Rout the Insert and the Hole With Just One Template

BY BLAIR HUBBARD

Router Inlay Bushing PlatesRouter Inlay Patterns

Decorative shapes or practical patches, a router makes Inlay work fast and accurate. The right bit and guide-bushing combination lets you rout the hole and the insert with the same template.

hen the need arises to inlay one piece of wood into another, there are a great many methods and tools that will work. When I'm faced with an inlay job—especially one that involves multiples of the same shape—I reach for a router. With a template the shape of your inlay and the right combination of router bits and guide bushings, it's possible to rout both the inlay and the hole into which it fits with the same template. Once you've made the template, you can cut the same shape again and again. Best of all, the inlay is always a perfect fit. My template technique has all sorts of applications, both practical and decorative. I use it most often for inlaying patches to cover defects in boards. And I also find it handy for setting decorative ceramic inserts into furniture surfaces. It's also possible to produce inlays in geometric shapes like circles, squares and stars | or most any random shape. The primary restriction is | that, without some hand work, the inlay can't have a £ smaller radius than the radius of the router bit.

While the technique is quite simple, some of the £

concepts aren't easy to visualize until you've actually tried them. If you find yourself getting confused as you read, the drawings and photos will make things clear.

Guide Bushings and Bits

A guide bushing guides the router around the template. In case you aren't familiar with them, a guide bushing is a small cylinder of steel that fits into the base of a router. The cylinder part surrounds the router bit and protrudes slightly below the router base as shown in the photo and Fig. 1. The guide bushing rubs against the edge of a template to guide the router through the cut. Guide bushings come as standard items with some routers and are available as optional accessories for most routers.

Guide bushings come in different sizes and you'll need two—a large bushing to rout the hole and a small bushing to rout the inlay. Not just any two guide bushings will do, however. The sizes are important.

Guide-bushing specifications in tool catalogs nor-mallv list two diameters. The smaller diameter indi-cates the largest bit that will pass through the opening. The larger diameter is the outside diameter (o.d.) of the cylinder—the part that rubs the template. The offset between the outside of the bushing and the cutting edge of the bit is a crucial factor in template routing as shown in Fig. 2. The offset is measured differently depending on whether you are routing the insert or the hole.

When routing the insert, you measure the offset from the outside of the bushing to the farthest cutting edge. When cutting the hole, you measure the offset from the outside of the bushing to the nearest cutting edge. Keeping the offset the same for the insert and the hole allows you to cut both with the same template.

You need to select a combination of guide bushings that give you the right offset. This isn't easy to visualize, but the drawing in Fig. 2 should make it clear. The chart in Fig. 2 lists practical combinations of router bits and guide bushings and the offset that results. If you want to experiment with other combinations, here's the rule of thumb: To rout both the hole and the insert with the same bit, the outside radius of the large guide bushing must equal the radius of the small bushing plus the diameter of the bit. (Note that guide-bushing dimensions are usually given as diameters, while most computations for template routing are made using a radius. Beware.)

While I'm on the subject of guide bushings, I want to mention that some router manufacturers offer a wider selection of guide bushings than others. Porter-Cable, Ryobi, Makita and Hitachi all have a large selection of sizes. I like to use my Ryobi plunge routers for inlay work because there are nine different guide-bushing sizes to fit these routers and the guide bushings can be changed without removing the bit. Another advantage is that the Ryobi guide bushings protrude only '/a in. below the router base, which allows me to make my templates from V-t-in. thick stock. If your

FIG. 2: BUSHING/BIT COMBINATIONS

SETUP FOR ROUTING HOLE

FIG. 2: BUSHING/BIT COMBINATIONS

LARGE GUIDE BUSHING

OFFSET

For cutting hole, measure from outside of bushing to near cutting edge.

LARGE GUIDE BUSHING

OFFSET

For cutting hole, measure from outside of bushing to near cutting edge.

SETUP FOR ROUTING INSERT

SMALL GUIDE BUSHING

For cutting insert, measure from outside of bushing to far cutting edge.

For cutting insert, measure from outside of bushing to far cutting edge.

ROUTER BIT/GUIDE BUSHING

COMBINATIONS

ROUTER

SMALL GUIDE

LARGE GUIDE

BIT D!A.

BUSHING

BUSHING

OFFSET

V

V

Vu

♦/,*•

V

V

V

7/

V

V

FIG. 1: GUIDE-BUSHING NOMENCLATURE

Offsets For Router Collar

MOUNTING NUT

Guide bushing protrudes from router base.

Rubbing collar follows template.

FIG. 1: GUIDE-BUSHING NOMENCLATURE

MOUNTING NUT

Guide bushing protrudes from router base.

Rubbing collar follows template.

FIG. 3: ROUTING A RECTANGULAR INLAY

Router Bushings Cutters

ROUTING THE HOLE

Template corner radius matches radius of large guide bushing.

HOLE

Bushing follows edge of template.

Depth equals thickness of insert stock.

TEMPLATE

ROUTING

Inlay Router Collar For Dewalt
A guide bushing is a steel cylinder that protrudes from the router base. It nibs against the edge of the template to guide the router through the cut

guide bushings are longer, you have the option of using thicker template stock or shimming the base of your router. One significant disadvantage of long guide bushings or thick templates is that they effectively shorten the usable portion of your bit.

Next. I'll walk you through the process of making a simple, rectangular inlay. I suggest that you start with a simple shape like this before tackling a more complicated pattern.

Routing a Rectangle

Start by sketching the shape of the hole full size on paper. Keep in mind that any points or sharp corners will be rounded to the radius of the router bit.

Next, decide on a combination of bit and guide bushings, taking into account the minimum radius you want on your inlay. I normally use either a 7i*-in. bit or '¿»-in. bit for cutting the hole and the insert. In

TEMPLATE

OFFSET

7« DIA. GUIDE BUSHING

Router Bit Patterns Chart

TEMPUTE

OFFSET

7« DIA. GUIDE BUSHING

THE INSERT

TEMPUTE

FIG. 4: ROUTING A STAR INLAY

FIG. 4: ROUTING A STAR INLAY

OFFSET Vn*

74 -dia. guide bushing

Template has

Router Bushing Chart

at corners.

Trim point with chisel.

Pivot router around corners.

GUIDE BUSHING

TEMPLATE

Wood Router Templates

Move router clockwise.

ROUTING THE HOLE

OFFSET Vn*

74 -dia. guide bushing

ROUTING THE INSERT

Trim point with chisel.

TEMPLATE

GUIDE BUSHING

Move router clockwise.

Template has

Pivot router around corners.

this case, let's use a Vie-in. bit, and a guide-bushing combination from the chart in Fig. 2 —a Vs-in. o.d. bushing and a 'A-in. o.d. bushing. As shown in the chart, this combination of bushings, together with a Vift-in. dia. bit, gives an offset of in.

Making the template is the next step. Phenolics, plastics and metal are all acceptable template materials, but I prefer to make my templates from '¿»-in. tempered hardboard. Whatever you choose, the template must be larger than the hole to provide support for the router base and room for clamps to fasten it to the work piece.

The template opening must be larger than the hole on all sides by the offset measurement —in this case V>2 in. Lay out the template opening on a sheet of '/¿-in. hardboard. I set a drawing compass to the offset and use it to draw around the outside of my original hole drawing. Wrhile I'm at it. I write the bit and guide-bushing sizes on the template for future reference.

When laying out a template, carefully think through what will happen as the router is guided around it. What happens at the corners will often surprise you. The results will be different depending on the radius of the template corners and whether the corners of the template are rounded or square. When you've got the hang of the technique, you may want to do some experimenting. For now, however, make the radius of your template corners the same as the radius of the large bushing (in this case,'/«in.), as shown in Fig. 3, or you'll end up with an insert that won't fit the hole.

While sketching the template on paper, I consider the need for attaching a fence or a guide to the template to orient it on the work piece later. I'll leave extra material on the template for this, if necessary. If a locating block or two is needed to accurately place the template on the work, I plan for that as well, including any mounting screws.

Once the template is laved out on the hardboard. you can cut out the template with a jigsaw or a router, to get an accurate geometrical shape I normally rout out the template opening w ith a bit the same diameter as the o.d. of the large guide bushing I plan to use (in this case. '/<> in.). I clamp guides to the template stock and follow them with the router base. It's important for the guiding surface to be smooth.

Routing the hole for the inlay comes next. Mount the large guide bushing in the router base and insert the bit. To set the depth-of-cut for the hole, place the insert stock on a piece of Hat scrap and place the template on the insert stock. Place the router on the tem-

Animal Router Inlay Templates
To make the points of the star-inlay template symmetrical, guide the router base against a plywood template.

plate and lower the bit until it touches the scrap. If you want the insert to fit flush with the surface, lock the setting when the bit touches the scrap. I usually prefer to have the insert protrude slightly above the surface and then plane it flush later so 1 raise the bit a little before I lock the depth setting. This makes a hole that's slightly shallower than the thickness of the insert.

Locate the template on the stock exactly where you want it (keeping in mind that the hole will be smaller than the template opening) and firmly clamp it in place. It's important that this assembly be very steady while routing. I clamp everything firmly to a bench.

If the hole is large and you're routing several inlays, it might be worth setting up a second router with a larger-diameter bit to remove stock quickly from the center of the hole. Don't get too close to the edges.

Remove the bulk of the waste from the center of the hole with a wide bit, if you choose, then use the Vi6-in. bit and J/4-in. guide bushing to accurately follow the template for your finish cut. Hold the bushing firmly against the template to be sure of an accurate cut. I go around the template two times, in a clockwise direction, vacuuming and checking for chips against the template between passes.

Routing the hole is a much more forgiving process than routing the insert. If the guide bushing loses contact with the template, it simply moves into the waste area and you can go back and do that portion again. You don't have that luxury when you rout the insert.

Rout the insert afier vou've routed the hole. Com-pare the figure and grain of the inlay stock with that around the hole,and orient the template to give a complementary match. Clamp the template firmly over the stock.

Because you'll be cutting completely around the insert. it will break free at the end of the cut. To keep the insert from shifting (and being chewed up by the router) set the depth-of-cut '/m to Vioo in. less than the insert stock thickness. This thin layer of wood at the bottom of the cut will keep the insert in place, and it's easy to cut the insert out by hand. If your plunge router has multiple depth-stops, you could set one stop to leave about l/n in. at the bottom of the cut and another stop to just cut through the insert stock. Then, after routing around the template at the higher setting, lower the router to the full depth, and cut the insert free except at the corners. You can trim these later by hand.

Insert the small guide bushing (in this case, V« in. o.d.) in the router and set your depth-of-cut. I recommend placing the guide bushing in a corner of the template at the beginning of the cut. It is vital to maintain constant pressure against the template at all times— there's no room for error here. One hand should always be pulling the router firmly against the template, being especially careful around the corners. Move the template in a clockwise direction so that the bit pushes the guide bushing against the template.

When you've cut the insert free, it should fit right into the hole with little, if any trimming.

Routing a Star

Let's look at a more complicated shape—a five-pointed star. All four corners of the rectangle template were concave—the guide bushing nestles into them. A star-shaped template has concave and convex corners. As the guide bushing swings around these points, it always produces a radius equal to the offset as shown in Fig. 4.

You can make a star insert with sharp points if the radius of the template corners is less than the radius of the small guide bushing (see Fig. 4). The hole, however, will have rounded corners and you'll have to trim them to a point with a chisel so the inlay fits. I don't know of any way to get sharp points on the hole without moving the template or making multiple templates.

If the template is perfectly symmetrical, the star insert should fit into the hole in any orientation. However, the fit is always best when the template is oriented the same way for both the hole and the insert.

Other Possibilities

I use the router-inlay method a lot, and I've developed more complicated variations on the techniques described here. For example, sometimes I use different bits for the insert and the hole. The relationships and calculations can get pretty complicated and I won't go into them here. I encourage you to experiment with different combinations of bits and guide bushings and explore the possibilities yourself. A

Blair Hubbard lives in Knox\>ille, Maryland and works fur the Natiotial Parks Sendee. He's been a woodworker for 25 years.

Star Shaped Chisel
The points of the star-shaped hole are rounded to the radius of the router bit Trim point with chisel or knife.
Laufbuchsen
Guide bushings longer than 'A in. require a template made from V*ln. or Vi-ln. material.

Whirligigs

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Responses

  • Karin
    How to route a hole and a piece to fit in to it?
    8 years ago
  • Zula
    Which shape is the easiest to orient for insertion into the hole?
    5 years ago
  • Guglielmo
    How to insert hole router?
    9 months ago
  • peter
    How to rout a concave shape?
    6 months ago

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