Moving right along.

I remembered that before I can glue the braces to the top, I needed to align the bridge.

The rosewood RI bridge was drilled for the alignment pins, but didn't have any. So, I pulled some 3/16" hardwood dowel out of the scrap pile, and made my own alignment pins.

I sanded them to make sure they won't poke through the underside of the top when installed.

Measured and marked the location of the bridge alignment pins.

And, drilled the holes.

Perfect fit.

With that done, I can mark the underside of the top and start making the braces.

Number 1 brace is cut, rounded and scalloped. X-braces are cut, notched and scalloped. Finger braces are cut.

Shown next to the original top. The only things missing is the X-brace reinforcement, which I'll cut once the braces are glued to the top, and the fiberglass strip.

I'll do the fiberglass strip first using MGS epoxy resin, before any of the braces are glued down. Then, once the resin is dry (24 hours) I'll start gluing the braces down.

Although I used hot hide glue to join the top pieces, I'll be using Hysol epoxy to glue the braces, because that's how it was done on the original. Both MGS and Hysol are aerospace-grade epoxies and both dry very hard and will transmit the vibrations very well.

The first step to building the top is to apply the fiberglass cloth reinforcement strip across the lower bout.

A layer of visqueen (Saran wrap) was laid onto the gobar deck, then the top was placed and a few gobars were put into place to keep the top flat and to keep it in place while I applied the fiberglass.

Close examination of the original told me that the factory used the same 8.5 oz. 2x2 twill cloth for this strip as was used to make the bowls. This strip looks like a single thickness of the cloth whereas the bowl uses two layers.

Typically, when glassing a surface, a layer of resin is applied with a brush, then the cloth (1/2" x 12-1/2") is put onto the resin and the cloth is wet out with the brush. This is the process I used, but the cloth looked a little dry, so I applied a thin top coat of resin.

Lastly, I put the rest of the gobars into place so the top is dead flat.

I'll let this cure overnight and I'll be ready to apply the braces tomorrow.

Hey Dan,

Exciting stuff! Hey I have a couple of questions about the fiberglass cloth reinforcement strip.

What exactly is its purpose?

Has Ovation always used it?  And if not, why did they stop?

Has any other guitar maker used it or a method like it?

Thanks

jay

Howdy Jay!

Here's what the patent has to say about the construction of the soundboard. (See: Guitar Construction US 3474697 A) 

The soundboard 16 is longitudinally tapered from a maximum thickness at its upper end to a minimum thickness at its lower end, as best shown in FIG. 2. For structural reasons it is desirable that the soundbox be of greatest strength in the region where the neck is joined thereto, and for this reason the soundboard is of greatest thickness in this upper region. The tapered configuration of the soundboard provides ample thickness in the region of the sound opening 18 and the bridge 28 while the decrease in thickness in the region of the lower bout 42 permits maximum excursion in the latter region. For added strength and durability it is desirable that the soundboard be further reinforced. Accordingly, a plurality of relatively flexible wooden ribs are *adhesively bonded to the soundboard rear surface 56 and are arranged in a manner illustrated in FIG. 6. A relatively heavy rib 64 extends transversely of the soundboard between the sound opening 18 and the upper bout 40 to reinforce the longitudinally extending grain structure of the board in the region of the neck connection. Diagonally extending ribs 66 and 68, somewhat lighter than the rib 64, cross each other below the sound opening 18 and in the vicinity of the bridge 28. Further reinforcement is provided in the bridge region by a thin gusset plate 70 secured to the rear surfaces of the ribs 66 and 68 proximate the point of crossing. Relatively light reinforcing ribs 72, 74 and 76 cooperate with the aforedescribed ribs 64, 66 and 68 to form a reinforcing structure surrounding the sound opening 18. In the lower region of minimum thickness the soundboard 16 is further flexibly reinforced by at least one elongated fabric strip 77 bonded to the rear surface 56 and extending transversely thereof.

There's a couple of interesting parts in this paragraph.

First, it says that the soundboard was longitudinally tapered from the neck to the bottom of the lower bout. I measured the original sound board and it is tapered from the top to the bottom. The upper bout is about .125" (1/8") and the lower bout is about .110". Interestingly, I measured the center of the lower bout and it tapers to a little less than .094". (3/32")

So, the center of the lower bout, which is the largest open, unsupported part was the thinest part of the whole soundboard. This means that, as the last sentence of the patent states, the purpose of the fiberglass strip is to reinforce the thinest part of the soundboard, presumably to keep it from cracking and splitting.

This brings up an interesting point. In order to completely duplicate the construction of the original would require that the sound board be tapered, not only longintudinally, but also that the center of the soundboard would need to be tapered from the edges inward.

The tapering from top to bottom could be accomplished by using a thickness sander that can be set up to sand one side thicker than the other, or one that changes the thickness as the piece moves through the machine. The other part, sanding thinner in the center as it tapers would be a bit more difficult.

So, did Ovation use use this custom thicknessed soundboard on the RI? I couldn't say. To find out, we would need to talk to the people who built them or take one apart and measure it. What I can say is that it would certainly complicate the construction process.

A lot of other guitar builders use tapered soundboards, and for the same reason --to increase the vibratory response for better sounding guitars. Usually though, they do it the opposite way, where the edges are thinner than the center. Taylor guitars don't taper the soundboard. Instead, they route a shallow groove around the periphery of the soundboard next to the kerfing so they get the same effect as tapering the thickness, but without all the trouble.

I couldn't say whether Ovation has always used the strip. We'd have to look at later models of guitars that used this original X-brace pattern and whether they had the fiberglass strip. I reviewed all the patents Charlie held and only this one mentions the strip. The 1970 German patent drawings show this strip, but I would say that is simply one to patent method of construction in Germany.

To my knowledge, no other acoustic guitar manufacturer has used fiberglass in the construction of the soundboard. The closest would be the cotton cloth used to reinforce the x-brace joint.

I'd imagine that the question on everyone's mind is, will a non-tapered soundboard, such as what I'm using on 485, sound as good as the original? I believe so, and here's why. When I was measuring the original top to determine how thin to take down, I did notice that the upper bout was a good .125", which is about the same as the wood I ordered. When I rebuilt my 1619, I intentionally had that sanded to .094". While the 1619 does sound really good, I have to use extra light strings to keep the bellying under control. So, I split the difference on this soundboard and had it sanded to .110", which is as thick as the original soundboard when measured in the area of the bridge.

Today's job is to glue, or as Charlie's patent says, 'adhesively bond' the braces to the soundboard.

Dan

Dan,

Thanks for the research and reply….

This means that, as the last sentence of the patent states, the purpose of the fiberglass strip is to reinforce the thinest part of the soundboard, presumably to keep it from cracking and splitting

 That is interesting…I wonder, since #1911 remained in pristine condition (and of course we will never know) if it was thickness sanded? Something had to be different, to make it an exception to the norm… I think. Acoustically, you couldn't tell it apart from 485.

So, did Ovation use use this custom thicknessed soundboard on the RI?

I would bet they went for look…not exactness. Having owned both..the RI is a beautiful guitar … but, imo, it fell short of replicating the feel and response…which might be attributable to the head start the originals have in “opening up”…if that is indeed a factor. And of course the originals were totally hand made. I never looked at the bracing of my RI…I wonder if they were braced the same, using the fiberglass strip???

Ok...just one more question...why use a fiberglass strip, instead of a couple more braces, like Martin did with the D45 and Ovation did with the modified X?

Who is still around that was there in 66/67?

I don't see any reason why 1911 would have been built any differently than 485. I would say that if it has the fiberglass strip, then the top was probably tapered. Since they were acoustically alike, I'd say that would make it likely they were built the same way.

It would be easy enough for someone with an RI to look inside to see the brace pattern. The factory might have added the fiberglass strip for aestetic purposes.

Speaking of opening up, I'm not sure if you're familiar with the torrefaction process for musical instruments, but the idea is to pre-age the wood so that it duplicates the cellular strucure of old wood. Basically, the wood is put into an autoclave, the oxygen is removed and the wood is brought up to a temperature of a few hundred degrees. This process 'cooks' the wood and alters the cellulose and resinous lignin as well as a substance known as hemicellulose. Yamaha calls their process. Acoustic Resonance Enhancement. (A.R.E.) Martin, Taylor and Bourgeois have all jumped onto the torrefaction bandwagon. Even Stewmac is selling torrefied wood now.

I bought some torrefied red spruce to use on my 1617. I wanted to use torrefied wood on my 1619, but couldn't find any. So, I'm going to use it on my 1617 along with the identical brace pattern I used on my 1619 to see the difference in sound between the two guitars.

The point of this is one of the characteristics of torrefied wood is that it becomes completely opaque. I compared the torrefied red spruce to 485's original top and there are a lot of areas that are opaque, which means that the wood has aged and is becoming similar to torrefied wood in cellular structure. So, this aged wood certainly has a lot to do with the difference in sound between the originals and the RI.

WRT adding braces, recall from 'The Book' that Charlie used the D-45 as the standard of sound that he was trying to duplicate. I'm sure that while he wanted to get the sound, he didn't want to have someone look inside his guitars and say that Ovation simply copied the Martin brace pattern, as so many others did, and still do. But, remember that the additional braces between the lower half of the X-braces are about sound, not structure.

Back to the build.

I decided to sand the fiberglass strip to smooth it out, and thin it slightly. To keep from scarring the inside of the top, I laid two strips of masking tape.

And, it sanded smooth. This was actually also done on the original.

Taped some visqueen to the gobar deck.

Made the center gusset using the original as a pattern.

Got the Hysol 9462 ready and clamped the top to the deck.

Brace #1, the X-braces and the gusset are all glued, er, 'adhesively bonded' and clamped.

Finger braces are 'adhesively bonded' and clamped.

I could pull the top out of the deck tomorrow, but technically, 9462 takes 72 hours to fully cure. So, I'll just leave it clamped until Thursday. In the meantime, I'll start sanding on the bowl and neck getting those ready to refinish.

I wanted to add that if you really wanted to get the opened-up sound of the original I could remake the top using torrefied Sitka spruce soundboard and braces from Stewmac.

The soundboards and uncarved brace wood isn't that expensive and I'm not so far along in the process that we couldn't take a couple of steps back.

Stewmac torrefied Sitka Spruce Soundboard
Stewmac Uncarved Guitar Braces

Once the soundboard is glued, er, 'adhesively bonded' to the body, this would become a lot more difficult. So, if you'd like to get that opened-up sound right out of the gate, now is the time to do it. I wouldn't mind taking a few steps back if you're willing to buy new wood.

There's always a chance that with this rebuild using brand new wood, 485 will sound more like a RI than an original.

If we compare the new sound board to the original one, the original one has the deep colorization of the torrefied wood.

Just something to think about.

Identical except for that tone bar across the bottom

I sanded the neck today.

I could be mistaken, but I don't think they were using EIR back in the mid-1960s, which means the beautiful rosewood veneer on the headstock is probably Brazilian.

Sanding also exposed the beautiful two-piece mahogany neck and ebony heel cap.

The two-piece neck is unusual. I wonder why.

To simulate the final look once the finish is applied I sprayed the headstock with naptha. Simply gorgeous. When I first started, the finish had darkened so much that it was hard to tell the mahogany from the rosewood. Not any more.

Here's what the back of the neck will look like once the finish is applied.

The color of the wood is actually darker than what can be seen in the photos. The flash lightens the color a little bit.

Tomorrow's task is to sand the bowl and get it ready to patch the hole where the pick-up jack used to be located. This guitar will be a pure acoustic. I'm also going to make a bone nut and use a bone saddle.

After some discussion, Jay and I decided that this guitar deserved every chance to have the most original sound it could.

So, Jay ordered some torrefied Sitka spruce soundboard and brace stock from Stewmac and I'm going to re-do the top.

Here's one of the sets of the soundboard we got. It's got nice tight grain with good silking. Since I'll need two sets to make three 5-3/4" planks, Jay also ordered another set. But that set didn't really match the grain pattern of this set, so I'm returning it to Stewmac and asked them to match this set as closely as possible.

Both the soundboard and the brace wood have the aged look seen on the underside of the top.

While I'm waiting for the other wood, I'm going to finish sanding the bowl, patch the hole in the bowl left by the strap button jack. Then, cut and shape the brace wood.

I finished sanding the bowl and got the braces ripped and shaped today.

Brace stock is ripped to size.

Brace #1 is cut, rounded and scalloped. X-braces are cut, notched and scalloped.

Once the torrefied wood has been sanded, it's not as dark as the original braces.

But, it's a lot darker than the new spruce. And, it's a lot more resonant. When I drop the braces on the workbench, they ring.

When I drop the braces on the workbench, they ring.

How exciting is that...! 

This will be 485.1

Thanks, TPA.

Jay,
Yeah, I don't think we'll be sorry for the extra time and expense of using the the torrefied wood. It's going to sound really special once it's done.

For those who want to see a comparison between a torrefied top and normal top, here's a video made by John Hall of Blues Creek guitars. He built two guitars with the only difference being the top wood: one torrefied spruce and the other normal spruce.

Torrefied Top Comparison