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Winter 2013-2014

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Template Routing

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Template Routing

Simple to advanced methods for precisely duplicating parts.

By Lonnie Bird


No other method for shaping is as fast or efficient as template routing. It works like this: the part to be shaped is fastened to the template; the router follows the template as it is guided around the template’s perimeter (Photo 1).

Template routing ensures that each part is identical; whether you’re shaping six parts or sixty, each one matches the template (Photo 2).

Template routing is versatile, too. You can use this method for shaping almost any part, large or small. It works for making straight cuts, curved cuts, and even for moldings. The part can be as ordinary as a straight-sided shelf for a corner cabinet or as complicated as a serpentine drawer front, which has a convex section between two concave ones.

There are many methods of template routing, which I’ll explain below. They range from simple techniques, such as routing that corner cabinet shelf, to advanced setups, such as shaping a complex S-curve molding (see Routing A Gooseneck Molding).

Template routing is not just for production work. In fact, there are some cuts, such as shaping the entire edge of a curved tabletop or cutting a curved groove, that cannot be routed any other way. Once you understand this technique and use it a few times, you’ll begin to imagine other possibilities for its use. I even use a template for routing some joints (Photo 3).

 

Straight-sided parts

Even though most straight-sided work is crosscut or ripped on a tablesaw, there are times when the tablesaw is not as practical as using the router and a template. For example, the diamond-shaped shelves of a corner cabinet have straight sides, but most of them are not parallel. Odd shapes such as these are quickly and easily shaped with a router, a template and a flush-trim bit (Photo 4).

 

Curved parts

Curves can add a lot of interest to a piece of furniture. Routing these curves, following a template, is one of the best ways to ensure that the curves are uniform. Curved legs and drawer fronts, for example, are easy to duplicate (Photo 5). All you have to do is to make one perfectly shaped template, and the router bit will do the rest of the work for you.

Seemingly difficult curves, such as a gooseneck molding, can be easily shaped with a template. After the rough shape of the molding is created with a bandsaw, a template and a flush-trim bit can be used to smooth away the bandsaw marks and fair the curves. Afterwards, the molding profiles can be shaped using an overarm guide at the router table–more about that later.

 

Routing grooves and dados

Although there are a number of ways to cut grooves and dados with a router, using a template is among the most accurate methods–and in some cases the only choice available. When constructing fine casework, a template ensures accurate alignment of dividers and partitions (Photo 6). Instead of measuring and marking the location of the dados, a graduated set of templates, which register to the side of the case, provide pinpoint accuracy.

Tambours slide in curved grooves and disappear when opened. Routing matching curved tambour grooves, both S-curved and semi-circular, is no problem with a template (Photo 7).

 

Methods of guiding the router

The key to making various cuts with a template is to guide the router through the intended path. There are essentially four methods of doing this:

1) Using the guide bearing on the end of a bit;

2) Using a bushing attached to the router’s sub-base;

3) Using the sub-base of the router;

4) Using an overarm guide attached to the top of a router table.

The guide bearing method

The most convenient method for guiding the router is with the bearing on the end of a bit. Most profile bits have a guide bearing which can be used to shape the edge of a curved surface such as a tabletop. Router bit guide bearings are precisely machined and mounted concentric to the bit’s profile. This ensures that the profile’s depth remains consistent along the entire edge that’s being shaped. The small diameter of most guide bearings allows the bits to be used to shape tight contours (Photo 8).

Flush-trim bits also use a guide bearing. These bits are ideal for smoothing irregular shapes, such as the sloped edge on the sides of a slant-front desk, as well as smoothing tight bandsawn curves.

Most flush-trim bits have a bearing below the bit, but others have a bearing above the bit, on the shank. These bits are often called “pattern bits” in tool catalogs, and are quite handy when it’s more convenient to mount a template on the top of a workpiece, rather than on the bottom.

Some flush-trim bits have two guide bearings, one on the end of the bit and a second bearing on the bit’s shank (Photo 9). This design allows you to always cut “downhill” with the grain and avoid tearout. When routing a semicircle, for example, you rout one half of the arc with the template positioned below the workpiece, riding on the bearing on the bit’s shank. To rout the other half, you flip over the workpiece and template, so the template is above the workpiece. Then you readjust the bit’s height and ride on the bearing at the end of the bit. This bit is very useful for any S-shaped curve, where the grain of the workpiece is likely to change direction.

Designing a template to use with the guide bearing method is quite simple. Just make the template the exact size and shape as the pattern you wish to duplicate.

The guide bushing method


When cutting on the end of the bit, such as when routing a curved groove, I use a guide bushing. (Guide bushings are also called “template guides” in tool catalogs.) The guide bushing is just a metal ring which fastens to the base of the router (Photo 10). These rings come in a variety of diameters and lengths for use with different diameter bits. When selecting a guide bushing, keep in mind that there must be at least a 1/64” gap between the bit and the bushing, so the bit doesn’t cut into the bushing. The inside diameters of many bushings are 1/32” larger than the diameters of commonly used straight bits.

Unfortunately, guide bushings are usually not perfectly concentric to the router collet, because the router’s sub-base isn’t perfectly centered on the base. This means that the gap between the bit and bushing may be different on one side of the bushing than on another side. The practical result is that the distance between the bit and template may vary, depending on how you orient the router to the template. However, most of the time the slight amount of eccentricity is not an issue. When eccentricity matters, I mark a spot on the base and am careful to always guide the router from that point. This ensures that the distance from the cut to the template remains constant.

When you’re designing a template to use with the guide bushing method, first select the bushing and bit and install them in your router. Next, measure the diameter of the bushing and subtract the diameter of the bit (Fig. A). Divide the result in half to give you the distance between the template and the cutting edge of the bit.

The sub-base method

Using a router’s sub-base to guide a cut is straightforward and convenient, especially when routing certain joints (Photo 11). When using this method, I prefer a square or rectangular sub-base as opposed to a round one. Guiding each cut from the same side of a square sub-base ensures that the spacing is consistent. Some plunge router sub-bases have one straight side, for example, and I prefer to reference from that side when template routing. I have also made or bought square or rectangular sub-bases for some of my routers to use when accuracy is critical. However, you can also achieve consistent results by guiding off of a round sub-base. Just mark a spot on the sub-base with bright red paint and keep that spot against the template.

When designing a template to use with the sub-base method, you must also factor in an offset, similar to the guide bushing offset above. Measure the diameter or width of the base, subtract the diameter of the bit, and divide the result in half. This will give you the distance from the template to the cutting edge of the bit.

The overarm guide method

An overarm guide is a shop-built device that mounts on top of a router table (Photo 12). It consists of a long arm whose end is curved to match the smallest radius on the template, a support for the arm, and a bearing securely fastened to the arm. You may purchase the bearing at an auto supply shop or borrow a bearing from a router bit.

This method is similar to using a guide bearing, but unlike a guide bearing, the overarm guide can be positioned eccentric to the bit’s profile. This allows for shaping into the interior of the stock where a bearing-guided bit cannot reach. I use this technique when shaping large molding profiles on curved surfaces (see Routing A Gooseneck Molding). The arm is positioned above the bit and follows the curve of the template. After each cut, the arm is backed away from the bit to increase the depth of subsequent cuts.

Designing a template for use with an overarm guide is usually pretty straightforward. Make it the same size as the shape you’d like to duplicate, as when using a bearing-guided bit. The offset is created by moving the arm, rather than by adjusting the size of the template.

 

Template material

One of the most important elements in template routing is the material of the template itself. Although I’ve used a number of materials through the years, I prefer cabinet-grade plywood, which is solid and stable.

All plywood isn’t created equal, though; cabinet-grade plywood is free of voids, which can catch the guide bearing and spoil the cut. Less expensive plywood may have voids, which you won’t be able to see until you cut into it. Cabinet-grade plywood is easy to cut and shape, and it is readily available at hardwood lumberyards.

After many uses, the edge of a plywood template can begin to show signs of wear. Before any problems develop, I usually make a new template from the old one with a flush-trim bit.

 

Making the template

When making a template, I take the time to make it perfect; any irregularity in the template will be duplicated in the workpiece, or dozens of workpieces. On a straight template, I make sure that the edges are truly straight, and the angles are correct. This is not a good time to take anything for granted.

I use a number of methods to draw curves on a template. I may use a compass, a French curve or draw freehand. Often I draw the shape on the computer with AutoCAD, print the drawing, and glue it to the template with contact cement.

After bandsawing the profile, I carefully smooth the curves with files and sandpaper. This is the fussy part. I carefully inspect the template to make sure the curves are fair, checking by eye and by feel. If there’s a hump or flat spot, it’s back to the file or sanding block.

When making a template, I extend the template ends beyond the length of the workpiece by at least an inch or two (Photo 13). The guide bearing then makes contact with the template before the bit makes contact with the workpiece. This ensures a smooth entry and exit when making the cut.

 

The template jig

I often use a template jig for heavy cuts or for securing small work that would otherwise be unsafe to shape with a router (Photo 14). Template jigs demand a little more work than just making the template. The purpose of the jig is to securely fix the workpiece as it is routed. This requires adding stop blocks on the jig to position the workpiece and to counteract the forces of the spinning bit. I begin by making the template (the jig’s base), then glue the stop blocks in position and fasten them with screws.

 

Sawing the workpiece

Once the template or jig is complete, I use it as a pattern for laying out curves on the workpiece. After tracing the template, I use a bandsaw to cut just outside the layout line. I aim for a 1/16” margin. If it’s less than 1/16”, I run the risk of cutting within the template’s outline. A margin greater than 1/16” requires a heavy cut, which can cause tearout or pull the workpiece loose from the template.

 

Fastening a template

I use brads, screws, double-faced woodturner’s tape or toggle clamps to fasten the template to the workpiece. The easiest method is just to attach the template with a few brads. This method works well for small work and light cuts; it’s fast and the nails grip well. For larger and heavier cuts, I opt for screws.

With either method, it’s critical that you position the fasteners out of the path of the bit. Although nails and screws both leave holes in the finished work, that’s not necessarily a problem. Usually, the holes will be hidden from view in the completed workpiece.

When holes from a metal fastener will not be acceptable, I use double-faced woodturner’s tape (Photo 15). The tape is made of cloth and has tremendous holding power. Because the tape is pressure sensitive, I clamp the workpiece to the template prior to routing.

Toggle clamps are ideal for template work, especially when there are a large number of parts to be routed (Photo 16). They open and close quickly and have good holding power. I use toggle clamps on most of my template jigs. Usually, I have to add a block to the jig to bring the toggle clamp approximately level with the workpiece.

Once your template and stock are prepared, you’re ready to make the cut. Remember to adjust the bit’s height. If you’re using a bearing-guided bit, position the bit so that the bearing makes full contact with the template.

 

The router table is best

Whenever I have a choice between using a hand-held router or a router table, I always opt for the table. This also holds true when template routing. Even though I’m not using the router table’s fence to guide the workpiece and limit the cutting depth, the fence provides dust collection and a mounting point for a guard (Photo 17). Using the router table is cleaner and often safer than pushing a router across the work.

Click any image to view a larger version.

1. Template routing is a method for guiding a router bit with a shop-made pattern, or template. Here, the bearing on a flush-trim bit follows a plywood template.


2. Identical parts with smooth, uniform surfaces are easy to make using a template.


3. Precision joints can also be made with shop-made templates. I designed this template for routing half-blind dovetails in a drawer front.


4. A straight cut that’s not parallel to another side is hard to set up on a tablesaw, so it’s an ideal candidate for template routing. This is a diamond-shaped shelf for a corner cupboard.


5. Curved parts, both large and small, can be duplicated by template routing. Here, I’m using a tall flush-trim bit to shape a small serpentine drawer front.


6. Templates are also useful for routing grooves and dadoes, such as this dado for a partition inside a cabinet. The template precisely locates the dado.


7. Using a curved template is just about the only way to make a curved groove. This groove will receive a tambour door.


8. There are many ways to guide a router bit around a template. The simplest method is to use a bit with a guide bearing. Here, the template was fastened to the top of the workpiece.


9. Some flush-trim bits have two bearings. These bits are ideal for avoiding tearout when routing curves. By flipping the template and workpiece, you can always rout downhill, with the grain.


10. A bushing mounted in a router’s sub-base is also a common method of guiding a bit around a template. This method is well suited for cutting grooves of any width.


11. A router’s sub-base is also a good guide for following a template. Here, I’m routing mortises inside a carcase. Setup is straightforward and convenient.


12. An overarm guide on a router table is a fairly sophisticated device for following a template, but it allows you to use router bits that don’t have a bearing, or make cuts where a bearing would get in the way.


13. I prefer cabinet-grade plywood for making templates. I design them to extend an inch or so beyond the workpiece, which ensures a smooth entry when starting the cut.


14. When making a heavy cut or shaping small parts, I build a template jig to securely hold the workpiece. The jig usually has stop blocks to position the workpiece.


15. I use brads or screws to attach most templates to a workpiece, but where holes will mar a finished piece, I use woodturner’s double-faced tape.


16. Toggle clamps are ideal for holding a workpiece in a template jig, particularly when you have a lot of duplicate parts to make. Mounting a new part in the jig is quick and easy.


17. I prefer to use a router table for template routing whenever possible. Even though I’m not using the fence to guide the work, the fence provides dust collection and a guard.






This story originally appeared in American Woodworker August/September 2009, issue #143.

August/September 2009, issue #143

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