Tag-Archive for ◊ curves ◊

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• Wednesday, September 16th, 2020
1:4 French curves

These useful tools from Veritas are paired sets of French curves. The small and large members of each pair have the same curve pattern in a 1:4 ratio.

This allows you to draft on paper at the commonly used scale of 3 inches = 1 foot using the small curve of the pair and then transfer the drawn curve to the workpiece using the full size curve of the pair. Similarly, you can layout full size mock ups with the large curves, decide which one looks good, then use the corresponding small curve to incorporate the curved element into your design on paper.

Veritas French curves

The curves are made from 3mm-thick 3-ply birch. The largest one is 36″ long. The edges are not as smooth as plastic curves, so you might want to do some light touch up with sandpaper using a block to avoid rounding over. 

There are tiny holes at corresponding locations in each pair of curves that can be used as reference points to transfer a layout from one curve to the other in the pair. Numbering the holes, as shown here, helps keep track of the paired locations. 

1:4 French curves marked up

I often use long, very gradual curves in my designs, so I wish Veritas would also produce paired sets like these with very mild curves. I imagine this could be readily done with a CAD-CNC process. 

The key to using French curves is to mark the end points of a curve, then “fill in” the curve using at least one (usually two or more) additional reference point(s) to guide the placement of the template. Shift the reference points and use various segments of the French curve until the drawn curve looks the way you want. 

Consider using this wonderful rasp for truing curves in templates and workpieces. [If I made a buck from it, I might have called this a shameless plug.] 

By the way, why “French” curves? Beats me, but with a little online research, I learned that French curves are based on segments of the Euler spiral, named for the great eighteenth-century Swiss mathematician. The Veritas curves approximate a common Burmester set, named for German physicist-mathematician Ludwig Bermester (1840–1927). So, why aren’t these types of curves called “German curves?”

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• Friday, January 18th, 2019
RP rasp by Liogier

This rasp is unique: the toothed surface is flat across its width with a convex curve along its length, and handled at both ends. 

Grasp the handles intuitively – from the sides or over the top – and bring teeth near the leading end into contact with the wood (top photo), then ease the trailing part of the rasp onto the wood (photos below), using a pull or push stroke. Let the sharp teeth do the work; don’t force them into the wood. As you move along the desired curve, you’ll subtly feel more resistance over bumps, less over hollows.

curved rasp

This does not work like a compass plane or spokeshave because they have only one contact point that cuts. The rasp cuts all along its length, encouraging a sweeping motion

RP rasp

Curves are generally best worked in the downhill direction so as to work with the grain, but this can vary. I readily switch from a pull stroke to a push stroke as I work, gently tipping the rasp toward or away from me as needed. This tool encourages working instinctively.

The constant radius of curvature of the rasp makes all of this easy and intuitive. You can use any part of the rasp, changing from push to pull, and always know the curve you are presenting to the wood is constant. (Of course, this does not mean the rasp is restricted to working on curves of constant radius.) In my early designs for this tool, I found I could not work as fluidly with a variable radius. 

The stiffness of the rasp, the tang fit of the handles, and the smooth-cutting sharp teeth, magnificently crafted by Noël Liogier and his team, work together to provide excellent feedback to your hands as the curve takes shape under the tool. You can feel the curve becoming true even before you stop to look at it. 

I think you will be delighted with the performance of this rasp. Liogier sells it for €58, about $66, which is a bargain considering its durability, utility, and the incredible workmanship they put into it.

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Author:
• Saturday, January 12th, 2019
RP rasp

This unique rasp, handmade by Liogier in France, will allow you to deftly produce beautiful curves in your woodwork. 

The stitched surface is flat across its 30mm (1 3/16″) width with a shallow convex curve (radius = 320mm) along its 160mm (6 1/4″) length. The robust hardwood handles at each end can be gripped from the sides or over the tops to give you power and control with an in-line push or pull stroke.

You will feel exquisite tactile feedback as you fair gradual curves such as refining bandsawn curves in a table leg or rail prior to final smoothing with a scraper or sandpaper. I suggest grain #10 or 11 for general furniture work.

RP rasp

After years of wishing such a tool existed, I designed this rasp in my shop using wooden and sandpaper mockups, and extrapolating from other rasps. I experimented with various curves, lengths, and widths for the cutting surface, and also put a lot of time into trying different positions and shapes for the handles. I presented the design to Noël Liogier who produced it with his legendary skill. The result: c’est manifique!

It is now available from the Liogier website for €58, currently $66.57.   

RP rasp by Liogier

You may find it helpful to visit the post I wrote a few years ago about available options in tools for working curves by hand, and the two posts about the process of fairing curves. There are two key points. First, distinguish between two different processes: shaping the curve and smoothing the surface. Second, when fairing (shaping) the curve, you need a tool that provides continuous tactile feedback of the developing curve. The tool must have sufficient rigidity and length to reduce aberrant bumps and troughs. 

This new rasp is far better for fairing curves than other options such as an adjustable float, Surform shaver, or diagonally pushing the convex side of a half-round rasp. It also provides better control and power than do curved ironing rasps for this task. Shorter tools such as a spokeshave or scraper are less reliable for fairing. I also think you will find this rasp more user friendly than a compass plane or other curved-sole planes. 

new Liogier curved rasp

Liogier is one of the two best-in-the-world makers of hand-stitched rasps, both in France; the other is Auriou. This video shows some of the incredible workmanship that goes into these tools. There is nothing quite like using a hand-stitched rasp. This new design adds to the venerable repertoire. 

If you do give this new rasp a try, I’d love to hear what you think of it.

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Author:
• Saturday, December 30th, 2017

curved cork sanding block

Customized shaped blocks are a must for properly sanding concave curves. They are a key player on the Tools for Curves team. Cork has the ideal flexibility and resiliency for backing the sandpaper.

Lately, I have been making the blocks entirely from cork. These work better and are easier to make than what I formerly used, which was shaped wooden blocks with a layer of cork added to the working surface. By the way, I have experimented with pink foam board insulation and found it difficult to shape reliably.

To make these all-cork blocks, you need thick stock. It is wonderfully easily to cut with a handsaw or bandsaw, and shape with a moderate-grain rasp. The curve does not always need to be a constant radius – simply draw it freehand and saw. Refine it with the rasp, ensuring that it is just a bit steeper than the steepest section of the work piece.

cork block

Make the thickness of the block to your liking based on how you want to grip the block. The block pictured at the top is about 1 1/2″ thick. You can try to size the block for optimal convenience in cutting the sandpaper from standard 9″x11″ sheets, and to minimize waste, but good function and feel in the hand are the more important factors for me.

Saw kerfs 3/4 -1″ long about 1/2″ from the top face of the block to house the ends of the sandpaper. Hand pressure will naturally keep the paper in place (see below) even in fine grits and more so in coarse grits. No wedges or clips are needed. The chamfers at the beginning of the slots toward the working face are important.

curved cork sanding block

To install the sandpaper:

Enter one end just a little into the slot, then bring the other end around the block and push it almost all the way into its slot. Working back the other way, snug the paper around the block and then push the original end as far as possible into its slot. Make a final tightening of the paper by pressing the paper it against one of the chamfers then use your fingertips to goose the paper even more into the slot.

cork sanding block

The simple design of these blocks along with this paper insertion procedure produce a tighter hold on the sandpaper against the surface of the block than any commercial curved block that I have used (none of which I like).

Finally, the light weight of an all-cork block is an asset not to be underestimated in the countless (ugh!) reciprocation of sanding work.

Find thick cork by searching online. Try “cork blocks” or “cork yoga blocks.” I suggest the Corkstore (Jelenik Cork Group), which currently sells a 9×5″x5″x3.5″ yoga block for $19.25, and 12″x8″x2″ block for $17.10. This is a nice fine grain cork that is easy to shape reliably. Dick’s Sporting Goods sells a 9″x4″x6″ block, so you might be able to find it locally.

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Author:
• Friday, April 25th, 2014

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This unpretentious tool, for about six bucks, is surprisingly useful to modify concave curves on fairly narrow work such as table legs. I use it for fast, corrective takedown if my bandsawing has wandered off the layout line, or if I’ve changed my mind about the curve after having sawn it.

Its molded plastic handle and snap-in cutter certainly do not exude cool-tool cachet, but the varying curve of its sole, flatter toward the toe, steeper toward the handle, is quite effective. It cuts on the pull stroke. However, it tends to tear the wood and leave a surface too ripped up for efficiently transitioning to refinement with finer tools.

To remedy this problem, I hone the cutting face with a fine diamond stone. While this sharpens the cutting teeth, it has the more significant effect of limiting their depth of cut. This does make it a somewhat slower tool, but the resulting surface is considerably improved, so the whole process of refining the curve is actually faster.

The macro photo below shows the honed teeth, which have been lowered relative to the peaks of the “waves” on the cutting surface. (The cutting edges are facing upward. The honed area is the silvery line visible on each of the two teeth near the center of the photo.) This is similar to the working of an “anti-kickback” router bit, in that it limits the depth of bite of the cutter. If you go too far with the honing, the teeth will have too little bite or won’t work at all, so proceed gradually with the modification and test the tool as you go.

IMG_1216_edited-3

The tooth lines are angled to the length of the tool, pre-skewed, in effect, so I find it works best after this modification by pulling it with little or no additional skew.

IMG_1219_edited-2

A great tool it is not, but it does the job decently well. I wish Stanley (or Microplane) would make a longer version, say four or five inches, retaining the varying-radius curve, with room to place a second hand on the front of the tool. Not currently made, but perhaps a Shinto rasp in such a profile would be useful, or larger rasps in the style of curved ironing rasps, both with a knob at the toe for greater control and power.

Other options for a tool that is curved along its length and flat across its width include: metal and wooden compass planes, Auriou and Liogier curved ironing rasps, shop-made curved sanding blocks, and a new flexible rasp by Liogier that they call “The Bastard,” which I have not tried.

The Stanley Surform Shaver now comes with a bright yellow handle. Nuance that.

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