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Posts: 1674
Joined: Jan. 29 2012
From: Seattle, Washington, USA
Bridge Thickness and String Height
I have a customer who wants the string height at the bridge to be 7.5 mm (with an action of 2.5 mm at the 12th fret). My flamenco bridges are normally a quarter inch thick or 6.35 mm. Barely more than a millimeter of saddle extending above the bridge wood is not enough to make a sufficient break-over angle, in my opinion, so I will shave the wood down a little. I am curious how other luthiers deal with such requests and what your standard bridge thicknesses are.
Ethan, I make my flamenco bridges 6 mm high of wood so you could get a little extra there, maybe even go down to 5.5. If you haven't already I would advise this customer that they might not want to start so low. I don't go lower than 8 mm on a new guitar. I have seen so many expensive Spanish guitars that started out too low with no room to lower the action over time, and now have 4 mm action at the 12th fret with 6 mm string height at the bridge.
Posts: 1674
Joined: Jan. 29 2012
From: Seattle, Washington, USA
RE: Bridge Thickness and String Height (in reply to Andy Culpepper)
Thanks, Andy.
My guitars usually end up with a 12th fret action of about 2.7mm and a string height at the bridge of about 8 to 8.5 mm. So what I am planning to do is make the fingerboard a mm thinner and what you suggested with the bridge. It's not a drastic change from what I normally do.
I do find that after a new guitar has been strung up for a few weeks, things change, I think because the soundboard finally decides how it is going to react to the string tension. Since my necks are reinforced, I'm not too worried about it warping.
I am also about to make the bridge for my guitar... Before I installed the frets I measured with a long straightedge lying on the naked fingerboard. The distance between the soundboard and the straightedge was 3mm at the treble and 2mm at the bass side. Does that sound right to you?
Posts: 1674
Joined: Jan. 29 2012
From: Seattle, Washington, USA
RE: Bridge Thickness and String Height (in reply to mango)
Mango, I've been seeing your work and it looks very fine, so I think I must misunderstand what you are saying here.
A long straight edge lying on the naked fingerboard (naked = with no frets) could hang over the area where the bridge (saddle) goes. Obviously there has to be enough room under the straight edge at that place for the bridge with saddle (minus the height of the frets that will be installed). 3 mm does not sound like enough. I think most flamenco bridges are around 6 mm tall, and the saddle adds some height, maybe 2 mm more (for example) in which case you would need 8 mm minus the fret height.
Wait, it's more complicated because the strings don't lie down on the fingerboard. You need to account for the space between the strings and the frets. I would just make a full-size drawing to see what's going on, of the whole thing from the side.
But off the top of my head, I guess you would subtract twice the action at the 12th fret from that 8 or so mm, and get...what you said, 2-3 mm!
Geez, Ethan. A simple “yes” would have sufficed. Hahaha.
Seriously though, the suggestion to make a drawing is very good advice. Doing so helps demonstrate how the entire design of a guitar flows from the bridge. It’s a fundamental.
RE: Bridge Thickness and String Height (in reply to Andy Culpepper)
quote:
I don't go lower than 8 mm on a new guitar. I have seen so many expensive Spanish guitars that started out too low with no room to lower the action over time, and now have 4 mm action at the 12th fret with 6 mm string height at the bridge.
Not sure I understand. Is this because the neck would pitch forward overtime?
Either the neck can pitch forward a little or the top pull up behind the bridge. If you use a carbon fibre bar the neck will likely don’t move though. In other words, if this happens the luthier didn’t reckon the tolerances of the wood properly. 8 mm at the bridge and 3 mm at the 12 fret it’s quite the security standard for makers nowadays even though players may prefer a lower setting either at the bridge or at the 12th fret. I think some guitars give their best with low bridge and high action (3.2 mm or so) particularly in live performances. Btw Many Reyes are 9 mm standard at the bridge and many Ramirez 7 mm.
RE: Bridge Thickness and String Height (in reply to JasonM)
quote:
Not sure I understand. Is this because the neck would pitch forward overtime?
Likely a combination of bending and pitching forward. It's something that to *some* degree is almost guaranteed to happen on the typical Spanish guitar. I reinforce my necks with carbon fiber but I still budget in some movement over a time frame of 5-10 years+.
Mango, I've been seeing your work and it looks very fine, so I think I must misunderstand what you are saying here.
A long straight edge lying on the naked fingerboard (naked = with no frets) could hang over the area where the bridge (saddle) goes. Obviously there has to be enough room under the straight edge at that place for the bridge with saddle (minus the height of the frets that will be installed). 3 mm does not sound like enough. I think most flamenco bridges are around 6 mm tall, and the saddle adds some height, maybe 2 mm more (for example) in which case you would need 8 mm minus the fret height.
Wait, it's more complicated because the strings don't lie down on the fingerboard. You need to account for the space between the strings and the frets. I would just make a full-size drawing to see what's going on, of the whole thing from the side.
But off the top of my head, I guess you would subtract twice the action at the 12th fret from that 8 or so mm, and get...what you said, 2-3 mm!
Thank you Ethan! I really enjoy to watch you thinking... ;-)
Barely more than a millimeter of saddle extending above the bridge wood is not enough to make a sufficient break-over angle, in my opinion,
The break angle thing is a big concern for a lot of luthiers, and in my experience a non issue. I had a guitar (student’s actually) with zero break angle repaired not because of volume issues, but because when the saddle was lowered, the D string, being thin, was buzzing as it bounced against the saddle! . With no angle the string was barely touching the saddle, just shot straight across into the tie block, unless played hard. The repair involved filling the string holes and re drilling them a hair lower at downward angle. Just enough break angle was needed in other words, and with the new angle no new increase of volume was achieved because the confusion about volume and bridge height involves ACTION over the fingerboard, not break angle beyond saddle.
I can imagine that bridge height is designed to be quite low on purpose for these Condes I have that achieve 7mm at bridge and 3mm at 12. Seems dangerous, however, they had the balls to do it again and again like that. Many condes don’t have any bone showing even. Check out the under string camera shots here at 0:46 and elsewhere:
Any luthiers that has the guts to make a guitar like that for a pro of this guy’s level, I applaud you sirs!
If Parilla de Jerez wanted a guitar from me I would inlay purple unicorns on the fingerboard if he asked for it... Good eye Ricardo the strings are just about on the wood it looks like.
RE: Bridge Thickness and String Height (in reply to Andy Culpepper)
quote:
Good eye Ricardo the strings are just about on the wood it looks like.
Andy, it seems that there are so many differences in playing style, that when building spec instruments, you, as a builder, will have to hit a happy medium and hope for the best.
I got this opinion from GSI many years ago about them wanting me to build concave finger-boards.
Everyone has their own opinion.
I've come to a conclusion that I try and cut the fingerboard a little over 1/4" thick with the idea that there is enough wood to re-level its thickness later when things change.
Some players might like your tone but have their own repairman to alter the finger board the way they want it.
The same with the bridge; keeping the string holes low to the plate as well as the saddle slot to where the player can have from 7 to 9 MM height adjustment on the saddle.
I'm sure you know this already, I'm just posting this for the new-by's.
Posts: 1674
Joined: Jan. 29 2012
From: Seattle, Washington, USA
RE: Bridge Thickness and String Height (in reply to Andy Culpepper)
quote:
I reinforce my necks with carbon fiber but I still budget in some movement over a time frame of 5-10 years+.
Funny you should mention that, because I just got back one of my guitars on which the action went too high. I lowered the bridge (wood and bone) and it went back to being too high under string tension. I noticed that the neck was flexing. I thought maybe I forgot to put in the pultruded carbon-fiber reinforcement. I spent an hour getting the fingerboard off and found that the reinforcement is there. All I can think of to do is add more reinforcement. There are already two eighth-inch by three-eighths-inch bars in there (vertically, of course). I guess I'll add two more. This is the first time I've seen this problem in a reinforced neck. It has me reconsidering cedro as a neck wood.
I've been using blanks I cut from a 12' x 16/4 plank for years. Maybe it's a softer piece.
Almost makes me wonder if there’s something else going on, like a batch of frets with narrower tangs or something like that. Or a weak lateral brace above the soundhole? Seems strange that only one neck cut from the same board is problematic, and two CF rods for reinforcement is pretty sturdy stuff. It’s a puzzler.
Posts: 1674
Joined: Jan. 29 2012
From: Seattle, Washington, USA
RE: Bridge Thickness and String Height (in reply to RobF)
Thanks for your interest, Rob. Well, it's not a brace: I was able to see that the neck flexed in the middle of the shaft. Also, the fret wire is from a 1-pound package that I've used wire from before and since. Quite possibly there are other neck blanks from the same plank waiting to cause me trouble.
RE: Bridge Thickness and String Height (in reply to Andy Culpepper)
Huh, I guess I should put a carbon insert in this neck blank while I still can. I guess the downside is that you don’t get that natural relief from string tension as much?
Speaking of buzzing D string, I’m wrestling with this right now. Don’t think it’s break angle. I’m going to see if it’s the saddle contact area, but it’s frustrating. Plan is to get this addressed and make a wider nut this weekend and record a video of this axe. Think this will be nut number 4 now lol
Adding two more bars of pultruded carbon fiber did not fix the problem; apparently the upper body was flexing. So I removed the fingerboard again and replaced it with a new one that was a little thicker and tapered a little towards the nut. This solved the problem.
In the process, I realized that I had made the original fingerboard of Indian ebony, which I found to be difficult to plane without tear-out and so it had become a little thinner than usual.
I am curious how other luthiers deal with such requests and what your standard bridge thicknesses are.
So this might not be for everyone but I try to get two bridges out of one blank. They end up in the order of 6-7mm depending. I noticed on bridges with one stringing hole, there is a tendency for the loop round to pull the string up and this can be a problem, as you've stated with the break angle. Consequently, I drill a double hole and this means as the string leaves the bridge for the saddle the angle of the string is not interfered with. I drill quite low down too about 2 - 2.5 mm centre. I also make quite a deep groove for the saddle. As said earlier, there will always be some kind of movement, so at some point maybe there will be adjustment accordingly. Presumably you will have flagged this one up to the customer. Trick is to try and have some inbuilt calculation to compensate a bit at a later date. Hopefully this won't be too much. We are not astrologers though, so you can only do your best - but this seems to work pretty well for me. I think drawing out is a good way to start and getting the neck angle calculated to suit this as obviously this has a impact too. You make good guitars, you have skills -you'll work something - good luck.
Printable Version
. With no angle the string was barely touching the saddle, just shot straight across into the tie block, unless played hard. The repair involved filling the string holes and re drilling them a hair lower at downward angle. Just enough break angle was needed in other words, and with the new angle no new increase of volume was achieved because the confusion about volume and bridge height involves ACTION over the fingerboard, not break angle beyond saddle. 
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