LumberJocks

HOW TO DRAW A PERFECT OVAL BY A PAIR OF COMPASS

  • Advertise with us
Project by Sam Shakouri posted 09-21-2010 04:23 AM 42930 views 139 times favorited 28 comments Add to Favorites Watch

A 75 year old friend of mine, named Werner, used to work as cooper, an old trade in building wine and whisky barrels, taught me how to draw a perfect oval by using a regular pair of compass. This method was used to build oval barrels. Werner was still excited about that method and insisted to teach me how to do it. I think it maybe a good idea to share it with you all L Js. So I took all the task of writing and drawing to achieve that…. hopefully.
Just follow the 4 steps and you will be able to draw the oval in the size you want.

Step 1 with pic. 2: Draw a line that represents the length of the oval and divide it into 3 equal parts and name it A, B. C and D.

Step 2 pic. 3: Open the compass as long as one third of the line, say A to B. and draw 2 circles using B and C as centres. These 2 circles will be crossed each other in 2 points name them as E1 and E2.

Step 3 with pic. 4: Create new 2 points on each circle by using the compass, without any change, and by using A and D as centres. Name them as F1, F2, F3 and F4.

Step 4 with pic. 5: Adjust the compass as the length between F1 and E2 and run it from F1 to F2 using E2 as centre. Repeat this step and draw the line from F3 to F4 by using E1 as centre.
GOOD LUCK!

-- Sam Shakouri / CREATING WONDERS WITH WOOD.....Sydney,Australia....





28 comments so far

View RonPeters's profile

RonPeters

708 posts in 1547 days


#1 posted 09-21-2010 04:26 AM

Wow! The past comes into the future! Thank your friend for the tip!

This kind of resembles how to draw a violin using a compass and a straight edge. That comes from geometry back in the 1500’s…

-- “Once more unto the breach, dear friends...” Henry V - Act III, Scene I

View whit's profile

whit

246 posts in 2643 days


#2 posted 09-21-2010 04:50 AM

YES!!! I KNEW there’d be a use for that Geometry class!!! It just took a 75-year old friend of a fellow woodworker . . . and 37 years . . . to find it.

Whit

-- Even if to be nothing more than a bad example, everything serves a purpose. cippotus

View Ecocandle's profile

Ecocandle

1013 posts in 1732 days


#3 posted 09-21-2010 05:01 AM

I love Geometry. I have never thought about drawing an oval. This is a fantastic post!!! Thanks. I love it when it get smarter.

-- Brian Meeks, http://extremelyaverage.com

View garriv777's profile

garriv777

115 posts in 1531 days


#4 posted 09-21-2010 05:54 AM

Nice tip, thank you.

View savannah505's profile

savannah505

1703 posts in 2253 days


#5 posted 09-21-2010 05:58 AM

Thanks for posting Sam.

-- Dan Wiggins

View Grumpy's profile (online now)

Grumpy

19480 posts in 2518 days


#6 posted 09-21-2010 06:01 AM

That’s now in my favourite box Sam. Geometry is one of my interests as well. I will come in handy one day.

-- Grumpy - "Always look on the bright side of life"- Monty Python

View Tony's profile

Tony

978 posts in 2697 days


#7 posted 09-21-2010 07:16 AM

simplicity at it’s best

-- Tony - All things are possible, just some things are more difficult than others! - SKYPE: Heron2005 (http://www.poydatjatuolit.fi)

View Sodabowski's profile

Sodabowski

2028 posts in 1499 days


#8 posted 09-21-2010 12:29 PM

Well, while this is a nice idea, it’s not an absolutely accurate oval. The exact mathematical definition of an oval is: the ensemble of points at an equal total distance from two fixed (given) points.

To achieve an accurate oval, it’s even easier than that:
- put two nails in a board at locations B and C,
- attach a string to join them, so that when you pull the attached string towards the left, the bend is at point A (or D if pulling to the right),
- put a pencil in between and trace around the figure, keeping the string under tension with the pen.

Do that on both sides and you have your mathematically acurate oval :)

-- Holy scrap Barkman!

View Sandy's profile

Sandy

137 posts in 2591 days


#9 posted 09-21-2010 02:09 PM

Actually, with all due respect to Sodabowski, Sam is correct.

In geometry, an “ellipse” is defined to be the locus (path) of a point in a plane whose distance to two fixed points (such as, but not necessarily B and C) adds to the same constant. On the other hand, an “oval” or “ovoid” is any curve resembling an egg or an ellipse, but which is not an ellipse. Unlike “ellipse”, the term “oval” is not well-defined and many distinct curves are commonly called “ovals”. What “ovals” share is that they are differentiable (smooth-looking), simple (not self-intersecting), convex, closed, plane curves; their shape is similar to, but different from, an ellipse; and they have at least one axis of symmetry.

Thus, while Sodabowski’s nails and string method will produce an “elipse”, it will not produce an “oval”, which is what Sam properly claimed he was producing. With respect to producing an ellipse, though, even Sodabowski’s method should be revisted, as an ellipse has both a major axis (i.e., A-D) and a minor axis (While not defined in Sam’s drawings, it would be a line passing through E1 and E2 from arc F1-F2 to arc F3-F4. Let’s call the endpoints G and H). You must consider the length of both axes (A-D and G-H) when determining the length of the string and placement of the nails, which means that while Sodabowski’s approach (placing the nails at B and C) will give you “an” ellipse, it will not give you the closest ellipse to Sam’s oval. In order to get the “closest” ellipse to Sam’s oval, you will need to take G-H into consideration when determining the length of the string and placement of the nails (i.e., along line A-D, but not at B and C). In fact, using B and C for the placement of the nails will actually give you a string length of “4L”; a major axis having length “3L”, where L is equal to the distance from B to C, and 3L is the distance from A to D; and a minor axis whose length is the square root of 2 times L (i.e., L * sqrt(2)), whereas the “minor axis” (an admitted misnomer corresponding to G-H of Sam’s “oval”) will be a bit different (I’ll allow you LJ’s to do the math as a homework assignment).

As long as the subject is geometry, allow me to digress from the “ellipse/oval” issue to point out another issue which many woodworkers will consider absolute heresy, namely, that the “accepted” method of confirming square (90 degree) corners, by confirming that the diagonal lengths are identical, is not strictly accurate, as it assumes that the opposing sides are of identical lengths. Accordingly, if only one set of opposing sides has identical lengths, it is possible to have identical diagonals with no square corners. Instead, you will have a “regular” or “isosceles” trapezoid, which has two identical acute angles, along with two identical obtuse angles, but no right angles. Each acute angle/obtuse angle pair will, of course, be supplementary (i.e., they will add up to 180 degrees, although neither will be 90 degrees). This means that you should always cut your top/bottom and sides at the same time, or at least hold them together to confirm that they are identical in length before attempting to assemble them.

That all having been said, the most important tools in my woodshop for getting accurate shapes are still sandpaper and wood putty.

Sandy (MIT ‘69)

View Cozmo35's profile

Cozmo35

2198 posts in 1702 days


#10 posted 09-21-2010 02:23 PM

Dat’s purdy! :-P

I used this in a drafting class I took many many moons ago. I had forgotten about it till now. Thanks for jarring this old memory!

-- If you don't work, you don't eat!.....Garland, TX

View Sandy's profile

Sandy

137 posts in 2591 days


#11 posted 09-21-2010 03:44 PM

Whoops… the minor axis in my calculation should have been 2L*sqrt(2). Sorry about that.

Sandy

View Ken90712's profile

Ken90712

14978 posts in 1855 days


#12 posted 09-21-2010 03:49 PM

Great help. Thank-you I will be using this in the shop. Sandy is right. Of course I read his explanation twice with scratch paper at 6am ….Man I need more coffee figures hes MIT LOL Thx again!

-- Ken, "Everyday above ground is a good day!"

View Sodabowski's profile

Sodabowski

2028 posts in 1499 days


#13 posted 09-21-2010 03:53 PM

You’re right Sandy, I messed up with “ellipse” and “oval”.
And indeed, when back in the shop, sandpaper and wood putty rule! :D

-- Holy scrap Barkman!

View Dusty56's profile

Dusty56

11663 posts in 2354 days


#14 posted 09-21-2010 04:21 PM

Thanks to you and your friend for sharing this with us : )

-- I'm absolutely positive that I couldn't be more uncertain!

View jpwatson's profile

jpwatson

28 posts in 1702 days


#15 posted 09-21-2010 06:00 PM

Thank you, Sam (and thanks to your friend) for sharing this. Thanks to you, Sandy, for the “oval vs. ellipse” clarification.

-- Ones' greatest strength is most often their greatest weakness.

showing 1 through 15 of 28 comments

Have your say...

You must be signed in to post the comments.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics

HomeRefurbers.com

Latest Projects | Latest Blog Entries | Latest Forum Topics

GardenTenders.com :: gardening showcase