Drawing circles

[bobsmyuncle]

At the attached link is an article I wrote for an upholstery journal on how to draw circles. The last two method are especially helpful for drawing large diameter arcs without having to have a forty foot trammel beam.

http://cincinnatiwoodworkingclub.org/Po ... _Mealy.pdf

[jstrubberg]

Seems like a lotta work. I just use a piece of cord and a pencil. Come up with a center point, tie the cord around the pencil, make the distance between the pencil and the center the radius of your circle, and draw away.

[Oldragbaggers]

I use a long strip of wood, put a nail in one end (I drive this shallowly into the piece of wood I'm drawing my arc on.) Then I drill a hole of sufficient diameter to put the pencil through and you can draw perfect arcs. I think they are more precise than a piece of string which depends on how consistent you are at holding it taut.

You can use the same piece of wood to draw as many different size arcs as you need just by drilling your pencil hole at different lengths.

[bobhenry]

Seems like a lotta work. I just use a piece of cord and a pencil. Come up with a center point, tie the cord around the pencil, make the distance between the pencil and the center the radius of your circle, and draw away.

I always had trouble with a wobbley pencil so I finally got wise and cut a equilateral triangle out of a 2x6 and drilled a hole for my pencil in the center. I drilled a small hole thru one point and attached a length of masons line. I can now tie off the pivot end to a nail pull the cord tight and mark my line without the dreaded pencil wobble. If you are marking for halo trim multiple holes can be drilled the desired length apart.

[aggie79]

At the attached link is an article I wrote for an upholstery journal on how to draw circles. The last two method are especially helpful for drawing large diameter arcs without having to have a forty foot trammel beam.

http://cincinnatiwoodworkingclub.org/Po ... _Mealy.pdf

Nice guide - thank you for posting it.

I made a beam compass out of some t-track and scrap plywood.



I also made a router base out of 1/4" mdf so I could use the same beam compass to route arcs.

[Facemeltingly Epic]

Seems like a lotta work. I just use a piece of cord and a pencil. Come up with a center point, tie the cord around the pencil, make the distance between the pencil and the center the radius of your circle, and draw away.

That's the same technique I used when I laid out the sides of my trailer. It works best if you pull the string really tight!

[Facemeltingly Epic]

At the attached link is an article I wrote for an upholstery journal on how to draw circles. The last two method are especially helpful for drawing large diameter arcs without having to have a forty foot trammel beam.

http://cincinnatiwoodworkingclub.org/Po ... _Mealy.pdf

Nice guide - thank you for posting it.

I made a beam compass out of some t-track and scrap plywood.



I also made a router base out of 1/4" mdf so I could use the same beam compass to route arcs.

I like this idea. Since Build Number Two will start with the acquisition of my own tools, I just might fab up something like this...

[angib]

I think they are more precise than a piece of string which depends on how consistent you are at holding it taut.

I think the problem is that 'string' is usually quite stretchy, so you have to not only keep it taught, but also use a constant force to keep it taught.

A piece of wood is certainly much easier.

[Crazy4Kits]

The string thing was a mess for me.......not stable enough. I've been using one of these for awhile and love it. So much easier.......


http://www.woodcraft.com/Product/200381 ... mpass.aspx

[bobsmyuncle]

One of the reasons I posted this was there are some methods that might be unknown or forgotten. On another forum this week, someone asked how to divide a circle into thirds using compass and straightedge. I was shocked at the bumbling and mis-guesses at how this could be solved. Now I have more math than the average bear, but really, this was something I learned how to do in seventh grade.

In particular, if you are doing a really low profile arc, it's not practical to have a 40 foot beam. Or if you know three points (any three points), there is exactly one circle that goes thru them.

[halfdome, Danny]

The only time I'll use a string is when making an ellipse.
I made a lot of radius reception desks using up to 3 sections of 10' of aluminum with a 3 HP router edge guide taken apart and reversed.
Much like in the first photo. Not much math involved. Danny


I'd place lots of saw horses around the shop and pocket screw sheets of particle board together for some very accurate radius work.
My customers were surprised I could do it with no CNC and in a small shop.