From PDF to MDF: Making a guitar body routing template part 2

A couple of days ago, where I described the first stages of turning a PDF plan into an MDF template, we got as far as having a printed plan. Now let us turn that printed plan into a template we can use for routing the body shape.

The last step in the last episode was to double check all the measurements – well in my experience double checking is never enough. Stop what you’re doing and go and check it again.

First we need a piece of MDF. The recommended approach to doing this is to first make yourself a master template, and then use this to create a working copy of the template. For the master you’d use 9mm (because it is easier to work with and to sand to shape) and for the working copy 18mm (so you’ve got enough depth for the router bit to run against). Because this build is a one-off I’m just going to go straight to 18mm MDF.

Many people recommend gluing the paper template to the MDF, but I have previously had problems with the glue causing the plan to expand slightly as it dampened. I suspect you could overcome this problem using spray mount adhesive but I now choose a different approach. I tape the plan down to the MDF at four or five points and then hatch lines across the edge all the way round. Once the paper plan is removed it is a piece of cake to join the ends of the lines.

Then it is a matter of using a bandsaw or jigsaw to cut close to the line…

…and finish of by sanding to shape – continually checking against the paper plan.

A word of warning here. Spend time making sure the edges of the template are smooth and exactly as you want them to be. Don’t just look at the edges – close your eyes and feel them too. The first time I made a template I left a couple of bumps, knowing that I could tidy them up when I was sanding the final body. I quickly learned that a sanding job that would have taken a matter of minutes on thin MDF became a herculean task when I was doing it to 1.75″ of hardwood. Get the template right and you don’t have to do it later!

Now you’ve already checked the measurements three time but you know what… Do it again before you put the template anywhere near that chunk of expensive timber.

From PDF to MDF: Making a guitar body routing template Part 1

One of the questions that I have been asked a couple of times is “Where can I find a guitar body plan and how do I make that into a router template”? This series of posts will outline how I do it. It definitely isn’t the only way. It may not be the best way. But it is the cheapest and consequently they way I do it.

The first challenge is finding a good accurate plan. My first port of call for Fender style designs would be TDPRI. There are also several excellent plans available over at www.gitarrebassbau.de.

Most plans are available in PDF format, and that is what I’ll be talking about primarily, but occasionally you’ll find a plan in DXF format (AutoCAD’s interchange format). In these cases you can use the free online version of AutoCAD (requires registration) to convert to PDF.

Download and install Inkscape, a free vector drawing program. Head over to http://inkscape.org/ and download the version relevant to whichever operating system you prefer. Once you’ve got it installed fire it up and we can get started.

The first decision to make is what orientation of paper would best fit the plan. For most guitar body shapes (Strat, Tele, Jazzmaster, Les Paul, etc) I’ve found that four landscape sheets (2×2) is about the most efficient, but for a larger body shape you may find you need six portrait (3×2).

In Inkscape, to change the document orientation, you choose File -> Document Properties (or Shift-Ctrl-D).

Next we’re going to import the PDF plan into Inkscape. Choose File -> Import (or Ctrl-I) and select the PDF file. Accept the default suggestions in the next step.

Now we could just print off the plan just as it is, but to help align the sheets as they’re stuck together I like to overlay the plan with a pattern of diagonal lines.

To draw the lines;

  • Select the Bezier/Straight Line tool (Shift-F6)
  • Click once then hold down the Ctrl and drag the mouse out diagonally. Click a second time and then press enter.
  • Duplicate the line by pressing Ctrl-D and then flip it horizontally by pressing “H”. This gives us two diagonal lines at right angles to each other.
  • We now want to duplicate these lines many times over. First we need to group the two lines into a single object so select them both and press Ctrl-G.
  • With that still selected, choose Edit -> Clone -> Create Tiled Clones.
  • We want 100 rows and 1 column (to repeat the pattern 100 times).

  • On the “Shift” tab we define how much each subsequent copy should be moved. For “Shift X” choose 5% per row and 0% per column. For “Shift Y” use -100% for both row and column.

  • Click the “Create” button and you’ll find yourself with a pattern of intersecting diagonal lines.

  • Drag to select all of the lines and group them into a single object (Ctrl-G).
  • Now drag the grid pattern over the top of the plan. If it is not big enough, you can grab any of the corners to resize.
  • Select both the plan and the overlaid grid pattern and group these together (Ctrl-G).
  • You can now grab the whole thing and move it over the page image, and print overlapping areas of the plan.

You may find that the lines on the plan are much more faint than on the grid. You can correct this by selecting all of the items (Ctrl-A), pull up the dialog that allows you to change fill/line properties (Ctrl-Shift-F), on the “Stroke Paint” tab, make sure the stroke colour is set to black. On the “Stroke Style” tab set the stroke thickness to 1px.

Then it is just a simple matter of trimming the edges (assuming your printer doesn’t print right to the edge) and taping them together. And in best Blue Peter fashion, here’s one I prepared earlier.

And now comes the most important step of all – take a good ruler and CHECK IT IS THE RIGHT SIZE. Please don’t ask me how I know.

The next instalment will cover the making of a template from the paper plan.

Additional resources

BigPrint is an excellent application that can do all of the above for you, working from a picture or photograph. It is not free but is well worth the money.

The Minibass: Decisions, decisions.

Before I get any further into this build I need to firm up some design decisions. At the moment I’m just preparing the body and neck blanks which, to a certain extent, I can do without much regard to the config of the final instrument (other than know it is not a thru neck).

This post is really nothing more than me jotting down my thoughts about all of those decisions; the ones I’ve made and those I’ve yet to make. It is this latter category I really need to focus on, to make sure I don’t miss anything that would impact an early stage of the build. Some of the other decisions can be postponed, and be made immediately prior to the build step they impact. Normally I wouldn’t do this – I like to have a very clear idea of absolutely every minor detail before I make any sawdust. As something of a prototype this one is different though – and I will want to review and revise those design decisions based on current progress.

OK so let us start at the head of this mystical “Minibass” and work our way down to the tail.

Headstock

Should the headstock be flat and parallel to the fretboard (like a Fender) or angled back like a Gibson? On this one I’m going to go angled – only because I’ve never made a scarf jointed headstock and I’d like to add the skill to my “portfolio”. Because this bass uses these polypropelene strings the neck is not under as a great a tension as usual, so it should be a safe playground for me.

Type and layout of tuners? I really like the plain simplicity of the Fender style big-eared open tuners. Added advantage is that they’re not overly heavy and relatively cheap. For the layout I want the headstock to be as compact as possible, in keeping with the overall concept of a Minibass. I’m going to go in a staggered 2+2 configuration, aiming to keep the string run as straight as possible over the nut to the tuner post.

Nut

Because I’ve chosen a Gibson-esque headstock it makes sense to use a Gibson style nut too. The nut rests on the neck itself and butts up to the end of the fretboard, rather than the Fender approach of having a thinner nut that sits in a slot on the fretboard. The nut is going to be made from bone. If you’re interested in how I’ll be preparing the bone see this post.

Neck

This is the aspect that, at this stage needs the most careful planning. I need to decide scale length, whether it’ll be fretted or fretless, whether it flat mounts to the body or is angled back to clear a higher bridge, fretboard radius, width at the nut, taper, shape of the neck profile, type of truss rod, what fret markers I want. Phew! Lots to think about.

First off, because this instrument relies on a piezo pickup mounted in the bridge, I want a good downward tenson on the bridge saddle. This means a steeper break angle between the bridge and the string anchors, which in turn leads towards a higher bridge. Therefore it’ll be an angled back join with the body. As on many of my previous builds It’ll get a glued neck join, with a decent sized tenon into the body.

next is the decision about the truss rod. It probably doesn;t need one because of the low string tension but, because I may want to add relief to the neck (a slight bow forward) I’ve decided to install a double action truss rod. When I was building my Voodoo Tele I found this aspect one of the most difficult and I’d like the opportunity to practice and see if I can get it better this time.

In deciding the scale length I have a number of limitations. First this style of bass usually has an 18-19″ scale, although they can go up to around 23-24″. Secondly, the fretboard supplied by Steve Benford is pre-slotted for a 25.5″ scale length. That is too long for my needs so, if I chop it at the 1st fret slot, making that the zero fret, it would give me a scale of ~24″, at the 2nd fret, ~22.5″, at the 3rd fret, ~21.5″ and at the 4th, ~20.25″. I’ve dithered between 22.5″ and 21.5″ for a while but, making a decision right this moment, I’m going to stay true to the principle of, making it smaller at every opportunity (whilst still being playable) and go for the 21.5″ scale length.

I’ve also struggled with the decision about whether it should have frets or not. I would love a fretless, and I think this more acoustic sounding bass will really suit it. On the other hand, the shorter the scale gets the harder it is to play a fretless accurately. I’m also crap at playing a fretless, it would take a lot of practice to start maaking sounds that I like hearing and I’m worried that I’ll move onto the next project and this one will just gather dust in the rack. And that makes the decision for me. I’m going to save my first fretless project to be a 34″ scale. Sorted.

I want this neck to be of a medium width, but perhaps a touch flatter, both front and back, than usual. It’ll get a fretboard radius of between 12″ and 16″, probably erring towards 12″. I’m going to have a go at making either my own radiusing jig or, more likely, a radiused sanding block.

Last choice should be the easiest to make but is another one I struggle with. What sort of fretmarkers should it have? I’m not quite sure why but, stylistically, fret markers have taken on a huge significance for me, and I want to do something really cool. I really like the thumbnail fretmarkers on Gretsches so I’m going to haave a go at doing something similar in appearance. It will be a very different technique though. At the point where the neck outline is marked on to the fretboard and neck (before the fretboard is glued on), I’m going to drill 8mm holes centred on that line. This will get a darkwood dowel or plug glued in place. Then, when I trim along the line, it’ll just leave a semi-circle slice of that dowel in the fretboard, looking like a thumbnail from the front and a rectangular block inlay from the side. For the 12th fret I’m going to drill a 3-4mm hole into the dark wood dowel and glue in a light-wood dowel. When cut in halt this will make a double mark when viewed from the side

Body

Whereas the body shape is usually the first thing on the drawing board, this is completely different. I’m going to set myself some hard constraints (position of bridge, size of the blank, type of string anchors, position of neck pocket, position of control cavity, etc. I’m going to leave the design of the silhouette until much later.

Because the blank is of a sandwich construction and the neck tenon will be visible on the top, I have to decide whether to feature this or whether to add a thin cap of a single timber, such as a figured maple. This is another decision I’m going to postpone until I can see how it looks. If I like it I’ll feature it, if not I’ll cover it.

Bridge

As I mentioned earlier this will be a relatively high bridge, to make sure I’ve got a good break angle. Because it is an acoustic style bridge, and because I yet know exactly how these strings will react with regards intonation, I’m initially planning for this to be a floating bridge. once I am happy with the intonation, I’ll glue it down, and can finalise drilling the holes to properly install the electronics.

I haven’t yet decided what materials to use to make the floating bridge. In keeping with the rest of the guitar I’ll aim to use something out of my offcuts bin. I’ve got a few decent sized pieces of maple that will be used for the first attempt. Essentially all I need is a block of wood with a slot cut into it to hold the piezo element with a bone saddle riding on top of it. Turning that block of wood into something that fits with the guitar’s aesthetic will be the challenge.

Because I’m initially going with a floating bridge I need a separate method of anchoring the strings. For this I’m going to use a string through approach, but instead of coming through from the back they’ll come through from the tail end. Hard to describe, but you’ll see what I mean when I do it.

Electrics

I’ve ordered a piezo element and small on-board preamp. I’m waiting for these to arrive because it is difficult to accurately plan out installation until they’re on-site.

Finish

Regular reader of this blog will not be surprised that I’m going to choose Danish oil again. That was the easiest of the decisions.

Top carve completed and more besides

Up bright and early this morning and headed straight down to B&Q to grab a random orbital sander. I’m not half glad that I did. Even with this fantastic piece of kit, finishing off the top took a hard 3 hours. I was so pleased that my routing mistakes (or “opportunities” as Steve Benford described them) were recoverable and I was able to sand them away without breaking through to the mahogany underneath. It was very close though and, at the edge, the maple cap is only 3mm thick.

Next job was to fabricate the rig to allow me to chamfer the front edge of the body to align with the neck angle. This rig is made up of a box to surround the guitar and an MDF plate to sit on top with a slot for the router cutter. The box is shimmed up at one end to make the 3 degree angle.

And here’s the finished chamfer. A quick pass with the sander took out the lines.

Then I clamped a straight edge to the chamfered body face and checked it against the bridge. Note the shims the same thickness as the fretboard to raise the line away from the body. Looks just about perfect to me.

I then spent an hour making a jig for the neck pocket. It was vital to get this absolutely spot on, to match the size of the neck heel and to make sure it is perfectly aligned with the centre line. I’d tried doing this by eye until I noticed, while I was taking the picture with my phone, that it has guidelines on which I was able to use to double check the alignment

I made the first cut…

And here’s the finished neck pocket.

The neck fit into the pocket absolutely perfectly.

A very snug fit, with just enough grip to allow me to grab the neck and hold the guitar horizontally.

I then made a jig for the P90 soapbar pickup, and, still using my angled jig, to keep the pickup perpendicular to the strings, routed the cavity. It is a very shallow cavity, and I still need to rout a slightly deeper channel to clear the cable and the two round-head screws in the baseplate of the pickup.

The top carve continues

Despite only getting a couple of hours on “Project RockMangle” I made decent progress today. I finished the routing of the final two steps of the top carve and then got busy with the sandpaper. This is going to be a looooong part of the job, although I may cheat and head down to B&Q tomorrow morning and buy myself a random orbital sander.

This first picture shows the state of play after the completion of the step routing and a couple of minutes of sanding.

This view gives a good idea of the shape and depth of the carve.

And this final one shows how far I managed to get before it got too dark to work outside. Taking shape nicely, even if I do say so myself.

Calculating the guitar’s neck angle

I awoke to find it raining heavily and, according to the forecast, it is here for rest of the day. No routing for me today. I’ve used the time to review and add more detail into my plans.

Now that I’ve got the wraparound bridge I can work on calculating the neck angle.

I want the bottom edge of the end of the fretboard to sit flat on the top (there is a short overhang past the end of the neck). The height of the bridge, at its very lowest, is 19mm. The fretboard (incl frets) is 7mm thick. The end of the fretboard is 168mm from the bridge saddles. This means that the neck inclination needs to be a drop of 12mm over 168mm distance which. Reaching back into the dusty recesses of my maths degree (who knew that it would ever come in useful, eh?) this equates to very close to 4 degrees.

If you’re interested the calculation is Angle = ArcSin (height/distance) = ArcSin (12/168) = ArcSin (0.07143) = 4.09604 degrees. I used this online calculator.

Here’s a diagram of what I mean;

Of course with that geometry it would mean the strings were far too low, but I reasoned that this is the very lowest that the bridge would ever need to go.

And just to help me visualise the angle, I tried this;

The matchsticks lift the bridge of the body the same distance as the bridge studs. And yes I know it is worthy of “thereifixedit“, but it works for me.

Update: After an email from the ever helpful and insightful Steve Benford, of Benford Guitars, I realised that I’d measured the thickness of the fretboard at the edge and not the centre! This was a small but significant error. The drop should actually be 9mm over the 168mm distance from bridge to fretboard. This is 3 degrees and not the 4 from my original calculation.

Midway through the top carve

Well the last couple of days have been something of an education! Lesson number 1 is that I should have done a lot more practice on pieces of scrap wood. Lesson number 2 is that if there’s something you don’t want a router to do, that’s what is going to happen. It is a sort of woodworking Murphy’s law in action. But looking on the bright side, I’ve still got all of my fingers.

The project is still on track but I’ve got a lot of remedial sanding to do. At this stage my biggest worry is that my first cut (on the lowest step) was too deep. I’d planned to take the maple cap down to 5mm, which I did. On reflection, I wish I’d cut it to 8 or 9mm. Flaws in my router technique mean that I’ve got a lot of sanding to do and there is a real chance that I’m going to break through the maple to the mahogany underneath. If that happens then all that is left to me will be to plane off the maple cap, and do another one. If so, then it is not the end of the world, and I’ll have learned some very valuable lessons. Although I suppose I could cover up with a solid colour.

I am going to do the majority of sanding by hand, rather than my original plan to use power tools. This should give me more control and minimise the chance of sanding through the maple. It’ll be a great opportunity to work on my biceps and triceps too.

Next time I try a carved top I’m going to take a very different approach. This differs from every other approach I’ve seen. I’m going to carve the top before cutting out the body shape from the blank. What I’d do is to mark up the body shape on the blank, draft out the carves and make up the templates in the same way I have done. Then, by adding an “outer template” on to the section of waste body wood, it’ll give me support on both sides of the router and get rid of the need for building extra guides and jigs. Once the top is carved I can then cut out the body shape.