Drawing Arcs

[niki]

Good day

Today I made some picture frames (of course 45°...it's the fastest and easiest) but I was also "playing" with some idea of drawing arcs.

Everything is on the pics but I just want to emphasize that each of the sticks must be at list at the length of the distance between the "nails" so if you'll build something big, you'll need long sticks but it works like a charm and no math required...

Best regards
niki

[BobSch]

Great idea, Niki!

Thanks for the pics. They make it that much easier to understand the process.

[Pappy]

That's a trick I've never seen before. Thanks for the info. I have scribed arcs using a string method, but it isn't nearly as accurate.

[pelligrini]

Cool idea!

Wouldn't holding the pencil on the opposite side (in-between the short legs) aid in keeping the device in contact with the nails?

[Uncle Cracker]

I have just now awakened from what i can best describe as a geometry coma...

[niki]

Thank you so much

Pelligrini
Yes, you can hold the pencil on the "outside" of the sticks...I did not try so I cannot tell you how much it helps to hold positive contact with the nails...but, all the idea is that the arc will be at the dimensions that you decided and measured...between the nails...
If you will use the other side of the sticks the arc lines will fall beyond the nails...if you don't mind, no problem...

Uncle Cracker
I'm in this "geometry coma" already 40 years and it looks like I'll never wake-up...that's the reason that I'm looking for simple ideas without all those "Pythagoras" laws...

Regards
niki

[niki]

I have a mistake...

The method to draw the second arc is incorrect...actually, I'm drawing two circles (or arcs) of the same radius or diameter and that, will never give me consistent width along the arc...

To get same width all along the arc, I had to change the circle diameter while still using the same center point for both circles...

Sorry for my mistake

Here are some new pictures for the correct way
niki

[rnelson0]

I have to ask. Is there a reason you didn't just draw the arc by placing your center point off the board and scribing the arc with a chalk held at the end of a straightedge? Seems a little simpler.

[niki]

I have to ask. Is there a reason you didn't just draw the arc by placing your center point off the board and scribing the arc with a chalk held at the end of a straightedge? Seems a little simpler.

Yes, it is simpler but, in my opinion...it is simpler only in theory...
Practically, you shall need a trammel long at list as the circle radius and you don't exactly know the radius...
After that, you shall need (maybe) a long table (depends on the circle radius) to clamp the trammel and the board so they will not move and than a few trials and errors to find the correct radius....

What I'm doing instead is; I know the length of the arc (the distance between the nails)
I know how much I want the curve to be in terms of height from the "level line" (the line that connects the two nails) at the center of the arc...I bang 3 nails set the sticks angle, pull out the center nail and go.

Anybody can do it at the way that looks for him the simplest...

Regards
niki