Drawing circles

[Allan]

What does everyone use to draw a large circle or radius?
I use a stick with a pencil in one end and a screw in the other end
Not ideal for adjustments

What does everyone else use?

Allan

[SteveA]

You could substitute a string for the stick - wind and unwind for adjustments
SA

[Allan]

Steve
I tried the string but keeping the pencil vertical on a large radius makes for inaccuracy

Allan

[MinUph]

I also use the string.keep the string close to the tip of the pencil or chalk it helps.

[Darren Henry]

Lee Valley carry a two piece "compass" that fits on a standard wooden yard stick. The one end has a needle on it and the other a pencil holder. You stand the yard stick on edge and then slip the two pieces into place and tighten them down.I've got to get off to work,but will try to find a pic for you.In the mean time you might try there website.

I also just use string,and Paul is right about keeping the string low---makes a big difference.

[bobbin]

Good question!  I use a point and then whatever measuring stick meets the criteria for size.  I could never quite master the vertical pencil and string method, either.  

When I was a kid every teacher had a large, wooden compass that held a piece of chalk so they could draw on the blackboard.  I have looked and looked for something similar to no avail!  I'd like to have a compass for use on my floor cloths.  

[byhammerandhand]

Ha!   I wrote an article on this over at Carr's Corner a few years ago.  There are lots of ways to do this.
http://cincinnatiwoodworkingclub.org/Portals/0/activeforums_Attach/Drawing_Circles_by_Keith_Mealy.pdf


It really depends upon what "large" is.    The last few arcs I've needed were about 60" radius.   I used trammel points.  But on one end of the stick, I drilled a hole large enough for a pencil and another in from the end of the piece where I added a 1/4" threaded insert so I could tighten the pencil in place.

The string-and-pencil method is not a very good one.   It relies on the string not stretching and the pencil being held at a constant angle.  If you have a non-stretching string, you could do it like you would an ellipse with a loop and not just tying the string at either end to the pencil and pivot point.

Some people use a fairing curve AKA drawing bows to draw arcs.   These are pieces of material that are stretched into a curve by either pulling the ends or fastening the ends and the middle in position.  I'm not sure that gives a true circle, it may be a parabola or even a catenary.  You need to be careful not to distort when you press your pencil against it. It also relies on homogeneous material to make your board.

I'm on my way out on an errand right now, but reply with what you need and I may have some other methods.

[Mike]

The o ly time i need a acuate curve is when i making smiley zippers in vinyl voat windows. Ive used the pencil string when i dont have a bucket the right shPe to trace. I trace it on cardboard and make. Template fot all the windows to be the same

[sofadoc]

If I need a 14" diameter circle, I take a yardstick, and poke a hole at 7". Stick a T-pin through the hole, and spin the yardstick around while holding my marker against the end. For large circles, I fold the fabric in half, and calculate accordingly.

I just have to lay a piece of wood underneath the fabric, so the T-pin doesn't damage my cutting table. If it's vinyl (or something that I can't use a T-pin on), I make a template first using the above method, and then trace around the template.

[Darren Henry]

http://www.leevalley.com/en/wood/page.aspx?p=32628&cat=1,42936,42938

These are the gadgets I was talking about. They are slick.

I make a template first using the above method,

I use string mostly, but I have made a set of templates for the sizes I require most. I usually only make a half pattern (semi-circle) so they don't take as much room and 50% less chance of error LOL. I've learned to label them and to write down the circumference  ;)

[mike802]

I bought some of those gadgets Darren is talking about, they did not fit on my yardstick.  So I ended up making my own compass not that difficult really.

[MinUph]

Yes Darren mentioned templates. I do the same for small circles. 4-18" or so. Punch a hole where the compass point was and hang them on the wall. We do also have a wooden compass that is good to maybe a 30" radius or. Larger circles I go with the pencil and string.

[byhammerandhand]

This came across my screen yesterday, courtesy of "The Family Handyman" magazine:

DIY Tip of the Day: Drawing Large Circles. Use big paint stirrers to make a compass for large circles. Drill a 1/16-in. dia. hole at the bottom of one stick, then tap in a 6d nail. Snip off the head at an angle for a pivot point. On the other stick, attach a binder clip to hold a pencil. Join the sticks with a machine screw, lock washer and Wing-Nut. Place a toothed lock washer between the sticks for a tight grip.