OK. Someone tell me the right way to do this

[Alan Lightstone]

I have a cabinet I'm building with a curved bottom front piece. It's a very subtle curve (gaining 1-1/2" over 30" of length):

199901

The only way I could figure to trace the curve smoothly was with a beam compass/trammels. Unfortunately, that small a curve demands a pretty good size beam compass. As it turns out, a 17 foot beam compass:

199902

Now clearly, this is kooky (though I think I deserve some points for actually having the persistence for seeing this through to completion).

What's a more reasonable approach to doing this? What do people actually use to draw long, large radius curves for making patterns and furniture pieces?

[Peter Scoma]

Make a jig to bend a thin, flexible piece of steel. Kind of like a bow and arrow. Flexible drafting curve will work also.

Peter

[John Coloccia]

If you want an actual section from a circle, look up the "long compass". I believe I even gave a little tutorial on this a while back if I remember correctly. Maybe not. It's a very simple device made from a couple of sticks super glued to each other.

If you just want a nice looking curve, take a thin strip of wood and bend it. You can just drive a couple of nails outside the boundaries of your piece, take a strip of wood and push up on the center, against the nails. Secure it in the middle somehow (string, duct tape, whatever) and trace with a pencil. This usually looks nicer than an actual circle. If you really really want a circle, though, the long compass is a slam dunk.

[Andrew Gibson]

A yard stick or piece of scarp that you can bend to make the curve works for me. I have a 40 inch rule that I use quite a bit for this.

The thing to remember is that on a curve like this, your curve does not have to be perfect to look perfect to the eye.

[Alan Lightstone]

If you want an actual section from a circle, look up the "long compass". (snip).... If you really really want a circle, though, the long compass is a slam dunk.

Boy, that makes it look simple. Here's the link from your post:
http://gicl.cs.drexel.edu/people/sevy/luthierie/compass/Long_compass.html
And the pieces aren't 17 feet long either.

Any other techniques people use to do this.

[Dan Friedrichs]

Draw the curve in Sketchup, print out full-size, and trace.

[Bob Wingard]

Sounds weird, but I have several 10'-12' aluminum extrusions laying around the shop. One has a hinge mounted on one end, and one has a router base on one end. I place two or more of them side by side, clamping them at the appropriate length, and use it as a huge trammel jig to route the piece directly. The few minutes I spend setting up is more than saved by the sanding time eliminated ... PLUS ... the arc is perfect every time.

[Russell Sansom]

I think the primary method over the years is the "fair curve" drawn with a batten as mentioned above. If you already have a curve described, it's not that difficult to get a batten to follow it smoothly. You can usually do it with two endpoints and third point sticking up somewhere else along the curve.
I commend you to wooden boat building where you will find special spaces devoted to "lofting" a boat. The boat loft is the place to drive awls into the floor and to up battens among them for the lines of a boat. A little probing of how it's done will teach you just about everything you'd want to know about making curves this way.

[david brum]

I have successfully used the very low tech method of tying a string on one end to a pencil. The other end gets tied to something heavy like a big brick. The brick gets moved away until the desired arc can be drawn. Worked great for me. I really like Bob's giant router trammel idea though.

[Gary Pennington]

Alan,
I biult that exact piece this past winter, here's pics:
http://www.sawmillcreek.org/showthread.php?157354-Credenza-style-entertainment-center&p=1610963&highlight=#post1610963

I used a piece of aluminum 1/8" X 3/4" x 6' as a guide. I clamped the thin edge in the center 1-1/2" from the bottom, then pulled each end down to the corect spot on the bottom edge and clamped in place. Then drew a pencil line and zipped it thru my bandsaw. Picked up the aluminum some time ago in a bin in the local hardware store, it's found a lot of uses around my shop.

Good luck with the build, it's a great piece. Gary

[Alan Lightstone]

Gary:
Looks nice. Beautiful build, especially for a first project. Well done.

I've modified the piece to fit a unique hidden room in the house where my son hangs out and plays video games. I wish I had posted here first before fussing with the beam compass. It did work, so I just need to head to the bandsaw and finish the pieces. I knew there had to be an easier way of doing that with projects, as that isn't an uncommon process.

David:
The only string I had around was far two stretchy. It would expand while I was drawing, and didn't work at all.

Dan:
I've downloaded sketchup, but haven't tried it yet. How do you print it out in full size - multiple pieces of paper taped together? It has that capability? Or does this involve a Kinko's run for a specialized printer?

Russell:
Lofting a boat? And I thought that my 17ft compass was huge. wow!!!

[Dan Friedrichs]

I've downloaded sketchup, but haven't tried it yet. How do you print it out in full size - multiple pieces of paper taped together? It has that capability? Or does this involve a Kinko's run for a specialized printer?


Yep, you can print full size on multiple sheets and tape them together. For a 30" piece, you'd only need 3 or 4 pages.

[Ray DuBose]

build you one of these: http://www.leevalley.com/US/wood/page.aspx?p=44631&cat=1,42936,50298&ap=2 or order one but they are usually easy to build.. I have a strip of wood about the thickness of a yard stick but longer and I just bend it to my side and clamp both ends down to the piece.

[Zach Callum]

This is what I do: Draw out 1/2 of the curve(freehand) onto a template piece. Cut with bandsaw. Smooth out the roughness on the spindle sander. Then take the 1/2 curve template and transfer it to a full-size template. This will give you a symmetrical curve. Then back to the bandsaw and sander. Now you can use the template to make multiples of that same curve. That is how I did the curves for these pieces...199983199984

[raul segura]

Id take the partial circle 30 inches divide in half,15 then run 90 degree out like (T) use the heavy anchor and pendulum trick.
You could use the line of a plumb bob as it would have little flex and Launa board (mockup) to copy to then use router to mirror the shape to your project.
Boat builders used the flex stick for there hull shapes (Wally World has orange fiber glass rods in there sign area 36in. long or more). if you are in need of exactness you could fold large newspaper in half 15 inches each side then line out half the ark with the stick,cut and unfold ... walla you have balance. Most difficulty for me would be to cut the round shape and sand by hand.
You could also use the pendulum thing, Nail at arks length then run wire from nail to a router or pendulum and over the Launa panel.
Tool limitations force one to use drastic measures at times. Good luck !

[Jerome Stanek]

take a look at this web page on making an ellipse.

http://zo-d.com/stuff/squares-and-measuring/how-to-use-a-framing-square-to-draw-an-ellipse.html

[Chris Fournier]

Grab a very straight grained piece of wood in your shop and cut a batten from it. Experiment with the thickness of the batten until you have one that is flexible enough for your needs. Lay out your drawing on a sheet of something or other and expeiment with bending the batten into the arc of your dreams. I'll tap in nails or clamp sticks here and there to direct the arc.

[lowell holmes]

Plus 1 for the batten. It works.

[Greg Portland]

Boy, that makes it look simple. Here's the link from your post:
http://gicl.cs.drexel.edu/people/sevy/luthierie/compass/Long_compass.html
And the pieces aren't 17 feet long either.

Any other techniques people use to do this.Also note that you can make ellipses by using a string tied to the 2 brads. The string should be longer than the distance between the 2 brads and you'll move the pencil while keeping the string tight at all times.

[shane lyall]

I did a flat screen tv stand with open shelf below last year for a customer. The piece was very much like you picture. I used a piece of 3/4 pvc pipe and drove brads at the end and mid point. Cut it on a bandsaw. Clean up at spindle sander and you done.

[Myk Rian]

I've downloaded sketchup, but haven't tried it yet. How do you print it out in full size - multiple pieces of paper taped together? It has that capability? Or does this involve a Kinko's run for a specialized printer?
I wouldn't bother with that method.

[matt swiderski]

I use a thin dowel rod, clamp the ends and clamp it in the middle and just trace the curve. Then cut it out with a bandsaw. Works for me. Hope this helps.
Matt

[Dan Friedrichs]

I wouldn't bother with that method.

Just out of curiosity, Myk, why not? It may not be preferable to some people if you don't know how to use it, but I could draw the curve and have a full-size, perfectly-accurate template printed out in <2 minutes. It would probably take me longer to find a flexible strip of wood and some nails.

[Myk Rian]

Several sheets of paper to align and tape. Then cut the curve, trying not to cross the line. Tape it down, and trace it.
After that you wad the paper up and toss it in the trash. A waste of paper.

A bowed strip is the easiest way.