Replies

1. 
   piko | Nov 16, 2005 09:58pm | #1

   Perhaps the only improvement - if you're being exact - is to use 1x instead of string, and clamp your saw to that. What's the problem...nowhere to lay out, or accuracy?

   All the best...

   To those who know - this may be obvious. To those who don't - I hope I've helped.

    

1. 
   Dagwood | Nov 17, 2005 12:50am | #8

   This method works well... Try using a drywall screw to hold the pencil in a hole drilled through the end of the board.View Image

2. 
   FRICH | Nov 17, 2005 03:19am | #10

   My question is really about large radius cuts, like a 30 ft radius. Is laying the piece out on a large floor area and marking the curve full scale with a string the best, or only way, to draw/cut that curve on a board or piece of plywood? What if you don't have a large layout area, or the radius is 50 ft? Is there a way to draw that gentle curve without having 50 ft+ of flat layout space?

1. 
   Timuhler | Nov 17, 2005 03:25am | #11

   I'll find the pics I have that someone posted in the past.  I thought Joe Fusco had an article about it too, but I couldn't find it on his site.

   When I get back from climbing, I'll try and post it.

   Good question though, every time I do this, I forget the technique. .  . .including now :-)

2. 
   Mark | Nov 17, 2005 04:20am | #12

   The only two methods that I know have already been pointed out.  Either you need to have the actual distance of your radius available in which to work,  or the "cheater" method,   of establishing your two end points, your highest point in the center, and bowing a length of pvc pipe then tracing it.

   I've gone out and used an empty parking lot before when I had to do a big radius.  Take your cordless hammer drill and some tapcons along.   And forget the string.  Way too much stretch, flex, and just plain not accurate.   If you have to scab four or five  12" rips of plywood together,  then so be it.  I always skip the pencil part and attach my router directly to the plywood,  this way it takes way less time (you cut the radius as you go, instead of trace it then try to follow the line with a saw.)  and you get a perfectly flawless arc.

    Just make sure you're not in the church parking lot and unbeknownst to you,  Bingo is going to be starting in a half hour.    :-)

   " If I were a carpenter"

   Edited 11/16/2005 8:28 pm ET by Mark

2. 
   FastEddie | Nov 16, 2005 10:06pm | #2

   Yes there is.  Hard to describe, easy to see.  Mark the end poiints and drive a finish nail there.  Mark the center of the high point.  Get something long and flexible and push it against the two end nails and bow it up to the high mark.  If the 'bow' flexes evenly, you'll get a nice curve that you can trace with a pencil.  Sometime a thin rip off a 2x4 will work, maybe 1/4" thick.  If it has a knot, or if the grain does funny things, you might not get a smooth curve.  A piece of 3/4" plastic pipe will work.

    

    

   "When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it."  T. Roosevelt

1. 
   Dagwood | Nov 17, 2005 12:49am | #7

   Edit - Sorry - the third point would maintain a circular arc.

   (Previously read {this would create a parabolic arc})

   View Image

   Edited 11/16/2005 4:53 pm ET by Dagwood

2. 
   FRICH | Nov 17, 2005 03:10am | #9

   Is there a way to calculate mathematically what the offset dimension would be to the middle nail for a given radius?

3. 
   paul42 | Nov 16, 2005 10:18pm | #3

   Mark three points on the curve, two of them at the very ends.  Drive finish nails in the two end points.  Make a loop of string that is just barely long enough to go around the two finish nails and a pencil placed at the third point.   Then just keep the loop of string tight as you move the pencil between the two nails.

    

    

1. 
   pickings | Nov 16, 2005 10:48pm | #4

   This will create half of an oval w/ a constantly changing radius.

   Handy for arched doorway headers, but not an "arc" of any single / given radius.

2. 
   blue_eyed_devil | Nov 17, 2005 12:46am | #5

   Paul, that isn't going to work. You're mixing up some other technique.

   blue 

3. 
   Dagwood | Nov 17, 2005 12:48am | #6

   This creates an ellipseView Image

4. 
   ruffmike | Nov 17, 2005 04:29am | #13

   I don't know if an architect is involved in your project, but when we have large radiuses walls or soffits, we sometimes request them to supply points of reference for the radius.

    I believe someone with a cad can do this. I even had one architect bring a real size print out of a large radius that we used repeatedly to cut plywood jigs.

    I also believe there was a discussion here about getting points of a radius off a straight line and someone found a math website that provided the function to do it.

    I also find myself out in the parking lot with a 100' tape and a nail and a sheet of rock to make a jig. Hey that *** just ran over my tape! ; ^ )

                               Mike

       Trust in God, but row away from the rocks.

5. 
   DougU | Nov 17, 2005 04:56am | #14

   Heres a way to do it.

   Doug

   
1. 
   slykarma | Nov 17, 2005 05:05am | #15

   I was reading through wondering if someone would mention the math method. Glad you did it, because my CAD skills are not good enough to draw what you did and I doubt if I could have described it adequately in words. Now he just needs a transit to shoot the angles. The chord length principle can also be used to lay out an arc where the centre point is not accessible.

   Lignum est bonum.

   Edited 11/16/2005 9:07 pm by slykarma

2. 
   Mark | Nov 17, 2005 06:25am | #16

   Sorry buddy,

   Maybe I'm stupid,  or maybe there was some text in your attachment that I didn't see, (I didn't see any text,  just a diagram )        but  I don't get how what you posted helps someone create a template for a radius. 

   What am I missing?

   Cause if there's an easier way to do anything, I'm all about learning it." If I were a carpenter"

1. 
   DougU | Nov 17, 2005 06:41am | #17

   Mark

   Its just plotting points, that's about it. Then connect the dots.

    

   Doug

6. 
   Timuhler | Nov 17, 2005 06:49am | #18

   I'm attaching 3 pics that I got from this forum a few years back.  I think they exlain things really well.  I used this method once and it's pretty slick.

   The pics aren't in order

   http://pic9.picturetrail.com/VOL293/2163851/4541023/119050742.jpg

   http://pic9.picturetrail.com/VOL293/2163851/4541023/119050745.jpg

   http://pic9.picturetrail.com/VOL293/2163851/4541023/119050751.jpg

   http://pic9.picturetrail.com/VOL293/2163851/4541023/119050791.jpg

   http://pic9.picturetrail.com/VOL293/2163851/4541023/119050893.jpg

1. 
   saulgood | Nov 17, 2005 10:09am | #19

   Tim, if a picture's worth a thousand words, I guess I don't speak that language. Is the corner of the "scrap" what ends up scribing the line? I'm definitely intrigued by this method, but it would help if you'd walk us through it.

1. 
   Timuhler | Nov 17, 2005 05:04pm | #21

   Its been a couple of years since I used this method and to be honest, I can't remember what I did beyond study the pics.

   Sorry

2. 
   alrightythen | Nov 17, 2005 10:39am | #20

   That looks pretty cool. I think I follow what is happenning.

   But would This work ( in a practical manner) on such a large radius. The radius in the diadram looks pretty tight.

   ...as I'm typing - 'm thinking I guess it would....it's wouldn't be so much the radius but the lengh of the radius that would be limited by this method. But usually one is dealing with nothing bigger than a 4x8 sheet of plywood. which once drawn one can become a template.

    

7. 
   houseboy | Nov 17, 2005 08:13pm | #22

   Does this help?

   
1. 
   JoeBartok | Nov 18, 2005 12:04am | #23

   I would calculate and mark points on a piece of plywood or masonite and connect the points to make a template. You only need make a section of the circular arc. To lay out a large section of arc use the template to mark a section of arc on the work, lap the template and draw more arc ... Joe Bartok