RandyJohnson

Digital Woodworking – The Next Generation

Randy Johnson — Fri, 26 Apr 2013 02:28:00 GMT

From the Editor’s Desk - March 2011

When it comes to tools and machines, woodworking is still a very traditional craft as practiced by most small shop woodworkers. The types of tools on the “I own, I want” check list haven’t changed much in the past 100 years—or thousands of years if only hand tools are considered. Whether done with hand or power tools, woodworking still involves the same cutting, leveling, drilling and shaping processes that Noah used to build his big boat!
Now jump to 2011. We enjoy cordless drills, electronically controlled variable-speed routers, smart saws with flesh-sensing safety technology, and some of the finest hand tools ever made. But none of these have altered the fundamental practice of the craft. That’s about to change—slowly perhaps, but as surely as the cell phone has gone from a convenience to a necessity, we’re going to see changes in the way many woodworkers pursue their craft. The tool that’s going to make this difference is the Computer Numerically Controlled (CNC) router.
CNC technology has actually been around for decades. It has already significantly influenced woodworking at the commercial level, because CNC routers are highly efficient at machining both regular and irregular shapes. With the availability of affordable professional machines (e.g. ShopBot) and the recent introduction of benchtop models (See “Benchtop CNC Routers,” page 44), the technology is steadily making its way into small professional and home shops. In many ways, a CNC router is just another tool; but for being “just another tool,” it holds tremendous potential for small shop woodworkers.
As a technology for the small shop, CNC routers are drawing both skepticism and curiosity. Three years ago, I decided to get off the “wait and see” fence and jump into the world of CNC/digital woodworking. It’s been an exciting ride. I welcome your comments and questions about CNC routers and invite you to join the discussion at AmericanWoodworker.com/CNC.

Keep the chips flying,

Randy Johnson

Benchtop CNC Router Review

Randy Johnson — Fri, 01 Feb 2013 14:59:00 GMT

The buzz is growing around computer numerically controlled (CNC) routers--particularly around benchtop CNCs for the small and home shop. Why? I believe there are four reasons. First, an increasing number of small shop and home shop woodworkers are discovering the creative possibilities these machines offer. Second is the cost, which ranges from about $2000 to $6000. A benchtop CNC is still a major purchase when compared to most other pieces of small shop woodworking equipment, but the versatility of these machines is convincing many woodworkers that they’re worth the price. The third reason is size. Like other benchtop tools, you can store a CNC in a corner of your basement or garage. They easily fit on top of a mobile shop cart. Finally, is the general intrigue I believe most of us have with technology. Benchtop CNCs are pretty approachable even for the average non-techy woodworker.

Download complete story (PDF).

CNC Spring Joint Box

Randy Johnson — Tue, 01 Jan 2013 23:54:00 GMT

Spring Joint Box

Self-locking design requires no glue.

By Randy Johnson

Squeeze and snap! That’s all it takes to assemble this CNC-routed box. Th e joint’s flexibility comes from a series of slots that allow the hooked tenons to be compressed, so they slide into the mortises. When released, the tenons spring back into position, locking the parts together. While not as rigid as a glued joint, the assembled spring joints are surprisingly stiff . And you can enjoy assembling and disassembling the box as oft en as you like.

The key to making this joint fit well—neither too tight nor too loose—depends on several things. Th e primary factors are the spacing, length and number of the slots as well as the tolerances between the tenons and mortises. Th e springjointed front and back are also 1/8" taller than the mortised ends. This small difference in height keeps the hooked tenons slightly compressed aft er assembly, which adds additional stiffness to the joint. Th e type of wood and the thickness of the parts also affect the joint’s flexibility.

Accommodating all these variables can be a bit of a challenge —I made eight prototypes before I found a fit that I liked. But similar to mastering hand-cut dovetails or mortise and tenon joints, the time spent working out a solution for this box was a very satisfying learning experience.

The slots become part of the box’s design and variations are almost unlimited. However, I kept the shape and arrangement of the slots for this box simple in order to show how the parts are made. Plans and tips for routing this box can be found at AmericanWoodworker.com/CNC.

Click any image to view a larger version.

Wedge the parts in place

Holding parts secure is important for all CNC work. For this project I used 3/8" deep pockets—the same thickness as the parts—cut into 3/4" MDF. I then added 1/2" thick MDF wedges to secure the parts. The wedges are very easy to install and remove with a couple mallet taps. Plans and tips for building this type of jig are available at AmericanWoodworker.com/CNC.

Rout the front and back parts

First cut around the tenons (1). Then cut the grooves (2), the two outer end slots (3), the three inner end slots (4) and finally the center slots (4). This cutting order is important because it keeps the router bit from chattering as the part becomes increasingly flexible. It’s also important to use a down-spiral bit, which pushes the part down during routing.

Test-fit the parts

Rout the mortises and check the fit of the tenons. The parts should fit together snugly, but without binding. I found cutting the mortises .015" larger than the tenons provided a good, slightly tight fit. Once the faces of the parts were finish-sanded and the corners were eased, the fit was perfect.

Rout the latch parts

The lid’s two latch parts are cut from one piece of wood but connected with a thin tempoary tab between the parts. These parts are somewhat delicate to machine, so the down-spiral bit really proves its worth. An up-spiral bit can lift the parts and chew them up—I speak from experience!

Test fit the latches

Rout grooves on the underside of the lid for the latch parts and test their fit. The groove for the fixed latch runs the full length of the latch. The groove for the spring latch is shorter, since the ends of the spring latch must be free to flex (as shown below, "Working the Spring Latch"). The latch parts are glued into the slots after all the parts are sanded.

Assemble the first three parts

Two dimensions are key to making this joint work. First, the five 1/8" wide end slots allow the tenons to be compressed up to 5/8". Second, the through mortises are spaced so that the hooked tenons only need to be compressed 1/2" to pass through. This 1/8" leeway eases the assembly. Anything less than 1/8" makes the parts difficult or impossible to assemble.

Insert the bottom panel

The 1/4" thick bottom panel fits into grooves in the front and back parts. These parts also have grooves near their top edges, which serve as clips for the two latch parts. These grooves are all the same size, so the front and back parts don’t have a top or bottom. The ends have a single groove for the bottom panel.

Snap on the last part

Slip the remaining end over the hooked tenons, working the mortises down equally. Pressing one side down first will only rack the end and cause it to bind. If the parts have been correctly cut, this last end should snap into place with a satisfying pop. If not, a little additional sanding should ease the fit.

Working the Spring Latch

Opening the box is a bit of a puzzler, because the springlatch system is completely hidden when the lid is closed. Here’s how the system works: Tabs at the ends of the spring latch flex about 1/4" (right, above). These tabs fit about 3/16" into the latch groove in the back of the box. When the lid is pressed from the front (right, below), the spring latch flexes deeper into the groove at the back, allowing the fixed latch to slip inside the box. Releasing the lid relaxes the spring latch, which in turn engages the fixed latch in the groove in the front of the box. The lid is now locked in place, because both latches are clipped into the latch grooves. To open the box, simply press on the front of the lid and lift.

DOWNLOAD VECTORS

DXF file for all project and jig vectors on layers

PartWorks and Vectric V-CarvePro file

This story originally appeared in American Woodworker December/January 2013, issue #163.

DOWNLOAD STORY PDF

CNC Linker Logs Blanket Hut

Randy Johnson — Thu, 01 Nov 2012 20:15:00 GMT

Linker Logs Project

Have fun while learning to fabricate with plywood.

By Randy Johnson

Although linker logs are made with the aid of a computer— once complete, they’re a great way to get kids (and parents) off the computer for an afternoon of old-fashioned fort building and pretend. The techniques shown here— including pre-finishing the plywood, programming correct joint tolerances, arranging parts, locating hold-downs and placing tabs—can also be used for other plywood projects. Th e inspiration for making these building planks comes from a story titled “Plywood Play Planks” that appeared in the December 1953 issue of Mechanix Illustrated magazine. Th e original designers used 3/4" plywood and a dado blade to cut the joints. That technique can still be used, but using a CNC provides more freedom when designing the shape of the planks. Bill Young (a ShopBot guru from Virginia) adapted the idea for the CNC by creating a wide variety of planks, all with a standard notch spacing. The playhouse shown below is similar to the original Mechanix Illustrated design—but I added the puppet theater window and marquee board. Also check out the Blanket Hut below, with with its custom barrel vault roof.

Start by finishing

A coat of shellac followed by a water-based topcoat provides a durable finish for Linker Logs —and most other plywood projects. Finishing a sheet of plywood is much easier than finishing dozens of individual pieces, so applying the finish first makes lots of sense. Shellac dries quickly and seals the wood so the water-based topcoat won’t raise the grain, and gives the plywood a nice amber tone. See “Pre-finishing Plywood” (page 68) to learn more about finishing plywood.

Click any image to view a larger version.

Measure the plywood

The thickness of the plywood must be consistent so the cross-lap joints that fit properly. I recommend a tolerance between sheets of plus or minus .005". Most good-quality AC or AB sanded plywood will be consistently sized. The sheets of 1/2" plywood that I used to make this playhouse measured .47" thick. Measuring after applying the finish ensures the most accurate measurement.

Cut a single part to test the joint

Rout a test part. When you test the fit in the next step, the width of the notch is the only thing that matters, so you can make the test part out of almost anything. I used 1/2" MDF. The test notch measured .48" wide, which should provide the desired .01" clearance when the cross-lap joint is assembled.

Check the joint’s fit

A mechanic’s feeler gauge works well to measure the gap between the parts of the cross-lap joint. Ideally, this gap will be .01", but anything from .005" to .015" is acceptable and will hold the Linker Logs together while still allowing them to be easily assembled and disassembled.

Nest parts and locate screws

Most CNC design programs include a “parts nesting” feature that automatically fits multiple parts to the plywood. The Linker Log parts shown here are nested .27" inches apart—slightly larger than the 1/4" bit that will cut them out. Once the parts are nested you can still move them around to attain the exact layout you want. This allows you to safely locate the hold-down screws that secure the plywood sheet.

PROJECT PLANS ARE AVAILABLE AT THE BOTTOM OF THIS PAGE.

Add connecting tabs

The next step is to add tabs between the parts to keep them attached during routing. Since there is no waste material between most of the parts, tabs need to be added opposite of each other. The tabs added here measure .1" thick x 1" long. An alternative to adding tabs is to adjust the routing depth to leave a thin layer of material (a skin) at the bottom of the kerf. A skin of .05" would work fine for this project.

Secure the plywood with screws

Program the CNC to mark the location of each anchoring screw with a shallow plunge cut. Locating the screws in your drawing and transferring them to the plywood guarantees that the router bit won’t run into the screws while cutting the parts.

Use a down spiral bit

A down-cut spiral bit pushes the wood down while cutting, so it leaves a nice, clean edge at the top of the plywood. The bottom of the cut is also clean, because the spoil board under the plywood prevents blow-out.

Separate and roundover in one step

Remove the connecting tabs. A straight flush-trim bit works well for this, but I used an Amana 1/8" roundover bit (#MR0112) with a miniature bearing. This bit removed the tabs and rounded the sharp edges. It also allowed the joints to fit fully together, because the logs’ rounded-over edges match the rounded inside corners of their CNC-routed notches. I left the edges and notches unfinished.

Combo Puppet Theater and Play House

A combo puppet heater and play house that all kids seem to enjoy, It features a marquee with room to engrave or paint your kid's theater logo.

Project plans, Vectric Aspire, .dxf, and SketchUp files for the two playhouses can be downloaded at the bottom of this page.

Additional plank designs that included angles and curves can be found at LinkerLogs.com. You supply the kids.

Alternate T-bone notch

If you want to keep the plywood edges square, use a “t-bone” notch design. Most CNC drawing programs have a built-in tool that lets you quickly add the right size “t-bone” to your joints. As you can see, this modification lets the plywood fully seat in the bottom of the notch.

Download parts info (PDF)

Download Vectric Aspire file

Download DXF files

Download SketchUp File

Autodesk 123D files (Pending)

See more Linker Log ideas at www.LinkerLogs.com

This story originally appeared in American Woodworker October/November 2012, issue #162.

DOWNLOAD STORY PDF

CNC Linker Logs Puppet Theater

Randy Johnson — Thu, 01 Nov 2012 19:26:00 GMT

Linker Logs Project

Have fun while learning to fabricate with plywood.

By Randy Johnson

Start by finishing

Click any image to view a larger version.

Measure the plywood

Cut a single part to test the joint

Check the joint’s fit

Nest parts and locate screws

PROJECT PLANS ARE AVAILABLE AT THE BOTTOM OF THIS PAGE.

Add connecting tabs

Secure the plywood with screws

Use a down spiral bit

Separate and roundover in one step

Blanket Hut

A twist on the blanket-over-a-table fort that all kids seem to enjoy, this design features rounded gable ends and half-planks for rafters.

Project plans, Vectric Aspire, .dxf, and SketchUp files for the two playhouses can be downloaded at the bottom of this page.

Additional plank designs that included angles and curves can be found at LinkerLogs.com. You supply the kids.

Alternate T-bone notch

Download parts info (PDF)

Download Vectric Aspire file

Download DXF files

Download SketchUp File

Autodesk 123D files (Pending)

See more Linker Log ideas at www.LinkerLogs.com

This story originally appeared in American Woodworker October/November 2012, issue #162.

DOWNLOAD STORY PDF

CNC Two-sided Machining

Randy Johnson — Sat, 01 Sep 2012 13:33:00 GMT

CNC Two-Sided Machining

Two carefully placed index pins ensures accuracy.

By Randy Johnson

Skilled woodturners can easily match a bowl’s inside and outside surfaces by eye and touch. Creating two-sided shapes on the CNC, however, requires a different strategy: To ensure that both sides align, the top and bottom shapes must be positioned carefully during both the design and the machining steps. I’ll demonstrate the process using the lid of the box shown here. (The bottom of the box is machined using the same setup even though the bottom has a different shape and wall thickness.) To set this box apart from a typical round turning, I made it as an oval with a weave pattern on top. In fact this process can be used with almost any shape—one of the many benefits of CNC machining.

Click any image to view a larger version.

Step 1: Work from the Center

Layout each side of your design on a pair of centerlines. Then locate index holes at opposite ends of the long centerline, outside the machined area. Here, I’ve started with the lid’s bottom side (Side 1). Its concave oval shape measures 1/2" deep x 4-1/2" wide x 7-1/2" long. This lid is designed to be made from 3/4" thick stock."

Step 2: Layout Side 2

The size of side 2 determines the thickness of the project. To create the 1/4" thickness for this lid, I added 1/4" to the measurements of Side 1. Thus, the model for the top side of the lid (Side 2) measures 3/4" thick x 5" wide x 8" long. In addition, I added a 1/2" wide flange around the lid to provide clearance for the small router bit used during the finish routing phase (see Step 7).

Step 3: Rout Index Holes in the Deck

Use a straight bit to rout a pair of index holes 1/2" deep into the deck of your CNC or use an auxiliary deck board. For this project, I fastened a piece of 3/4" MDF to the aluminum deck of the CNC Shark Pro Plus I was using. The centerlines on the deck served as the X-Y (left and right) reference point for setting the router bit’s location.

Step 4: Rout Index Holes in Side 1

Fasten your work piece to the deck and rout 1/2" deep index holes into it. This establishes Side 1 of your project—the underside of the lid in this case. The index pins I used were 1" long so the 1/2" deep holes worked just fine. The workpiece does not have to be perfectly centered with the centerlines on the deck for this step, because the index holes and pins will correctly align the blank when it’s turned over to rout Side 2.

Step 5: Rout Side 1

To create the lid's concave underside surface, I used a 1/4" ballnose bit for both the roughing and finishing passes, but I routed across the grain on the roughing passes and with the grain on the finishing passes. The finishing pass left only light mill marks that were easily removed with 120 grit sand paper.

Step 6: Insert the Index Pins

Remove the blank and insert index pins in the deck. Then flip over the blank and install it on the pins. Here I used 1" x .30" dia. aluminum dowels for index pins, but I’ve also used nylon dowels (both are available at most hardware stores). Pieces of a round pencil also work quite well. They’re cheap and easy to replace when eaten by the dust collector.

Step 7: Rout Side 2

Machine side 2 similar to Side 1. Start with roughing passes across the grain, using the 1/4" ballnose bit. The flange around the lid is routed during the roughing phase. To achieve more detail in the lid’s weave pattern, I switched to a 1/8" dia. ballnose bit for the finishing pass (shown above). The finishing pass stays on the weave, and the flange provides clearance to keep the small bit from contacting the tall shoulder.

Step 8: Cutout and Complete

Rout around the oval and through the blank using a 1/4" straight bit. Leave tabs to keep the lid attached. Remove the blank and finish cutting out the lid on the bandsaw. Then use a disc sander to smooth the lid’s edge. Clean up the edges of the weave pattern by hand with a V-Parting carving chisel. The 3D model for this project can be downloaded at AmericanWoodworker.com/CNC.

Modeling files for the two-side lid.

Files for the topside of the LID

Download vector (DXF) files

Download GREYSCALE (BMP) files

Download 3D MODEL (STL) files

Files for the bottom side of the LID

Download vector (DXF) files

Download GREYSCALE (BMP) files

Download 3D MODEL (STL) files

This story originally appeared in American Woodworker August/September 2012, issue #161.

DOWNLOAD STORY PDF

CNC Wooden Chain

Randy Johnson — Sun, 01 Jul 2012 21:51:00 GMT

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.

DOWNLOAD PROJECT FILES BELOW

Download jig plans below

PDF file (150 KB) - (Please visit the site to view this media)

Adobe Illustrator file (140 KB) - (Please visit the site to view this media)

DXF file (1.2 MB) - (Please visit the site to view this media)

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

Download Story PDF

Creating CNC Textures

Randy Johnson — Tue, 01 May 2012 22:26:00 GMT

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"

Randy Johnson — Fri, 02 Mar 2012 02:17:00 GMT

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.

CLICK TO ENLARGE VIEW OF HANDLE

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.

Twists are also possible

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

DOWNLOAD STORY PDF

CNC Project Gallery

Randy Johnson — Mon, 02 Jan 2012 02:33:00 GMT

CNC Project Gallery

By Randy Johnson

As CNCS become increasingly common in small woodshops, an amazing variety of work is emerging. Although this confirms the technical versatility of CNCs, it’s an even greater testimony to the creativity and ingenuity of woodworkers, designers and artists alike. The following projects are but a sampling. To see more, follow the web links in this article.

Allura Side Table

This table by Brooke M. Davis is available in Honduran or African mahogany. It is one of several “luxury” designs that Brooke markets through her website BrookeMDavisDesign. com. See page 18 for another pierced CNC design by Brooke. Brooke also owns and operates (Make+Shift) atx, a design-on-demand shop in Austin, Texas.

Click any image to view a larger version.

Rinaldo Chair

Plydea, a furniture company in Seattle, Washington, manufactures this chair from zero-VOC prefinished birch plywood. Plydea makes a growing line of readyto- assemble products utilizing snap-together joinery. See more at Plydea.com.

My Home Made Chair

Richard Garsthagen, of the United Kingdom, designed this chair in Adobe Illustrator and cut it from 12mm birch plywood. An animated slide show of the chair being assembled can be viewed at AmericanWoodworker.com/cnc.

Pattern Study

Jennifer Anderson, of San Diego, explored the versatility of CNC in creating this piece; the deep pleating in couture fashion provided inspiration for the pattern. Jennifer finished the table with milk paint and shellac. More at JenniferAndersonStudio.com.

Shelter 2.0

Robert Bridges designed this for Design It: Shelter Competition, a 3-D design contest organized by the Guggenheim Museum and Google SketchUp. Robert and collaborator Bill Young envision this design as an inexpensive, quick-to-construct shelter for homeless and disaster-stricken people around the world. Cutting the project on a CNC takes about 12 hours; it requires 36 sheets of plywood plus hardware and vinyl sheeting. More information at Shelter20.com.

Bronzed Mahogany Bowl

Ed McDonnell turned this bowl on a wood lathe and then embellished it on his shopmade digital CNC ornamental lathe. The bowl measures 5-1/4" tall by 7" dia. The exterior is finished with Sculpt Nouveau Bronze B and Tiffany Green Patina to create the look of aged bronze. The interior is finished with Minwax wipe-on gloss polyurethane. To view pictures of Ed’s ornamental lathe, visit Vectric.com/forum and search for the post “Wrapped and Sculpt Nouveau.”

Nice Carvings

Nice Carvings is the name of Melissa Jones’ sign business—a fitting name given the quality of her work. Melissa started her business carving signs by hand and many of the details in her current work are still added by hand, such as the distressed look of the Maximum sign. Most of Melissa’s signs are made of high-density urethane (HDU) foam sign board, such as the 36'' dia. Deerkill Day Camp sign, while wood is the material of choice for others, such as the Maximum sign. Melissa finishes most of her signs with a primer coat of Kilz and top coats of Sherwin Williams latex paint. Melissa creates her designs with Vectric Aspire CNC design software and cuts them on a Shopbot CNC. View more of Melissa’s work at NiceCarvings.com.

Intertwined

Brooke M. Davis designed this 55" x 18" mahogany table top. While this elaborate carving would likely be a one-of-kind table if done by hand, the CNC allows Brooke to reproduce versions in other woods and finishes to suit a customer’s needs. You can view the complete table (with legs) at BrookeMDavisDesign.com.

Doug Haffner

Doug Haffner, owner of Haffner Signs, Wyoming, Illinois, creates what he calls “dimensional signs — ones that you can walk around.” His own business sign (photo far left) highlights his “dimensional” approach to signmaking, as well as his designing and sculpting talents. The base of the sign reads “THE SKY IS THE LIMIT UNTIL YOU DECIDE IT’S NOT.” and the other side says “A GOOD SIGN CAN TAKE YOU A LONG WAY.” Doug works in multiple materials including wood, foam, sculpting clay, plastic and metal. He’s very pragmatic about his approach; while he uses a CarveWright CNC for much of his work— such as shaping the inner foam layers for his rocket and carving letters for the panels on the sign’s base—many of the details are modeled by hand. This includes the rivet heads on the base. So each rivet would look unique, he added and shaped each one by hand. See more of Doug’s work at HaffnerSigns.com. While you’re there, make sure to check out his awardwinning Robot sign.

Rose Window

Using Vectric Aspire software, Michael Mezalick designed this small-scale replica of the famed window of Notre Dame Cathedral. Michael machined his replica out of 3/4" MDF on his CAMaster CNC, and finished it with Valspar “Stone” spray paint. This window and other CNC-made products are available at Michael’s website Shop.CarvedDetails.com.

Autumn Wreath

Jim Creco of Mebane, North Carolina, machined and finished this project. The design was created by Michael Taylor, a graphic artist turned CNC project designer. This is one of hundreds of CNC designs that Michael has created. His plans are available through his website CarveBuddy. com, as well as CarveWright.com and VectorArt3D.com.

Bison Plaque

Tim Merrill, of Henderson, North Carolina, carved this bison out of mahogany. He highlighted it with a dark stain and set it in an alder backboard. The bison and landscape background designs are available through VectorArt3D.com. Tim holds the well-deserved title of “Vectric Archimage” on the Vectric.com forum for being the member with the most posts and a reliable source of helpful information.

Carved Blanket Chest

Reuben Foat, a graduate student, made this in the furniture design program at San Diego State University. Although most of his designs start on paper, Reuben is also an avid Rhino CAD user. As for the CNC, Ruben says, “It wasn’t until graduate school that I got my hands on a CNC. It has been a game-changer for me.” See more of Ruben’s CNC (and laser) work at ReubenFoat.com.

This story originally appeared in American Woodworker December 2011/January 2012, issue #157.

December 2011/January 2012, issue #157

Purchase this back issue.

CNC V-Carve Inlay

Randy Johnson — Thu, 01 Sep 2011 14:32:00 GMT

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.

Download PDF of story

Digital Probe Duplication

Randy Johnson — Sat, 02 Jul 2011 02:15:00 GMT

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.

Download STL file for Shell

Download Grayscale for Shell

Download DXF flies for Shell and Box

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.

Download STL file for Shell

Download Grayscale for Shell

Download DXF flies for Shell and Box

Video - PENDING

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

Download Article PDF

V-Carving in 10 Easy Steps

Randy Johnson — Mon, 02 May 2011 02:02:00 GMT

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.