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Loose Tenon Joinery

Loose Tenon Joinery

Rout 4 variations of these super-strong joints with a versatile shop made jig.

By Bill Hylton


I've used a number of different methods to create mortise and tenon joints, but I keep coming back to loose tenons, because they're easy, strong and versatile. Instead of cutting a tenon on one part and a mortise in the other, I rout identical mortises in both parts, and connect them with a fitted strip of wood—a loose tenon. Loose tenon joinery is perfect for casework, tables and doors of all sizes.

The only tools you need to start making loose tenon joints are a plunge router equipped with an edge guide, straight bits designed for plunge cutting and a mortising block—a shopmade jig I've designed that you can make in a day.The mortising block minimizes layout work and allows routing both edge and end mortises from the same router setup.

You can use off-the-shelf bits and just about any plunge router, but a precision edge guide is a must. I use the Micro-Fence edge guide, which I think is the best available (see Sources, below).

 

The mortising block

This jig holds the workpiece, supports the router and controls its movement (Fig. A, below).The jig consists of the mortising block itself, a top extension, an L-bracket and a clamp board for bench mounting.

The face of the block has dadoes and mounting-bolt holes for the two work holders—horizontal for edge mortising and vertical for end mortising. The router sits on top of the block and overhangs the workpiece.The router's edge guide is housed in a track formed by the L-bracket (Photo, opposite). Adjustable stop blocks set the mortise length.

 

How the jig works

• The jig's registration line locates the workpiece.

• The jig's L-bracket tracks the router and keeps the mortise aligned with the edges of the workpiece.

• The mortise's width is determined by the bit's diameter.To create mortises wider than the bit, you reposition the fence and make a second pass.

• The mortise's depth is controlled by the router's plunge mechanism.

• The mortise's length is governed by the jig's adjustable stop blocks.

• The mortise's lateral (side-to-side) positioning is controlled by the router's edge guide.

 

Build the jig

1.Mill stock for the main parts and cut the pieces to final dimensions (Fig. B, below).The mortise block's body and the horizontal work holder must be exactly the same length, because you reference from the ends to rout the vertical keyways.

2. Rout 1/4" deep vertical keyways in the mortising block and the horizontal work holder.

3. Rout single 1/4" deep horizontal keyways in the mortising block and the vertical work holder.The block’s keyhole is stopped.

4. Rout mounting-bolt slots in each work holder, using a plunge router and an edge guide.

5. Plane 1/2" thick stock to fit the work holder keyways. Cut pieces to length to create the keys. Attach them.

6. Clamp the horizontal work holder to the mortising block.Tap a 1/2" brad point drill at both ends of each slot to transfer its location to the block. Remove the work holder and scribe vertical lines on the block through the four points you marked. Clamp on the vertical work holder, mark the slots and scribe a pair of horizontal lines.

7.Drill holes for the work holder mounting bolts at the four points where the horizontal and vertical lines intersect.To secure the 3/8" bolts, I cut threads in the wood itself.To do this, drill the four holes with a 5/16" bit and use a 3/8"-16 tpi tap to cut the threads (see Sources).No cutting fluid is needed; just turn the tap into the hole, then back it out. Alternatively, you can use Tnuts or drive threaded inserts into the body to secure the bolts.

8.Glue and clamp the top extension to the mortising block. Clean off any dried glue after removing the clamps. Then joint the assembly to ensure that its top surface is square to the face.

9. Attach a 3/8" thick wood fence to your router's edge guide.Then size the L-bracket parts to create a groove that will house the fence.The fit should be snug, so the fence slides without any wobble.Glue the L-bracket parts together and install them.

10.Make both stop blocks from one long piece of 5/8" by 2-3/4" stock. Rout the 1/4" deep keyway and two mounting bolt slots. Cut the stops to final length.Make keys and attach them.

11. Rout matching keyways in the top of the mortising block.

12. Set the stops in place on the block and mark locations for mounting bolt holes.Drill and tap the holes for 1/4"-20 tpi bolts.

13. Install toggle clamps on the work holders (see Sources). I installed longer threaded spindles on all the clamps and used a 500-lb.size on the vertical work holder. Be sure to mount the clamps so they don't interfere with the router.

14.Draw a registration line centered on the face and top of the mortising block.

15.Glue on the clamp block.

 

Create the basic loose tenon joint

1. Lay out an edge mortise (Photo 1). It doesn't have to be elaborate, just lines marking the mortise ends and centerline. Only one line is essential: a centerline across the mortise. This mark aligns with the jig's registration line.

2.Position a test piece on the jig, using the horizontal work holder (Photo 2).

3.Adjust the work holder so the edge of the workpiece is flush with the jig's top. Line up the workpiece centerline with the block's registration line (Photo 3).Adjust the toggle clamps to hold the work securely.

4. Install a bit designed for mortising in the router.Up-spiral bits are popular these plunge cuts, but they're not essential.

5. Install the router on the jig and test-slide the edge guide's wood fence in the L-bracket groove. Apply wax, if necessary.

6. Bottom the bit onto the workpiece. Then move the router to center the bit on the mortise centerline (Photo 4). Lock down the edge guide and set the plunge depth.

7. Install the stop blocks to establish the length of the mortise (Photo 5).

8. Rout the mortise (Photo 6). That's all it takes. As long as the faces of the workpieces are oriented the same way on the jig, all the edge mortises routed with this setup will be the same, regardless of where they fall on the workpiece. Just scribe a centerline across each mortise, and align it with the registration line on the block (Photo 7). If all of the mortises are located in the same place on each workpiece, you don’t even have to mark them. Instead, just fasten a stop on the jig against the end of your test piece and use it to register the workpieces.

9.The only change you have to make to rout the matching end mortises is to switch work holders (Photos 8 and 9).

10.Mill loose tenon stock to complete the joint. First, plane a length of stock to fit the mortises. It should slip in without wiggling or binding. Rip the blank to width, slightly less than the mortises’ length.Next, round the blank’s edges to match the mortises. Then cut individual loose tenons from the blank.

 

Reinforce a cope and stick joint

Routed cope and stick joints look great, but their stub tenon construction may not be suitable for large cabinet doors. Adding loose tenons strengthens these joints.

Rout the mortises before you rout the cope and stick profiles, so you don't have to work around stub tenons on the ends of the rails. (The mortises won't interfere when you rout the profiles.) Center the mortises across the thickness of the workpiece.They probably won’t align with the stub tenons produced by the cope cuts, but that doesn’t matter, because everything will be hidden in the assembled joint.

Start with the end mortises.Offset them away from the rails' inner edges, so the panel groove won't cut into the mortises (Photos 12, 13 and 14). Locate the edge mortises in the stiles according to the rails' offset end mortises.

Be mindful of the rails' offset mortises when you rout the profile and panel grooves. It's all too easy to rout the wrong edge.

 

Twin mortise joints

In post-and-rail constructions made using thick stock, you can make stronger joints by doubling the loose tenons.The inside mortises on the posts of these corner joints will intersect, so they must be shorter; their tenons are mitered.The outside post mortises are deeper, so their tenons can be longer.The rail mortises can all be the same depth.

Orient the workpieces with their outside faces against the mortising block. Set up and rout the outside mortises.You'll have to change work holders when you switch from routing edge to end mortises. Reposition the bit and rout the inside mortises (Photo 15). Reduce the final plunge depth when you rout these mortises in the posts.

 

Loose tenon table joint

In this construction, the apron usually is inset from the leg faces.My approach is to set up for the mortises in the legs (Photos 16 and 17).To rout the aprons, I use double-faced tape to install a shim equal in thickness to the inset between the apron and the block (Photo 18).Be sure to install the aprons outside-face-in before routing their mortises.


Sources

(Note: Product availability and costs are subject to change since original publication date.)

Micro Fence, microfence.com, 800-480-6427, Micro Fence Edge Guide.

Buy Destaco, buydestaco.com, 800-560-9292, De-Sta-Co Horizontal Toggle Clamps, #215U; #225U (500 lb. cap.).

Tap and Die sets are available at hardware stores and home centers.


Fig. A: Loose Tenon Mortising Jig

Despite their name, loose tenon joints fit as precisely as traditional mortise and tenon joints, and are just as strong.


Fig. B: Dimensions

Mortising Block


Stop Block


Horizontal Work Holder


Vertical Work Holder


This story originally appeared in American Woodworker April/May 2009, issue #141.

April/May 2009, issue #141

Purchase this back issue.

Click any image to view a larger version.

Adapt your router to the jig by installing a fence on the edge guide that fits the slot formed by the jig's L-bracket.This keeps the bit aligned as the router slides back and forth. To move the bit laterally, you simply adjust the edge guide.


The Basic Loose Tenon Joint


1. Lay out one edge mortise on a test piece to set up the router and jig.The mortise centerline is used for positioning the workpiece on the mortising block—it's the only layout mark required for every mortise.


2. Set up the jig to rout the edge mortises. Install the horizontal work holder and position the test workpiece so its edge is flush with the top of the jig.Then tighten the bolts.


3. Align the work's mortise centerline with the jig's registration line.Then lock the test piece in position.


4. Install the router and adjust the edge guide to center the bit on the work.Then adjust the router's plunge-depth stop to the desired mortise depth.


5. Install the stop blocks. Move the router to one end of the mortise and align the bit's edge with the layout mark. Slide the stop against the router and tighten the bolt. Set the second stop the same way.


6. Rout the mortise with a series of shallow cuts. Plunge the bit about 1/8", feed quickly to the far stop, retract the bit, return to the starting position and go again.


7. Mark your stocks' outside faces and always orient the same face against the mortising block when you rout. Once all the edge mortises are routed, switch to the vertical work holder to rout the end mortises.


8. To mount the vertical holder, clamp a workpiece with its mortise centerline aligned with the jig's registration line. Slide the holder against the workpiece and tighten the bolts.


9. Install the router and rout the end mortise. The length, width, depth and placement of the mortise don't change when you switch work holders.


10. Size a loose tenon blank. Plane a length of stock to fit the mortises. It should slip in without wiggling or binding. Rip the blank to width, slightly less than the mortises' length.


11. Round the tenon blank's edges to match the mortises.Then use a crosscut sled to cut individual loose tenons from the blank.


Reinforce a Cope and Stick Joint


12. This variation requires offsetting the rail mortises, so they don't interfere with the panel groove. Lay out the offset mortise on a pre-routed rail.Then use this rail to position the vertical work holder.


13. Rout the mortises before you rout the cope and stick profiles.Your initial set-up positions the mortise in only one end of each rail, because both ends of the rail must be routed with the same face against the block.


14. To position the mortise in the other end, install a shim equal to the panel groove's depth between the work stop and the rail.


Twin Mortise Joints


15. Rout twin mortises in two steps. Lay out and rout the first mortises in both the edges and ends. Reposition the bit for the second mortises and go again. Always orient the same face against the fence.


Table Joint

 

16. With table joints, the aprons are usually inset from the legs.Start by mortising the legs. Clamp the leg with its outside faces against the block and the work-holder.Position the bit, set the stops and rout the mortise.


17. Flip and rotate the leg to rout the second mortise. It doesn't matter that the leg now extends in the opposite direction, because the mortises are centered on the jig's registration line.


18. To inset the aprons from the legs, you offset their mortises by the amount of the inset. Attaching a shim of the desired thickness to the jig automatically offsets the mortise correctly.

 

CNC Wooden Chain

CNC Wooden Chain

Lessons in small parts jigging.

By Randy Johnson

My inspiration for this project came from a wooden chain I made years ago using a handheld plunge router and plans from Patrick Spielman’s New Router Handbook (1993). Since making the chain involved routing a bunch of the same parts, it seemed like a good project for a CNC. Patrick used a one-link-at-a-time routing jig setup that partly relied on the router’s base to hold the links steady during routing—something not possible with a CNC. So making the links on the CNC became a good exercise in designing CNC small parts jigging. I had three goals in mind while developing the jigs. I wanted them to be simple to make, easy to use, and sufficiently durable. Aft er trying various methods involving clamps and hold-downs, I settled on a combination of recessed cutouts, wedges and small turnbuckles. But the real secret to these jigs came from the CNC’s ability to easily and precisely create matching parts that fit snugly together like puzzle pieces.

Click any image to view a larger version.



Jig 1: Routing Inside the Links

Rather than make this jig out of separate pieces of wood, I found it easier to rout it as a recess in a piece of MDF. I used three wedges to hold the workpiece in place while routing. The bottom wedge forced the workpiece tight against the upper end of the jig, while the two side wedges pushed the workpiece to the left. The wedges were also created with the CNC, so matching the tapers in the recess to the angle of the wedges was a breeze. The wedges have a 1 in 20 taper, which made them easy to secure and remove with a couple stiff mallet taps. The wedges proved very secure, as they never once vibrated loose during routing. I also routed an undercut around the bottom of the recess with a T-slot router bit. The undercut insured that the workpiece didn’t hang up on any stray wood chips at the bottom of the jig.



Jig 2: Routing Outside the Links

Creating the second jig required the most experimenting. I initially created it as a recess similar to jig 1, but the MDF proved too weak and the center posts easily broke off. A piece of Baltic birch plywood glued to the top of the MDF created a much stronger jig. I made the center posts .05" shorter than the thickness of the work piece. This made it easy to apply pressure with the turnbuckles. The center posts were also .05" smaller in diameter than the inside of the links. This slight gap was needed so the workpiece could slide onto the posts without binding, but was still snug enough to prevent the workpiece from shifting during routing. A couple workpieces were slightly warped, which made them hard to slip on to the center posts. A few taps from a mallet solved that problem. Once the links were routed into separate parts, they were easily removed.



Rounding Over the Outside

Jig 2 served a dual purpose. Once all the links were routed into separate parts, I switched to an ovolo bit and rounded over the outside corners. The links were flipped over to do the other side. The snug fit on the center posts and the turnbuckles helped to hold the link securely in place for this step.



Only Three Bits are Required

The 1/2" dia. straight bit did the heavy work of removing stock from both the jigs and the chain links. The slotting bit created the undercut at the bottom of jigs 1 and 2 to prevent stray wood chips from getting in the way. The 1/4" radius ovolo bit gave the links their round shape.



Jig 3: Rounding Over the Inside

Similar to the first jig, the third jig used wedges in a recess to hold the parts in place. This jig really took advantage of the CNC’s ability to cut parts that fit together like a glove. The recessed pockets for the links were cut the same size as the link, without any clearance gap. This created a very snug fit and required a couple extra mallet taps on the wedges to make sure the links were fully seated. This snug fit insured that the links didn’t move or vibrate while I rounded over the inside corners. After the first side was done, I flipped the links over to rout the other side.

Note: Although CNC’s are capable of precise machining, you should always test your setups and adjust the dimensions of your jigs, parts and tool paths to accommodate slight variations in materials and bit diameters.



A Quick Sanding

Sanding each link took a minute or two per link, but removing the machine marks at this stage was easier than doing it after assembly. Next time I’ll use a flap sander or inflatable drum sander and save my finger tips.



Break Every Other Link

A quick hit with a mallet was all it took to crack the links in half. I used quartersawn boards for this project because when broken, they tend to create flatter joints than plainsawn wood. The flat joints made reassembly easier.



Glue and Clamp Back Together

I assembled the chain by adding two unbroken links to each broken link. Then I assembled these three link sections with more broken links until the chain was complete. Because the links were broken on the grain, the glue joints were nearly or completely invisible. Using a light application of glue and removing the squeeze out while it was still soft made cleanup sanding easy. After it was done, I dipped the chain in an oil finish a couple of times and rubbed it dry with a cloth.



The Dimensions

The six links started out as a board measuring 5/8" x 2" x 20". The .6" spacing between the links provided the necessary clearance for the 1/2" dia. straight bit and the bottom end of the ovolo bit. The six links produced 11-1/2" of finished chain. Drawings for the three jigs can be downloaded at AmericanWoodworker.com/CNC.




This story originally appeared in American Woodworker June/July 2012, issue #160.

 

 

Creating CNC Textures

Creating CNC Textures

By Randy Johnson

CNC routers are opening up lots of new ways to create textures in wood. Here are my three favorite ways of creating textures using a CNC. Th e fi rst method uses the repetition of shapes to create a design that is routed using one or more bits. If you enjoy doodling patterns, this is a technique that you will enjoy. Th e second method uses programming built in to the design soft - ware to generate a texture design that simulates a handcarved pattern. Th e third texturing method starts with a photograph and converts the light and dark areas into the routing paths. Each method has a few basic rules to follow, but add some imagination and the variations you can achieve are virtually limitless. I used Vectric Aspire CNC design soft ware to create the textures for this article, but other soft ware packages such as ArtCAM and EnRoute can also be used to create textures.


Shape-Based Textures


Shape-based textures are created by repeating a pattern of either asymmetrical or symmetrical shapes. Patterns can be hand-drawn or drafted with a CAD program such as Google SketchUp. Hand drawn designs need to be scanned or digitally photographed so they can be imported into the CNC design program. CNC design programs are also capable of creating shape-based patterns. One creative aspect of this type of texturing is that you can rout on the lines or between them to achieve different effects. I routed the crackle texture shown below using a 1/4" dia. 60° v-bit. It took about 60 minutes to carve the design into this 10" cherry lid. The dome shape of the lid was created first using a 1/4" dia. ball nose bit.

Click any image to view a larger version.




Software-Based Textures


Using the built-in texturing program that comes with most CNC design software packages is an easy way to create a simulated hand-carved texture. As shown in the program window to the left, there are several options to choose from when designing this type of texture. Adjusting these variables enables you to create a wide variety of simulated hand-carved textures, ranging from those with long, closely spaced cuts, to those with short, widely spaced cuts— and anything in between. Once the options are selected, the program creates a semi-random pattern of lines (see middle image below) for the router bit to follow. I used the settings shown here to create texture on the walnut lid show below. I used a 1/4" ball nose bit to create the texture, but other profiles such as straight bits or v-bits can also be used, expanding your options even further. It took about 60 minutes to carve the texture shown below.





Photo-Based Textures


Another way to create a CNC texture is to start with a photo. Not all photos work equally well, however. That’s because the CNC design software reads the light areas as high points and the dark areas as low points and tells the CNC router to carve accordingly. A good photo image is one that is evenly lit without long shadows, but yet has good contrast. As you can see in the alligator skin photograph below, the highlights accent similar areas, while the dark areas are consistent in the rest of the photo. This type of photo will create a texture that closely resembles the contours of the original. Carving a photo-based texture requires the use of a small ball nose bit to attain the details. For the design below, I first roughed out the texture and dome shape of the lid with a 1/4" ball nose bit and then carved the final shape and details using a 1/8" ball nose bit. It took about two hours to do the final routing and about the same amount of time for the roughing passes.




Texture Variations


Shape-based textures can take many forms, from low relief to high relief, and from subtle to bold. The three textures above are just a sampling of options that are possible with this approach to designing textures for the CNC. The one on the left was created using a collection of small circles that were then routed around with a 60° v-bit. The middle design is simply an array of concentric squares, while the one on the right uses a grid pattern made with a 120° v-bit.


Software-based textures are the easiest—and often the fastest—to create, and can be run on top of a shape (left), around a shape (middle), or overlapping in different directions (right). These options allow you to be selective and creative in where and how the texture is applied. Using different bits will also expand the variations you can create with this method of texturing.


Photo-based textures are an easy way to simulate existing textures—as seen in these three examples. The weathered end grain (left) shows a surprising amount of detail, as does the cloth texture (right). The stones (middle) create an interesting pattern, although they are rendered quite flat. Additional depth can be added to the stones through the use of other modeling tools, if so desired. The thing to remember about creating textures from photos is to always start with a photo that has even contrast.




This story originally appeared in American Woodworker April/May 2012, issue #159.

 

 

CNC "Woodturning"

CNC "Woodturning"

By Randy Johnson

A rotary indexing head allows a CNC machine to create 3-dimensional shapes in the round. It’s an accessory that can be added to most CNC machines. Some companies even make it as a stand alone machine. A rotary indexing head looks similar to a standard woodturning lathe, but its approach to shaping wood is quite different. In fact, it’s more like milling than woodturning. One of the best features of a rotary indexing head is its ability to create shapes that aren’t easily turned on a standard wood lathe, such as this hexagonal chisel handle. Intricate round relief carvings are also possible. Because it’s CNC based, a rotary indexing head is capable of great precision and easy repeatability. However, since the shaping is done with a router bit in small increments (as small as 1/50" per pass), the milling process can take a while to complete. Machining this chisel handle took about 2-1/2 hours, but its unique shape was intriguing to design and mill. It also makes an attractive addition to my tool box.


You need to think a little differently.



Think flat

CNC turnings usually start out as a flat design, so the first step is to “unwrap” the cylindrical profile. CNC design software uses a variety of drawing tools that assist this process. One tool automatically calculates the flat design’s width, based on the maximum diameter you specify for the turning. Another tool takes complex shapes such as the hexagonal cross section of this handle and converts it into the flat shape.

Click any image to view a larger version.



Think round

The design software converts (wraps) the flat design into its cylindrical shape to give you a preview of the final piece.



Think parts

Each part of a CNC turning is created separately. The parts are then joined to create the final design. The basic steps used to design this chisel handle appear below.



Basic Parts Creation



Each 3-dimensional part is created using a line drawing of its cross section to extrude (or “sweep”) the shape along a path. The tapered tenon and the round pommel are extruded across the width of their designs, while the body of the handle is extruded along the length of its design. The handle’s contoured hexagonal body is created using three different cross sections and a software tool (or “gadget”) that automatically unwraps the hexagonal shape into its corresponding flat shape.



Parting tabs are added to the ends of the final design to connect the part to the unmachined ends of the billet. The tabs are created using the same drawing tools used to create the tapered tenon and the round pommel.



Basic Machine Steps



Step 1: Create a cylinder

The first step is to round off corners of the billet to create a cylinder. The CNC design software includes a gadget that automatically calculates the cutting paths needed to remove the corners, based on the dimensions of the square billet and the finished diameter of the cylinder. To create the hexagonal chisel handle I started with a 2" square billet and rounded it to 1-3/4" diameter using a 1/4" dia. bullnose bit. Rounding this 22" long cylinder takes about 20 minutes.



Step 2: Rough rout the shape

The same 1/4" bullnose bit roughs out the handle’s hexagonal shape. In this case, the cutting passes are programmed to run the length of the cylinder and remove a 1/8" deep x 1/8" wide a strip of material with each pass. The last pass leaves 1/32" of material to be removed in the next step. Roughing out this shape takes about 25 minutes.



Step 3: Finish rout the final shape

The final (finishing) pass removes the last 1/32" of material and leaves a smooth surface. To do this, the 1/4" bullnose bit is programmed to “step over” each previous pass by only 1/50". This tiny step-over leaves a surface that’s easy to clean up with 180 grit sandpaper. This finishing pass takes about 50 minutes to complete.



Step 4: Add details

The surface of a CNC turning can be embellished with additional details, including lettering. For this chisel handle I combined a 60° V-bit and a script-style font to create a look similar to metal engraving or laser etching. These finely detailed 3/4" tall letters demonstrate the precision of a CNC’s operation. Routing them takes only a minute.




This story originally appeared in American Woodworker February/March 2012, issue #158.

 

 

V-Carve Inlay

V-Carve Inlay

A simple method for creating precision inlays from almost any design.

By Randy Johnson

V-carve inlay takes advantage of a CNC’s ability to precisely rout matching parts. In this case the parts are made as opposites and fit together to create a precise-fitting inlay. The sides of the parts are beveled and fit together like the lid on jack-o’-lantern pumpkin. The technique is surprisingly easy to learn and implement, in spite of the fact that it would be nearly impossible to create these parts any other machine or by hand. It’s truly a technique that’s unique to the CNC. The fact that almost any design can be used, opens up many creative opporutunites. As CNC’s become more common in small shops, I fully expect to see v-carve inlays showing up on furniture in some intersting ways.


Step 1

Layout your design. Almost any design will work, but all individual parts of the design must be made with a single continuous line so the router has a complete path to follow. A shape that is open-ended or has a gap in the line will not be recognized by the v-carving program. I designed this pattern (right) in about 15 minutes, using V-Carve Pro from Vectric. I started with a single “petal” shape and then copied it using a function called “copy circular array” to create the 12 identical shapes. There’s no need to shy away from sharp details such as corners or points. V-carving programs excel at capturing such detail. For more information on v-carving see “V-Carving in 10 Easy Steps”.

Click any image to view a larger version.


Step 2

Set the flat area cutting depth for the pocket portion of the inlay to .15”. Setting the depth to this dimension provides clearance under the inlay to ensure that it doesn’t bottom out in the pocket. The dotted line represents the location of the pattern, which in this case is the surface of the board.


Step 3

Set the cutting depth for the inlay in two stages. First set the “start” cutting depth at .10” and then the cutting depth at .10”. Setting the cutting depths in this fashion will ensure a small amount of clearance between the inlay and pocket boards. The dotted line also represents the elevation or the location of the pattern in the board.


How it works

The angled shoulders of the inlay and pocket intersect to create a tight, wedged fit. The cutting depths for these parts are set to provide clearance between the parts (Steps 2 and 3). The excess top portion of the inlay is removed down to the dotted line to reveal the final pattern (Step 7).


Step 4

Rough rout the background and wide areas with a straight bit. Rough routing removes the majority of the wood in the large areas. This reduces the amount of material the v-bit needs to remove in Step 5 and shortens the overall machining time for the project by about 15 minutes. I also routed the cutout profile around each part at this time, although the parts are still attached to the outer boards with tabs. It took about 20 minutes to rough rout and profile this design.


Step 5

V-carve the design details with a 90° v-bit. Notice that the inlay on the left is a mirror image of the design on the right. They must be opposites in both relief and orientation in order to fit together. This is important to remember when laying out and programming your design. This step took about 25 minutes.


Step 6

Apply glue to both parts. A small brush makes it easy to get the glue into the v-carved areas. The inlay portion has been trimmed to rough size on the bandsaw.


Step 7

Tighten the clamps lightly at first and then add a little pressure to each clamp until they are all fully tightened. Applying uneven pressure can cause misalignment of the parts. Leave clamped until glue is completely dried.


Step 8

Rout off the excess material to reveal the final inlay. The ability to control the cutting depth in increments as small as .001” makes it easy to precisely remove the extra material. For this project I used a 3/4” straight bit and programmed it to remove the majority of the material in 1/8” deep passes until it got to within .02” of the surface. I then continued with .005” passes until the bit removed just enough material to expose the inlay and get rid of the dried glue. This step took about 10 minutes.




This story originally appeared in American Woodworker August/September 2011, issue #155.

 

 

Digital Probe Duplication

Digital Probe Duplication

By Randy Johnson


Router duplication has been around a long time. Early machines used stiluses to follow the shape of a pattern or master, while on the other end of the machines, routers did the carving. In a similar but computerized fashion, CNC routers are also capable of duplicating existing carvings and furniture parts. A digital “touch” probe is first used in the CNC to sense the surface of the object, while the probe’s accompaning software creates a digital image of the part. The digital image is then coverted to a 3D model and used to program CNC routing paths for a replica. To test the capabilities of this technique, I hand carved a traditional scallop shell measuring about 4" x 4" to use as my original. My test revealed that a CNC digital probe is quite capable of accurately recording the shape of an object, with one exception; due to its ballshaped tip, the probe rounds off the inside corners of fi ne details such as the veins on this shell. A little bit of hand carving easily adds the missing details. The three carvings in the photo below are duplicates of my orginal (photo above). Watch the digital probe in action at AmericanWooodworker.com/CNC.

Click any image to view a larger version.



Step 1

Set the scanning parameters. The software control panel is used to set the size of the scanning area, the precision or resolution of the scanning action, and the speed of the scan. The Scan Limits of X and Y represent the width and length of the scan area, while the Z Scan Limit represents the range the probe travels vertically. The Step Sizes are the X and Y distances the probe moves between measurements. The Scan Velocity controls the speed of the probe as it moves across the part’s surface. The Part Coordinates show the location of the probe during operation. I used the Shark CNC Pro Plus to scan the shell for this article, but most CNCs, including the CarveWright and Shopbot, are capable of probe scanning.



Step 2

Scan the part. I set parameters for this shell carving as shown in Step 1. The X and Y scanning limits are penciled on the backer board. The Z limit was set at 1” to provide sufficient vertical travel for the carving’s 5/8” thickness. The step sizes of .005” for this shell equals 800 passes across the shell for a total of 680,000 steps, or measurement points, and took about 12 hours. ( I ran this overnight). The Shark CNC probe has a .075” dia. wear-resistant industrial ruby tip, so certain details such as the fine veins on this shell were not fully captured; but the remainder of the surface was captured with surprising accuracy. A larger step setting can be used on objects with less detail, such as a chair seat. Doubling the step size reduces scanning time by a factor of four.



Step 3

Adjust the digital image. The scanning creates an .stl file, which is a common file type used in 3D modeling. The scanned area surrounding the shell is not needed and is removed at this time.



Step 4

Create the 3D model. The .stl file is converted to a 3D model with CNC design software such as Aspire by Vectric. I also used Aspire to increase the thickness of the shell’s base to 1/4”.



Step 5

Smooth the surface. If needed, the design software can also be used to smooth the surface of the model. My scan was fine enough so I only needed to remove a couple scratches.



Step 6

Remove the background. I removed the background to get the waste material out of the way in order to make it easier to add the final hand carved details in Step 10. I programmed the toolpath for the 3/4” straight bit at a .1” depth-of-cut per pass and a stepover (pass width) of .2”. The tool path was also programmed to leave the shell profile .125” oversize. Removing the background for the three shells took about 30 minutes. The board started out .875 (7/8” ) thick and the routed background is .25” thick. The shell will have a final thickness of .75”.



Step 7

Rout the final profile and tabs. The final profile is made using a 1/4” straight bit that cuts all the way through the material. Tabs are left to hold the shell in place. These tabs can also seen in bottom photo on page 15. A piece of plywood underneath protects the metal machine bed from damage. I programmed the toolpath for the 1/4” straight bit for .125” depth passes. The profile and tab routing of the three shells took about 8 minutes.



Step 8

Rough rout the shape. To accomplish the rough routing I used a 1/4” ballnose bit programmed to a .1” depth of cut and .1” step over (pass width). This roughing phase removes the majority of the material. The amount of material left by the rough pass is adjustable, with .02” being common for a carving such as this shell. Leaving this small amount allows the final pass to be completed in one pass, saving time and wear on the finishing bit. The rough routing of the three shells took about 60 minutes.



Step 9

Rout the final pass. The final carving is done with a specialty .0625” (1/16”) ballnose bit (available at BeckwithDecor.com). I programmed this bit to make .01” wide (1/100”) passes. The tiny tip of this bit is capable of recreating a considerable amount of detail, and leaves a surface that only requires a light sanding with 220 grit sand paper to make it ready for finishing. The final routing of the three shells took about 70 minutes.



Step 10

Detail by hand as needed. Complete the carving with some touchup hand carving of the veins and finish sanding. There are CNC operations where the goal is to create a part that requires no additional hand work—this application is not one of them. A CNC is a tool capable of many things, but a realistic expectation of what it can do is also important. In the case of these shells, I accepted the fact that I would need to do some hand detailing to achieve the results I wanted, similar to scraping or sanding a board after jointing and planing.



Step 11

Make the boxes. After making the shells, the box shape is simple to program using the profile of the shell as a pattern. It took about 150 minutes to rout the 3 boxes on the CNC using a 1/4” up-spiral bit. They were cut out of 1-1/2” material.



Project Time Card

CNC the lids: 55 minutes each

CNC the boxes: 50 minutes each

Set up and material prep: 15 minutes each

Detailing and sanding: 45 minutes each

Staining and finishing: 20 minutes each

Total time: 3 hours 30 minutes each

I spent 5 hours 15 minutes (total for all three) doing something else while the CNC ran.




This story originally appeared in American Woodworker June/July 2011, issue #154.

June/July 20011, issue #154

Purchase this back issue.

 

 

V-Carving in 10 Easy Steps

V-Carving in 10 Easy Steps

By Randy Johnson

V-carving is one of the simplest ways to create attractive carvings on a CNC router. With special software and a little practice, it’s possible to transform almost any lettering style or 2D design into a carving that requires only minimal cleanup before finishing. I use V-Carve Pro software from Vectric, but the steps are similar with other v-carving programs. The software tells the machine to raise the bit at the inside corners; the machine then uses the tip of the v-bit to create corners that are clean and crisp—as opposed to the rounded corners made by a handheld router guided by a template. For more examples of v-carving visit AmericanWoodworker.com/CNC.


Step 1

Layout your design. All it takes is a simple hand sketch or photograph. This can be imported directly into the program and then outlined using the drawing tools in the v-carve design program. Since both letters and shapes can be carved, there are not many limits to the kinds of designs you can v-carve. You also have the choice of carving on the inside or outside of letters or shapes.

Click any image to view a larger version.



Step 2

Make sure all shapes are closed. This is one of the cardinal rules of v-carving design. A circle, square or the outline of an object qualifies, but a single line or parallel lines with open ends will not work. The v-carve programs need a continuous outline to follow. Some outlines may look continuous, but even a little break in the line will cause problems. Fortunately, v-carve programs are able to recognize shapes that have small openings and will automatically close them for you.



Step 3

Set the cutting depth for the background of your carving and the inside of the letters (as needed). This cutting depth is mainly a design decision, and of course it cannot exceed the thickness of your board. The cutting preview (example at right) will show you how your chosen cutting depth looks.



Step 4

Select your router bits. Use a straight bit first to rout flat areas. The diameter of this bit determines how much cleanup the v-bit will need to do inside a corner. A large diameter straight bit removes material faster but leaves more for the v-bit to cleanup. A small diameter straight bit leaves less material inside a coner but takes longer to clear the flat areas. I typically use a 1/4" diameter end mill for drawer front or cabinet door carvings.

The three most common v-bit angles are 60°, 90° and 120°. I prefer using a 90° and 120° v-bit for wide or large letters and a 60° v-bit for small or fine letters. If possible, I also prefer to use a v-bit with a cutting radius that’s slightly wider than the width of the final bevel. This allows me to make one final cleanup pass (if needed) to remove any step marks left by the initial passes.



Step 5

Create cutting paths for the recessed background and export them from your v-carving design program to your CNC machine. The cutting paths (shown above in red with tiny arrows) show the areas that will be routed. Here I’m using a 1/4" end mill bit to rout the flat background area. I’m accomplishing this with 1/8" wide passes (shown by the distance between the red lines). This dimension is referred to as the “stepover” measurement. The cutting depth per pass can also be programed, as can the feed (travel) rate of the router, expressed in inches per minute.



Step 6

Rout the recessed background area. To ensure a smooth background on this plaque, I used a couple techniques. First, I routed the background area in two .06" (about 1/16") deep passes, plus a light .01" pass to reach the final depth of .013". Three passes take more time than one, but create a surface that requires only light sanding. Second, I programed the router to cut with the grain (see Step 5). This reduces sanding, too. Milling the background for this plaque took about 20 minutes.



Step 7

Create cutting paths for the bevels around the shapes (the hand plane and perimeter rectangle in this case) and export them to your CNC machine. For this design, I will be using a 90° v-bit, which produces a 45° bevel. The shaded areas above the handle and below the depth-adjustment knob are closely-spaced tool paths where the v-bit needs to make many close passes to mill the background flat. These areas are too narrow for the 1/4" end mill bit to get into.



Step 8

Rout the bevels around the shapes. This requires removing the straight bit and installing the appropriate v-bit. I used a 1/2" diameter 90° v-bit. It has a 1/4" tall bevel—more than enough for the carved bevel, which will be only 1/8" tall. This step took about 20 minutes to rout. Except for some light hand sanding and a little touch-up with a carving chisel, this part of the carving is now complete.



Step 9

Create tool paths for the lettering. This requires a separate step because I’m changing to a 60° v-bit. I prefer a 60° bit for small letters such as these because it creates a deeper, more distinctive v-groove than a 90° bit. The tool paths above show how v-carving requires two lines to carve between. The two lines are parallel in these letters, but they can be any shape or spacing. For example, the outline of the hand plane and outer rectangle represents the pair of lines that were used to create the hand plane carving.



Step 10

Rout the lettering. Notice that “No. 4” is routed into the surface of the plane whereas as the logo is carved into the background. I programed the difference in cutting depth into the cutting paths while designing the plaque. This final carving step took about 8 minutes. To view a video on how I designed and machined this plaque from start to finish, visit AmericanWoodworker.com/CNC.




This story originally appeared in American Woodworker April/May 2011, issue #153.

April/May 2011, issue #153

Purchase this back issue.