Edge Joining Along A Curved Line With The Router

Inlay work docsn t have to be done using die internal (or female) template. You can make an external (or male) template for the job. All you have to do is reverse the bushings used for the two cuts.

To cut the recess, apply the template to the stock with double-sided carpet tape. Install the snwila of the two guide bushings on the router, and make the perimeter cut. Keep the bushing tight against the template as you work. Pry off the template, and rout out the rest of the waste.

Then stick the template to the insen stock. Switch to the larger of the two bushings, and rout around the template. The resulting insen should fit the recess perfectly.

A male template, also known as an external template, is less common in inlay than in other sorts of template work, probably because it is a hit more involved. For example, to form the recess, you Iwnd the template to the workpiece, then guide the router around it. Thai pass forms the perimeter. To complete the recess, you remove the template. You also remove the guide bushing from the router and reset the depth of cut.

A male template, also known as an external template, is less common in inlay than in other sorts of template work, probably because it is a hit more involved. For example, to form the recess, you Iwnd the template to the workpiece, then guide the router around it. Thai pass forms the perimeter. To complete the recess, you remove the template. You also remove the guide bushing from the router and reset the depth of cut.

The insert can be cut from any piece of stock; it doesn't have to he thin. Rout what will be the insert in any stock of the right grain and color and size, cutting alwut'/«inch deep. At the hand saw, stand the stock on edge and cut a slice about Vs inch thick. As it clears the blade, the insert will fall into your hand.

The basic range of inlay worfc is displayed in this tulip. The stein represents string inlay: the blossom and leaves, regular tern plate-guided inlay.

As you make the cut, keep the guide bushing firmly against the template. You can't afford to let your attention ¡lag for an instant, for the Spent it does, the router is sure to drift into [he insert and ruin it. Be especially careful on curves and at comers. These are the most likely spots for the router to drift. Feed the router around the template in a clockwise direction. This is working against the bit rotation, so it will help force rhe guide bushing against the template edge.

When you are done, the insert should drop right into the recess. If sis loose, your bit is probably slightly cwrsizcd. If it is too big to fit the nccss. the bit is probably undented. Assuming the insert fits correctly. g)ue it in place, and sand it. Perfect!

String Inlay

For centuries, craftsmen have decorated panels, tabletops, drawer fronts, and the like by carefully carv-iagddicatc grooves and patterns and filling them with inlays of contrasting wood. These inlaid lines, especially cuned lines, are traditionally called "suing inlay" or "stringing." You can do the same thing easily by cutting the grooves and shapes with j router guided by a template.

Design your inlay from the Stan so that you can cut the grooves with 3 router and so that the inlay wood doesn't have to be bent too much during installation. Narrow inlays hive a delicate appearance and look | difficult to do. But since the narrowest router bit you'll find is a Merinch single-flute bit in high-speed steel (Bosch #85091, for example), Fred suggests that you design your inlay !or Ktrinch-wide lines.

A template guides the router for

The basic range of inlay worfc is displayed in this tulip. The stein represents string inlay: the blossom and leaves, regular tern plate-guided inlay.

smooth, flowing curves and tnily straight lines. Since it takes time to make the template, try to include repeated or mirror-image curves in your design. That way, you can use the template severa! times, or at least flip it over to produce a mirror image.

Bear in mind that you have to fit wood into the grooves that you rout. You can miter the inlay pieces at sharp corners and bend the wood into reasonable curves, but it's difficult to bend most M-rinch-thick strips any tighter than a Winch radius. Avoid the frustration of broken inlay pieces by designing the curves no tighter than you can bend the inlay wood.

Try the whole process on some scrap wood, so you develop a good feel for what the wood can do.

Templates. As you know, when it's being guided by a template, the bit cuts a groove that's offset from the template. The distance fioin the centcrline of the groove to the edge of the template will always be half the diameter of the template guide. You'll simplify making the template if you design your inlay by drawing a line for the centcrline of the groove instead of drawing two lines for the two edges of the groove.

To make the template, first trace the inlay design onto the template stock. Set a compass to half the guide bushing diameter, and strike a series of arcs on the template side of the line (nor rhe waste side). Draw a smooth curve connecting :he high points of the arcs, and saw out the template. Sand the edge to assure smooth, even curves.

To try out the template.clamp it in place on a scrap piece of wood, adjust the router to cut about Ys inch deep in the scrap, and cut the groove. Keep the template guide tight against the template as you cut. Clean out the grooves, and sand lightly to get rid of any whiskers raised by the cutler. Now check that the groove matches the pattern.

Cutting and fitting inlay strips. The next step is to cut inlay strips for the grooves. Choose an inlay wood with tight, straight grain, and cut several Mf-inch by Mfinch strips several inches longer than the groove. If your saw leaves deep saw marks, cut the strips a bit thicker than xAt inch

The tulip stem requires only a modest undulation, and the tem/.ilate can be cut quickly on the band saw. Only a single pass is necessary to rout the string inlay groove, which is ty pically routed with a Yn-inch bit.

mer to scat the strip firmly inio the groove.

Let the glue dry, and then sand the strip down flush with the surrounding surface. Be careful not to split die strip while you are sanding it down. A split could easily ran down below the surface and show in the finished job.

And that's it—you've inlaid delicate curved lines.

JOINERY CUTS

If you think template work is strict!)' decorative stufF. you arc misinformed. Remember that commercial dovetail jigs are all template-based units. Check out the chapter "Dovetail Joints." You'll see that die jigs require you to use either a template guide or a pattern bit.

But cutting dovetails isn't the only template-guided joinery work you can do. You can use templates to guide mortising cuts. A template stuck to a table or chair leg so you can finalize the contours with a router may also have a "window" in it to guide a mortise cut. See the chapter "Mortise-and-Tcnon Joints" for more details for using templates to make these joints.

And page through the chapter "Lap Joints." A dandy variation is the mitercd half-lap. Cut this one with a set of templates. Also, a dove-tail half-lap is a tcmplatc-guidcd joinery cut.

Multiple Blind Spline Joint

A template is essential to making this joint, which is a strongly reinforced miter joint.

Though it is unobtrusively, attractive, the miter is weak. Thai's

To bend the inlay strips, rest a thin strip of wood across the shaft (NOT the tip) of a hot soldering iron and press lightly to bend it. When the wood is hot enough, it will bend easily, if not hot enough, the wood will crack, and if too hot, it will scorch. You may waste a few strips before you get the hang of it.

so you can sand out the saw marks and still produce a good fit in the grooves.

If you've designed an inlay with very easy curves, you may be able to fit the strips in the grooves without prebending. but with most designs, you must prebend the strips to the shape of the design. The easiest way to bend the strips is with heat. You can bend them over the round body of an electric soldering iron. Lay a strip of wood across the hot iron and press lightly to bend the strip around it. Start at one end of the design, bending the strip to match.

and work your way from curvc to curve, checking the bent strip against the design as you go. Try to be accurate with the bends. You'll be able to spring the strip a little, but the closer it is to the proper shape, the easier it will be to install. Leave the strip a bit longer than the groove.

When the strip matches the groove fairly closely, place a small amount of glue in the groove and press the strip in, starting at one end, as shown. Trim the strip to length before pressing the hist end into place, then set a block of wood over the strip and tap it with a ham-

Apply a scan r bead of glue to the groove, then set the bent strip into place. Start at one end, as shown, and work toward the other, flexing the strip as necessary to fit it. Be gentle, of course. As you seat the strip, be especially careful not to break off its protruding top ridge;you want to sand this flush and not have any spli ts descending into the inlay.

Roulitig the multiple blind spline joint is just like routing dovetails. Clamp the template to the stock, as shown, and rout the spline slots, directing the router into and out of each slot in the template.

Assembling the joint is a bit laborious, since there are lots of splines, and each is a separate, tiny cube of wood. You'll have the least trouble if you glue them into the slots in one workpiece, then apply glue to the second, mate the pieces, and clamp.

¡because it's end grain to end grain. :Thc splines used in this particular joint are small, but there are enough ofthcm to dramatically increase the j-grain-to-long-grain gluing surface. Equally important, the splines 'in completely invisible. The joint ¡looks like a miter.

Each spline is like a loose tenon. ¡You cut a recess in both mating surfaces, and link the mating pieces together with the spline that fits into erne recess and extends into die other. If the joint is to line up perfectly, the [ sockets for the splines have to line up.That's where the template comes in. By cutting the sockets in both pieces using the same template, you can virtually guarantee the sockets »ill align.

In theory, the closer together you place the splines, the more of them there will be, and thus the | stronger the joint will be. But the more splines there are, the more work there will be in cutting and [assembling the joint. Here's a practical compromise.

I. Make the template. Cut a 20-inch by 12-inch template from Zi-inch pl^vood. The template has a scries of slots along one edge, as shown in Multiple Blind Spline Joint. The size of the slots is determined by the guide bushing's outside diameter. The bushing must fit into the slot without any play. Cut the slots using a box-joint jig. (See the chapter "Box Joint" for details on making and using this jig.)

Cut a series of 1-inch-deep dadoes along one long edge of the template. The exact spacing is not critical, but making the space between the slots about twice the size of the slots achieves that practical compromise between strength and labor.

Roulitig the multiple blind spline joint is just like routing dovetails. Clamp the template to the stock, as shown, and rout the spline slots, directing the router into and out of each slot in the template.

2. Rout the spline joint. Mark one short edge of the template "Front." Always place the template with its front edge flush with the front edge of the piece to be routed. This automatically aligns the spline slots. Clamp the template to the miterecl edge of the stock as shown in the photo above. The fingers extend over the miter: the base of the slots lines up with the heel of the miter.

Rout the multiple spline slots Vi inch deep. With a '/2-inch chisel, square the rounded edge of the slot flush.

3. Cut splines to match the slots. Plane several lengths of wood to fit into the spline slots. Rip the required number of splines to width, and crosscut them to length.

4. Assemble the joints. Glue the splines into the spline slots in one mitered edge, then glue and clamp the mitered corner together.

Without a router, the only way to make this joint would be by hand. You'd have to lay out the sockets.

Assembling the joint is a bit laborious, since there are lots of splines, and each is a separate, tiny cube of wood. You'll have the least trouble if you glue them into the slots in one workpiece, then apply glue to the second, mate the pieces, and clamp.

Bushing Guide Router

USE THIS SUOP-MAOE TEMPLATE TO ROUT THE MULTIPLE BLIND SPUME JOIMT

guide &usm1mc offset molds cut shy or wrtfl's heel.

v muart routed slots augn suns template guide &usming dadoed slot between slots cam varv.

x* diameter of guide busiung. for (vest results, use smallest bushing tuat will accept bit «.inc. used.

Inlay Bit Adjustable Bushing Guide

then chiscl them out one by one. Only your layout skill could ensure they line up from one workpiece to the next. And without a template, there's no way you could align a router-cut joint. The t cmplate guidance system makes it work.

Edge-Joining along Curved Lines

Want to join two workpieces perfectly along an irregular contour? An undulating curve, for example. Not easy, is it?

The difficult)' arises from the fact that when you cut a board in two. you are removing material. This isn't a problem if it's a straight cut— ripping a board in two, for example. The two pieces should go back together perfectly.

But if the cut is curved, the two parts won't go back together perfectly. The curvc's exact contour on one pan will be different from the contour on the other because of the matenal that was removed. Think about it now. If you use a router and trammel to cut a circlc, the disk removed is smaller in diameter than the hole it camc from. The difference will be twice the diameter of the bit you used.

And even if you cut only a part of the circlc, only an arc. the contours of the two workpieces will be different, because the radius of the convcx arc will be different—by the bit diameter—from the radius of the concave arc.

The difference between the two lines is called the offset. (It's the same deal as the difference between die outside diameter of a guide bushing and the diameter of the bit.) To achieve a perfect fit. you have to eliminate the offset.

Woodworkers who do inlay work confront and overcome this problem in every projcct. (Sec "Inlay Basics" on page 151.) They do it by-using combinations of template guide bushings. They introduce offset in one cut. then remove it in the complementary cut. So this process of routing boards for edge-joining is simply an extension of inlay techniques. You control the offset you introduce so that you can. in effect, back it out at the right stage of the operation. A major difference is that inlay work usually involves a single template that's used for both the recess and the insert. Here, two separate templates are used, though both are generated from the same master pattern.

Here, in a nutshell, is the procedure.

1. You make a master pattern, whose edge contour represents the joint line.

2. Use a pattern bit guided by the master pattern to cut two templates that you'll use when routing the workpieces. Let's call them the left

YVhat's sifecial about this box is ofoious. Getting a good, tight joint along the curv ing lines is virtually impossible. But a router, guided by a template, can do it. We joined two long boards of contrasting color along an undulating line, then made them into a l>ox.

If you really want to save time, use the left workpieee as the master pattern. This will allow you to eliminate a few routing pnocedures.

Cut the desired joint line on the workpieee with a saber saw or on the hand saw. Sand it smooth. Use it as the pattern to rout the right template, and with that template as the guide, shape the mating workpieee. Glue up the two workpieces, and you are done.

and right templates, just to keep them straight. The left template will be a duplicate of the master pat tcm, and in fact, you can use the master pattern as the left template. The right template will be offset by the diameter of the pattern bit used.

3. When you rout the left workpieee. you use the left template (or the master pattern) to guide a pattern bit. making a duplicate.

4. When you rout the right work-piece, you use the right template to guide a homemade pattern bit or a bit and guide bushing. The bearing (or bushing) must be larger in diameter than the cutting diameter of the bit.The difference between the diameters must equal twice the offset.

(Before going into detail on this template-guided approach. 1 do want to mention that you can satisfactorily edge-join two boards along a gemlv curved line if you joint them using a fence referenced by the router baseplate. The details of this procedure are in the chaptcr "EdgeJoints.")

Deal with the offset. The trick here is to introduce an offset that you can remove, without getting into bi2ane combinations of bit and guide bushing or bit and bearing. Stick with the system you are most comfortable with: home-brewed, pattern bits or guide bushings.

Make your initial cut with the smallest-diameter bit you can. This reduces the offset. A 3/a-inch bit (on a 14-inch shank) is the smallest-diameter pattern bit I know of. (It's available from Woodhaven; see "Sources" on page 337.) To back this offset out requires a 1-inch-diameter bearing (or bushing) with a 'A-inch bit. This is manageable.

To back out the offset if you use a /2-inch bit for the initial cut, you'll need a combination like a L'A-inch-diameter bearing or bushing with a '/■-inch bit, or a l'/i-inch-diametcr bearing (or bushing, if you can find one that big) with a /¿-inch cutter. Clearly, any offset in excess of Vi inch requires an unwieldy (and unlikely) combination of bearing or bushing and bit. Bear in mind that your options are not endless. You'll find the range of bushing sizes is limited, as is the range of available ball bearings.

All right now. Arc you flummoxed by this business with the bearings? I know you won't find in any catalog a bit that has a bearing on its shank that's larger than the cutting diameter. You have to make

The bearing must be larger than the cutting diameter. That's essential in an offset pattern bit, but so is having a shoulder between the cutter and the shanh to catch the bearing. Slide the bearing onto the shank and trap it between that shoulder and a collar.

up these bits yourself. It really isn't difficult. It is. after all. what the bit manufacturers are doing to create pattern bits.

You can buy the bearings from a number of bit vendors, including Woodhaven, CMT. Amana. and Eagle America. (See "Sources.") What you want is a ball bearing with an inside diameter that matches the shank diameter, and an outside diameter that creates the offset you need. Theoretically, you shouldn't have to do anything to keep the bearing in place. It's trapped between the cutter and the collet. If it does ride up the shank, you can add a stop collar, which you can buy from a number of bit manufacturers, including Woodhaven and CMT. The loose knot here is that '/»-inch bit. which won't have a shoulder between the cutter and the shank. You need to use a couple of stop collars on this bit. Some woodworkers use a fluid called Locktite—you can buy it at an auto-parts place—to "glue" these bearings in place. With a stop collar, you can remove the bearing. I'm not sure if you can after you've locked it tight with Locktite.

If you don't want to get into "making" your owti pattern bits, use those guide bushings.

The bearing must be larger than the cutting diameter. That's essential in an offset pattern bit, but so is having a shoulder between the cutter and the shanh to catch the bearing. Slide the bearing onto the shank and trap it between that shoulder and a collar.

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  • tim
    How to cut matching curves to glue template router?
    7 months ago

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