#1
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Setting neck angle in Cumpiano book?
I'm working on getting my neck angle set in relation to the bridge. In the Cumpiano book on page 304 he says "on our guitar the bridge will be 3/8" thick; thus the airspace can vary between 25/64 and 7/16 inch. On page 30 there is a picture with him measuring the distance with a caption that says "Airspace at the saddle location must be 1/64 to 1/16 inch greater than the height of the bridge. Confusing.
Right now on my guitar I have 3/32" airspace from the top of my brig to the straight edge. My bridge is 3/8" thick. For some additional information when I started building this guitar with my luthier friend he said it was lightly braced and I should use light strings on it if I wanted it to last for many years. What am I missing? I don't feel comfortable flossing any more until I get it straight in my head. It's kind of a one shot deal. |
#2
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As a general rule, we typically aim to have a straightedge lying on the frets, and hope it just grazes the top of the bridge with no saddle in place. Then, with a 3/16" high saddle, the action will wind up near 3/32" as the space between the bottom of the string and the top of the 12th fret.
I'm not particularly a fan of jacking the bridge/saddle up too high, so I'm conservative about neck angle.
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Cheers, Frank Ford |
#3
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#4
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To make it easier, let's get rid of the fractions, rather than deal with common denominators: 3/8 = .375 1/64 = .0156 1/16 = .0625 3/32 = .0938 Page 304 states, as you quoted, that the bridge is 3/8" (.375) and there should be an airspace no more than 1/16" (.0625) and no less than 1/64" (.0156). That gives the total height from top to bottom of straight edge of between 25/64 (24/64 + 1/64) and 28/64" (7/16") (=6/16+1/16). Thus the total vertical height should be not less than 25/64 (.3906) and not more than 28/64 (7/16") (.4375), which is what is stated on page 304. The caption on the photo on page 306 reiterates the same information of an air gap no less that 1/64 and no more than 1/16". You have a bridge of .375 (3/8) and an air gap of .0938 (3/32) for a total of .468. That is .031" higher than the book's distance. (That means your saddle will be .031" (~1/32") taller, which is fine.) How thick is your fingerboard compared to what is stated in the book? The book states, on page 273, a finished thickness of 7/32". If your fingerboard is thicker, that will increase the gap. Ditto, if you are using taller frets. Ditto if you have used a different top radius or flat vs. radiused. Ditto if you've used a different shape, or different bridge position relative to what is used in the book. |
#5
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My fingerboard is thicker. It's .25" maximum thickness and my frets are StewMac medium/medium frets with a crown of .039". My top radius is 25 feet and my bridge is .375" thick and is just the standard Martin style ebony type. The bridge location is based off the StewMac dreadnought plans which I belive are based on a prewar Martin.
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#6
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On new guitars, I set the neck angle so that the straightedge placed on top of the frets is 0.030" above the bridge. Most of the time, I make the bridge 0.360" thick. That means the straightedge would be 0.390" above the top.
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#7
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Thanks to all for the help. I got it down to 3/64" and am happy with it. I can't seem to get the pictues to post for some reason. I'm sure it's operator error but I can't figure it out. You should be able to click on them to open. At least I hope.
https://www.flickr.com/photos/150599...posted-public/ https://www.flickr.com/photos/150599...posted-public/ https://www.flickr.com/photos/150599...posted-public/ https://www.flickr.com/photos/150599...posted-public/ Last edited by Albert D; 06-20-2017 at 04:00 PM. |
#8
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Here is the way I see it...Bridge is 3/8" thick...Saddle height is 1/8"high....Top will rise approx 1/16" when the strings are installed...If you don't allow for that rise then your saddle height will be only 1/16"....You need to compensate for the rise....
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#9
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After spending a good part of the day working on it I'm getting a better understanding of what I'm doing. I will floss some material off the bottom of the heal and maybe take a tiny bit off the bridge too. According to my friend who started me on this journey I need 1/8" or maybe a bit more. That's what he did and it worked. Since mine is braced the same as his it should work for mine too. He goes into the hospital day after tomorrow for quadruple bipass surgery.
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#10
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I always shoot on the high side of Cumpliano's measurements. 1/16th of air space across the frets over the bridge. Make sure you have the frets in place, I made that mistake once
I like the high side because I tend to build light and get more top lift and bridge rotation. Plus once the guitar settles in after so many months or a year then you can sand the saddle down and have a nicely broken in guitar for many years. 3/64th will work perfectly. |
#11
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I am very grateful for all the help and input from everybody. It means a lot that you are all willing to share you're knowledge with a new builder. It makes me want to try another one. I would sure like a smaller bodied mahogany guitar. |