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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-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

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