Early in my building career I learned the value of a good jig and the use of a proper tool. Like most early builders I plodded along using one method or another, never being happy with the end result. After 4 or 5 guitars I found the concave disk and I never looked back.
What you decide on as a radius is up to you. I like to use a 1 ½ degree neck angle so I can do a set up of ½ in at the bridge and a 28 foot arc will equate numerically to that angle. So with this in mind I will show you how I finally zoned into a process that not just works, but is repeatable and you don’t need to spend a lot of time and wasted motion.
Tools for the process
Here are the set up tools. The mold , spreaders 2 pieces of wood that are parallel and the same size to hold the mold true to the disking platform and the dowel pins to hold the mold while I am working on the set. I also use chalk and pencil to mark the edges of a set so I can watch what is happening as I work. The process starts with the side set , and I do pre-contour the set to avoid a lot of work. You can plot a pattern off an existing guitar or do the ½ in wedge on the back. Once you have a trued side you can make a pattern for future use.
With the side set trimmed and contoured, I set this into the mold. In a perfect set up I want the waist to just start to come off the mold so when I push against it with the spreaders I get a very tight fit. If you have a question on how to do this, you can use masking tape and tape that along an edge on the mold and tape it on your set and trim with about 1/16 extra on each end.
Use the spreader and parallels to set up your mold as in the picture below:
Next you will mark the edge of the side with chalk so you can see what is happening as you use the disk. You need to try and allow the weight of the disk to do the work and do not apply a lot of pressure. Check the set as you work so you can avoid an imbalance .
Side marked and ready for the actual sanding process.
The radius platform will secure the mold so the body is centered. The disk will rotate on the pin so you will have a nice uniform dome formed to the back. The blocks and kerfing will be applied later as this is just the roughing in. Once you have it roughed in you can trim the blocks very close, leaving them about 1/32 proud.
Some people allow a 5 degree tilt but you will see that isn’t the true case. The angle is dynamic and in constant flux along the side. This process will create that effect very accurately.
Once the disk is flush to the edge you will have established a perfect contour for yourself and you will be ready to apply the blocks and kerfing. You will true the kerfing and blocks in the same process. I found that doing it in this order will get you more accurate doming. If you have the blocks and kerfing on first , you have more material to remove and it won’t be uniform. That will increase your chance of causing issues.
Now the contour for the back is complete you can add reference points if you take the set out and reset it reasonable close. Now we can flip the mold and set up for the top. The top is more critical as we are creating the transition area for the fret board to come onto the top in as straight a line as possible. This will help to take the 14th fret hump out of the equation and get you very repeatable in your process.
Doing the top we have a lot to contend with. Curves , angles and a flat area. For the top I use a 28 foot radius. I mark the set up as I did in the back. Watching the removal is very critical. If you make a mistake now you have so much more work to do. This is where you need to be detail oriented.
To help you visualize what we need to accomplish you have to understand the location of the fret board and bridge. You can see some reference arrows on the mold so I can watch the process as it unfolds. If you look at the mold , you will see 2 arrows. This marks the areas of the extension , the area of the sound hold and forward bridge area , then the lower bout.
With this process we will establish the 1 ½ degree angle for the neck , and the dome for the lower bout. I have the mold set up on higher parallels so the mold is even to the platform and the side set is secure and will not be acted upon other than the disk. You may use more spreader if you feel you need to.
I will start to sand the wood and I want to watch the wood as it come off. I only want to radius the areas of the fingerboard extension and below the bridge. The key here is to create this angle so take you time. As the wood is removed you create a transition area. I marked this area in pencil and the radiused area with chalk.
When you have this wood removed , you can check your angle by applying a little weight on the dish . This will rise and show you clearly the geometry you now created. I like to see about 1/16 at the bridge transition area , and about ¼ inch at the tail block.
The sides are now ready to have the block and kerfing glued in. With the sides now true you can set things in very precisely and retrue your kerfing and block. This should help your building by making the neck set much easier. The more you get comfortable with this process, you will see that you can do this in under half an hour .
Master this process and you can also make more accurate joints for less stressful final assembly.
I also use the disks for gluing clamps when I place the top and back for glue up. The disks are very useful for gluing in the bracing also. You no longer need to eyeball or guess what the geometry is , as you can now control it.
Have a look at Blues Creek Guitars’ new online catalog of guitar parts and guitar building supplies for acoustic guitar builders and hobbyists’. Click here to go to the catalog.
October 2, 2006 | News | Building Info
Top thickness
ADIRONDACK .100-.110
SITKA .110-.120
CLASSICAL TOPS .070
BACKS .115
SIDE .080
BRIDGE PLATES .100
May I introduce my friends from Custom Pearl of Malone NY Lee Nadine and Dave. All I can say is they are the best and supported me and taught me so much.
Dave and Lee teach building and pearl inlay. Dave’s inlay skills are extreme and there isn’t anything he can’t do!
Thanks Guys.
As the web designer for this new version of Blues Creek Guitars (maybe we’ll call it Blues Creek 2.0?), I would like to welcome all visitors to the site. I hope you find the information and products you are looking for, and I hope you enjoy the updated design of the site.
The new design maintains the “old” logo, but updates the technology of the site. Under the hood, the construction is completely done with css (appearance and layout) and php. The parts you see have been restyled with cues from classic acoustic guitars. The page background color is my impression of a nicely aged spruce guitar top, and the herringbone pattern should be familiar to all Martin guitar players!
In the future on the website you can look forward to additional images to illustrate the tutorials, lots of news and activity on the blog here, and a complete online catalog where you can shop for all the guitar building supplies you need within the next few weeks. Those kits looks pretty cool too, I might try one some day even though I am terrible with sandpaper (hey, I’m a web designer!). It has been a pleasure working on John’s site so far, please feel free to comment or drop by my own website to see a little more of my work in web design and art.
Enjoy the site!
Ducati
