how to draw an elipse

[mickthetree]

Just saw this on the web.

here

You may have seen it before, but for those who havent, it might prove useful.

Cheers

 

[MikeG.]

Goodness, it doesn't have to be that complicated: 2 nails and a loop of string is all you need. Nail the nails in, put the loop of string over them, and holding it taut at all times, move your pencil around........

 

[Derek Willis.]

Mike, we've been down this road before, and agin I submit the following.
Derek.

 

[wizer]

yebbut if you had a plotter that can print exactly what you draw.... you have no need for these primitive solutions....

 

[MikeG.]

I've a plotter, Tom.......but I don't suppose most could plot out an elliptical arch 3 feet across, (which, incidentally, I have set-out on site for bricklayers in the past, using the string and nails technique on plasterboard, to make a former).

Primitive it may be........but all our cathedrals were set out like this!

Mike

 

[Derek Willis.]

I must say you are not the only one, I have, I recollect, on two occasions had to set out large ellipses using methods described here, in my capacity as a builder and later on as a site manager.
derek.

 

[johnf]

The string and the nails works a treat

 

[deano]

i used the string method to lay out a shop ceilin feature 20ft by 10ft worked a treat

 

[Steve Maskery]

Personally I prefer the lath and pins method. OK it's not quite so quick, but I never trust the elasticity of the string to prevent errors.

It's not a problem for tabletops, perhaps, but sometimes you need more precision than that.

S

 

[Wanlock Dod]

Well, it seems that the lath and pins method (same as the "eclipse engine" in the video) is generally preferred. I think that I would probably use this method as well because you can set out the dimensions of the eclipse (with the 2 pins and loop of string the size and proportions will depend on the relative positions of the pins and the length of the loop of string, that could be a lot of trial and error to get the shape you're after).

I tried to turn an elliptical bowl recently, and took the simple solution of drawing a shape on the PC (actually I think it was described as an oval), printing it off, cutting it out, sticking it to the blank, then cutting round it, before mounting it on the lathe. The problem I encountered was that I wasn't quite sure where the centre point was, mounted it not quite centrally and struggled from there on in. I'll be trying the method as suggested by Mick, Derek and Steve next time.

Cheers,

Dod

 

[Steve Maskery]

WD

You don't need much in the way of trial and error with the pins and string method. The pins have to go in at the foci of the ellipse.

1 Draw you centre lines - here I'm assuming that the ellipse is wider then it is high

2 Mark the limits of the axes.

3 Set a pair of compasses (or a trammel bar) to half the major length

4 With that length set, put the point of the compasses at the top of the short axis and mark the points where the pencil lead crosses the major axes.

5 That's where the pins have to go.

Cheers
Steve

 

[lurker]

I've a plotter, Tom.......but I don't suppose most could plot out an elliptical arch 3 feet across, (which, incidentally, I have set-out on site for bricklayers in the past, using the string and nails technique on plasterboard, to make a former).

Primitive it may be........but all our cathedrals were set out like this!

Mike

[-( they didn't have plasterboard

coat, hat, gone.

 

[Wanlock Dod]

Thanks Steve,

That sounds frighteningly like maths in an understandable way, maybe I will use a piece of string next time I try.

Cheers,

Dod

 

[TobyB]

I've been thinking about this ... OK, so I have drawn my ellipse ... but how would you cut it ... I'm thinking of a tabletop ... I could do a round sidetable on my lathe, or with the router if I set up one of those circle-cutting bars ... but how has anyone cut the ellipse? I could use the jigsaw to cut close to my line and then plane/spokeshave/sand up to the line I drew ... but are there any neater solutions? Not sure I fancy swinging a router through a loop of string (wire) with 2 pins placed ...

Cheers

Toby

 

[Steve Maskery]

Anything I've done elliptical has been done by sawing close to the line and cleaning up with a spokeshave.

I seem to remember someone having a router jig that worked on the principle I described above - a trammel that slid along both axes. I think it may have been a Trend item and I also think that it is in one of Jim Phillips' books.

Last year I went to the Pietra Dura museum in Firenze and they had the identical tool there for cutting oval stone inlays, so it is at least as old as the 17th century.

and

 

[JohnBrown]

This might be useful. I used a similar method to route two elliptical bookcase fronts a year or so ago.
http://www.miterclamp.com/videos/Cutting_ellipse.wmv

I can't find the other video I had, which was some Aussie guy, but basically, the bought ellipse jigs have a cruciform track with two runners or bearings that constrain the trammel to the ellipse. To do it yourself, you can use the edge of the work as one of the guide tracks, and a piece of timber with a slot routed in it for the other. I have the other video on my computer, I just don't know how to post it.