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So you’ve decided to launch yourself into the world of CNC machining. You’ve done some research and lurked around many online forums and resources looking for information regarding which model to choose and what features the unit needs. You’ve plonked down your hard earned cash and a big cardboard box has arrived in the mail containing a bright, shiny new CNC router. It’s been assembled and set up on your desk. Now what? Fundamentally, most basic CNCs will have a bed which workpieces are secured onto and a overhead gantry that travels the length of the table. Onto this gantry a secondary carriage travels over the width of table. The spindle itself is attached to this carriage and can move vertically. The spindle rotates a cutting tool at high speed to remove material from the workpiece. The three movement directions (side-to-side across the table, up and down the length of the table, vertically up and down perpendicular to the table) are the three axes of motion that the machine can operate in; X, Y and Z respectively. Each axis is independently controlled by specialised motors known as steppers, which are designed to rotate either direction by precisely known amounts. The rotation of these motors is translated into simple linear movement (backwards and forwards). Commonly, threaded rods ("lead screws") pulleys or toothed belts are used for this purpose. Larger machines can sometimes use these in combination (such as pulleys for X and Y, leadscrew for Z). Each have their respective advantages and disadvantages in accuracy, cost, speed, load capacity, etc. Lead screws are most common in small CNCs for all three axes. The precise rotation of the stepper motors is controlled through the application of electrical pulses. By co-ordinating the number, length and frequency of the electrical pulses, the CNC machine can be made to execute precise synchronous motions to move the cutting tool around the workpiece in complex paths. The generation of these control pulses is performed either by dedicated standalone control consoles or by software on a common computer. Non-production level CNC tends to utilise the second option; the steppers driven by a simple external interface unit that sits between the machine and PC which handles the translation of the software stepper signals into the heavier-duty control signals that drive the motors. Software generation requires that a motion control application be installed on the host computer. Two of the most popular motion control solutions at the moment are Mach3 or Mach4 (for Windows based computers) and LinuxCNC for (Linux-based operating systems). In this article we will use LinuxCNC to illustrate how to set up the desktop CNC router; fundamentally the operating principles are similar between the Mach-series software and LinuxCNC. Both options require the host computer to have a parallel port for communicating with the control interface. Laptops and USB-to-parallel adaptors are not recommended for software stepper pulse generation. The main advantage of favouring the "old" parallel port standard is that many signals can be sent simultaneously; despite being far faster, USB is purely serial and asynchronous; one piece of information at a time and "arrives when it arrives". Parallel is far closer to being a real-time interface, which USB to parallel adaptors do not reliably replicate. PCI parallel port cards on the other hand are a satisfactory option if your host computer doesn't feature a parallel port. Installation of a Linux operating system and the LinuxCNC application is beyond the scope of this article, however it is extremely simple; LinuxCNC is available as a LiveCD installation, whereby the user has the ability to boot a pre-compiled version of LinuxCNC from a CD, DVD or USB memory stick without installing the operating system onto the computer. This operating system image is available to be downloaded from the LinuxCNC website. A permanent installation of Linux and LinuxCNC can be performed from the LiveCD if the user so chooses at a later date. The first requirement in setting up the CNC machine is to create a configuration file. This contains the specifications of the CNC motors so that they are driven at the correct speed/rate, acceleration, direction, etc. From the menu bar Click ‘Applications’, navigate to ‘CNC’ and select ‘LinuxCNC StepConf Wizard’. If this is the first time that StepConf Wizard has been run a new configuration must be made. The user also has the option of opening an existing configuration to either adjust existing settings in their recently created configuration, or use another configuration as the basis for their new CNC router. In this case we will create a new configuration from scratch. Click ‘Forward’ to move to the next page in the StepConf Wizard. In the next screen the configuration can be given a meaningful name and basic setup parameters defined, such as units of operation (millimetres or inches), how many axes the machine operates with (in our case three axes – XYZ), parallel port addresses and driver signal timing. If your CNC machine comes with data or a user manual then use this to set the driver timing settings. If there is no data supplied you may have to search online to find some information regarding the suggested timing parameters, or experiment to find the best trade-off for reliable operation of the CNC router. Step Time and Step Space - the width of the electrical pulse applied to each stepper motor and the subsequent gap between each successive pulse, expressed in nanoseconds. Too small a step pulse or space and the motor will miss a step. Too long and the CNC axis movement can become unacceptably slow. Direction Hold and Direction Setup - In addition to the step pulses themselves, secondary signals are generated by the motion control software that change the order of the pulses being applied to the steppers. Changing the order of the pulses changes the rotation of the motors from clockwise to anti-clockwise. The "Direction Hold" and "Setup" parameters define the amount of time the direction signal applied to a stepper motor needs to remain activated after a step pulse has been issued, and the amount of time the direction signal needs to be applied to the stepper before issuing the next step pulse. Too small a direction hold or setup and the motor can miss a change in direction and overshoot its intended stop point. Too long and the CNC axis movement can become unacceptably slow. In most cases the values shown will work as-is and require no further adjusting. The last key item that requires attention on this page is the ‘Base Period Maximum Jitter’ setting. Instructions to the CNC (via the interface) are generated by software, so there is a potential that something occurring in the computer or operating system outside the control of the CNC machining application may interrupt the continuous supply of timely instructions (eg. graphics redrawing on the screen, hard drives being accessed, etc). Consequently we need to ensure that any interruptions that do occur do not interfere with the normal operation of the CNC machine. To find out what this minimum safety net should be the StepConf Wizard includes a ‘Jitter Base Period Test’ function. After running the test for a few minutes this returns a suitable ‘Base Period Maximum Jitter’ value. This states how much the system might be expected to be delayed during normal operation; the configuration then makes sufficient allowance to avoid interruptions in the generation of the stepper control signals. Click ‘Forward’ when all fields have been filled in. Leave the Advanced Configuration Options unchecked at this stage and click ‘Forward’ again. The Parallel Port Setup screen is where we define what each pin of the parallel port on the computer is expected to do when connected to the CNC machine. Again, consult any data or the manual supplied with the CNC router to determine how each pin is to be connected. As we are configuring a basic 3-axis machine the minimum required pins to be configured will be X Step, X Direction, Y Step, Y Direction, Z Step and Z Direction. The other important pin to configure is the Emergency Stop (or E-Stop) input from the machine. Nearly all CNC machines will be fitted with a large E-Stop switch that the user can hit in the event that the machine begins executing some unintended moves, and signals the motion control software to unconditionally stop moving the axes. The next three screens are used to configure the behaviour of each stepper motor; their speed, acceleration and limits of travel. Each axis is configured independently but the options presented are identical: Motor Steps Per Revolution – how many steps the motor needs to perform to complete one full rotation of the shaft. Manufacturers of stepper motors often express this value as degrees per step. If your stepper motor has this value specified as 1.8 degrees per step then Motor Steps Per Revolution is equal to 360 degrees divided by the degrees-per-step value, or 360/1.8 = 200. Driver Microstepping – the resolution of a stepper motor can often be increased by the action of microstepping. The basic degrees-per-step specification of the motor is enhanced by the driver forcing the motor to make an intermediate ‘soft’ step in between each 1.8 degree ‘hard’ step. In the same way that a picture with higher resolution can display more detail on a computer screen, a stepper motor with more resolution can perform finer movements. The trade-off is that the more microstepping you add the less torque that motor is able to generate. In practice a microstepping value of either 2 or 4 is a good compromise. Note that if you set microstepping to 2 it will require that Motor Steps Per Revolution be increased to 400 to maintain the relationship of the number of steps to complete one revolution of the motor shaft. Setting microstepping to 4 will require Motor Steps Per Revolution to be set to 800. Pulley Teeth – only required for CNC machines that use pulley systems to drive the axis. This is where you would specify the gearing ratio of the pulleys. We are using a lead screw in the desktop CNC machine so leave these two fields set to 1. Leadscrew Pitch – the pitch determines how far each axis will travel when the lead screw is rotated one full revolution, and its setting is critical to ensure that the axis travels the correct distance when commanded to do so. If the units of operation specified earlier were inches then the lead screw pitch is expressed as threads per inch. If millimetres were specified then this value is expressed as millimetres per revolution. Consult your CNC machine datasheet for information on the specifications of lead screw fitted. As an alternative most lead screw pitches can be measured reasonably accurately by using a ruler to count the number of thread ‘peaks’ within one inch, or the distance in millimetres between two successive thread peaks. Maximum Velocity and Maximum Acceleration – sets the maximum speed and acceleration of the axis before the CNC machine starts missing steps or losing accuracy when changing directions. As no real life object can accelerate from a standstill to full speed instantaneously, we need to specify a value in the ‘Max Acceleration’ field to limit how quickly the CNC motion control software tries to make the machine change its speed when either accelerating from zero, coming to a stop at the end of a manoeuvre, or changing directions suddenly when transitioning between two trajectories. In general this is set by experimentation with your particular machine, but the values presented here should work with the smaller desktop CNC routers as a starting point. Home Location – the default location the axis will set itself to when the machine is told to ‘return home’. The home location can actually be anywhere you like within the axis limits of travel, but is typically set at 0 (which would equate to the lower-left corner of the table with the Z axis at maximum height). Every time the software is started up the physical location of the CNC machine is undefined. Until the CNC machine is homed it cannot know where its limits of travel are (below) and therefore cannot commence a machining job. Table Travel – specifies the ‘soft’ limits of motion that the axis can move within, and is expressed as either millimetres or inches depending on how the units of operation were set earlier. For each axis this is typically set to the maximum travel that the axis can move to before reaching the end stops. When the motion control software detects that the axis has reached its soft limit it will not attempt to drive the CNC router beyond this value. Note that when setting the Z axis the Table Travel fields are normally set as a negative number to zero, rather than as zero to a positive number. The convention here is that the Z axis moves negatively with respect to the surface it is bearing down upon. The last option for each axis is the ‘Test this Axis’ function. Clicking on this will bring up a window that allows the user to see if the configuration created thus far is appropriate for their machine. With the CNC router connected to the computer and powered up the axis under test can be manually moved using the two ‘Jog’ arrow buttons, or the axis can be set to automatically swing back and forth by a set amount according to the ‘Test Area’ fields. This is useful for determining if the axis is moving by the correct amount based on the ‘Motor Steps Per Revolution’ and ‘Lead screw Pitch’ settings, and also if the ‘Max Velocity’ or ‘Acceleration’ settings are going to result in missed motor steps. Assuming that step direction was set up correctly earlier under the ‘Parallel Port Setup’ window for each axis, clicking the right ‘Jog’ arrow should make the X axis move towards the right of the table, the Y axis move away from the front of the table and the Z axis move vertically upwards. Clicking ‘Forward’ after configuring the last axis and then ‘Apply’ will create an icon on the desktop allowing the user to launch the motion control software using the created configuration file. And that’s it! If you’ve made it this far you’ve successfully created a configuration file to suit your CNC router. By double-clicking the 'launch CNC-router' icon on the desktop, the configuration file will pre-load all the necessary parameters for the CNC machine and start up the motion control software. ---------- In the next article we will begin creating a basic G-Code file to run the CNC router with. In doing so we will also verify that the machine operates correctly, and the axis motion is correctly scaled to create 1:1 cuts in preparation for applying the CNC machine's abilities to creating luthiery-related components.

Recently I made the decision to step into the world of CNC routing machines and augment my small workshop and tool collection with a modestly-sized unit. With the rise in quality of low-end Chinese-made machines in recent years it has become easier than ever to purchase a small CNC router for home use capable of high precision. A quick search on online auction sites will reveal a vast array of pre-assembled units for sale starting in price from less than $700, with cutting beds up to 600mm x 900mm in size. While I am still a novice at CNC, hopefully my experiences can help others decide if taking the plunge is for them too. So, why choose a small CNC router? There were several reasons why I personally decided to purchase a desktop machine with the intention of applying it to guitar work: I had a limited budget and a small area where I could set up such a machine. A CNC router capable of directly milling a guitar body from a timber blank is physically large, noisy and expensive; I was after a way to improve the appearance of my builds by including professional-looking headstock logos and markings, and had thus far been dissatisfied with many of the solutions that utilised decals or transfers; I wanted a quicker and safer way to create templates for routing smaller shapes and components used in guitar construction (eg, pickup cavities, headstock outlines, truss rod covers); Having decided to explore multi-scale instruments I needed a way to make accurate drilling templates for the individual bridge assemblies commonly used for these instruments; Despite wanting to automate some of the construction process, I still wanted to retain the hands-on nature of building an instrument rather than transfer the bulk of the cutting and shaping work directly to a machine; The increased accuracy afforded by the machine for particular tasks was attractive (eg, scribing fret slots directly onto a fretboard blank, creating perfectly-fitted control cavity covers). The CNC machine I eventually settled on was at the smaller end of the scale; a 3-axis desktop unit with a similar footprint to a mid-sized inkjet printer, having a cutting bed of 200mm by 300mm (X- and Y-axis respectively) and a vertical travel of 50mm (Z-axis). The spindle is rated at 200W, with a 1/8” collet which allows the changing of cutters using a wrench system similar to that used on many handheld routers. The build quality of the frame and gantry seems quite acceptable, although for the price paid I would expect some shortfalls in terms of frame flex and milling accuracy of the spindle due to runout and eccentricity. However if you don’t work the CNC router too hard any errors in the finished milling process will be minimal, and achieving sub-micron precision in a material such as timber is probably a moot point anyway. A separate controller interface unit is supplied featuring variable spindle speed via a dial on the front panel and PC connectivity through a parallel port on the back. It is worth noting that most of the models which utilise a parallel port to interface with the computer require a desktop PC rather than a laptop, as the battery power management features of the latter are not conducive to reliable operation of the CNC router. Commonly available USB-to-Parallel Port adaptor cables are also incompatible with these units. However, if your host computer does not have a built-in parallel port you can purchase and install an aftermarket PCI parallel port card, which is exactly the path I chose. The unit also came equipped with a selection of endmills, a set of rudimentary work piece holding clamps, a number of allen wrenches and spanners and an evaluation copy of the Mach3 CNC motion control software. While the supplied endmills are satisfactory for learning the ropes and experimenting with different cutting operations, you may wish to invest in a small collection of higher quality endmills, which afford a far superior finish and longer working life than the factory-supplied ones. The controller is connected to the CNC mill via several cables with locking collars to prevent them inadvertently working loose. An unexpected bonus feature of the particular model I chose was that the controller circuit board is fitted with several unpopulated connectors that allow the retro-fitting of axis limit switches. On more fully-featured units these limit switches are fitted to the moving components as a safety measure to prevent the software accidentally driving the CNC machine past its maximum limits of travel, or to allow automatic homing of the cutting head (more in this in future articles). On the subject of software, there are two main options for driving a parallel port-based CNC router; the above-mentioned Mach Series software which is for Windows-based machines and LinuxCNC (formerly known as EMC2) for Linux-based systems. As LinuxCNC is a well-supported open-source option for these machines I elected to take this option and install a Linux partition on my host computer. Conveniently, LinuxCNC offer several LiveCD versions of their software, which has the motion control software pre-installed on a Linux operating system. The operating system can be run directly from CDROM or DVD without having to be installed on the PC. If the user decides that they would like to continue using Linux, they can choose to install the operating system and motion control software directly from the LiveCD. As these machines are directly exported from China or imported via an agent, technical support tends to be quite limited. The units require some software configuration in order to move the axes in the correct direction at the correct rate. The machine itself is incapable of knowing where it is positioned relative to the cutting bed, or how many turns of the axis motors are required to move it an exact distance without some form of calibration data maintained by the host software. Fortunately there are several online resources to help users configure their CNC routers in order to achieve precise operation. Once configured to run from the motion control software, the user can load files into the application to direct the cutting head to manoeuvre around the work piece at pre-determined directions, speeds and depths in order to create the final object. The language used in these files is known as G-Code and consists of text entries directing the axis motors to move in a specific direction at a certain rate. Other specialised commands in G-Code are used to command the spindle motor to turn on and off, make the program pause at key steps in the routine, or cause the axes to move in predefined ways such as cutting an arc or drilling a hole. While it is possible to create a G-Code file from scratch by typing commands one at a time in a text editor, it is far easier and quicker to use a Computer Aided Drafting or Computer Aided Machining (CAD/CAM) application to draw the intended cutting paths and convert the subsequent drawing to its component G-Code commands. The user has the ability to quickly mock up an outline of, say a pickup routing template, export the resultant drawing as a G-Code file, open the file in the motion control package and cut out the routing template from a sheet of MDF with sub-millimetre accuracy in a few minutes. While some CAD and CAM applications are integrated into one common application, there are also many offered as separate software solutions. Some packages are open-source and free while others cost anywhere from a few tens of dollars to well in excess of $1000, all with varying levels of ease of use, feature sets and functional integration. Below are a few examples of what operations are possible using the small desktop CNC machine when applied to guitar building. This headstock logo was first engraved while being held in a simple jig to allow the workpiece to be accurately positioned without moving. The work was done in two passes, with the larger of the two pieces of text milled using a 0.8mm diameter endmill, and switching to a 0.7mm endmill for the smaller text. The resultant cavities were filled with black-tinted epoxy and sanded flush: Cavity covers can be directly cut on the CNC router from thin timber stock, including drilling the screw holes in one pass. To create a matching routing template for recessing the cover into a body it is a trivial matter to take the original cavity outline and scale it in CAD. The resultant file will create a perfectly fitting routing template for that cover. As I was unsure if the machine would struggle to mill such a thick piece of perspex, I milled a 'master' template from 6mm MDF and then used a handheld router fitted with a pattern-following bit to transfer the MDF template to the perspex sheet: If your router has a bushing guide or pattern-following plate attachment you can use it in combination with a small diameter bit to cut cavities with tighter radius corners than woud be possible using a typical 1/2" template bit with integrated bearing. The problem with using a bushing guide is that the template used must be created oversize by the radius of the bushing minus the radius of the cutter. Creating such a template in CAD and then milling it on the CNC router is simple. In the following example I have created a routing template to suit the bushing guide for my router. The cutter used was a 1/4" straight bit and the bushing guide is 16mm in diameter, so the template has been created with a consistent (8mm - 3.175mm) 4.825mm offset to achieve the intended cutting profile for a humbucking pickup cavity: Accurately positioning the independent saddles used on multi-scale instruments can be tricky, as the risk of misalignment is increased compared to a one-piece bridge. Determining the angle of the saddles for the differing scale lengths can be problematic, and if you are constructing instruments where the scale lengths used differ from build to build, making a drilling jig by hand is time consuming. This drilling template was milled and engraved into 1/8" perspex in about 15 minutes and includes the mounting holes for the saddles, the through-body holes at the rear of each saddle, a centreline to assist in positioning the template on the body and the intonation reference mark for the scale lengths used: The CNC machine can also be used to create simple tools for use in building and setting up instruments. The time taken to create this four-sided radius gauge was about half an hour, from mocking up the basic shape in CAD to removing the perspex sheet from the machine's cutting bed. If the tool was to get lost or damaged, creating a replacement should only take a few minutes: Pros: A ready-to-go solution out of the box with minimal assembly required Competitively priced with good accuracy and construction quality Excellent finish achievable on the object being machined Capable of machining a wide range of raw materials (MDF, plywood, timber, plastic, soft aluminium) Good support from open-sourced software solutions Small footprint for installations where space is at a premium Cons: Generally not suitable for direct cutting/shaping of the major components used in guitar construction (eg, cutting body outlines, neck profiles, cavity routing) or machining harder materials (eg, making custom metal components for bridges) Minimal after-sales technical support The control interfaces supplied with the smaller and cheaper units usually require a desktop PC fitted with an archaic parallel port. The software used can be challenging to get to grips with if you’re not familiar with Computer Aided Drafting principles and terminology. Hidden costs associated with using a CNC – purchasing good quality cutters and CAD/CAM software for example ---------- In future articles I will explore calibrating the desktop CNC router and covering some of the basic operations of the associated CAD, CAM and motion control software packages.

It is difficult to construct an electric guitar without reaching for the router. Control and pickup cavities, neck pockets and tremolo recesses are all operations that require the use of this versatile tool, and all of these examples are made much easier and safer by the use of a template and an inverted pattern bit to guide the router around the intended cut. One routing pattern that can be difficult to execute accurately is for a Floyd Rose Original tremolo, particularly the recessed version whereby the arm can be raised or lowered above and below its equilibrium point. The following article describes a system that lends itself well to performing this difficult routing operation by the use of a master indexing plate on to which a number of different templates can be attached to create the complex routing pattern. The system can be adapted for other patterns as well such as pickup cavities or other tremolo systems. The System Referring to the PDF plans attached to the bottom of this post, the Floyd Rose routing templates are based around a master indexing plate (Sheet 1). The centre of the plate has a 120mm x 100mm window which can accept a matching template insert. Near the perimeter of the plate are mounting holes for installing further templates which may be overlaid on top of the indexer to provide extra tool height for shallow cutting operations which would otherwise cause the router bearing to ride higher than the template. The templates used in this example have been created from clear Perspex, but MDF can also be used. Perspex however has the advantage that it is possible to see through the template to help position it against reference guidelines drawn on the body to ensure perfect alignment. Sheet 2 shows the insert that is installed within the window of the indexer and contains the guides for drilling the tremolo post holes and the penetration for the trem sustain block. Sheet 3 details the overlay template that is attached on top of the indexer for routing the cavity for the bridge plate of the Floyd Rose. With the end stop shown on Sheet 4 fitted to the overlay template, the extra depth required for the fine tuners at the rear of the bridge can also be routed. Sheet 5 describes the template for routing the rear of the body for installing the springs. Constructing the templates Begin with the indexer. After cutting the perimeter of the plate mark the centreline and intonation reference lines as shown on the diagram as squarely as possible. If using Perspex scribe these lines on the underside of the template. Having these lines under the template assists with lining up the location of the template on the guitar body. The window cut-out in the index plate can be created using a coping saw to rough out the cut, followed by a router guided by temporary fences to ensure straight, square edges. Note that the indexer can be as large as you like, so long as it remains easy to attach to your guitar. Cut and shape the outline of the insert plate and check the fit in the indexer window. The insert plate needs to be a snug fit with no slop while remaining easily removable. With the insert fitted to the indexer mark the cut-outs and drill locations detailed on sheet 2. Performing the marking of the insert while fitted to the indexer ensures the locations of the cut-outs remain square and true relative to the centreline scribed on the indexer. Remove the insert and complete the cut-outs as carefully as possible. Move on to the overlay template. Again, use the centreline on the indexer as a reference to aid in aligning the two when marking the locations of the cut-outs in the overlay template. With the templates constructed as shown in the plans the front edge of the overlay needs to be on the same alignment as the front edge of the indexer. If you chose to make the indexer wider ensure that you maintain the same horizontal positioning of the overlay template so that the resultant rout is at the correct location. The four 4mm holes should be drilled while the two pates are clamped together so that they remain in perfect alignment. These holes are used to lock the two plates together while routing. Removable pins or screws should be installed to align together them when routing provided that they do not protrude, and either damage the surface of the guitar body or hinder the movement of the router. The removable end stop can be constructed using two strips of material laminated together to make the required step profile. Two screw holes should be bored through the overlay template into the end stop to allow the two components to be secured together when performing the routing operation. The final template, the spring cavity rout can be created separately to the indexer. Mark or scribe the dashed line shown on the drawing as perpendicular as possible to the centreline. Tools required for using the templates Plunge router with adjustable depth stop Drill press with adjustable depth stop 1/2" diameter inverted pattern router bit with bearing, length 19mm 1/2" diameter inverted pattern router bit with bearing, length 32mm 3/8" diameter inverted pattern router bit with bearing, length 19mm 10mm brad point drill bit Optional - Forstner bits for removing excess timber prior to routing Clamps Using the templates 1. At this stage you should have a guitar body ready to be routed to accept the Floyd Rose bridge. A centreline should be marked on the body along with an intonation reference line drawn at right angles across the full width of the body at your chosen scale length. In the following example a scrap piece of pine has been used to rout the bridge cavity. No intonation line has been marked, but your actual build will require this to ensure the Floyd Rose is installed at the correct distance from the nut. 2. Align the index plate with the centreline and intonation reference line drawn on the body and clamp it securely. Test-manoeuvre your router around the indexer to ensure your clamps do not interfere at the extremities of the window in the plate and adjust if required. Alternatively you can use double-sided stick tape provided it is of good quality and doesn't allow too much lateral movement of the templates once adhered. Fit the insert plate into the window and using the two 10mm template holes as a guide bore the trem post holes using a 10mm brad point bit to a depth of 10mm or so. The exact depth at this stage isn't critical. Were just establishing the location of the post holes to start with. 3. A Forstner bit can be used to remove some of the waste within the 24mm x 76mm cut-out of the insert template to a depth of approx. 25mm to minimise wear on the router bit. Using the 1/2 diameter, 32mm long inverted pattern bit rout this template to a depth of 29mm. 4. The insert plate can now be removed from the indexer and the overlay plate installed over the top. Again, use the Forstner bit to remove some of the waste to a depth of 5mm. Use the 3/8 diameter, 19mm long inverted pattern bit and rout the whole area to a depth of 6mm. 5. Creating the rear well that allows the bridge to be pulled backwards when raising the trem arm requires routing a secondary depth at the back of the cavity of an additional 6mm. This is achieved by fitting the small stop bar to the overlay template that reduces the router lateral travel by 16mm. Run the router within the template to a depth of 12mm below the face of the guitar body. 6. The indexer and templates can now be removed from the body. Using a drill press bore all the way through the body down through the bottom of the sustain block rout. The exact location and size of this hole isn't critical, just as long as it is as close to the front edge of the rout as possible. Where the drill exits the body at the rear, mark a line perpendicular to the centre of the body that touches the tangent of this drill hole. This line should now align with the front edge of the sustain block rout and is used for locating the final template for routing the spring cavity. 7. Fit and clamp the fourth template, aligning it with the centre and sustain bock reference lines on the back of the body. Assuming your body is a typical Strat thickness (45mm or so), rout this template to a depth of 16mm using the 1/2 diameter 19mm long inverted pattern bit. If your body is a different thickness this will change how deep this rout must be. The rout needs to be deep enough to allow clearance for the springs and sustain block, but not so deep that you risk punching through the underside of the pickup routs. Ideally this depth should be [thickness of body] - 29mm. 8. An additional depth to the rear edge of the spring cavity is required to allow clearance for the sustain block to swing backwards when the trem arm is depressed. This depth is again dependent on the thickness of your body but should be [thickness of body] - 15mm. For a typical Strat this will result in a cutting depth of 30mm. The resultant rout will leave a small 3mm ledge of timber that is visible when viewing back through the sustain block cavity. Use the 1/2 diameter, 32mm long inverted pattern bit to complete this cut. Take care not to run the bit into the forward edge of the sustain block rout. A temporary fence may be clamped to the work piece to prevent the router being accidentally moved into the front wall of the sustain block rout. 9. The last step is to bore the final depth of the trem bushing holes. Remove the last template and flip the body over. Measure the length of your trem bushings and set your drill press depth stop to this value. Using a 10mm brad point bit on the drill press bore down the two 10mm holes that were established in step 2. Once the holes have been drilled the bushings can be pressed into the guitar. They should go in with firm hand pressure. An alternate method is to use a drill press with a short piece of dowel in the chuck to press the bushings in. Be careful when applying pressure however, as the small amount of supporting wood behind the bushing holes is fragile and can be easily split if the bushings require excessive force to be pressed in. 10. Test fit the bridge and check to see if there is sufficient clearance to allow the bridge to swing up and down without binding on any of the routs. Adapting the system Because the routing templates can be removed from the master indexer the user has the ability to create other template inserts and overlays for different routing tasks. Any shape that can fit within the dimensions of the 120mm x 100mm window has the potential to be made into a template for repetitive or complex routing operations. Pickup cavities, battery box cavities, Kahler and Wilkinson tremolos are some examples. ------ DOWNLOADABLE TEMPLATE SHEET FILES FR Routing Templates.pdf