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Discussion Forum

Barrel Vaulted Dormers

| Posted in General Discussion on August 8, 1999 09:20am

*
Jonathan-
In my few years as a framer simplicity has paid great dividends. Try headering the rafters at the dormer opening (main span), and cut plywood radii 1 1/2″ larger than the rough radius you want. Screed the inside of the radius with 2×4 and let them run into the 10/12 ceiling. Screed the 10/12 ceiling, also. If you align the screeds and cut the intersection with a sawzall, the plasterer will have many good things to say about you. 1X4, 1X2 may also work, depending on span.

JRNicholson
SuperCarps
the cleaner framer

P.S. I specialize in framing large (5-20K sf) custom homes in the Houston area. Years back, one had intersecting barrel hallways, some with compound arches. After nearly scratching a hole in my head, I prayed for wisdom. No way could I come up with this tip on my own, its too simple, too perfect. The plasterer (another high end sub) has referred me plenty since then.

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Replies

  1. Gay_Rodge | Aug 09, 1999 03:15am | #18

    *
    Ken is right, Joe. In the conic sections, the cut that is parallel to the opposite side is a parabola. The cuts between perpendicular-to-the-axis and parallel-to-the-opposite-side form ellipses. The cuts between parallel-to-the-opposite-side and parallel-to-the-axis form hyperbolas.

    For a cylinder, a plane intersecting parallel to the the opposite side will form a line when tangent or two lines when chordal. If not parallel, the intersection is either a circle or an ellipse. Imagine extending the cylinder and the plane out to infinity. No matter how slight the angle to the opposite side, the plane will always intersect it, thus closing the ellipse. A parabola never closes although the opposite sides approach - but never reach - being parallel. (An interesting note: a parabola, like a circle, has only one shape)

    If a barrel vault is truly cylindrical, then the intersection with a flat roof forms an ellipse.

  2. Guest_ | Aug 09, 1999 03:41am | #19

    *
    Joe,

    Actually, this little "exhange" we've had here in Breaktime has probably gone too far already. As I've said, you've already made up your mind about this discussion. It doesn't matter to you that the misinformation about parabolas and ellipses that you've put down here will be read by others, young and old.

    I challenge you one more time. Retract your statement about the line of the valley being a parabola.

    IT ISN'T. IT NEVER WAS, AND NEVER WILL BE.

    This isn't a matter of me or FredL providing acceptable proof to you that your information is incorrect. It goes beyond that. I don't have to prove anything to you. What I am talking about is mathematical information that has been known for thousands of years. For you to come into Breaktime, read all over the world, and insist that the line of the valley is a parabola and not an ellipse, is totally irresposible.

    Why not stop by the nearest University in your area, and find the Dept. of Mathematics? Ask them for an opinion about your ideas, and when your meeting is over, you'll feel comfortable about buying me LUNCH.

    1. Guest_ | Aug 09, 1999 05:06am | #20

      *Joe,You're the best!I'm beginning to feel like Vince! I love you man!You definitely have a unique talent..I've never met anyone who could say or write so much as you that means basically nothing. You indeed, have expounded.

      1. Guest_ | Aug 09, 1999 06:30am | #21

        *Joe,I'm glad that your dog finally got a decent lunch after all these years, even if it was at my expense. And I'd wager that it's a reasonably smart dog, capable, with a little training, of understanding the difference between an ellipse and a parabola.

        1. Guest_ | Aug 09, 1999 07:10pm | #22

          *Joe,"Why do I explain to you the difference?"Because it appears that you still believe that the line of the valley is a parabola. Or have you changed your mind?

          1. Guest_ | Aug 10, 1999 02:55am | #23

            *Joe, The only thing that I may possibly CHOKE on are the two lunches that you owe me, as I'm sure that all that you will be willing to pay for is a greasy burger and fries.Post by Joe Fusco, Aug 7, 8:57 p.m., EST "Actually, the valleys are parabolas"Post by Joe Fusco, Aug 7, 11:04 p.m., EST"....wanta go for double or nothing?....go get your math book and look under "conics" for a lucid answer to why this is a parabolic shape and not elliptical"So you tell me Joe, are they still parabolic in your mind or are they elliptical?I'LL LET YOU OFF ON ONE OF THE TWO LUNCHES THAT YOU OWE ME IF YOU WILL JUST ANSWER THAT QUESTION, EVEN IF I HAVE TO CHOKE DOWN A COLD GREASY BURGER. IT WOULD BE WORTH IT TO HEAR YOU ADMIT, FOR THE FIRST TIME IN YOUR LIFE, THAT YOU WERE WRONG!

          2. Guest_ | Aug 10, 1999 05:00am | #24

            *Joe,Proof of what?That the valley line is elliptical ( as has been explained to you by myself and others here in Breaktime) and not parabolic? OR PROOF THAT YOU ARE HARD-HEADED, STUBBORN, AND, DETERMINED NOT TO ADMIT THAT YOU ARE MISINFORMED?Still willing to choke down a fat, cold, greasy burger at the intersection of Hollywood and Vine, after you have had 7 days to draw a crowd, as soon as the light comes on for you.And BTW, I'm not at all intimidated by your style, like some others, so dig in for the long haul, or pay up and get out early.

          3. Guest_ | Aug 10, 1999 06:00am | #25

            *Joe, Ken,How is this helping our friend build his dormers?If you want to have a pissing match, please do it by email.Thanks,Ed. Williams

          4. Guest_ | Aug 10, 1999 06:14am | #26

            *Ed,I couldn't agree more.Only problem is, Joe has a habit of POSTING e-mails he doesn't like for everyone and his brother to see here at Breaktime." E-MAIL FROM A FRIEND" ring a bell?So, if my e-mail is going to end up back here anyway, I may as well put it here in the first place, by my choice, not his.In my opinion, he stepped way over the line with his actions there, and I'm not willing to give him that opportunity with my "personal" mail.

          5. Guest_ | Aug 10, 1999 02:57pm | #27

            *Jonathan,I'd really like to see a sectional view for one of these barrel ceilings, ( A slice through the main part of the dormer, perpendicular to the ridge board where full common rafters occur ). It wouldn't be possible for the barrel to span from wall to wall, or it would protrude through the 8/12 roof, unless it were dropped down considerably below the 8/12 rafters, which from your description, doesn't appear to be the case. Therefore, it seems to me that there would have to be two vaults for each dormer. The bottom sides of the 8/12 rafters would be the first vault, and at the point where they intersect the 3' 9" diameter circle, the second vault ( the barrel ) would begin, resulting in less than a full "half barrel", if you will.If this were the case, the bottom sides of the 8/12 rafters would intersect the 10/12 rafters of the main roof to form an irregular valley, (just as you would get in double pitched roofs), up to the point where the barrel cuts in, and then your elliptical shaped valleys would begin.Could you or perhaps JR Nicholson, FredL, or Ed, or anyone else, comment on this?P.S. Thanks for your post Ed.

          6. Guest_ | Aug 11, 1999 01:59am | #28

            *Joe,I'm doing my best to take Ed Williams advice, to get away from this pissing match, but I just can't help myself.You rag on me for two days about providing "proof" that the valley lines are are not parabolas ( which they aren't), then you turn around and provide ( via your nice drawings) evidence that the valley lines are ellipses, which is what several of us have pointed out to you, and what this pissing match is all about. Where are you coming from?I will compliment you on your excellent CAD drawings. You certainly are a step beyond most, if not all of us in that area here at Breaktime. Also I checked your major axis measurement, ( 70.29") by mathematical methods and it is on the mark.My question about this, and I do not mean anything negative by it; does your CAD software calculatethis measurement, or do you have to work it out using the Pythagorean Theorem, then add it to your drawing? Either way, I'm impressed.

          7. Guest_ | Aug 11, 1999 05:45am | #29

            *Ken,Just trying to keep the peace.Anyone can argue any point to death.I don't do CAD nor do I do math very well for that matter.The guys who built castles back in the 16th century probaly had little if any knowledge of either.Somehow they built what we only dream of.Ed. Williams

  3. JRNichlson | Aug 11, 1999 02:33pm | #30

    *
    Jonathon-
    Ken has a good point. I assume the plan will clarify this. If the barrels are half round you may need a 12/12 pitch at the dormer.

    JRNicholson

  4. Guest_ | Aug 11, 1999 07:48pm | #31

    *
    JR Nicholson,

    Thanks for the response.

    If you make a quick sketch, you'll see that even with a 12/12 pitch, it still wouldn't be possible to put a full barrel ( wall plate to wall plate ) in any of the dormers, unless the barrel were dropped down lower into the room ( which may not be desireable or possible ), so that it could fit under the rafters.

    A second option is the double vault as I described.

    A third option would be to let the ceiling start out level for about a foot or so before beginning the barrel. This would allow for a full barrel, but with a smaller diameter, and certainly, a different appearance.

    Each of the three methods would result in different lines of intersection with the 10/12 main roof, which I'm sure would be a consideration.

    I hope to hear more from you and others, especially Jonathan about this topic. I find it interesting and am curios to hear about what the plans call for.

    1. Guest_ | Aug 13, 1999 10:46am | #32

      *Joe, Thanks for the drawing! Unfortunately guys, I'm missing a detail from my plans (I havent even started framing the house yet.) I'll look for the detail, but from what I can put together, the barrel doesnt need to be a full half round (plate to plate) but rather just an arc. The arc may even be dropped lower than the plate line. The dormers are small tighly fitted package, I'm sure the barrel will be pushed up tighly to the underside of the 2x8 rafters. some additional specs for you to chew on--dormer exterior width (frame only)4'0"--2x4 exterior walls--window 3o56 w/rnd top As you can see the barrel raidius could only be 2 1/4" larger than the window to get a half round barrel (hardly enough room to case the window.) Should I push to keep the half round barrel? (My thinking is that I should.) I'll work on getting the dormer detail posted (probably next week)

      1. Guest_ | Aug 15, 1999 09:03am | #33

        *Joe - Nice use of the old gray matter, and your CAD skills as well. Did you devise this? How about this - you frame these on the ground, like a truss. Maybe even raise the plates one more 2x4 to "barrell out" at just about plate height. - jb

  5. JRNicholson | Aug 16, 1999 12:28am | #34

    *
    Way to go, Joe! -----JRNicholson

    1. EH_ | Aug 16, 1999 07:00am | #35

      *I also am constructing a home with several barrel vault roofs. My question is how can a crown moulding be milled to attach to the exterior of this roof profile. Is there a mathematical way of creating this mould on the flat then sprung into place?

      1. Michael_Leistiko/Builder | Aug 16, 1999 07:13am | #36

        *Joe it seems I remember you saying in past that you use AutoCad for drawings. Just wondering if you use any Add on program to make elevations etc. What release ACad ? Did you take a course or class to get up to speed on ACad. I have ACad but have been using Softplan for 3 years which makes learning to draw with ACad quite a challenge. I know with SP you can get a reading on line length, and with Acad as well. It seems Acad you can even get to 5 decimal place accuracy if wanted. I've found that using cad for builder is much the same benefit Joe has used here. Helps to communicate one way of doing framing, detail, or cross section to get the idea across. Do you do design work with program? Just wondering.

        1. Peter_DeBoer | Aug 18, 1999 06:40am | #37

          *I have framed several of these dormers with the curved dormer ceiling dying into a vaulted ceiling--it's really not that bad. Really, though, you've got to know when to toss out the primadona mathematical attitude and get the job done. Build the dormer roof. I cut the curves from inch and an eighth plywood, fill in the blocks. Tack a piece of 3/4 plywood on the inside over the area where the rooflines will intersect, set flush with the flat vaulted roof. Get up in the dormer with a dreaded strait-edge sharpened to a point and scribe points every two inches on the back of the plywood where the dormer ceiling planes out. Pull down the plywood, connect the dots and cut it out. Put it up, nail it. Get out the sawzall and sculpt the plywood edge to plane--you will take the most off the top, none off the edge. Now you can get paid and go home to tear out your hair for a week of calculating in vain, trying to really, really understand!!

  6. Guest_ | Aug 19, 1999 08:00am | #38

    *
    There you go.......

    Forget the CAD and the calulator and just do it.

    Ed. Williams

    1. Guest_ | Aug 19, 1999 07:37pm | #39

      *Peter, Ed,I certainly would agree that occassionally there are times to put down the calculator and break out the strings and straight edges, etc., but on the other hand, I don't necessarily see this situation as one of them, although I certainly wouldn't criticize anyone for doing so.The diameter of the circular arc is given as 45 inches. This gives you the minor axis of the ellipse that will be the intersection of the circular ceiling and the 10/12 vaulted roof. Total time = 1 second.If you have a Construction Master calculator, enter the diameter, 45", as the rise, 10" as the pitch, then push diagonal, and you see 70 5/16". This is the major axis of the ellipse.Total time = 10 seconds.On a piece of 3/4" plywood, snap a line lengthwise on the sheet and mark off a line equal in length to the major axis, 70 5/16". At the midpoint of this line, draw a line square to it and measure either up or down from the midpoint 22 1/2 inches, the radius of the arch. From this point, measure 35 1/8+" ( half the major axis ) back to the major axis to find the two foci. You can now easily draw the curve and cut it out. Total time = about 15 minutes.Now take it up to the dormer and tack it up. You'll find that it planes in nicely , as long as the involved framing has been done reasonably well.Now you can take your sawzall and sculpt.I don't see this as having a "primadona mathematical attitude". I see it as an alternative approach, that has served me very well, and I'm certainly not tearing my hair out over 15 minutes work, even on occassion, when things don't work out right.

      1. Guest_ | Aug 19, 1999 11:35pm | #40

        *And someone else will have yet another approach, that will yield good results and give them a sense of accomplishment. That is one of the greatest things about our profession, "the proof is in the punch", or, it matters little HOW you do something, as long as the results are acceptable. One thing I've noticed here at Breaktime, is that some folks think their approach is the ONLY right way. And when two (or more) of those folks attempt to solve a challenge, each in their own way, these flame fests occur. "There is more than one way to skin a cat" and there sure as hell is more than one way to frame a barrel vaulted dormer. No one way is going to be "right" for everyone. We're all gonna do the job, based on our experience and intelectual strengths. Some folks work well in abstract terms, some folks are more spatial. When we learn to embrace, and enjoy our differences, we'll all be better off. - jb

  7. Nick_Pitz | Aug 20, 1999 01:18am | #41

    *
    It looks like there is enough info here already, but I will add a brief two cents. Just built one of these myself a while back, little different then Joe Fusco's, but basically the same. Main difference was that I had two 3x10 Doug fir collars coming across where he shows his plates. In any event, I also cut ribs from 3/4 plywood, screwed to 2x6 rafters, used a straitedge to get them close, then screwed up 1/4" plywood (tough to get in, but smooths out irregularities between ribs). Next made up a piece of 3/4" plywood to span from double rafter to double rafter, and rough cut in place with sawz-all. Then used two layers of 1/4" flexible drywall ( a special product - not just regular 1/4") screwed to ribs. One advantage of using the 1/4" plywood underneath is that you have screwing anywhere you want it, if you are careful not to overdrive the screws. Then plenty of durabond and joint compound to smooth it out. Mine was not a half circle, either, just part of an arc.

  8. Guest_ | Aug 20, 1999 07:21am | #42

    *
    I've heard all my life that if you ask twenty carpenters how, you will get twenty different answers. Seven months of reading this board hasn't turned up any contrary evidence.

    Rich Beckman

    1. Guest_ | Aug 21, 1999 05:42am | #43

      *I can go either way one this one. Whatever produces the product with good results is surly the best way to go.Jack

      1. Guest_ | Aug 21, 1999 07:08am | #44

        *Jonathan Stonely,You've seen all the rhetoric, now what are you gonna do?Ed. Williams(I bet the job's done by now)

        1. Guest_ | Aug 22, 1999 05:18am | #45

          *Ed, I'm going the mathematical route this time. For me the satisfaction of being able to think the construction through from start to finish without lifting a board gives me a lot of job satisfaction. I start framing the house this week, but I have 13000 sqft of house to frame before I even get to the roof. I'll be sure to let you all know how it goes. Maybe some pictures as well. JonP.S. I'm using a trammel to plot the ellipse of the valley, Something I picked up from an old book at the library (American House-Carpenter.) It's more accurate than the two nails and some string method. I'll post it later

          1. Guest_ | Aug 22, 1999 11:01pm | #46

            *Jonathan,I'm familiar with the trammel, and how to draw part of an ellipse, or, an entire ellipse using it. I still maintain however, that you can get the same degree of accuracy (or perhaps better) by using two small finish nails (4d perhaps) at the foci and picture hanging or picture frame wire instead of string. The picture frame wire does not stretch ( or kink) as string always will, and you will find that as you retrace the ellipse, you will get the same result, no matter how many times you retrace. With string, each time you go around, you will get a different result, because string stretches. In addition, it is a faster method.The length of the piece of framing wire will always be exactly equal to the length of the major axis.Since the pitch of the main roof for the house you are working on is 10/12, you can find the length of the major axis by simply multiplying the diameter of the circular vault, by 1.562.For example, if the diameter of the circular vault is 45", the 45" X 1.562 = 70.29" ( For those that are curious, 1.562 is the cosecant of 39.8 degrees, which is the "roof angle" for a 10/12 pitch roof.)Good luck. Looking forward to hearing how things work out for you.

  9. zoe_e. | Aug 24, 1999 07:25am | #47

    *
    I'm a novice carpenter building a house for myself in which i designed a barrel-vaulted dormer and porch. I don't know if it's the same thing as what you guys are talking about, since the outside of the roof is curved too. I went by the "just build it" method since my backgrouhd is in art, not geometry. However i found the info and drawings here fascinating and i wish i had visited this site before i built the darn things (just finished tonight). I too would be interested in leaning more about these things. I found a book through the Woodcraft catalog called "Circular work in Carpentry and Joinery" ( a reprint of an old book) but had a hard time making use of it. I'd be interested to see a more contemporary book. I'm glad to see that so many other people are doing things like this. What i'd really like to know about now is how to roof these things so they don't leak. Once again the plan is to just do it, but any input would be appreciated.
    zoe e.

  10. Guest_ | Aug 24, 1999 07:25am | #48

    *
    I am looking for literature or information on barrel vaulted dormers. I'll be framing a house with six of them soon. This home also has an eyebrow dormer that may or may not be vaulted as well. I believe I could trudge through, and frame them aceptably, but I'd really like to nail down (please excuse the pun) the mathematics and thoery behind them.
    For your info, the main pitch is a 10/12, the dormer is an 8/12 and the vault inside matches a half round lite in the dormer.
    I would like to learn how to plot and cut it all on the ground, please dont reply with scribing or stringline techniques. Im also looking for literature on all sorts of framing "in the round" ie... arches, elipses, towers, eyebrows

    1. Guest_ | Aug 08, 1999 05:10am | #1

      *Dear FredL, Thanks, I really needed some good sound advice and hey . . . thats just what you offered. I guess all those neanderthals that have gone on before me just guessed at it too. That takes a load off my shoulders. Thanks, JonP.S. Koffman/Broad just opened a 250 home subdivision with just four plans, maybe you would be intrerested in framing a few.

      1. Guest_ | Aug 08, 1999 05:20am | #2

        *Joe, Yes, but the barrel intersects with a 10/12 vault. The information I'm really interested in is the valley that connects the two planes. Is it elliptical? Thanks, JonI saw your string on ellipes, why are people so antagonistic?

        1. Guest_ | Aug 08, 1999 05:20am | #3

          *Joe,I liked you before but after seeing that picture think I just fell in love.Very nice.Vince

          1. Guest_ | Aug 08, 1999 05:27am | #4

            *Joe, your work? VERY nice!!! Geoff

          2. Guest_ | Aug 08, 1999 05:34am | #5

            *Vince,That's not love, it's lust. You'll get over it once you've built a lot of that sort of thing.Jonathan,Being a neanderthal myself, I'm looking forward to what FredL has to offer. Yes, the valley should be an elipse. But don't plan on cutting it on the ground and running up on the roof and "poof" it's done. Sorry, it just don't work that way. You'll have to tweak it somewhat. Wood is an imperfect medium used to build imperfect structures. Even a good machinist will tell you that a 3/4" bar will not go through a 3/4" hole.Perhaps after your search for perfectionism in woodworking ends in frustration, you might appreciate the string and scribe method that us "neanderthals" have been using since before you and I were born. Maybe there is a reason for that?Good luck,Ed. Williams

          3. Guest_ | Aug 08, 1999 05:35am | #6

            *The weddings off then Joe,hey what the hell I love ya anyway.Vince

          4. Guest_ | Aug 08, 1999 05:43am | #7

            *Ed,you're right about the lust. I've been trying to get over it for years.But every time I try to get out they just pull me back in.Vince

          5. Guest_ | Aug 08, 1999 06:10am | #8

            *Jonathan,You may want to refer to the February 1991 issue of Fine Homebuilding to read an article by James Docker on methods for constructing eyebrow dormers.As far as the other 6 dormers that you mention, the barrel ceiling framed below the 8/12 dormer roofs will intersect the plane of the 10/12 roof resulting in an ellipse ( part of an ellipse ). The shape of the ellipse is fairly easy to determine, and depends only upon twohings. 1) the diameter of the barrel ceiling, and 2) something you already know, the slope of the main roof, which you say is 10/12.Is there any further information that you could provide us. It's difficult to speculate when all of the details are not known, for example, what is the radius of the half round lite that the barrel has to match? are the dormer walls 2 X 4? what is the span for the 8/12 rafters at the dormers? What size rafters? Do you plan to cut the radii into the rafters, or cut them from plywood and nail them to the rafters to form the barrel?I would not agree with Joe's assertion that the resulting shape would be a parabola. Whenever a circular object ( a cylindrical object such as a piece of round pipe or a circular barrel ceiling ) intersects a roof in the manner you describe, the resulting line of intersection will always be elliptical, not parabolic, which is definitely a horse of a different color.

          6. Guest_ | Aug 08, 1999 07:42am | #9

            *Joe," In section? "Clarify please

          7. JRNicholson | Aug 08, 1999 09:20am | #10

            *Jonathan- In my few years as a framer simplicity has paid great dividends. Try headering the rafters at the dormer opening (main span), and cut plywood radii 1 1/2" larger than the rough radius you want. Screed the inside of the radius with 2x4 and let them run into the 10/12 ceiling. Screed the 10/12 ceiling, also. If you align the screeds and cut the intersection with a sawzall, the plasterer will have many good things to say about you. 1X4, 1X2 may also work, depending on span. JRNicholsonSuperCarpsthe cleaner framerP.S. I specialize in framing large (5-20K sf) custom homes in the Houston area. Years back, one had intersecting barrel hallways, some with compound arches. After nearly scratching a hole in my head, I prayed for wisdom. No way could I come up with this tip on my own, its too simple, too perfect. The plasterer (another high end sub) has referred me plenty since then.

          8. Guest_ | Aug 08, 1999 11:25am | #11

            *Lets start with one of the smaller dormersBarrel diameter 3'9"framed with 2x4 wallsdormer rafters are not called out, most likely 2x8 or 2x1010/12 rafters are 11 7/8" tji other items are still optional, like plywood rafters or using sawn lumber of a larger dimension.the lite is pressed up tightly to the ceiling line so it might be prudent to cut the barrel right into the rafters.

          9. Guest_ | Aug 08, 1999 06:42pm | #12

            *Joe, First of all Joe, I'm not down one lunch. If anything I'd say that I'm owed a lunch from you for the help I gave in correcting the math on your web page ( Modern Roof Framing ) several months ago.I'm familiar with the conic sections that you attached to your message. The only problem is, that we don't have a situation where a plane is intersecting a cone. We have a plane ( the 10/12 roof ) intersecting a cylinder ( the barrel ceiling ) The result is an ellipse, not a parabola.Please send a check for $20.00 ( two $10 lunches )

          10. Guest_ | Aug 08, 1999 07:45pm | #13

            *Johnathan,JRNicholsons tip will get you where you need to go. All the barrels we build are built in this manner. If you let your flat screeds run wild into the inside of the pitched roof, you won't have to mess with trying to create a valley. It basicly becomes a matter of going back in and filling in the holes. The good thing about what you have to build is that you don't have a barrel roof on your dormer. That can be a little more tricky, but thinking this method through a little farther, you should come up with the answers on your own on how to create that.If anyone ask you "why is this taking so long?", just hand them the hammer. What you're about to do is not easy. Good luck,Ed. Williams

          11. Guest_ | Aug 08, 1999 10:00pm | #14

            *If I were building these things, I would create them first in CAD. They could be examined and dimensioned from every point of view, including scale drawings of the "valleys" on the plane of the roof.

          12. Guest_ | Aug 09, 1999 12:53am | #15

            *Joe, An ellipse and a parabola are two different animals. It isn't possible to write a single mathematical equation that results in a parabola AND an ellipse. If it were, there would be no need to have two different words for the same shape, or two different types of equations to define them. That is the proof that you ask for. If I may add one more thing to clarify this even further, If I write an equation for an ellipse and then draw it, it is impossible for you to write an equation for a parabola that results in exactly the same shape.Don't try to rewrite the last 4000 years of mathematics Joe. You're not up to it. Instead, write a check for my two lunches. And please don't add anything to your web page about parabolas and ellipses until you understand the difference between the two. HALF OF AN ELLIPSE IS NOT A PARABOLA. And one more time, when a plane is passed through a cylindrical surface ( a barrel ceiling ) in the manner that Jonathan mentions for his dormers, the result is an ellipse ( half of an ellipse ), not a parabola.

          13. Guest_ | Aug 09, 1999 02:12am | #16

            *this is why i stick to string lines and scribing

          14. Guest_ | Aug 09, 1999 02:43am | #17

            *Joe,Obviously, you have your mind made up, so don't let me confuse you with the ( mathematical ) facts. Just retract your statement about the line of the valley being a parabola, WHICH IT ISN'T, and I'll buy my own damn lunch. Or do you wish to go on record here in Breaktime, insisting that the line of intersection is a parabola?

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