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I'm on my first build ( OM ) and mostly using Cumpiano's book and two sets of plans - Michael Payne's OLF OM, and Kinkead's - for guidance. My body shape is almost exactly the same as the OLF OM.

I'm about to notch the X-braces, and I'm not sure what angle they should be at.

The OLF OM plans show 90 degrees between the X braces, and Kinkead's shows 98 degrees. Also, the OLF plans show the X-crossing center to be about 2.5 inches from the saddle, and Kinkead's shows that space to be about 1.5 inches.

To complicate things more, I laid out the key dimensions for this guitar using Cumpiano's method ( with 25.34 inch scale, and the 21st fret being just above the soundhole edge) and I ended up with the soundhole ( already cut, with rosette installed ) at the same location as Kinkead's, but about 3/4 inch south of the OLF OM.

So, any suggestions?? What X - angle do people use for OM's, and how far from the saddle should I place the X-brace crossing? If I use the OLF bracing plan, I would end up with almost no space between the X braces and the soundhole, so, I guess that partially answers my question.


I'm using an engelmann top, at 0.115 ( 0.105 at the lower edges) and I plan to use non-scalloped bracing ( also engelmann) with the X braces - at the crossing - having a width of 0.31 and height of 0.5. I figured since the engelmann is a bit less dense and less stiff than sitka , the 0.31 width ( instead of 0.25) would make up for that.


By the way, I met several of you OLF-ers at Bob's place in Fort Erie in 2006. I was exited about building and had great intentions then, but other priorities kept showing up. Finally, I've gotten started.

Thanks for any help

Phil

You're confused because you're looking at plans that contradict one another. You could potentially get in trouble if you try to come up with a hybrid thing. Pick one thing you like and copy it. I like early 30's Martin's with the "X" 1 inch from the soundhole, and a 100-degree angle. So that's what I've been doing.

_________________
"...you have to get over your strict adherence to your largely imagined notion of absolute perfection..."

I just cut the cross braces for an OLF OM several days ago and they weren't 90 degrees. I'm thinking it was more like 88.5 degrees? Not to offend but you're not looking at the back X angle are you?

_________________
Steve Smith
"Music is what feelings sound like"

Since you're not following one plan what I would do in your situation is.

Mark where the saddle needs to be given your scale length, including compensation.

Then mark your bridge footprintl given the saddle position.

Also mark where the upper traverse brace will be since you already have a sound hole.

Now you can see how much room you have to play with the angle of the x. You want the legs to fall under the bridge outline (and not bump into bridge pins) and not bump into the upper traverse brace.

With all that taken care of you can't go too far wrong. If you could meet the conditions I outlined and still take Martin's advice with the X 1" from the sound hole, then that's what I would do but there are other possibilities too.

John

Hi, Steve

No - the back X angle on the drawing I have is 70/110 degrees ( and labeled with the angle). The top X-brace angle is not labeled, but it's drawn at exactly 90 degrees.

My set of drawings is at least 4 years old, so it's possible there is a revised set out now that's different. Mine is labled " OM 14 fret 25.4 " scale with X-brace back optional" by Michael Payne. There is no date that I can find, and it's a set of three sheets.

Thanks

Phil

From my course notes with David Freeman, where we didn't build to a plan, but focussed on principles:
1. "Usual" X-brace angle 100-110° between lower legs (can vary a LOT!)
2. Wider angle = increased stiffness across top, less angle = looser
3. X-brace joint minimum of 44 mm in front of saddle
4. X-brace MUST intersect wings of the bridge
5. Less intersection with bridge = looser, more bass
6. More intersection = stiffer, faster attack, increased treble and sustain

Make your own choice based on what you're trying to achieve.

Hey Phil,

Same set of drawings except mine are probably only 2 years old and I got them through StewMac so possibly they were updated. I did not measure from the drawings, mine had the angle noted on the drawing but they're rolled up and down in the shop. Maybe Michael will show up, he is the definitive source.

_________________
Steve Smith
"Music is what feelings sound like"

If you want to pattern this after CF Martin X bracing here is what you need to know. The strength of the X brace is in the layout and how the X braces capture the bridge.
In bracing 101 ala Martin here is how to plot the main X. Verify the scale length and make a mark to the actual scale length. From that point draw a 1 by 6 rectangle so the width is across the top. 1 1/4 inch below the sound hole mark a point. From the lower corner of your box draw a line so the 2 sides of the X brace intersect at this point. This is the leading edge for the brace. The first finger brace is set to catch the front rectangle.
The bridge plate will start about 1/8 in front of the bridge and the first tone bar will locate against the end of the plate. ( 1 3/8 widp plate ) and the lower tone bar about 1 1/2 below the first.

_________________
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

Phil,I was going to post a closeup of the X-brace from my plans but the copyright notice says no. I did verify the angle and it is 87 degrees so it appears I have an updated set. I can also say that my set works with the OLF OM template. I have no doubt that what John advised will work just fine.

_________________
Steve Smith
"Music is what feelings sound like"

Thanks to everyone for all your suggestions on this.

Using your ideas ,and based on my top so far (soundhole and saddle location) I laid out a bracing plan that ended up looking a lot like Kinkead's, with a 98 degree angle between the lower X-brace sections.

I think I figured out why the OLF OM brace plan is so different from Kindkead's ( and Cumpiano's) and the source of my confusion :
The old OLF OM plans that I have (at least 4 years old, but there is no date on the drawings) have the soundhole top edge at the (imaginary) 20th fret, and for my design, I used Cumpiano's guidelines that locate the soundhole edge at the 21st fret (like Kinkead's and most other OM's I've seen, now that I know to look for that).

It looks like the current OLF OM plans have the soundhole in the more common 21 fret location - although the X-brace angle is now even more different from typical, with the angle between the lower X-brace sections being about 87 degrees between the lower X-brace sections ( so, the X is taller than it is wide).


In any case, I now have a plan and I'm cutting and radiussing the braces to fit that plan. I'll post some pictures when I can show the braced top.

Thanks, everyone

Phil

For John Hall,

'box' meaning the guitar itself?

Thanks,
Hugh

<LOL> 2 people say they are following my plans (ie. the OLF OM) and neither got the angle right and it is clearly dimensioned on the plans. the angele is 87 degrees the tolerance is +/- 1 degree (not a biggie). This is designed for a 25.4 scale neck with the sound hole as shown on the plans If you use a differnt scale or angle or sound hole position while following my plans; you will need to adjust the shape of the brridge plate to accodate your X-brace angle and location also the tone bar and finger brace location dimensions will not work out exactly the same if you change the X-brace angle and location. come to think about the cound hole reinforcement bracing will have minor changes as well.

If you are not fairly well experianced in how and why it is better to follow a single plan. If you like something about one plan and something about another and want to incorperate the two. Draw it up!!!! layout the change complete!!! See what affect the dimensional change of the components willl have. you can't make a dimensional change bind and expect all components to fit properly. this is why god gave us pencils

Nope Phil, you are far off on your assuption. That is coinsidental but not the reason at all. The original OLF OM plan was braced based off a tracing of a Martin that came in to my shop many years ago. The later versions of the OLF-OM plans were just minor tweeks.

I am glad to see that you fell you know what I am thinking and why I did what I did. That sure make it easy for me. Now i can dramticly reduce the amount of posting I need to make to explain why I do things the way I do.

My first was from memory, as I said. I went back and checked the plans, as I said, and 87 degrees it is.

_________________
Steve Smith
"Music is what feelings sound like"

here is a little more insight into how I came up with the 87 dgrees on the OLF-OM (Stewmac distributed) plans As Phil noted the very first set of the OLF-OM plans were 90 degrees with the center of the X 8" form the neck joint. As I continued to build the OM I refined the X so that the plane of the X was tangent to the sound hole at 1/4" offset. that put the sound hole intersection of the X 1 7/16" from the lower quadrant of the sound hole. This gave better support to the area of the cound hole with out having to use a thickness doubler. this also captured a larger crosssection of the bridge wings wich ment higher energy transfer into the X-brace without overly loosing the top structure.

One thing to understand is that my bracing was developed over time to what works for me. No to designer/builders will develop bracing exacly the same. There are governing principles to follow as explained earlier. I thinner bracing that Cumpaino or Kinkead, I use differnt locations for my fingers and tonebars. That is the beauty of doing your own designs adn proto-typing them. you get find what works for you.

I will not discourage you form using features of more than one plan set to build by but if you do you need to lay it out becasue many components are dependent on the Xbrace and other components.

Hi, Michael

Thanks for the clarification on this. I apologize if I was out of line. I was just trying to settle my own confusion and understand why this particular design was different from the other two I had been studying. I guess I was still confused. Now I have a clearer idea of what's going on and feel more confidant moving ahead with my own ( first) guitar.

Thanks again

Phil