Chris Schwarz's Blog

I am That Nutjob

Sometimes with woodworking, what seems crazy one day can be quite sensible the next.

I distinctly remember reading in the late 1990s a manuscript from an author who was building some Morris chairs. He used an 8′-long beam compass to lay out the shallow curves on the chairs’ stretchers and had to enlist his sons to help him strike the arc.

Fellow editor David Thiel and I chuckled about that detail when we read it. It seemed like a lot of trouble for a shallow curve that we would strike using a flexible piece of thin hardwood and a couple nails.

But this week I’m not laughing anymore.

This week I’m building a Stickley sideboard for the next issue of Woodworking Magazine, and one of the prominent features of the piece is a shallow curve on the front rail. When I built the prototype of the project I used the flexible-stick-and-nails approach to lay out the curve.

After staring at that curve for many months on the prototype, it bugs me. It’s not a perfect arc. It’s a subtle thing, but I think the arc is a little flat.

So yesterday I built a monster beam compass that was more than 4′ long. The beam itself is 1/2″ x 1″. At one end I drove a #8 x 2″ screw through the beam. At the other end I drilled a 1/4″-diameter hole. Then I whittled a pencil to fit snugly in that hole. (Good luck trying to find the right drill bit to fit a standard pencil. Are pencils metric?)

I drove the screw into my benchtop just a tad then secured my sideboard’s stretcher to the bench with a holdfast. I struck the arc then cut it out. It’s perfect.

What’s next? Am I doomed to build a jig that holds too-thick biscuits so I can sand them to perfect thickness? Am I going to build a router table with a micrometer built into the fence?

Shoot me if I do.

- Christopher Schwarz

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34 thoughts on “I am That Nutjob

  1. Matt

    I made a really long, low bookcase and needed a very large radius curve for the front. I wound up doing what Bob Lang described: made a huge (14′) beam compass with my router attached to the end of it. I used that to create templates and then pattern routed the actual pieces after cutting off the bulk of the waste. My rig was huge! I made a plywood base and stabilized it with my toolbox, a 5 gallon paint can and other heavy things. My neighbors must’ve thought I was crazy. The arcs are PERFECT though. Tried the hardwood bow too, but the curve wasn’t consistent as others mentioned.

    You’re in good company Chris!

  2. Bikerdad

    Of course its not a perfect arc. If it was, model railroaders wouldn’t have been using the stick method for decades to draw easements. An easement "eases" into a curve, something that prototype railroads usually do, and something that those Lionel trains NEVER did. Remember how they would "slam" into the curve?

  3. Christopher Schwarz

    Cosmo,

    I’ve done this. It works. You have to have good hand skills to keep the pencil at exactly 90°. Any deviation and your arc is off. Sometimes this doesn’t matter. Sometimes it does.

    Chris

  4. cosmo

    Didn’t I see a technique somwhere that uses a string to create an arc? Put two nails at either end of your arc. Tie a string to both nails so that the slack, when pulled taught, will create a third point at the exact apex of the arc you want to draw. Then mark your line with a pencil, pushed through a router collar,or sewing machin bobbin, by riding along the string from nail-end to nail-end. The result should create a perfect arc. No?

  5. Christopher Schwarz

    Dale,

    I don’t have a plotter, so large curves require several sheets tiled and taped. The trammel was faster I think.

    For small curves, I definitely make paper templates. Thanks for mentioning that.

    Chris

  6. David Stansberry

    How about going to the handy-dandy CAD drafting program (Sketchup), drawing an arc of the desired radius, printing it off on a piece of paper and tracing it on your project?

  7. Keith Mealy

    Chris, Chris, Chris.

    It is dead easy to make an arc with two sticks and a couple of nails. No need for extra long trammels nor square roots. I’ll send you an article I wrote.

  8. Gary Laroff

    (I tried to post this earlier this morning but obviously did it wrong. Apologies if this shows up twice)

    There is nothing wrong with using a (long) compass arm when drawing an arc. Even ARChimedes would have done so even if he didn’t have easy access to #8 screws. There are other applications than Stickley sideboards that require accurate arcs. Rocking horse rockers are the perfect example. When mass cutting a set of rockers from a long 4′ wide slab of laminated oak, I use a 5′ long oak 1" x 1" as the compass arm, a #6 screw at one end and a pencil in a 1/4" hole at the other. A kerf at the pencil end expands the wood enough to accommodate the first pencil I find. A similar length of 6" wide 1/4" plywood with the pencil replaced by a plunge router serves to cut the rocker ends smoothly in a perfect arc. (photos available in Chris cares)

    Gary Laroff

  9. Mike Witteveen

    Or you could tie a string the length of your radius to a nail, and to a pencil. Strike your arc while holding the pencil perpendicular to the board. Am I the first one to realize this technique? It is now hereby copyrighted and I’ll expect the royalty checks to start flowing in.

  10. Bruce Jackson

    Hi, I’m Bruce and I’m a nutjob. Here’s my take:

    Richinsd above has almost exactly my approach to this long radius problem, although I confess I like the bending stick approach, too. So, here I am, trying to figure out how to fair a leg with an arc only a half-inch high by some 29 inches long. How long a trammel will I need?

    Whip out trusty 39-button calculator. Get envelope to draw picture. Set up formula from picture using Pythagorean theorem:

    (r – 1/2)^2 + (29 / 2)^2 = r^2

    r^2 – r + 1/4 + 210 1/4 = r^2

    r = 210 1/2 or 17 ft 6 1/2 in

    I don’t think I have a long enough anything in my shop to make this trammel, unless I figure a ball of string, which is what was used long ago, in days bygone when no tools had tails, except for this level imported from Egypt. For this shallow an arc, seems to me that the bending stick will work just fine (I hope).

    As for filing down biscuits, isn’t that like shaving tenons with a shoulder plane?

    And for router table fences with built-in micrometers, well, it might keep you from having undesireable fillets.

    In short, as an old colleague from a completely life (in hospital finance – please, let’s not go there) once said, you can rationalize any insanity.

  11. Richinsd

    For what it’s worth, I have had marvelous results drawing long radius curves using a steel locking tape measure with the end stop removed. I drill a 1/8 hole near the end of the tape for the pencil lead to fit through and fasten the body of the tape to a small nail using a loop of string through the tape measure back. It’s rediculously simple, fully adjustable. Just feed out the length you need to get the curve you’re looking for and lock it in place. Since the tape is resting on the work piece and is only holdng the point of the lead, the angle of the pencil poses no significant issue.

  12. Richard Stevens

    I’ve done both, although my preference is accuracy and therefore a trammel bar and pencil/router. The longest trammel I’ve ever made measured in at 10 feet long with a router stuck at the other end. Interesting and challenging task indeed.

    The other method I also use to ensure symmetry is using a flexible stick to mark out half an arch and then cut it to shape. Repeat the process for the other half. I’ve used this where a true semi circle is not needed and that a balances elliptical curve is just fine.

  13. Carl Stammerjohn

    I much prefer a radius to a bent-stick arc. It just looks better.

    There is another way to achieve a large radius that hasn’t been mentioned, the stick method. Jim Tolpin describes it in his book, Measure Twice, Cut Once.

    http://books.google.com/books?id=V8L8y1J8YcgC&pg=PA76&lpg=PA76&dq=radius+draw+two+sticks&source=bl&ots=qHH8CmlMcs&sig=dh8qYhXUG-g-tq5Ly_WH1akvh4s&hl=en&ei=5ma5SdmqIIHwsAOxksE5&sa=X&oi=book_result&resnum=2&ct=result

    Combining this method with Stephen Wilson’s formula (previous comment), and you can draw any radius you want if your sticks are long enough. I’ve posted a couple of photos of my jig on my blog.

    http://stammerjohn.com/2009/03/12/drawing-arcs

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