scd
Sore Fingers
Posts: 9
|
Post by scd on May 18, 2021 15:17:05 GMT
There does not seem to be any published detail on the shaping of soundboards for the ‘flat top steel strung’ guitar. The only book available fifty years ago was John Bailey's 'Making a folk guitar' which suggested making a slight curve on the struts to give a curved soundboard.
I made mine by defining a profile on the centreline and then at 1” intervals found the curve that went through it and joined the top of the ribs. Along the line of the actual struts you can then determine the height of the soundboard at these sections above the ribs and hence the profile of the strut that will produce a curved top that sits evenly on the top of the ribs.
A spherical board will produce a large gap in the waist area that would distort the soundboard to close – I am assuming that the ribs are level although it seems some people vary their height to match the profile of the spherical board.
I have illustrative drawings of the above and the jigs/fixtures for making such a curved soundboard but need help in putting it into a 'thread'.
|
|
|
|
Post by andy3sheds on May 23, 2021 19:56:58 GMT
Hi Roger
There’s some guidance on inserting photos in the information section.
|
|
scd
Sore Fingers
Posts: 9
|
Post by scd on May 24, 2021 20:07:17 GMT
The question I am asking is how can you fix a soundboard that has been formed on a spherical dish onto a set of ribs that are flat? Thew soundboard touches the ribs around the lower bout, almost, but there is a gap of over 3mm on each side at the waist. If the soundboard is clamped onto the ribs like this it will induce large stresses in the soundboard as well as the ribs.
|
|
|
|
Post by lefranglais on May 24, 2021 22:34:00 GMT
The question I am asking is how can you fix a soundboard that has been formed on a spherical dish onto a set of ribs that are flat? You don't. You sand the ribs in the spherical dish.
|
|
francis
C.O.G. 
Posts: 2,474 
My main instrument is: Whatever I'm building...
|
Post by francis on May 25, 2021 12:39:15 GMT
I do the same. I profile the ribs in/on? a spherical dish. i use 20 foot radius for my front profile and 15 foot radii for the back. I then use the front profile as a reference and when marking out the back profile I tilt the rib assembly above the dish to give me the correct heel / tail dims.  |
|
|
|
Post by jwills57 on May 25, 2021 23:54:09 GMT
Check out a book called GUITARMAKING: TRADITIONAL AND TECHNOLOGY by Cumpiano and Natelson. It's the bible for beginning and even experienced guitar makers. Might give you some insights.
|
|
scd
Sore Fingers
Posts: 9
|
Post by scd on May 26, 2021 14:18:31 GMT
I thought the top of the ribs were supposed to be flat - isn't this from the term 'flat top steel strung guitar' came from? Also the shape from the neck to the sound hole varies from approx 2.5deg to 1.3deg - a complex shape to fit the finger board to?
|
|
garynava
Luthier / Guitar Maker
Posts: 460
My main instrument is: Stanley No.5
|
Post by garynava on May 26, 2021 14:48:32 GMT
I take it that you're not Roger Williams the luthier?
Cheers Gary
|
|
scd
Sore Fingers
Posts: 9
|
Post by scd on May 27, 2021 9:26:02 GMT
|
|
ocarolan
Global Moderator
CURMUDGEONLY OLD GIT (leader - to join, just ask!)
Posts: 35,703
Mini-Profile Background: {"image":"","color":"c0cfe1"}
Mini-Profile Name Color: 182a3f
Mini-Profile Text Color: 733a1c
|
Post by ocarolan on May 27, 2021 10:29:09 GMT
scd ...if you copy the "hotlink for forums" directly into your compose post screen the diagrams will appear in your published post. Hope you don't mind me doing that! Keith
|
|
|
|
Post by lefranglais on May 27, 2021 20:59:20 GMT
Why do you think the tops of the ribs should be flat? A very small number of luthiers do make steel strung guitars with flat soundboards. In that case the tops of the ribs will be flat and perhaps that's where the 'flat-top' misnomer comes from. But most guitars are made with a dome, usually spherical but not always, to counteract the pull of the strings on the bridge trying to cave in the top between bridge and soundhole and to pull it up between bridge and tail block. Some, like the highly respected luthier Stephan Sobell make instruments where the top is straight from neck to tailblock but curved across its width. Howe Orme produced instruments in the late 1800's with a 'raised longitudinal belly ridge', flat at the outer edges rising to a marked longitudinal bulge in the middle. (Nigel Forster makes some like this). They also had, bizarrely, completely flat backs. In all these cases the ribs are shaped to match the curves of the soundboard. Does this help?
|
|
|
|
Post by andy3sheds on May 27, 2021 22:07:07 GMT
Here’s a pic (hopefully) of the Howe Orme that Nigel Forster brought along to the forum meet a few years ago I thought I’d got pics of the adjustable neck connection arrangement and of the end block I but I could only find this. What a fabulous guitar  |
|
scd
Sore Fingers
Posts: 9
|
Post by scd on May 28, 2021 20:23:24 GMT
Hello franglais and thank you for your comments. I am obviously not making myself clear about soundboard geometry. I have a Levin Goliath from 1963 which I think is typical of the 'flat top steel strung' guitars made commercially. The top of the ribs are flat and the soundboard is curved - I carefully measured it and it conforms to the diagram I put up a few days ago. The curve is for strength but also appearance because a flat soundboard appears concave and a convex one appears flat. I cannot understand how a sound board that is flat between the neck and the tail block can be curved across its width as you say? The centreline profile has to to be an extension of the neck angle and then curve away to the tail block with the high point being at the saddle. Making a soundboard as I illustrate on my recent post is not difficult just time consuming doing the drawings to get the profiles of the struts to produce the lateral curves that go through the longitudinal profile. However when done it produces a nice curved soundboard that fits perfectly onto the flat ribs. It is similar with the back but much easier as the struts follow the lateral curves you have decided on.
I am hoping to go to the meeting in Halifax where I hope to be able to discuss it with people like yourself with more experience than myself.
|
|
francis
C.O.G.
Posts: 2,474
My main instrument is: Whatever I'm building...
|
Post by francis on May 30, 2021 10:14:58 GMT
A soundboard that is straight from the neck block to the tail block and curved across width is part of a cylinder not a sphere.
|
|
Jo whoever he is.
