Last week we introduced the idea of adding guide bushings to your router's accessories. To help us understand how we use them in practice, we'll start by taking a second look at routing a simple soapbar cavity and we adjust template sizing for guide bushing use.
In spite of being pretty much the most simple type of rout, rectangular soapbar pickups require attention to the internal corner radii which makes them perfect for routing with a guide bushing. But why?
The EMG rout we used to demonstrate the simple technique needed corners smaller than most bearing-guided router bits can manage, so we drilled them by hand before routing the rest of the cavity. Not the most graceful method, but definitely a simple and easy trick that anybody can manage with on-hand tools. Introducing guide bushings into the mix makes this into a single-step process, with the added bonuses of reliability, perfect results and almost zero effort requirement.
EMG soapbar corner radius - 1/8" or 3,175mm
We titled this tutorial "intermediate" purely because it should satisfy the demands of all but the most exacting of builders. Since everything in this series serves as building blocks to increase your knowledge and ability, we'll take this one to the logical extreme later in a separate article to illustrate just how far we can take everything with our routing wizardry.
Overview and Objectives
Most of this tutorial will be similar to the working practices introduced in Router Basics: Simple Soapbar Pickup Routing however Router Basics: Humbucker Pickup Routing (with Pickup Ring) and Router Basics: Guide Bushings contain useful information and ideas applicable to this tutorial also; if you haven't had chance to absorb these yet, they'll definitely get you up to speed.
The linchpin of successful routing with guide bushings is the same as any complex job; good working templates. We'll describe the process of developing templates using the familiar EMG bass soapbar "standard". To open out the idea a little, we'll show how to make the template adjustable so that it can rout all three of the EMG soapbar sizes (35, 40, 45) similar to the template introduced in the simple humbucker routing earlier in the series. The same concepts and calculations can be scaled to cover rectangular routing templates of any dimension or end use, whether it be recessing a bridge or a rear tremolo cover plate.
The underlying objective of this tutorial is to enable you to take onboard the basic concepts of template-making for guide bushing router jobs. We'll tackle more complex guide bushing routing tasks as we go through the series, building on these core ideas and how we can counter exceptions and weird difficult jobs.
How Soapbar Guide Bushing Templates Work
Instead of a bearing running against the internal sides of the template, the bushing does the guiding work. Since a guide bushing's diameter is larger than that of the cutter passing through it, the templates internal dimensions need to be compensated by being offset in a size to match the difference between the bushing and the cutter. Beyond this distinction, the templates are built and function in exactly the same way as those for bearing-guided flush-cut template bits (surely there's a shorter name for those....).
Routing with a guide bushing
Since this is only an intermediate tutorial, we'll be relying on simple square-cornered templates illustrated above. More experienced template-makers will use rounded corners that are specifically radiused to guide a small cutter around internal corners instead of into them. The difference is subtle, so we'll deal with the basics before taking on more esoteric ideas.
What We Need
Making the templates only requires that we have clean dimensioned template stock such as MDF, plywood, Masonite, etc. Generally this only needs to be slightly thicker than how far the guide bushing sticks out from your router. Slightly thicker stock helps us glue and screw our completed templates so 1/2" or more is easier to work with. You can always make your template using whichever stock is most convenient at the time and then copy it down permanently to more appropriate material later.
- Hand router (plunge base preferred)
- Small straight template cutter with radius appropriate for the pickup (see Calculating The Offset)
- Sheet stock suitable for templating (plywood, MDF, etc) cut into strips or sized with two 90° edges (see Building The Template)
- Wood glue
- Shim stock (optional)
- Sheet stock for thin permanent templates (optional)
- Countersink (optional)
Calculating The Offset
The offset value is derived from the diameter of the cutter and guide bushings in use. Firstly, we need to select the diameter of router cutter we want to be using and then a guide bushing most appropriate for use with that size cutter. After we've done this, we can calculate the basic offset and make adjustments.
Choosing the router cutter is based on the corner radius of the pickup housing. EMG soapbars have a corner radius of 1/8", requiring a minimum of a 1/4" (6,35mm) diameter cutter (double the corner radius). As discussed in the previous article on soapbars, we add an "easing" gap around the perimeter of the pickup to increase the cavity size slightly to allow for the finish thickness, etc. This also requires an increase in the size of the corner radius so that the outline of the cavity follows the shape of the pickup corners.
Layout of an EMG-35 size soapbar showing corner radii/diameters and the result of 1mm of perimeter easing
The diagram above demonstrates simply how 1mm of perimeter easing increases the choice of cutter size from 1/4" to just over 8mm or 5/16". It isn't always possible to find the exact radius cutter to match this value, however the nearest size is fine in most circumstances so 8mm is golden. 3/8" or 10mm would definitely be too large.
Easing around a soapbar cavity (reminds me of Joe's Garage)
Generally-speaking, we should aim to select a guide bushing which is the closest size to our cutter. This produces a smaller and more manageable offset. Even though this isn't a hard and fast rule, the smaller the bushing used the more stability the router has on the template. That's always a good thing however you look at it!
For the example above, an 8mm cutter (just under 5/16ths) will need a guide bushing with an internal diameter at least that size. My own set has a 7/16ths (11,11mm) bushing with an internal diameter of 11/32nds (8,73mm). That's a little tight for my tastes, since chip waste could get trapped between the cutter and the inside face of the bushing. The next size up is the 1/2" (12,7mm) bushing with an internal diameter of 13/32nds (10,32mm) which is pretty much a perfect match.
Doing The Math
The photo below shows a cutter fitted into a router with a guide bushing attached. The offset value is the closest distance that the guide bushing will allow the router cutter to get to the template edges. This is calculated by subtracting the diameter of the router cutter from the outer diameter of the guide bushing, and then dividing the result by two.
Visual explanation of figuring out your offset value
For our 8mm cutter in a 1/2" (12,7mm) bushing, this gives us an offset of:
(12,7 - 8) / 2
4,7 / 2
Taking into account that we also want 1mm of easing around the perimeter, we add that to the basic offset to give us our final offset value, 3,35mm. Now we've got this figured out, we can move onto measuring out our template.....
Building The Template
Our templates will be made from any sort of sheet stock or thin dimensioned wood. Unlike templates made for bearing-guided bits which benefit from being thicker, guide bushing templates only need to be as thick as the amount that the bushing protrudes below the router base. For assembly however, thicker material allows us to produce adjustable templates plus we can glue and screw the components. The option to copy these templates down to thin stock after making them in thicker stock works too.
Two easy options are available for making the basic template. We can either use the fenced approach as we did for simple soapbar routing or we can make it stacked similar to that for simple humbucker routs. Mostly this choice depends on your ability to accurately dimension your template sheet stock. If you're able to cut wood to exact widths on a table saw, through a thickness planer, drum sander, etc. then the stacked template is the way to go for you. A fenced template is easier and can be made with minimal tools and materials as long as we have four pieces with two clean 90° edges.
Comparison of a stacked plywood template (left) and fenced MDF template (right)
Making A Fenced Template
Fenced templates need four pieces of stock with two flat perpendicular sides each. As the name implies, these fit together to form a fence around the object we're templating.
A simple fenced template
Rather than simply copying the outline of the pickup as per the example above, we need to expand that outline to take into account the offset that we calculated earlier. The easiest way for us to do this is by shimming the pickup outline using veneer, plastic card or other thin pieces of material of known thickness. This works like so:
Shimming the pickup using four pieces of 3,35mm thicknessed wood
It might seem obvious that we don't need to shim all four sides 3,35mm....but this works for illustration; in reality it's far easier to shim two sides using a double-thickness of shims (6,7mm). Either method is valid, it simply comes down to materials you have on hand. A surprising number of common household objects could be used....a credit card is 0,76mm (0,03") thick, so cut them up! Full-size SD cards are exactly 2,1mm (0,083") thick. Since we're only using them temporarily as shims, we can get away with all kinds of materials.
Shimming doesn't need to be an exact science here. Even though we're aiming for a specific value (in this case 3,35mm/6,7mm) we can always go a little either side of this as long as we understand what that will do to the template. For instance, if we used three SD cards either side (2,1mm x 3 = 6,3mm or 0,25") we're undershooting by (6,7 - 6,3) / 2 = 0,2mm (~0,008") each side. This isn't a lot and it shouldn't affect the end result visibly. Equally, using a stack of nine pieces of a credit card overshoots by less than a tenth of a mm. Far smaller than most people's working tolerances. Just confirm that the internal dimensions of the fenced template end up where they are expected to be once you've assembled everything in place.
For an EMG-35 (3,5" x 1,5" / 88,9mm x 38,1mm) with an eased offset of 3,35mm we need an internal area of:
(88,9 + 3,35 + 3,35) x (38,1 + 3,35 + 3,35)
95,6mm x 44,8mm (3,76" x 1,76")
We now have the choice of glueing/screwing together this fenced template, or sticking it down for copying to permanent templating stock. Just remember to confirm that the internal dimensions of your fenced template correspond to calculated values.
If you have the resources, custom thickness shim stock can be thicknessed with a drum sander, a thickness planing jig or even a Myka neck pocketing jig set to 0°. In a pinch you could even use the internal measuring jaws of your calipers to set everything in place!
Making A Stacked Template
If you are able to produce template stock to exacting widths, we can work primarily from the numbers and directly cut our template parts accordingly. For soapbar templates, this only requires us to make strips of template stock corresponding to the width of the template negative space, and that these can be crosscut with accuracy. The same calculations used to check the internal dimensions of the fenced template apply here also.
In the instance of an EMG-35 sized housing with 1mm of easing, we can produce a stacked template using strips of wood cut to 44,8mm thickness. For my own part, I cut strips at 50mm on the table, jointer planed one edge and thickness planed them down gradually until the exact size of 44,8mm read off my calipers.
These strips were then crosscut on a table saw to produce two long outer pieces and two shorter inner pieces. The only parts that needed to be a very specific width are the "surrogate" parts used to space out the template. These can either be cut on a table saw (if you can do this accurately) or by hand with your fret slotting mitre box. The general layout of the template is as follows:
The internal space is defined by using precision-cut surrogate parts. I produced one for each size of EMG soapbar, taking into account the eased dimensions. It's worthwhile marking out the original dimensions in addition to the modified ones along with the offset built in.
The template parts are assembled and glued into two identical halves, exactly in the same way as the adjustable humbucker template. For details on how to create the location holes, check that for a full pictorial.
Locating dowels allow the template to be assembled to work for all three EMG soapbar sizes:
Copying The Template To Thinner Stock
Optionally, we can use these thick master templates to create "working templates" in thinner stock. Whilst thick plywood such as this is excellent for constructing templates, it can reduce the maximum working plunge depth of our router. Check the clearance required for your bushing and select stock appropriate to that thickness before making a copy with a bearing-guide template cutter. Since bearing-guided cutters will leave their radius in the corners of the copy, use a bit smaller in diameter than the smallest guide bushing you might use so these don't interfere with the template in use.
Remember to back your workpiece up with scrap before routing all the way through!
Using A Guide Bushing Template
Use is very simple from this point onwards, and much like any other template routing operation. The bushing enables the routing to be carried out with small passes to ensure clean tearout-free work. Dust extraction may be difficult with a guide bushing in place, so take time to clean the rout out directly with your extractor hose. Mounting the template to the workpiece is best done with four pieces of double-stick tape in all four corners to prevent movement.
Router and template set up, ready to go.
Two shallow passes did the trick
Improving The Templates
The relative simplicity of guide bushing templates doesn't leave much room for improvement! The same basic addition as per the templates described in previous articles apply here also; drilling through from the underside and countersinking from the top to create centre and cross locating holes. We'd be interested to hear your comments and ideas on other improvements however, so pop down to the comments section and share your thoughts....
Simple guide bushing templates such as these are easy and quick to make, so much so that you can quickly find all kinds of places to use them in your work. We hope that this tutorial has inspired new ideas and we'd like to see how you use your new superpowers! Happy routing.....
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Router Basics: Intermediate Soapbar Pickup Routing by Carl Maltby is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
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