As you may have seen, I’ve been working on adding the tapers to my molds in an effort to improve consistency as well as efficiency in my process. I made a video that you can see here if you haven’t already. The video was mostly for entertainment purposes for those interested in having a look into the process of making a guitar. However, after receiving a few questions from other builders about the process of adding the taper and radius to my molds, I decided to better document the next one in photo form that would allow me to explain each step in text and in better detail.
The first question I have been getting is “why?”.
As we all know, the body depth and taper of a guitar play a role in it’s tonality. In terms of consistency, this is not something we want floating around and changing from build to build as we try and nail down how our guitars are functioning for us. So, in short- it is consistency, but also efficiency. I advertise a specific depth of my bodies for each model and they ought to be it when delivered.
In order to achieve this you can go one of two ways, alternatively. One- you could trim the sides to a given profile prior to bending and hope that you’re able to get them bent squarely enough that you’re not having to mash them into the mold to hold consistent shape and depth, or that the waist is in the exact correct place and also bent perfectly perpendicular to the plane of the top. Or you can bend them large and, once held squarely into the mold, mark the taper and radius on a dish with a pencil and trim it out by hand with saws, chisels and planes. I’ve tried both of these methods over the years and can tell you in no uncertain terms that my current method is by far my new method of choice.
This method I’ve adopted utilizes a small circular saw blade and arbor in a router to trim the sides. The router rides on the surface of the now tapered and radiused mold to create the side profile which will accept the back and top which are formed into a dome during bracing. And it’s quite important if you’re going to do this to trim the mold out to a line created in reference to a radius dish. The taper from tail to heel is not a straight line. It rises in the waist and falls in the bends of the upper and lower bouts.
So we’ve covered the “why?”. Now we’ll look at how.
The first thing you need is a mold the shape of your guitar. If you have that then you’re already off to a running start. But, if it is not thick enough to remove the amount of material that will create your taper, then you’ll need to add a layer as I’m doing here. I traced the shape onto a piece of MDF and rough cut it out on the band saw. Then attached it to the existing mold using dowels and epoxy.
Once the epoxy cures, route the new piece with a flush trim router bit.
Now that the halves are flush trimmed and cleaned up, I clamped them together and placed them on top of my radius dish. My radius dishes have sandpaper adhered to them so I laid a piece of poster board down on it.
For the top, you’ll need to determine what taper, if any, that you need to achieve your desired neck angle. Add in the desired amount of taper and trace a line around the inside of the mold as I will show here in the next step. You could also just leave the top portion of the mold flat since the material taken off for the top radius usually isn’t all that much. For the radius I use, my neck angle works out perfectly with no taper, so I just laid it flat on the mold and traced my line. Then flipped it over and set up the back taper in it’s respective radius dish.
For this model, the back taper is 7/8”. So I placed the mold on my 15’ radius dish and raised the tail end of the mold up by that much.
Placing a pen or pencil on a block of wood that puts the pen point at the proper height, I run the pen around the mold, being sure to keep it square to the point on the mold being marked, and creating a line that marks both the taper and the high and low points within it that create the dome profile.
Now I can unclamp the mold and take it over to the band saw to trim the mold to the marks I just laid out. My molds are thick and flush routed on the outside as well as the inside, and so are very wide and square which allows me to simply stand the mold halves up on edge for trimming. If your molds are thinner you may need to use a square fence to ensure the mold doesn’t tip during trimming. BE VERY CAUTIOUS! This is sort of a dangerous task. There is a lot to pay attention to, so be mindful of where your fingers are at all times in relation to the blade as it can be easy to get caught up in watching the line and guiding the mold. I can not stress this enough.
So, the mold is trimmed but now we need to finishing profiling in the radius. At the neck block, the back taper creates about a 3.5° angle and is around 2-2.5° around the perimeter and slightly less at the tail block- for my taper, body length and shape. So using a hand plane I roughed in the angle around the edges of the mold surface, staying away from the inner edge where I traced and sawed to my line. Just removing the material that would otherwise be removed on the radius dish. The nice thing about MDF is that it is rather soft, so you can really take large cuts with the plane with relative ease to get the job done quickly.
And checking the angle as I go along with a protractor to make sure I’m not taking off too much material. As this will be the surface that my router rides on later, I don’t want any dips or low spots.
Now that the surface is roughed in with the hand plane, we can take it over to the radius dish and finish it up. Mark the surface of the dish with a pencil or pen so you can easily see areas that are being sanded and areas that are not. It may be necessary to hit the areas which are still high with the plane to save a little time and dust. Also, check from side-to-side as well as ed-to-end with calipers as you go along to make sure the profile is being sanded onto the mold evenly.
Once the pencil marks are all removed and you have a nice uniform surface you’re good to go!
Other’s who use this method use a tool called a RotoZip for trimming. I didn’t want to drop the cash on the RotoZip and have a machine shop at my disposal, I opted to purchase the small saw blade for a RotoZip and simply turned an arbor for it on the lathe to fit into my laminate trimmer router. My trimmer is also variable speed so I can dial it down. A 3/4” saw blade spinning at 24,000 RPM just seemed frightening, haha, and also a good way to build up heat and wipe the teeth off the blade in a hurry. Here is the arbor and prototype router base lift I came up with.
And here is the result- ready for linings and achieved in about 20 seconds.
Thanks for reading! I hope this was helpful. If you’re not already please find me on Instagram @brad.the.guitarmaker and on Facebook at Oxwood Guitars. As always, feel free to email with any questions you may have!