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I am renovating an oval room that will have a eliptical plaster cove that goes a round the room.

the room is very large and tall. the eliptical cove will be 30″ deep and 72″ tall.If any one has a formula or technique to lay out an elipse it would be greatly appreciated.

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## Replies

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Don,

When you say that the ellipse is 30" deep and 72' tall, exactly what do you mean by the words deep and tall?

*Don,I'm with Ken on this one. Your post is a might confusing. Is this an applied plaster cove at the junction of the ceiling and walls that is 30" deep and 72" high?Richard Max

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Sorry for the confusing post. What I meant was the horisontal dimension is 30" and the vertical dimension is 72". Dimensions weren't what I was worried about. What I really need to know was how to lay the elipse out on a piece of plywood so I could make a bunch of ribs for the lath and plaster to attach to. Thanks for your reply ....Don

*Sorry for the confusing post. What I meant was the horisontal dimension is 30" and the vertical dimension is 72". Dimensions weren't what I was worried about. What I really need to know was how to lay the elipse out on a piece of plywood so I could make a bunch of ribs for the lath and plaster to attach to. I'll attach a simple drawing so you can get a visual on this. Thanks for your reply ....Don

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Joe,

Wow, ya learn something new everyday. I think I follow most of what your saying up to a point. The focal points actually....now that you've got them ,what do you do with them? I catch how you made them even though I think you meant that the radius of the circle is half the ellipses major axis. But I still dont understand how you use the focal points to swing the four elliptical arcs that make up the ellipse. The only ellipses I've ever had to make in the field were done with the two pieces of lath and two nails method. I would love to learn how to do it right.

Thanks,

Richard Max

*Don,Here's a simple method for drawing the ellipse you wish on a 4' x 8' sheet of plywood.1) Snap a line which divides the plywood into two equal parts along the length. Then snap a second line ( square to the first ) that divides the plywood into two equal parts width-wise. These two lines are square to each other and will intersect at a point which is the center point of the ellipse.2) Measure out 36" from the center point each way on the long "axis" and mark these two points.3) Measure out 15 inches from the center point each way on the short "axis" and mark these two points.4) Go back to the long axis and measure out 32 3/4" each way from the center point and tack a finish nail at these two points. Take a third nail and tack it at one of the points on the short axis that you marked 15 inches from the center point.5) Go to the Hardware store and buy some picture framing wire, at least 72" long. Make a loop on one end of the wire and place it over one of the nails that you tacked on the long axis. Pull it around the top of third nail at the 15" mark and then back to the second nail on the long axis, making a second loop knot around this nail.6) Remove the third nail at the 15" mark and insert a pencil in its place. Keeping constant even pressure on the wire, your pencil will mark out the ellipse as it moves along the plywood.Don't use string. String stretches. Picture framing wire is flexible like string but does not stretch. You'll like the results.Good luck......Ken

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Joe;

Your first drawing is a good drawing of the brick domed ceiling I built back in the winter, you are correct on needing many different shapes to form it.

I call the different arcs "fair curves because they are not actually elliptical as they dont come back on the ends to be perpendicular to the horizontal center point.

Aside from that my interpetation of what he was describing was an elliptical cove in a room with oval shaped walls, and that would be a horse of another color indeed.

brisketbean

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Joe,

The method which I described in my previous post is nothing new. The length of a piece of string, or picture framing wire as I highly recommend, is always equal ( loop knot to loop knot ) to the length of the major axis, in Don's ellipse, 72".

When I say that the piece of wire should be at least 72", it would have to be slightly longer so that you could tie some type of loop

knot at each end.

For those of you reading this who have never drawn such an ellipse, here's a very fast way to draw one like the one Don described at the job site. All it takes is two nails and a flexible tape measure, such as a 50' or 100' type.

On a piece of plywood, snap a line 8' long that divides the plywood into two equal halves.

Mark the center point of this line, that is, mark a point 48" from either end.

From the center point, measure out 32 3/4" in each direction and tack a nail at each of these points. These points are called the foci of the ellipse.

Now, hook the dumb end of the tape on one of the nails and have someone hold the 72" mark on the other nail. Push your pencil against the tape measure and move it from left to right, trying to maintain an even pressure against the tape.

This will result in a shape that is one half of the ellipse. Flip the tape to the other side of the line and repeat the process to get the other half of the ellipse.

Don't try to do this with your 25 foot tape that you normally use at the job. It's not flexible enough.

When you're finished, you should have an ellipse that has a major axis of 72 inches and a minor axis of 30 inches.

When it comes right down to it, there are three things that you must know to draw an ellipse in this manner.

1) the length of the major axis

2) the length of the minor axis

3) the location of the foci of the ellipse; the two points that you tack the nails.

The length of the major axis and minor axis are given on the plans.

To determine the foci points, take half of the major axis and square this number. In Don's ellipse, half of 72" = 36" 36 X 36 = 1296

Second, take half of the minor axis, and square this number. half of 30" = 15" 15 X 15 = 225

Subtract the smaller number from the larger. 1296 - 225 = 1071

Find the square root of this number. The square root of 1071 is 32.73 or about 32 3/4". This is the measurement to the foci each way from the center.

This whole process only takes a few minutes. Try it out with a friend during some free time at the job site. You'll like the results.

*Hey , I think I can help! After you have found the focii drive 2 nails in to them then attach a piece of string to both points. The string needs to be long enough to reach the point formed by the elipse and the perpendiclar bisector(the long leg of the rectangle) of the large circle in Joe's drawing. Look at it as though the string is the blue line from one foci up to the center of the long leg of the rectangle and back down to the other foci. Does that make sense? When I draw them I just hold a pencil inside of the string and keep it taught as I draw around the focalpoints!

*Joe,In your last post, you began by saying that there is nothing new about my technique ( for drawing an ellipse). If you reread my last post you'll see that I made this very point in the first sentence of my post.This method for drawing an ellipse has been in existence for at least 400 years.The only thing I may do differently from some others is using picture frame wire or a flexible metal tape to make the drawing. String stretches. The picture frame wire or the flexible metal tape does not, and hence gives a superior drawing. Try drawing a large ellipse, say 6' x 8' using string, then retrace it again. You'll find as you go around the second time that the two ellipses will not match. Using picture frame wire, you will get virtually the same ellipse no matter how many times you retrace it.

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Dear Don,

After reading all of these posts, I can see you have quite a dilemma. May I offer my services to you. We are a custom millwork shop that has the equipment and the technology to make any shape you desire. We can give you the frame work to build the walls in the same ellipse as you are needing the ceiling-one or both-as needed. We can fully assemble and ship or ship precut pieces. You may contact us at White Custom Millworks 316-488-3559. Hope we can help you. Jay

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Joe,

I've read your posts. The method you describe using a rectangle and a circle is correct. I'm sure you realize that your method amounts to the same thing as mine.

The main difference is that I simply need to snap one line and tack two nails at the foci. The wire or tape is always equal to the length of the major axis.

For large ellipses in particular, I would find the method you described as time consuming.

By the time I accurately snapped out a rectangle for an ellipse that was 9' x 12' and then swung arcs of a circle to determine the foci, I would have finished drawing the ellipse with the method that I use.

*Joe,You say in your second sentence that you gave no procedure to actually construct an ellipse.That's just my point. Don Leitheuser posts a message asking for help about the procedure for laying out an ellipse and you post a series of messages but never actually get around to the nuts and bolts as how to actually accomplish it in the field.I've at least done that. You've just made a bunch of cute drawings but haven't answered his question.

*Joe,I think your method using a rectangle and a circle would gain more favor if you would simplify it.It's not actually necessary to draw the rectangle or the circle to achieve your result.1) On a piece of plywood, snap a line 96" long that divides the plywood into two equal halves.2) Snap a second line, parallel to the first, that is 15" from it ( one-half the length of the minor axis).On the second line, somewhere near the middle of the the line, mark a point. Hold the end of the tape measure on this point and mark the two points on the first line that are 36" from it (one-half the length of the major axis). Those two points are the foci of the ellipse.Joe, would you consider making a drawing of this and post it for me?

*Joe,I've pretty much got the Milkbone Framing Challenge questions worked out but I thought I might wait to the weather cools down, sometime after Thanksgiving, to post The Challenge. The dead of winter would probably be the best time, when we tend to huddle indoors and are looking for things to do.

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I am renovating an oval room that will have a eliptical plaster cove that goes a round the room.

the room is very large and tall. the eliptical cove will be 30" deep and 72" tall.If any one has a formula or technique to lay out an elipse it would be greatly appreciated.