What actually goes into designing and building a new model?
 

We have recently begun working on an order for a new body size so I thought I would document some of what goes into a new model from our point of view, starting with the front end CAD design then on to building the body 1/2 template, 2 side bending forms, 2 waist cauls, 1 body mold and finally the actual build of the guitar. It will be very loosely based on what some may refer to as a M sized - OOOO body size.

Initially we used our HighLander model, which is our interpretation of an OM-ish shape and size guitar:
http://pic100.picturetrail.com/VOL89.../414444767.jpg





Then we stretched and morphed the HighLander into our new model using our CAD program called V-Carve Pro. The lower bout, of the yet to be named new model, is 16" wide with an overall length of 20-1/8".
http://pic100.picturetrail.com/VOL89.../414444769.jpg





The CAD drawings give us an idea what the outline of the body looks like before we ever cut the first piece of wood. Next we begin looking at how different scale lengths will look using both 12 and 14 fret necks:
http://pic100.picturetrail.com/VOL89.../414444768.jpg




The horizontal gray line in the above picture represents the approximate center line of the lower bout area. The closer the bridge is located to the center the more efficient the guitar will be.

Consider this analogy for a moment that the top of a guitar is similar to a drum head, which makes a lot of sense for me because I was a drummer in a former life. The closer one strikes a drum head in the exact center, the louder and fuller the drum sounds. Strike it off center with the same amount of energy and you hear a loss of volume, the timber changes and gets thinner and more tinny sounding.

In the simplest of terms this analogy is similar to what happens with bridge placements on a guitar's top. As the player sets a string in motion that vibrating energy is transferred through the saddle and begins to rock and twist the bridge in many different directions. The bridge transfers that energy into the top.

To begin with there is very little energy to work with coming from the string so the closer the point of central excitation is located to the center of the guitar's lower bout the more efficient that transfer of energy will be. As one moves the bridge further and further away from the center line the more energy will be lost.

Enough rambling for now. I have to get back to work and will update this thread as we progress. Thanks for looking and following along...

Tim,
Thanks much for doing this topic!

I think it's tremendously interesting for all builders as well as anyone considering a custom built instrument.

I recently went through the exact process to build a small bodied slot head all mahogany acoustic and posted the entire CAD drawing in the "Build and repair" forum.

https://www.acousticguitarforum.com/...d.php?t=579732

It was great fun and the finished instrument was way above my expectations. A totally "new" model will always be a bit of a craps shoot, even though we use all of the past experiance that we have to try and predict what's going to result at the finish line.

I'll follow your process with great interest!

Thanks for sharing this, Tim. Really cool to see the process all the way from the start!

Thanks for doing this, Tim! I use Fusion 360 and Carveco but since I'm only on build #2 I haven't even drawn anything in either program or even used my CNC to cut forms or fixtures. Soon, maybe, but it's cool seeing how you go through the process.

David

Very interested....
 

New shapes! Whee!!!

I will be interested to see if John Kinnaird chimes in here. He just built his second guitar in his new biggest shape, which I asked him to come up with, in my ongoing quest for major VOLUME from an unplugged axe... IT IS A COMPLETE MONSTER

The design owes quite a bit to Tim McKnight (and Mary too I figure). The CF struts that free the top from structural duties, for sure!

Thanks for all the incredible info you folks all share!!! We players get to reap the benefits...

Stay vigilant and stay well!!!

Paul

Thank you for sharing this process Tim it's really enlightening. The location of the 14 fret vs 12 fret placement with the horizontal line across the middle of the lower bout is particularly interesting.

One question for you. Would a 25.4" scale, 13 fret to the body placement place the bridge in a similar position as 24.9" scale, 12 fret to the body?

Always something to learn. This will be a very interesting thread Tim. Thanks for posting.

Thank you for the great question which is pretty easy to render and answer in CAD modeling.
http://pic100.picturetrail.com/VOL89.../414445261.jpg





The 13 fret neck to body join does place the bridge closer to the center but as you can see 24.9" scale is even closer and likely even more efficient. We could continue this journey by playing with other scale lengths to hone in on the exact center. CAD gives us a lot of flexibility in the design phase to play with visual aesthetics to see what the end result might look like.

Some may be wondering what the two circles are on the FB? They are not position marker but merely visual indicators I use to quickly locate the 12th and 14th frets. It just saves me time counting frets ;)

Thank you Tim this is really interesting to see. I think a 13 fret to the body placements offers tonal attributes of 12 and 14 and this graphic really illustrates that. I imagine the exact center might be 12 fret to the body, 25.25" or 25.4" scale.

That aside will you change your bracing in any way depending on the configuration? (12 vs 13 vs 14 fret to the body)

This is great Tim. I appreciate your doing this

Great information Tim, thanks.

Yes, bracing is fluid (for me) depending on scale length, total number of frets to the end of the FB, total frets to the body, sound hole location and bridge location. I've always preferred a "forward shifted" bracing pattern where the X brace is moved closer towards the sound hole. It also moves the X intersection further away from the bridge. What this allows is more torque and movement potential on the bridge. I still like my bridge to touch the lower legs of the X brace and feel this helps transmit more energy into the X and out to any braces that are coupled to the X.

When the sound hole is in the normal location I use more of a Somogyi-esque bracing pattern or a more traditional bracing pattern depending on the tone the customer wants. When I use an offset sound hole I generally use more of a radial bracing pattern. Lots of things are fluid on my bracing and its solely dependent on the tonal target we are aiming for.

John,
I sort of had you in mind when I started this topic. I hope this thread will provide you with some food for thought on the use and implementation of CAD and CNC in our shop. This is not the only way to do it and I am sure others have different ways they approach the same task. I am merely showing you the way we approach and tackles some of the common obstacles.

Cool idea for a thread, Tim! I went through a very similar process when I designed my Georgian modified dreadnought that I used for Jack's two guitars. I typically don't start my builds until cool weather hits Michigan, but I knew how much time would be needed to design the body, create templates, and make bending and building molds. If I was going to start building in October, I'd need to finalize the design, templates, and molds over the summer.

One important piece for me was to work up a design that got Jack the guitar he was looking for while keeping the design mainstream enough that it would appeal to other customers. Otherwise, the time commitment to build one guitar would be huge.

Design on!!

Ken

Excellent point Ken. There is a lot of time that goes into a designing and bringing a new model to market that players may not realize and its time that we take away from building other guitars that we must take into account. I also agree that for the design to be successful it has to appeal to the general market while being different enough to set it apart without being too unique that the interest would only appeal to a very small segment of that market. Its a tightrope walk for sure.