The Acoustic Guitar Forum

Go Back   The Acoustic Guitar Forum > General Acoustic Guitar and Amplification Discussion > Build and Repair

Reply
 
Thread Tools
  #31  
Old 09-25-2013, 12:21 PM
Rodger Knox's Avatar
Rodger Knox Rodger Knox is offline
Charter Member
 
Join Date: Jul 2013
Location: Baltimore, Md.
Posts: 2,406
Default

There's at least two schools of thought here. The first is the brace is flat and the top is forced into a curve by gluing the braces with a curved caul. Since there is some springback in this method, the radius of the curved caul is less than the desired arch on the top. There is also residual stress induced in the brace/top from two flat pieces forced into a curve and glued, and all of that residual stress acts on the glue line. The advantage is that the braces are "pre-stressed" against the string loading of the top.

The other method has the brace curved to match the desired radius, and a matching curved caul (or radius dish) is used to force the top into a curve for gluing. This method results in less residual stress, and is easier to get consistent geometry for the top dome.
__________________
Rodger Knox, PE
'56 Gibson J-50
et al
Reply With Quote
  #32  
Old 09-25-2013, 02:06 PM
charles Tauber charles Tauber is offline
Registered User
 
Join Date: Feb 2011
Posts: 6,533
Default

Quote:
Originally Posted by Rex Tremende View Post
Wow, all good questions. I don't have all the answers. I'm sure you're correct about this design from the 1920's not using a dish. I believe the gluing surfaces of the braces were intended to be straight. and forced into shape under pressure. I'm still researching it and haven't found much on it yet.
Assuming that your purchased drawings are correct - a BIG assumption - the drawing shows a longitudinal curvature that is NOT spherical.

What are the basic body dimensions for this guitar? (I can't read them on the photo.) Six back braces on a small guitar is over-kill.

Unless you have one to measure, I think you are best advised to decide what method of construction you want to use to make the guitar and use the plans as a guideline. For example, if you decided to go with a spherical arch on top and back, a dish would be the way to go, even though that isn't how the originals were made.
Reply With Quote
  #33  
Old 09-25-2013, 02:38 PM
Steven Bollman Steven Bollman is offline
Registered User
 
Join Date: Mar 2009
Location: SF Bay area
Posts: 596
Default

Quote:
Originally Posted by charles Tauber View Post
Assuming that your purchased drawings are correct - a BIG assumption - the drawing shows a longitudinal curvature that is NOT spherical.

What are the basic body dimensions for this guitar? (I can't read them on the photo.) Six back braces on a small guitar is over-kill.

Unless you have one to measure, I think you are best advised to decide what method of construction you want to use to make the guitar and use the plans as a guideline. For example, if you decided to go with a spherical arch on top and back, a dish would be the way to go, even though that isn't how the originals were made.
Thanks, Charles. I got the drawings from G.A.L. They were drawn up by January Williams. In issue #112 of American Lutherie magazine January Williams does a forensic-type assessment of an original Larson-Stahl Style #6 guitar. It is in that article that she says the top has a 12' radius and the back is a 10' radius. Since this is my first guitar (I know...don't say it...It's a big project...:-), and I've played a couple of original Style #6s and an amazing copy that Alan Perlman (SF) made taking all his dimensions off of an incredible one that Eric Schoenberg had him restore, I'm trying to stay as close to the plans as possible (at least from a structural point of view). I will take liberties with some of the aesthetics. The body length is 19 29/32" and the lower bout is 15".
__________________
Guitars: J-45 copy, Stahl Style 6 inspired copy
www.BollmanGuitars.com
Reply With Quote
  #34  
Old 09-25-2013, 04:11 PM
charles Tauber charles Tauber is offline
Registered User
 
Join Date: Feb 2011
Posts: 6,533
Default

Quote:
Originally Posted by Rex Tremende View Post
Since this is my first guitar (I know...don't say it...It's a big project...:-),
Ah, yes, I'd forgotten that.

Typically, a first guitar is for copying someone else's established method of construction, to learn the basics of the craft. Without those basics, it will be a challenge.

As an aside, unless the drawings are made from a 3D model of the object, liberties are often taken in the 2D representation of it, particularly with regards to curves at oblique angles. I can't tell from the photo if it is from a 3D model or not or how "real" is the depiction of complex curved surfaces. It is likely that the plan was created for those with "prior knowledge" of the craft who could fill in and extrapolate from what is shown.
Reply With Quote
  #35  
Old 09-25-2013, 04:34 PM
Rodger Knox's Avatar
Rodger Knox Rodger Knox is offline
Charter Member
 
Join Date: Jul 2013
Location: Baltimore, Md.
Posts: 2,406
Default

Another factor that's usually ignored on plans is that string tension tweaks everything. The neck bows, the top pulls up, and the bridge rotates forward. These are all very small changes, but they can make a difference, especially in the neck angle.
__________________
Rodger Knox, PE
'56 Gibson J-50
et al
Reply With Quote
  #36  
Old 09-26-2013, 01:21 AM
Steven Bollman Steven Bollman is offline
Registered User
 
Join Date: Mar 2009
Location: SF Bay area
Posts: 596
Default

Today I started to work on the neck.

Squaring up a big hunk of Mahogany for the neck. This block is actually big enough for two necks.





Smoothing the headstock with my Lie Nielsen low angle Jack plane. Glorious tool it is.



Some good looking quarter sawn grain.



More sawing with a Japanese Ryoba saw



Using the coping saw to get around the curve.

__________________
Guitars: J-45 copy, Stahl Style 6 inspired copy
www.BollmanGuitars.com
Reply With Quote
  #37  
Old 09-26-2013, 01:24 AM
Steven Bollman Steven Bollman is offline
Registered User
 
Join Date: Mar 2009
Location: SF Bay area
Posts: 596
Default

Quote:
Originally Posted by charles Tauber View Post
Ah, yes, I'd forgotten that.

Typically, a first guitar is for copying someone else's established method of construction, to learn the basics of the craft. Without those basics, it will be a challenge.

As an aside, unless the drawings are made from a 3D model of the object, liberties are often taken in the 2D representation of it, particularly with regards to curves at oblique angles. I can't tell from the photo if it is from a 3D model or not or how "real" is the depiction of complex curved surfaces. It is likely that the plan was created for those with "prior knowledge" of the craft who could fill in and extrapolate from what is shown.
Thanks Charles. The more I look at the more I think you're right.

Quote:
Originally Posted by Rodger Knox View Post
Another factor that's usually ignored on plans is that string tension tweaks everything. The neck bows, the top pulls up, and the bridge rotates forward. These are all very small changes, but they can make a difference, especially in the neck angle.
More good news! Seriously I really appreciate all of your insights and experience. Thank you.
__________________
Guitars: J-45 copy, Stahl Style 6 inspired copy
www.BollmanGuitars.com
Reply With Quote
  #38  
Old 09-26-2013, 10:25 AM
Sam VanLaningham Sam VanLaningham is offline
Registered User
 
Join Date: Nov 2012
Location: Bend, Oregon
Posts: 1,236
Default

Hey Rex - nice looking build. You are doing a nice job with the hand tools IMO! Anyways, I've been quite nervous about how to do the radiusing. I found a method for glueing radiused braces that seems really functional. Here's a link:

http://www.kennethmichaelguitars.com/contourtool.html

Have you seen this "3x5 cards" technique?

Good luck! Sam
Reply With Quote
  #39  
Old 09-26-2013, 11:50 AM
charles Tauber charles Tauber is offline
Registered User
 
Join Date: Feb 2011
Posts: 6,533
Default

Quote:
Originally Posted by Left of Sam View Post
Have you seen this "3x5 cards" technique?
I've used that method, and variations thereof, since 1978. It was one of several methods then taught by Charles Fox.

First, however, one needs to decide what geometry one is trying to achieve. Hence my previous questions. Once one knows that, then one can select a method of achieving it.
Reply With Quote
  #40  
Old 09-26-2013, 12:43 PM
Steven Bollman Steven Bollman is offline
Registered User
 
Join Date: Mar 2009
Location: SF Bay area
Posts: 596
Default

Quote:
Originally Posted by Left of Sam View Post
Hey Rex - nice looking build. You are doing a nice job with the hand tools IMO! Anyways, I've been quite nervous about how to do the radiusing. I found a method for glueing radiused braces that seems really functional. Here's a link:

http://www.kennethmichaelguitars.com/contourtool.html

Have you seen this "3x5 cards" technique?

Good luck! Sam
Quote:
Originally Posted by charles Tauber View Post
I've used that method, and variations thereof, since 1978. It was one of several methods then taught by Charles Fox.

First, however, one needs to decide what geometry one is trying to achieve. Hence my previous questions. Once one knows that, then one can select a method of achieving it.

Wow! Thanks Left of Sam and Charles!

This is exciting! It feels like it's right up my alley regarding budget and achieving correct radii.

A big question that I have which I don't think can really be answered without doing or experimenting is: After gluing up the braces (the X- brace is spruce/rosewood/spruce laminated) to the top, which is glued under tension how much spring back will occur. So if the design calls for a 12' radius on the top and a 10' radius on the bottom...Do I start with a 8-9' radius on the top and hope it springs back to 12'? Same situation for the bottom. I see the problems with following a design where measurements are taken off a finished guitar versus a design that is drawn up as the guitar is built.
__________________
Guitars: J-45 copy, Stahl Style 6 inspired copy
www.BollmanGuitars.com
Reply With Quote
  #41  
Old 09-26-2013, 04:17 PM
Rodger Knox's Avatar
Rodger Knox Rodger Knox is offline
Charter Member
 
Join Date: Jul 2013
Location: Baltimore, Md.
Posts: 2,406
Default

Quote:
Originally Posted by charles Tauber View Post
I've used that method, and variations thereof, since 1978. It was one of several methods then taught by Charles Fox.

First, however, one needs to decide what geometry one is trying to achieve. Hence my previous questions. Once one knows that, then one can select a method of achieving it.
+1 to that! Most of the techniques I'm familiar with use the construction process in one way or another to get the neck angle close enough so that only minor adjustments are necessary. Mixing techniques can screw this up, resulting in not so minor adjustments being required to get the neck angle correct.

What I mean by the correct neck angle is that the height of the strings above the top at the bridge is the design value AND the action at the 12th fret is also the design value. The tolerances to achieve this are very small, since the action is adjusted by changeing the height of the strings at the bridge.
__________________
Rodger Knox, PE
'56 Gibson J-50
et al
Reply With Quote
  #42  
Old 09-26-2013, 04:54 PM
vintageparlors vintageparlors is offline
Registered User
 
Join Date: Mar 2005
Location: Chester, Vermont
Posts: 1,524
Default

I see hard work by a talented man.
__________________
Steve C at www.vintageparlorguitars.com
Specializing in the repair, restoration and sale of vintage parlor and 12-fret acoustic guitars.
Reply With Quote
  #43  
Old 09-27-2013, 12:51 AM
Steven Bollman Steven Bollman is offline
Registered User
 
Join Date: Mar 2009
Location: SF Bay area
Posts: 596
Default

The height adjustment on my vise stand is unbeatable.



Finally cut the neck out of the hunk of mahogany.



I'm pretty happy with it so far.



Almost perfectly quarter sawn headstock.

__________________
Guitars: J-45 copy, Stahl Style 6 inspired copy
www.BollmanGuitars.com
Reply With Quote
  #44  
Old 09-28-2013, 02:09 AM
Steven Bollman Steven Bollman is offline
Registered User
 
Join Date: Mar 2009
Location: SF Bay area
Posts: 596
Default

Splitting the billet to make the brace wood.



I think this is pretty good. Pretty straight grain.



Woodworking tools can bite!



This brace is rejected. The grain is too wavy.

__________________
Guitars: J-45 copy, Stahl Style 6 inspired copy
www.BollmanGuitars.com
Reply With Quote
  #45  
Old 09-28-2013, 02:33 PM
Howard Klepper Howard Klepper is offline
Registered User
 
Join Date: May 2008
Location: Earthly Paradise of Northern California
Posts: 6,427
Default

Steve, from what I can see you have the wrong idea about splitting braces. The idea is not to detect wavy grain. It is to minimize runout. Toward that end, you split on a radius of the tree, just as you would do splitting firewood. You appear to be splitting on a tangent to the tree. The wavy look on the side just indicates that the grain in your split piece isn't vertical or perfectly straight; but that is something you can tell just by looking at it, unlike runout which is hard to detect. Once you know that you have minimal runout, you can just tilt the billet or the saw blade to get a vertical grain cut.

Your billet being wedge shaped indicates that it was sawn starting with a split and likely has little runout so long as the sawyer didn't make too many cuts before splitting again.

Hope this is making sense.
__________________
"Still a man hears what he wants to hear, and disregards the rest."
--Paul Simon
Reply With Quote
Reply

  The Acoustic Guitar Forum > General Acoustic Guitar and Amplification Discussion > Build and Repair

Thread Tools



All times are GMT -6. The time now is 10:15 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Copyright ©2000 - 2018, The Acoustic Guitar Forum
vB Ad Management by =RedTyger=