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Bracing Impression Visible on Top
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=30073		 Page 1 of 2
Author:  Ken C [ Thu Nov 25, 2010 12:39 pm ]
Post subject:  Bracing Impression Visible on Top
I had my #2 guitar out this week playing it for a bit. When done, I set it on a stand. Later I took a glance in that direction and the light reflection was such that I could see the most faint impression of the bracing in the top. Wood is organic and shrinks and swells, so a perfectly smooth top won't stay that way forever, but this surprised me. I picked up the guitar and inspected it closely. The impression was not visible up closely and could only be seen in certain lighting. The top radius was about where it should be. Top is red spruce with red spruce bracing and was built a couple of years ago.

Wondering if many of you have experienced this. Is it preventable without building 1/4" thick tops?

Thanks,

Ken
Author:  Bill Hodge [ Thu Nov 25, 2010 1:01 pm ]
Post subject:  Re: Bracing Impression Visible on Top
Hey Ken,

Happy Thanksgiving. Just curious, what did you thickness the top to? Along the same line, I have a Jumbo Takemine that I keep around for a road trip beater. I bought it new a few years back in a 40% off sale and it's been a decent guitar for a mid range factory unit. That said, in the correct lighting from across the room, sometimes I can see the outline of the bracing on the top. Mostly in the winter when the avg humidity here falls below 30%. It actually tends to be a bit more resonant in the winter. :)
Author:  Alain Moisan [ Thu Nov 25, 2010 1:13 pm ]
Post subject:  Re: Bracing Impression Visible on Top
I get this a lot. My tops are quite thin and I have experienced this, like Bill mention, mostly in the winter when the humidity is quite low.

Personnally, I don't see this as something important. Making a thicker top would probably avoid, or at least reduce this, but the negative impact on sound would be too great.
Author:  Ken C [ Thu Nov 25, 2010 1:14 pm ]
Post subject:  Re: Bracing Impression Visible on Top
Happy Thanksgiving to you as well, Bill! I thicknessed the top to 0.109", which I don't view as overly thin.

Ken
Author:  Jeff Highland [ Thu Nov 25, 2010 1:24 pm ]
Post subject:  Re: Bracing Impression Visible on Top
I have not experienced this yet but some classical guys seem to find that excess clamping pressure when gluing braces creates this effect
Author:  Pat Foster [ Thu Nov 25, 2010 1:35 pm ]
Post subject:  Re: Bracing Impression Visible on Top
Ken,

Probably not a problem if it sounds good and the belly isn't excessive after a few years.

I make a point of checking my guitars on a regular basis for this very thing. I want some to show, just not a lot. I have a guitar stand in our living room, with the guitar facing the window, so that I can stand close to the window and look at the guitar tops from a cross the room, with the window sill reflected in the lower bout close to the bridge. I look at how the line of the sill is distorted in the reflection as I move up and down at the knees, making the reflection move between the bridge and the tail. Also, looking above the bridge this way tells me what's going on up there too. I learn a lot about what the top is doing.

Look at old guitars this way in a shop sometime. You might be surprised.

Pat
Author:  douglas ingram [ Thu Nov 25, 2010 2:23 pm ]
Post subject:  Re: Bracing Impression Visible on Top
Jeff Highland wrote:
I have not experienced this yet but some classical guys seem to find that excess clamping pressure when gluing braces creates this effect


I have heard this from a number of builders. Something that I try and keep in mind when I build.
Author:  Bill Hodge [ Thu Nov 25, 2010 2:32 pm ]
Post subject:  Re: Bracing Impression Visible on Top
I haven't seen it on any of my builds either up to this point but I've only been building for 5 years. I do however, use vacuum clamping rather than my go-bar deck that I seemingly built for nothing but a catchall. :roll:
Author:  Haans [ Thu Nov 25, 2010 2:34 pm ]
Post subject:  Re: Bracing Impression Visible on Top
I look for a little telegraphing of the X braces and a little rotation of the bridge. This is a very small amount and with it is just a tad of belly. Usually, braces that travel more along the grain appear more, so tone bars usually don't show much.
On ladders, I usually don't get telegraphing, but do get a small amount of potato chip and bridge rotation. Tops are thicker and braces are transverse.
Author:  Parser [ Thu Nov 25, 2010 2:35 pm ]
Post subject:  Re: Bracing Impression Visible on Top
Seeing this doesn't mean that your guitar won't last, but I think it means that you are pretty close to the edge. .109" is towards the lower end of the spectrum for a steel string...

Trev
Author:  Haans [ Thu Nov 25, 2010 2:45 pm ]
Post subject:  Re: Bracing Impression Visible on Top
Trev, I've seen steel strings as thin as .090" in the center and .078" at the rim. A particular one that I measured sure was loud, but to my way of thinking, had no tone...
On the opposite end of the scale, I have a 12 string with A frame/ladder bracing that measures out at .165" where the ladders are fine, but the two A's are telegraphing a bit.
Author:  Jim Kirby [ Thu Nov 25, 2010 3:13 pm ]
Post subject:  Re: Bracing Impression Visible on Top
I don't think you even need an excessively thin top to see this in dry conditions. I can see the X brace on my Larrivee L-09 most of the time. I've never seen any other concerns for the guitar's structural stability at all.

I will concur that excessive clamping can possibly be a culprit from the outset. I have a classical top that is braced up with the Romanillos pattern and is getting ready to go in the mold, and I can see the fans before I even start. (Shane's Lutz for a top - mmm, mmm good.)
Author:  WaddyThomson [ Thu Nov 25, 2010 3:29 pm ]
Post subject:  Re: Bracing Impression Visible on Top
I can see the fans on all of mine, regardless of thickness of the top. Part of it is the narrow fans. I believe 7 mm wide fans would telegraph a bit less. However, I have noted that nearly every classical guitar concert I've gone to over the years, with the light on the guitar, most of them show some telegraphing of fans.
Author:  Joe Sustaire [ Thu Nov 25, 2010 8:31 pm ]
Post subject:  Re: Bracing Impression Visible on Top
I've had telegraphing on some of my builds also, thinner tops display more than thicker tops, but I've also wondered if sometimes it happens when I sand the box with the ROS, smoothing the top and thinning the edges. Seems likely that it sands differently over the braces, but I don't notice it until it's all finished and strung.

What you think?

Joe
Author:  Parser [ Thu Nov 25, 2010 11:12 pm ]
Post subject:  Re: Bracing Impression Visible on Top
The lighter you build, the more risk you run of building "too" lightly...it's as simple as that. Sure, it can be done, but you are sacrificing a little slice of your safety factor to do so. Granted, a lot of factory instruments are overbuilt (...and are purchased, played like crazy, and never returned for warranty work :D ).

Also, my reservations are more for steel strings, since I don't have much direct experience with classicals.

I think the best factory example out there is Collings. I think they build one heck of a nice looking and sounding guitar...and I also think they stay pretty close to .125.

Going back to Ken C's original post - it is interesting that it took a couple of years for the bracing to telegraph thru. My understanding is that the wood continues to creep for about 2 to 3 years before hopefully reaching equilibrium. Ken's guitar will either stabilize, or in another couple years we'll see another post about how the braces are telegraphing even more. It's hard to say exactly where the line is, when we're hoping to build instruments that will stand the test of time and we might not see issues for years...!

Lastly, I guess I'm cautious by nature, and I'd rather err on the safe side.

Best,
Trev
Author:  Ken C [ Thu Nov 25, 2010 11:28 pm ]
Post subject:  Re: Bracing Impression Visible on Top
Thanks for all the comments folks. You provide a great sounding board! The guitar sounds very nice. It has never been as full sounding as my latter builds, but I am using lighter bracing these days. Some day I may lighten the bracing on this one.

Nice to hear I am not alone. I only have a couple of the other ones I built still around, and I hadn't noticed telegraphing in those. I wasn't sure if this sort of thing is viewed as a bad thing by owners and players. Seems that the sound is still the key as long as the top remains structurally sound otherwise.

Thanks again, and I hope you all had something special to be thankful for today.

Ken
Author:  fric [ Fri Nov 26, 2010 1:42 am ]
Post subject:  Re: Bracing Impression Visible on Top
Did anybody looks at Smallman guitar on this way?
Author:  Parser [ Fri Nov 26, 2010 9:12 am ]
Post subject:  Re: Bracing Impression Visible on Top
Not all factories just take whatever comes in the door and cut it to "X". Some shops have processes that are pretty much indistinguishable from what a lot of small builders do.

A factory would uncover a 10% failure rate much more quickly than someone building 5 per year. If you build 5 a day for a few months, you'll learn pretty quickly what works and what doesn't...!

Trev

Todd Stock wrote:
I don't think you'll find out how light you can go without building a few that are pretty light. The advantage you have is that you can thickness and brace for the wood you are using, rather than for the 25 percentile from your supplier.
Author:  WaddyThomson [ Fri Nov 26, 2010 10:19 am ]
Post subject:  Re: Bracing Impression Visible on Top
The problem with that is that the factory builds for the average result, not the optimum result. It's the only way they can go and still make a profit. The optimum factory guitar is the exception, not the rule.
Author:  Parser [ Fri Nov 26, 2010 10:52 am ]
Post subject:  Re: Bracing Impression Visible on Top
Waddy, I think your statement applies only to low end instruments. All of the custom shops are staffed with people much like those who frequent this forum. This very discussion goes on in these shops as well - just like on this forum, there are folks on both sides of the line. Admittedly, there's no "one" answer as to the right top thickness since it depends on so much else (bracing, wood drying, voicing, etc.).

When we were setting up the PRS acoustic shop, this was a common discussion.
Author:  Colin S [ Fri Nov 26, 2010 12:02 pm ]
Post subject:  Re: Bracing Impression Visible on Top
Joe Sustaire wrote:
I've had telegraphing on some of my builds also, thinner tops display more than thicker tops, but I've also wondered if sometimes it happens when I sand the box with the ROS, smoothing the top and thinning the edges. Seems likely that it sands differently over the braces, but I don't notice it until it's all finished and strung.

What you think?

Joe


Joe has hit it on the head, the telegraphing of braces through a top is often the result of sanding, usually by machine, after the braces are on. This will be more noticeable with the thinner top, and also happens a lot with cedar. the top between the braces, being less stiff is pushed down when being sanded leaving the braced section of the top slightly proud of the surrounding wood and therefore the top over the braces gets sanded slightly more than the rest. As with most small variations in the top this will usually only show once finish is applied. It can also happen over the years as a result of the top wood shrinking slightly with age. I often restore instruments that are 2-300 years old and this effect is often very noceable in there old tops.

Colin
Author:  Joe Sustaire [ Fri Nov 26, 2010 1:35 pm ]
Post subject:  Re: Bracing Impression Visible on Top
Thanks Colin, was beginning to think my posts are invisible. :D

Joe
Author:  Haans [ Fri Nov 26, 2010 3:54 pm ]
Post subject:  Re: Bracing Impression Visible on Top
Joe, I do think there is some validity to what you are saying. Two other factors are humidity (or lack thereof) and vibration. I think tops expand and contract differently in the non braced areas, and just the shaking from playing in pops 'em out. Waddy's post seems to also confirm my suspicion about more parallel braces/bars telegraphing more. At any rate, last weekend I saw a pretty fancy Bourgeois that had telegraphed the X bracing.
Author:  Ken C [ Fri Nov 26, 2010 11:05 pm ]
Post subject:  Re: Bracing Impression Visible on Top
I really hadn't paid a whole lot of attention to this on other guitars, though I certainly have seen it. I am now much more curious and will pay much more attention going forward.

Regarding my own, I only sand my tops by hand once braced. But depending on the season and what I have going on, weeks could pass before I final sand the top prior to finishing. If the humidity has changed, even hand sanding may cause the same effect as noted by Joe.

Ken
Author:  warmong [ Sat Nov 27, 2010 3:34 pm ]
Post subject:  Re: Bracing Impression Visible on Top
My teacher told me that when glueing fan braces, you could get telegraphing from cleaning glue squeeze out with water (glueing with HHG).

not sure if that's something others here have noticed, but that's what I've been told.

cheers
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