How To Copy a Curve Shape Into Wood

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We have a project coming up in the spring that we have begun planning, for now, in mid-November.  It’s a moon gate for entry into the meditation garden under construction out back.  

Moon gates are circular openings in a garden wall (a bamboo fence, in my case) that are a traditional element in Chinese gardens.  They imitate the shape of a full moon and serve as an inviting view into the garden on the other side of the gate.  The part of the garden just inside the moon gate is to be a tease of sorts, a suggestion of what may lie beyond and through the gate.

It’s going to require the cutting of a curve shape into a piece of wood, and we’re going to need a steady hand to get it right.  In researching the options for methodology, it occurred that others may want to know the same things we had to learn.  This article will share that research and let you know how I finally decided to approach the project.

Creating a Curve Template For A Circular Cut

Milescraft 1219 Circle Guide Kit- Router Circle Cutter Jig For Cutting/Routing Small And Large Circles From 1.5in. Up To 52in. Diameter-Includes Bonus Offset Base For Edging Projects , Black

The obvious and logical plan for creating a curve template into the wood is to use a tack, some string, and a pencil or marker of some sort.  

Find the center of the wood (plywood will be my choice); 

Tack one end of the string to the wood, the length of which should be half the diameter of the circular cut I will need to make, coming as close to the edge of the plywood as possible.

Draw a circle on the wood using the string as your guide and mark it with a pencil or sharpie.

This would be the most direct and easiest way to create those curves on the wood, more simple than cutting a template from construction paper.  The importance of coming as close to the edge of the wood is so I can use a bandsaw to make the cut, and I want to waste as little wood as possible in making the cut. 

A bandsaw is the smartest choice and better than a coping saw (much too long to make the cut) or a jigsaw (hard to follow the line accurately, requiring a very steady hand for a slow cut).  

The bandsaw’s strength is its ability to make curve cuts.  It’s the best saw, for instance, in the making of cabriolet legs and cutting irregular shapes, and is well suited for the curve cut I will need to make for the moongate.  We’ve written about bandsaws in the past, and you’ll find a helpful piece about them here.

As for the choice of plywood, that’s an easy one, too.  I’m figuring a Grade B will be sufficient – if any knots are showing, a primer of Kilz or Bin will cover them before I put a couple of coats of paint on the piece.  Grade B plywood comes sanded already but is less expensive than a sheet of Grade A.

As for rating, I will choose either “Exterior” or “Exposure 1.”  The difference between the two can be overcome:

  • Exterior rating means the sheet has been waterproofed and can be used on outdoor structures that will be exposed to rain, snow, and ice.
  • Exposure 1 means the sheet has also been waterproofed but can only withstand exposure to the elements for a limited period of time.

The exposure 1 sheet will be less expensive, and I will prime the final piece before I install it and then get it painted and sealed quickly, so its exposure is minimal.  

Creating A Curve Template For An Elliptical Cut

This one is not quite as simple or straightforward as a circular template.  I dug deep back into the past in my research for this one, as far back as Archimedes.

Archimedes was a Greek mathematician, engineer, and inventor considered to be one of the leading scientists of his time, 287 – 212 BC.  Among his inventions was the trammel used for marking and cutting ellipses. 

A trammel of Archimedes is a mechanism used to define the shape of an ellipse.  It consists of two channels on a piece of wood that constrain the movement of a rod attached to two shuttles in one of the channels.  That rod’s movement is limited to the curves of the ellipse.

That may seem confusing, and it sort of is.  But, this video will show you how to build your own trammel of Archimedes, and it would make a very cool project in your shop.

When constructed properly, the trammel will give you an ellipse pattern every time, easily transferable to a piece of wood for cutting.  It will draw an entire curve with an exact curve every time. 

The size of your ellipse is determined by the length of the rod used with the trammel.  But you can count on an exact curve reproduction every time when using the same rod determined by your need for the project.

Copying An Existing Curve From One Piece To Another

Let’s say you need multiple pieces with curves created, and the curve reproduction needs to be exact and precise in each instance.  For just about every need imaginable for a woodworking shop project, someone has been there and come up with a jig or a device that will meet that need.

Such is the case with reproducing curves and transferring them to multiple pieces of wood for your project.  In our research for next spring’s moon gate, we came upon one that appears to solve this problem and fill the need. 

This device can handle complex curves and pretty much any curve shape.  It’s flexible enough to help you both form those curve shapes and then easily copy them from one piece of wood to another.

These flexible curve template woodworking tools are mechanical devices, just as the trammel of Archimedes is, but with much greater adaptive features that can conform to any curve on any flat surface.  So, copying and transferring a curve shape to another flat surface is made easy with them.

You can find them on the largest online retailer’s website, and they are also available on other retail platforms, including eBay, we found.  They are not expensive and will run you under $50 for a 37” tool.  

Creating a First Instance Curve Shape and Copy It To Another Piece of Wood

Have you ever heard of plastic wood?  There actually is such a thing, and no, it doesn’t come from trees.

Recycled plastic is used to create plastic wood that is used in place of regular lumber for outdoor furniture and decking and other outdoor projects.  It’s plastic, so it will not decay or rot in the elements.  

One of the talents of plastic wood is to bend without breaking or snapping. This can help you create a curve shape on a flat surface.  

 Clamp blocks to the piece of wood you need to create a curve shape on and spring-fit a 1 x 2 piece of plastic wood between them.  You can change the curve by moving and adjusting the blocks you’ve clamped to the piece of wood to the degree and shape of curve your project needs, and then mark the edge of the curve arc.

By keeping and using the same measurements for block placement and 1 x 2 piece of plastic wood, you can copy the arc onto other pieces of wood if you need more than one arc.  Or, you can simply cut the first arc and then use it to transfer the curve to another piece of wood.

Maybe it’s a frame for an arched opening or making curved brackets, or an arch-top casing that is a part of your project.  This method of using plastic wood can also do the job for you to make uniform curve cuts.

Finishing Curve Shapes on Multiple Pieces of Wood

Random Orbital Sander

If your project involves more than one curved piece of wood, we suggest you batch-smooth them. Whether you are using a file or rasp, to begin with, or will go directly to a random orbital sander for tight curves, clamp the pieces together and then clamp them to your workbench.  Depending on the size of the work pieces, a belt sander might also be a good choice.  

This will make it easy to get them ready for your chosen finish and ensure they are uniform in shape.  That is the point of the exercise – creating a curve shape that is the same in multiple pieces of wood for your project.

We found the solution to the moon gate project for next spring and, in the process, traveled back in time to Archimedes for his trammel mechanical device and then returned to current mechanical inventions for today’s woodworking tasks.  These other methods might be of some interest to you, too.

We do think a trammel of Archimedes would be a very cool project to tackle at some point, too.  Even if we never use it, we’re walking with one of the great mathematicians and scientists in history.  That alone might make the project worthwhile.  After all, we’re woodworkers, and that’s what we do.

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