Tag-Archive for ◊ curves ◊

Author:
• 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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Author:
• 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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• 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.

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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.

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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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Author:
• Tuesday, April 22nd, 2014

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As I said, I’ll use whatever tool it takes to get the desired result for a particular curve in a particular wood. So let’s take a look at the available players and which make the cut (pun intended). Most of the game is won or lost on concave (inside) curves; the outside curves are easy.

Spokeshaves perform well on relatively narrow work with cooperative grain, but they can disappoint on highly figured woods, even using a skewed attack. The round shave sees almost all of the action, while the flat shave spends most of the time on the bench because I generally don’t find it has much advantage over a block plane or other flat tools on gradual outside (convex) curves. It’s all in the wrists.

The convex side of a half-round rasp is a good workhorse but has some weaknesses. If it is held at an acute skew, such as for steep inside curves, the teeth start to function ineffectively as tiny knives slitting along the grain, but if the tool is pushed more across the work, tearout results at the far side. Also, the tool is really working the curve at different points, and thus possibly different radii, at once.

So, for more control on gradual curves, I call up the Auriou curved ironing rasps (fourth and fifth from the left in the photo). They have an excellent reliable feel on the curve but lack speed, so they are not for hogging off a lot of wood.

The compass plane, which is a shaping plane in my view, was covered in two earlier posts, but a different twist on curved soled planes deserves mention. As discussed in the previous post, the sole must be set to accommodate the steepest portion of a chosen length of inside curve, so a given setting is approximate at best. Thus, a reasonable alternative to an adjustable compass plane is a set of a two or three wooden fixed curve sole planes, vintage or shop-made.

Hunting on vintage tool sites will turn up a few wooden curved sole planes with an adjustable toe piece to accommodate different inside curves. I have not tried one but I wonder if any readers have.

The little Lie-Nielsen spoon bottom plane is a different type of player but performs well despite its lack of size.

A card scraper is a good player if used in the proper role – great for smoothing curves but poor for shaping them because it simply rides whatever curve it encounters.

Underestimated but well within anyone’s salary cap is the curved sanding block. Customized in length, width, and curve, they can smooth curves but also can be designed as pretty fair shaping tools using coarse grit paper.

Speaking of sanding, the Ridgid oscillating spindle sander is very handy because it can be set up as a sideways belt sander or as a simple spindle sander in a range of sleeve sizes.

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Back to the opening photo, the humble Stanley Surform shaver, a product of a program whose glory days are past, is an effective rough hogger. Surprisingly, it can be tuned to perform with a bit more finesse, as will be discussed in a future post.

The Allongee style gouge, #5 sweep, 38 mm, is a good reserve player for cross grain hogging in wide curved work, much like a freehand scrub plane for curves.

A couple of other tools are not in the TFC Team photo because, though they arrived with promise, were cut after tryouts. I found the flexible curved float file to be slow and awkward, and did not live up to the reputation of its flat cousins. The same was so for the Microplane flexible insert for a hacksaw frame. These are just this coach’s calls; you might like them.

When there is a simple curve in one plane, as shown below, to be made in multiples, I go to the pattern routing game plan, as represented by the pattern/flush cut bits on the right in the top photo.

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Of course, just about all curves start with good, accurate sawing, which usually means a well-tuned bandsaw. That’s the fan base behind the whole team.

Next: nuancing the Surform Shaver.

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Author:
• Saturday, April 12th, 2014

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The compass plane is an effective tool when thought of as a jack plane for curves. It is mostly a shaping plane, where the shape is a curve, not a flat surface as for a regular jack plane. It is mostly fantasy to think of the compass plane sleigh riding over varying-radius curves spilling out long silky shavings.

The most important step in efficiently forming true curves in solid wood is to saw consistently to a good layout line. However, there will inevitably be some lumps and bumps in the sawn surface, so the curve must be “faired” to make it pleasing.

Key to using the compass plane is that the sole must be set a bit steeper than the work piece for concave (inside) curves (see photos above and below), and a bit shallower than the work piece for convex (outside) curves. Furthermore, the planing should proceed into downhill grain, that is, with the grain, which means you may have to turn around often. Outside curves are generally easier to negotiate, and shallow ones can often be worked well with a flat-sole plane such as a block plane.

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This all sounds good except that most of the interesting curves in woodwork have a varying radius (i.e. are not circular) and some reverse from inside to outside. So that means a single sole setting is ideal for only a relatively short length of curve. As a practical matter therefore, for inside curves, the sole is set to accommodate the steepest portion of a length of curve that you choose to work in which the radius does not vary too much. It is a matter of feel and judgment. Which is to say that these planes are not very practical for abruptly changing curves.

Because we want the plane to remove lumps and bumps, the shavings, especially early on, will mostly be short, and the cutting edge will engage and disengage the wood as you take fairly short strokes. Then as the fairing proceeds, the shavings will lengthen; that is, if the planets are aligned.

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The compass plane is capable of fairing a nice gradual curve in the right circumstances and wood. Remember too, it can handle wide surfaces that are difficult to manage with spokeshaves and rasps.

Also, it is often helpful to initially remove some of the roughness of the sawn surface with a rasp (not a sanding block) to avoid a very rocky ride in the early stages of planing.

The anatomy of the compass plane does not permit it to transmit the wood-hugging stability that we expect from a good bench plane. I like to make the ride firmer and improve my feel of the plane’s interaction with the wood by placing my right hand as low as possible at the heel, sometimes with my fingers touching the top of the sole plate. Meanwhile, the palm of my left hand hugs down on the nose as my thumb reaches down onto the sole plate.

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Ultimately, it’s not about the tool, it’s making the product come out the way you want it that counts. I’ll use whatever tool it takes to produce the desired curve in a particular wood. Sometimes, that’s the compass plane.

Next: scouting reports on each player on the tools for curves team.

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• Friday, April 11th, 2014

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I enjoy incorporating curves in my work and so have explored lots of different tools and methods for shaping, refining, and smoothing them. Years ago I used a new Record #20 compass plane but then got rid of it. The problem, however, was mostly in my approach to the tool. I’ve harbored mixed feelings about the metal compass plane since, but have finally come to peace with the beast since owning this vintage Stanley #20 for the past year.

I’ll get into the function and handling of the tool in the next post, but here I will detail its tuning and modification.

This #20 was manufactured sometime in the years 1933-1941, as best I can tell. It arrived from the seller fundamentally sound – no cracks in the main casting, working sole adjustment, and japanning in excellent shape.

These planes need all the help they can get with chatter dampening so I replaced the thin Stanley blade and chipbreaker with a hefty Hock A2 cryo blade (#BPA175) and chipbreaker (#BK175), 1 3/4″ wide. I prefer the durability of A2 for the way I employ the #20, which I’ll discuss in the next post.

Patrick Leach notes that the #20 (and #113) have unique chipbreakers so I carefully checked the diagram on Ron Hock’s site. The critical parameters are the chipbreaker’s slot-to-edge distance and the length (the short dimension) of the slot. These worked out beautifully. The #20’s advancing fork engaged the chipbreaker slot very well despite the increased thickness of the blade-breaker set. Also, the disc in the lateral adjusting mechanism nicely engaged the blade slot.

Unfortunately, the thicker blade-breaker set caused severe pleating of shavings, and bad clogging. To remedy this, I disassembled the sole by knocking out the pin at each end of the sole and freeing the dovetailed connection between the sole and the body, then filed the forward side of the mouth to widen it (barely advancing into the row of pins that bind the flexible portion to the dovetail block), and added a slight forward angle to the throat, all to make more room for shavings to escape. It also proved necessary to round over the crisp bevel on the back of the chipbreaker.

This solved the clogging problem very nicely, and the beefy A2 Hock set outperforms the Stanley set! Suprisingly, I have not found the wider mouth to be a problem for planing curves. 

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The frog needed minor truing. I reattached it as deep as it would go, then, after reassembling the sole, filed the landing below the frog to be mostly level with the frog to increase support for the blade.

I flattened the sole around the mouth with a diamond stone. There is no point in flattening beyond the vicinity of the mouth in a compass plane with its flexible sole. A general clean and lube, and touch ups with a file here and there, finished the job.

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Consistent with the purpose that I assign to this plane, I sharpened the blade with a medium camber and made sure the corners would not catch the work piece.

There are other options in metal compass planes including a Record #20, Stanley #113, other variants of the #113 style, and current versions of the #113 by Kunz and Anant.

The metal compass plane is a bit of an odd animal and one must come to terms with it, as will be discussed in the next post.

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• Sunday, July 14th, 2013

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Sanding blocks with a curved face can be very effective for smoothing and, with coarse grits in the right circumstances, even shaping curved surfaces in furniture making. I use spokeshaves, specialty planes, rasps, and scrapers to shape and smooth curved surfaces, but not to the exclusion of the humble sanding block.

They can be made quickly and easily with the bandsaw or bowsaw. For working concave surfaces, the curve of the block should be slightly steeper than the steepest part of the curve of the work piece. For convex work, a flat block is adequate for working shallow curves. For working steeper convex curves, the block’s curve should be slightly shallower than that of the work.

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The top of the block should be shaped friendly to the hand using saws and rasps. I like to steeply cut down the corner of the block near the base of my right thumb, as well as the diagonally opposite corner.

The backing surface for the sandpaper should be have some type of firm cushioning, similar to a random orbit sander. For most broad surfaces, I like the high-friction cushion material available in with a pressure-sensitive adhesive backing from Lee Valley. PSA-backed 1/16″-thick sheet cork is firmer and thus good for narrower, smaller scale, or more detailed work.

Cutting regular sandpaper sheets and wrapping them around these sanding blocks is particularly annoying because of the curved surface. I much prefer using PSA-backed sandpaper that comes in large rolls, such as that available from Klingspor. It is quick, effective, and wastes less sandpaper, especially if the block is made to the width of the sandpaper roll. It is also reduces hand fatigue because there is no need to grip the paper to the block.

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A gum rubber block is usually associated with cleaning retained sanding dust from the sandpaper on power sanders, but it also works quite well on these sanding blocks, especially when doing heavy work.

As with any sanding, it is important to remember that only the coarsest grit – the first one in the sequence – should do any required  shaping. (Though most or all of the shaping will have already been done with other tools.) All the subsequent grits simply remove the scratches made by the previous grit until the surface is smoothed to your satisfaction.

In time, one accumulates a small collection of these curved sanding blocks, so some will coincidentally be just right for future projects. This is simple, effective woodworking – one more tool for working with curves.

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Author:
• Wednesday, February 20th, 2013

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When fairing a curve by hand, you need tools that give continuous feedback about the curve you are forming – a closed-loop system. The tool must have sufficient rigidity and effective length to reduce unwanted bumps and span aberrant troughs. For concave curves, the rounded contact surface of the tool must be a bit steeper than the curve being formed in the wood. The other key point is to distinguish between the shaping and the smoothing processes.

There are plenty of options. Here’s what I use.

Shaping

The Veritas round-sole metal spokeshave and Auriou “curved ironing” rasps, 30mm-wide #8 grain and 20mm #10, are my go-to tools for concave curves. The ride of the blade and teeth changes as they meet the varying resistance of bumps and valleys, so I can sense beneath the tool when the curve is becoming fair. The effective length and contact surface of these tools can be altered on the fly simply by changing the skew angle.

Working the surface of a curved leg to a slight crown across the width makes it easier going with the spokeshave, and in fact, I often finish it with this shape for appearance.

For quick hacking of big bumps, which might be present if I was daydreaming at the bandsaw, the inexpensive Stanley Surform Shaver works well.

The convex side of a half-round rasp can be used with some success on concave curves but there are cautions. The skewed stroke presents a varying contact profile as you push along a varying curve, so short strokes may be better. If the rasp is skewed too much, the teeth act like tiny knives and deeply groove the wood.

Convex curves are simpler to manage. A regular flat-sole block plane and the flat side of a half-round rasp work very well.

Smoothing

Smoothing the shaped surface is a different matter, much like smoothing and jack planes perform different functions. Here, card (hand) scrapers, especially in 0.024″ thickness, are my go-to tools, followed by light sanding.

Scrapers excel at smoothing, not eliminating, bumps and troughs, and so are not good for shaping, with the exception of light use on small, tight curves. With skewing, they may work for larger curves but it can be surprising how many lumps they preserve even when they seem to be shaping well.

Curved sanding blocks can be similarly deceptive. When working concave curves on legs, I find they are best left for smoothing because I just do not get as good shaping feedback as from rasps, spokeshaves, and planes. However, I have had success using carefully shaped sanding blocks with 60-80 grit paper to do the latter stages of shaping of broad concave surfaces. Also, a simple flat cork block does well on shallow convex curves.

Since I’m usually dealing with curly woods, rowed mahogany, or tough bubinga, I keep the spokeshave as a shaper.

What about spindle sanders and vertical belt sanders? I like my Ridgid combination oscillating spindle/vertical belt sander for many jobs, but use it only with trepidation for critical shaping or smoothing. I find it is just not as sensitive as hand tools, and it is more risky. Still, there are some curves where it is the best tool for the job, such as steep concave changes.

Pattern routing or sanding (with the Robo-Sander) with a template is a good option for single-plane curves, but I think is impractically complicated for multi-plane curves. Anyway, handwork is still required to make the all-important template.

I hope these tips help you become more comfortable, confident, and efficient with using curved elements in your woodwork. Choose the tools that are practical for you. No straightedge can be the arbiter of rightness for this work. You are a craftsman, so trust your senses!

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