Official Luthiers Forum!

Hi all.

I'm planning a pre-war Martin style dreadnought build. My understanding is that the X brace is moved forward an inch with pre-war, advanced, forward-shifted, whatever you might call it, bracing. Is this correct? Are the lower-face braces shifted forward as well? Finger braces?

When I was researching dreadnought bracing patterns several years ago I ran across this diagram of forward-shifted bracing on StewMac's website.



https://www.stewmac.com/video-and-ideas/online-resources/learn-about-building-instruments-and-kits/banjo-killer-the-scoop-on-forward-x-bracing-for-greater-guitar-volume/

_________________
Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Mine must be a hybrid because it is forward shifted (aka - not rear shifted ) but I kept the X angle at 98.

_________________
Insta - https://www.instagram.com/cbcguitars/
Facebook - https://www.facebook.com/cbcguitars

It's not an inch I don't think but who would know is John Hall if you ping him.

This discussion applies to 14 fret-to-body dreadnaughts only. 1" up to 1939, then 1-7/8" (sometimes erroneously noted as 1-3/4") through 1960 when Martin moved the bracing forward to 1-1/2" (again, sometimes erroneously noted as being concurrent with introduction of the HD-28).

There are a number of models being produced at present with varying X-brace setback distances... fully forward shift gives the bassiest response, tapered at 1-7/8" the best balance for mahogany guitars (but don't expect the huge, loose bass of the pre-1939 instruments), and 1-1/2" enough mitigation of the deep mid-range response scoop of some Golden Era guitars to represent a decent compromise. I've personally measured perhaps 30 or so of these 30's and 40's instruments, and within the last few years enough 50's to verify those numbers within the usual production variability and historical measurement error by repair people in a hurry and working with the 4R grad shop rules of the day. Also keep in mind that Martin often moves things around on supposed historical replicas based on a variety of reasons (e.g., a single measured example with significant deviation from mean, reproducibility, or warranty considerations).

Of all the various configurations, the late 1940's taper-braced mahogany guitars are my favorite for power, balance, and broad utility. Mr. Stock wholeheartedly agrees with me, while Mr. Filippo vehemently disagrees with added comments on my obvious lack of taste and faulty auditory equipment. I personally find his taste in dress footwear highly suspect, but that is the nature of preferences.

There are a number of discussions on the topic over at UMGF, and review of those threads may prove beneficial if only to gain some understanding of the nuances of related changes to X brace and tone bar angles.

_________________
For the times they are a changin'

- Bob Dylan

Haha, fantastic. Thanks, Woodie. I literally laughed out loud there with the shoes.

I'll definitely spend some time searching through the UMGF. In your experience, do the tone bars move relative to the position of the X as well, or are they fairly stationary?

Wow. One little search and I feel like I'm listening to people order their cappuccino's. I didn't realize there are so many variables.

Using the back of the sound hole as a measuring reference is usually fine, if you are working on a Martin, with a 25.4" scale length. Martin has been pretty consistent in placing the sound hole the same distance from the front edge of the guitar. On other brands or guitars you are building, the more reliable way is measuring from the 12th fret to the front of the X brace intersection. Of course, this means that you must determine how far the 12th fret is from the front edge of the guitar, since the neck is not on the guitar at this stage. This will take into account a different scale length as well as compensating for an ill-placed sound hole. Using the 12th fret as the anchor spot, and keeping the same X-angle will also make the legs of the X cross under the ends of the bridge at the proper location. If you change the angle of the X, you might need to move the X brace forward or backward enough to keep the legs going under the bridge at the proper location.
I've never seen Mr. Filippo's shoes, but I trust Woodie's opinion.

One of the reasons why the forward shift discussion is really limited to the 14 fret-to-body instruments is that the smaller bodied 14 fret guitars (O-OOO) are by definition forward-shifted compared to the D (or simply umolested re bracing versus the dreadnaughts), and that the company's production from the late 1930's onward to 1960 was largely dominated by that post-1939 configuration of 14 fret D. As seen in the illustration from the SM website, shifting the X intersection aft with regard to the edge of the soundhole requires a closure of the X angle (all angles measure relative to the longitudinal centerline) to properly support the bridge, and similar adjustment for the tone bar angles to provide the resistance to belly and unconstrained top movement that seems to have dominated Martin's thinking on brace system design. Also note the changes in neck block thickness and the upper transverse graft (aka, Popsicle brace) are meaningful, and reflect Martin's desire to minimize their warranty footprint as were all significant changes up to roughly the introduction of the vintage-styled instruments in the mid-1970s.

I don't know of any currently available guitar plan set which represents a definitively measured drawing of a Martin pre-1939 14 fretter, but we had some templates in the shop that were based on Mr. Hall's measurements and sketch, as well as one based on the UMGF's series of 'shadowgraphic' brace photos ported into a graphics program that corrected parallax, etc. Those were replaced with body shape and bracing templates from measurement of actual instruments that the boys saw as exceptional in one way or another.

One thing to note is that Martin production through the early 1980's was still dominated by hand processes and close - but not slavish - adherence to templates and molds that saw significant wear and tear in use. Today's largely automated processes have added a level of consistency to Martin's products that remove any room for the sort of discussions we see on UMGF re: minor variations. I suspect that - provided the general adjustments shown in the SM illustration are made to a fairly accurate modern Martin template - there would be a reasonable chance that a Martin prototype for that interpretation might very well exist from 1934-1939 production.

Good luck with your project, Mr. Orr. If you move on to Golden Era 12 fret-to-neck dreadnaughts, I believe that the fellows did a fairly decent job of measuring the museum's D-42 for their reproductions, and I would be happy to look for that drawing set and template the next time I am over that way. Alternatively, a note to Mr. Stock might get you a response, but don't expect a quick one... he is in welding nirvana for the next few weeks building out the steel tube body of his homebuilt airplane with a fellow builder.

_________________
For the times they are a changin'

- Bob Dylan

Martin 14 fret 0 and 00 braces were shifted rearward in 1935. The 14 fret 000's were shifted in late 1938, probably the same time as the 14 fret dreadnoughts. The Martin guitars that were always forward braced are the 12 fret versions.
I have an accurate drawing of my 1937 D-28 on PDF that I can send.

Sent from my SM-G950U1 using Tapatalk

_________________
John

John, I would be grateful to get the PDF as well.

Brad

_________________
Insta - https://www.instagram.com/cbcguitars/
Facebook - https://www.facebook.com/cbcguitars

Send me a PM with your email address.
BTW, I prefer the term forward braced, rather than forward shifted. Forward bracing is the original design. It is the rear bracing that was shifted.



The X angle was reduced from around 98 degrees to 94 degrees when the braces shifted rearward. Reducing the X brace angle (spread) places the X braces closer together at the bridge. That does tend to reduce belly since it markedly increases stiffness around the bridge. But if anything, I would want to INCREASE the angle when rear shifting, so that the braces are under the wings of the bridge, rather than under the thicker part.
The original designs had one characteristic that I like to stick with. The X braces intersect the lower corners on the bridge.
As a veteran repairman of vintage Martins, one recurring flaw I see with rear braced Martins is the frequency of loose X braces under the bridge. It is usually accompanied by a pronounced belly below the bridge. This is so common that it is one of the first things I check when doing an inspection. Having the braces under the thicker part of the bridge increases the stress on these joints. It is especially prevalent on those guitars with unscalloped straight or tapered bracing, since those braces are much stiffer in the bridge area.
Forward braced Martins and their clones rarely see this issue. The typical belly on those guitars tends to be a wider dome, with little or no crease at each end of the bridge.

_________________
John

It was said that sound hole remained in the same spot. I built this from 1937 plan. I notice the pick guard has a large gap between the bridge and back edge of the guard. It's been kind of bugging me and making me think i did something wrong. I bought the guard pre-shaped from SM.


Sent from my SM-A546V using Tapatalk

_________________
Hutch

Get the heck off the couch and go build a guitar!!!!

interesting discussion Mr Arnold makes some very good points. We have been doing this a long time , and there is a lot of misinformation or misunderstood information.
As John points out , this was all hand done. Martin used a lot of jigs and fixtures and they didn't actually have any blue prints until the 1970's when Dick Boak joined the company. I made my tracings off of 5 known guitars , 1 that Wayne henderson owns , 2 at the Martin factory and 2 of David Musselwhites.
when comparing these , the dates ranged for 1937 to 1935 and for the most part they line up within a reasonable amount. A wide pencil line more or less. The angles varied slightly and that I attribute to the actual gluing process itself. And I am talking less that a 1/2 a degree. I have a PDF of Mr Arnolds, and Wayne Henderson send me a template and they too are well within the same lines. So know where you are getting your information and have at it. One thing is the actuall shape of the braces , also being hand carved there are slight changes in the curves and points at the end scallops , Most on the scallops I see them to drop to about 5/16 in off the top. I am sure John A will be able to add a lot more info.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it