite proficient, but would still like to see a decent article on all the nuances.
*Mind full, may i be excused.Thanks for the advice, I'm starting to get a more natural feel for it.
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I have installed a lot of crown- pine, mahog, and
have found that the best way is to use an 18"
scrap with the standard cuts. I lay it flat (use a
compound mitre saw), and check the cope. With
practice, you can figure how many degrees the
angle is off- 1 -1 1/2 usually.Every corner seems
to be different, just like bucksnott billy
said(nice name!) I use a small grinder with 80
grit paper instead of a saw. It takes practice,
but its fast, and you get real accurate. It just
takes practice. G
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Um, could you define "rocking" and "radical top sidectomy"? I'll tell you what "res ipsa loquitor" means...
*I am changing my name, but, I'll always keep my grinder. Indespensible for oh so many things. And you be right, practice, practice, practice. And keep your fingers out of the way.BB
*Ombud, You caught me in two mistakes. "Rocking" should be "rolling" and "top sideectomy" should be "topside ectomy". In other words, change the crown's position on the saw fence by either moving it so it is higher on the saw fence and does not protrude out so far on the saw bed; or vica versa.The topside ectomy is a radical removal of wood on the top of the crown; that part which does not show when the crown is installed (the part which "should" be touching the ceiling.)I'd send you a quick profile, before and after but I'm sneezing pretty regular and don't want to give your computer the virus. Regards, Clampman PSI already know what theother stuff means. Its part of a checklistwritten by the head of OSHA "Respirator location".He obviously doesn't know how to use spell check.
*Oh good, they mean what I guessed. Couldn't figure out whether I was nuts or you were new to the English language. :)
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Two questions for CM experts.1. On the better grades of CM the top has a slight backcut.When cutting upside down etc. is the bottom placed flat against the fence or the top flat angainst the base? It does make a difference. 2. Can you use the bevel adjustment to correct for a slight misalignment when cutting upside down etc? ie a slight opening at the top or bottom of the joint.
*If I'm reading your question right, with a regular mitre saw,the top of the crown moulding is flat against the base of the mitre saw. We use a compound mitre saw, so we tip the saw instead and is easier this way. This way the top of the crown is flat against the back of the table.(facing upward)This is one of those times when it's a hell of a lot easier to show than to tell.With regards to tightening up the joint, I prefer to shave it off by hand, as I'm fitting the second piece. Every corner seems to be just a little different.
*WWW.delta.com used to have a chart for all the miter and bevel angles for crown you might want to check if they still do
*Mike,I wouldnt count on either the top or the bottom to be square. better to measure the height and depth of the crown and clamp a stop fence to the saw table or fence at the proper dimension to keep the crown standing at the correct angle.to adjust the cut with the crown standing only the miter angle need be adjusted, if cutting flat, the miter and bevel angles must both be adjusted accordingly. if the joint is gapped because the 2 pieces aren't level but the miter is good, try shimming the one end of the crown off the saw table to match the out of level angle.CARP.