drawing long ovals

[Bryce Masuk]

I have some what of a problem I have attempted to draw a long and narrow oval which uses a compass rather than just the basic triangle method

the method comes from a book I have called the geometry of sheetmetal


When the major axis is considerably longer than the minor axis, say 4 to 1, all the foregoing methods are not so satisfactory, but for general purposes this method, though not as simple, is workable for all proportions long or broad.

Draw the major and minor axis AB and CD, intersecting at O. Join CB. With centre O and radius OC, draw arc CE, cutting line CB at F. With centre F and radius FE draw arc EG. Draw GH parallel to OB. With compass point on B, make BR4 equal to CH. Join HR4. Bisect HR4 and extend the perpendicular bisector down to meet CD extended at R2. Then R2 is the centre for the side arc and R4 is the centre for the end arc. Make OR3 equal to OR4 to give the centre for the opposite end arc.


I have no problem doing this except when it comes to the part Bisect HR4 it does not describe what length to use, nor where from I have attempted many different combinations and have not correctly drawn the elongated oval.

maybe someone on here has done this before I know how to use the other basic method of drawing ovals but it does not work for long and narrow ones

[bigfootnampa]

I can't help you with that method except to suggest that it is an approximation system and likely vulnerable to increasing inaccuracies as you approach extreme examples (long narrow ovals for example). I prefer to plot points on graph paper making a template. With this system you need only plot one quadrant as a pattern for all four... meaning that standard graph paper can be used for an oval up to about 20 inches long. For larger ovals I would tape two or more sheets together.

[pkrankow]

Thanks for bringing back the nightmares from drafting class. Just kidding. I had a lot of difficulty with this particular assignment too, and my best effort had discontinuities in it. I haven't tried this since freshman year of HS and it took me 7 or 8 tries to get an almost acceptable oval. Most of the class chose to skip this assignment as it was extra credit. My college level drafting (last semester before it was dropped for CADD) did not cover ellipses or ovals because CADD had it covered much better.

For ovals up to about 10x8 inches you can use the oval function in Paint, or any other drawing program and scale to the page when you print. Then trace it using carbon paper or if on a laser printer or photocopier flip it over and iron it on with a steam iron. The steam iron works good on wood and some plastics, but I have never tried on metal.

Another trick is to make a loop of string and plot the two foci (centers) and make the string 2x length from the far focus to the edge through the near focus (that is there and back) put your scribe in the string and draw away making sure your foci do not move as you draw. This creates an ellipse.

All ellipses are ovals but not all ovals are ellipses.

Good luck.
Phil

[David E.]

First find a long narrow oval and draw round it.;)

[Bryce Masuk]

I think I figured it out

I went from r4 spaced the compass out to D fired once with the compass and went to h and did the same the only problem is it gives you only the one arc and this case you will need 4 of these same arcs so you must find the true lengths and such I am guessing, my drawing is somewhat of a mess I am going to completely restart the drawing


the book claims this will work for any oval there is only one way to be sure i am assuming

a couple of months ago I build a giant compass in the shop with my extender i was drawing 18ft circles flawlessly on the road,

only problem i had was consuming an entire kids sidewalk chalk per circle LOL


I am still going to try and make this work 100% correctly
drafting on a computer is all fine and dandy when you program it into a machine but when your doing it by hand you need a guide of some sort

I have also been playing with this Drawing An Ionic Volute

I used a few other methods but it did not entirely work I figured this kind of scroll would be paticularly useful when the scroll is to essentially to be the entire area between the cap and the bottom of a handrail.



I have realized one of the main shortcomings in my smithing at this point is the lack of a good drawing before I was free handing all scrolls and building everything by eye and guesswork.

then i progressed into drawing everything out to a small scale and dinking around with until it looks fairly correct, but I know it will make a huge difference if i know exactly what i want draw it all out to scale.

to do this there is no evading drafting, and i cant see anyway of doing it not by hand

besides i am really poor right now i start a new job pretty soon but i spent all the money i had in my hands to get my new powerhammer to my house and pay the taxes and fees and such, I still need to save up for all the steel for the base (which i should have bought with it but i had to have a few sets of dies instead because I figured the base would be easier for me to make rather than dies)

None the less since I have no propane I might as well increase my drafting skills and get a few projects on paper and make them 100% to the drawing no matter what it takes