Drawing an arc

[Niki]

Good day

Yesterday, 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

 

[Bean]

Interesting and useful Nikki

 

[dunbarhamlin]

Good stuff.

Believe this sort of long compass used to be used by draughtsmen and boat builders. I use it whenever I need a large (eg 15'/5m) radius.

I have seen pics of commercial versions with angle/radius guides. I've got the formula for setting the angle for a given radius - easy to google for Long Compass (or I can dig it out when I get home).

Cheers
Steve

 

[Steve Maskery]

And by having the right nail level with the top of the arc while you set the trammel, then move that nail to the top centre of the arc, you can draw an ellipse (well, a quarter of an ellipse).

Very useful for large arcs. Another one to bookmark!
S

 

[George_N]

I've seen a similar method described before but I had the impression that you needed to know the radius of the arc you wanted to draw and had to calculate the angle between the two arms of the compass. Your excellent explanation and pictures makes it much clearer...brilliant. I will certainly be using this technique in the future.

 

[Harbo]

A much easier way is to use a thickish piano wire and bend it around some pins.

We used to use this for designing road layouts before the days of computers.

Rod

 

[OPJ]

Great idea, Niki. Looks like an excellent way to draw large curve.

...But it still doesn't solve the problem of not being able to accurately cut to the line or leave enough of the line in before sanding! :wink:

 

[Niki]

Thank you so much

When I posted it on the Italian forum one of the guys noticed that...

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

 

[George_N]

Great idea, Niki. Looks like an excellent way to draw large curve.

...But it still doesn't solve the problem of not being able to accurately cut to the line or leave enough of the line in before sanding! :wink:

I saw a web article that used this type of setup but the "compass" was clamped to a router table with a straight bit where the pencil goes in Niki's version. A couple of pins in the workpiece ride against the legs of the compass and the piece is moved past the bit to create the arc. Unfortunately I didn't bookmark the page and I can't find it again. I think I would probably use this method to make a pattern or template rather than risk my actual workpiece though and the template would ensure identical copies.