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so great to have curt joining in!...check his gallery for some of his (well documented) & incredible work
https://www.oldschoolguitar.net/gallery-2/
his refinishing is as good as his repair work... he has an extensive background in paints and finishes
he's a busted guitar miracle worker!
cheers
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09-20-2020 03:39 PM
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I got intrigued and made this drawing for myself to understand how the forces in kerfed braces work:
As long as they don’t become unglued and as long as the strength of the lateral connections between and on top of the kerfes is not compromised (by runouts in the wood for example) they should in theory be just as strong as solid braces I think.
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Exactly.
Originally Posted by Little Jay
I got intrigued and made this drawing for myself to understand how the forces in kerfed braces work:
As long as they don’t become unglued and as long as the strength of the lateral connections between and on top of the kerfes is not compromised (by runouts in the wood for example) they should in theory be just as strong as solid braces I think.
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curts finished the interior work...replaced the bracing..and has updated his link with new photo's
Old School Guitar Repair >> Gibson ES-175N that’s sporting the broken brace issue. (still in progress).
cheers
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So, did you came to a conclusion about your ES? Do you still own it?
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Originally Posted by ruis
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Does anyone think this top looks sunken? I’m thinking the bridge looks jacked up abnormally high. This is a 1970 175. Haven’t seen it in person yet.
Last edited by RyanM; 11-20-2025 at 04:05 PM.
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Do you have other pics with different perspectives to share? That would help.
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Is that an ES-175 or a Greco S50?
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It's a Gibson. That's just a pic from the listing, I might check it out this week, he says there are no issues/plays perfectly. But I'm a bit paranoid because of threads like this.
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For a high quality guitar, kerfed braces are absolutely not the same strength as regular braces.
The most obvious reason is that, as in the diagram above, kerfed braces take ALL of their strength from the very top (or bottom) of the brace. If you break that chain, you don't have a brace at all.
Braces ideally aren't square. Per Trevor Gore, they are something approaching tent or V shaped. Regardless of your brace shape, it's ideally not SQUARE.
If you tent your brace, or even if you round the top over, you will lose a significant amount of that top surface and with that you will lose a significant amount of what is keeping that brace from failing.
Certain guitars (electric archtops in particular) might not take too much of a hit from having big heavy square braces, but this is ultimately a crappy way to make instruments, reinforced by the fact that pretty much no one else does this, and as far as I understand it, it started at a time when Gibson's quality control was at its lowest (which is saying something).
Definitely not the equivalent stiffness of a full cut brace. For the equivalent stiffness, you'd need a much heavier and thicker brace, which, in general, is not good. I think there are other reasons why they are poor performers but that to me is the most obvious. I mean, intuitively, it's a bad idea. In my brain, I like to think of little vibrations traveling around the guitar. The more unhindered they are, in general, the better (I might want to hinder them in certain areas). Little vibrations (in my brain, anyway) don't like to jump gaps. Whether that's actually a thing that's happening in a kerfed brace is totally questionable, but making guitars that sound great is hard, and just like randomly making something shittier is probably not good.
Oh yeah! I forgot. You probably want to shape your brace in the other direction (scalloping or whatever you want to call it). Kerfed brace is going to make that not possible or at least is going to restrict you significantly in the freedom of shaping your brace.
Pretty crappy.
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A bit difficult to tell from the picture but a (very) high bridge is usually a tell tale sign of a sunken top…. Originally Posted by RyanM
Does anyone think this top looks sunken? I’m thinking the bridge looks jacked up abnormally high. This is a 1970 175. Haven’t seen it in person yet.
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A sunken top would normally show as the inner edges of the f holes being lower than the outer edges. It's hard to tell from that photo, but it looks pretty normal to me. The angle of the neck set makes a difference, and a small change there can cause a larger change in the required bridge height. Gibsons are somewhat variable in how the neck is set.
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sgosnell is right about observing the edges of the f-holes. Hard to tell from the photo but they appear to be OK to me. What's a little off to my eyes is the height of the pickups; they appear to be cranked up rather high. Dropping the height will also mean lower the TOM saddle. Why are the pickups set so high? I hope it is not a neck angle issue.
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If there are no structural issues, I really wouldn’t worry too much.
My Wu archtop has a slightly sunken top as well, but the bracing is perfectly fine and it sounds wonderful (actually even better now than it used to, though that’s probably just because it’s been played a lot over the years
).
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I have an arthtop with the bridge raised up very high, and the pickup is pretty high too. That's because the neck/fretboard is installed rather high, and the neck is installed with it angled back a little. It came that way new. It was just built that way, and it results in somewhat increased break angle of the strings over the bridge, increasing the string pressure, and it's good for rhythm playing. Having a high bridge is not necessarily a fault, nor an indication of damage, although it could be. I also have some archtops with very low bridges, which can be an issue but isn't always. A low bridge and a shallow angle for the headstock has some advantages, mostly in giving a looser feel and easier playability. One has to look at the entire guitar and consider the relative benefits of everything. The bridge could be very low, or very high, and the guitar could still be fine. Or not, everything has to be considered.
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I’m going with neck angle. I’ve seen lots of sunken tops, and almost always the F holes tell the tale. I’ve had several guitars with high neck angles like that, the Gretsch G400C I sold a couple years ago comes to mind.
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If your bridge is maxed out, it might be they did a crappy job of setting the neck. If it's not designed for that, you're definitely increasing the pressure on the top, which ultimately may prove damaging to the guitar. Originally Posted by sgosnell
If someone designed it like that, it's a different story.
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The saddle isn't maxed out, it's just higher than my other archtops. The neck and fretboard are also higher off the top than most others I've seen. It's just a design choice, AFAIK. It's a custom build. I'm not concerned about it, just remarking that everything is variable, including bridge heights, and that alone is not proof of anything.
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The top might have sunk a little. If the bracings are intact then it’s not a big deal. Never hurts to inspect it with a dentist’s mirror and a flashlight. Sometimes the ends of the braces become unglued. Glueing those back and clamping it up will probably restore the arch…. it worked for a ‘54 ES-125 that I restored for a friend. That bridge looked like the one of the 175 in the pictures, the braces had become unglued near the neck. Originally Posted by RyanM
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