Official Luthiers Forum!

Its been a good couple of weeks for me since we are snowed in and I have gotten quite a bit done on my LMI Parlor (custom).

I have the neck almost done, the back bracing installed at carved to shape and I have all the bracing for the top radiused and ready to glue in but I have a question about the X bracing placement.

I ordered the kit but changed things up from the stock kit in that I ordered a 24.9 scale neck with 14 fret to the body. The stock parlor kit has a 12 fret to the body neck and the plans are for the stock 12 fret.

The plans show 1.75 in to the center of the X (where the 2 braces intersect.

Since I am building it with a 14 fret to the body neck with a 24.9 scale (not the 24.5) I know the bridge plate and bridge will need to be moved from where the plans show it.

Do I need to move the X bracing to reflect the difference or can I just move the bridge plate? If just moving the bridge plate down it will need to be wider to tie into the X bracing.

Since I don't have much experience with building I am not sure how shifting the X-brace and the Bridge plate down would effect the movement of the soundboard.

Opinions?

Thanks
Bob

braces are placed by the scale length. so think of it this way.
you draw the body shape and pay the fretboard with the fret on the rim at the neck. You now know where the nut is. Once you know that you will know where the saddle belongs and adjust the braces accordingly

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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

The way I like to do it is to lay out where the bridge will be located according to your scale length on the inside of the sound board. Then trace around the bridge. Now, after you have determined the angle of the X brace and have it assembled dry, move the position of the X to cross inside the corners of the bridge that you have drawn. Obviously, you can cover more or less of the bridge corners, this is where some experience comes in. To get an idea, draw the bridge on as per the plans and see where the X crosses the corners of the bridge.

Chuck

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The 14 fret neck will move the bridge about an inch towards the top, and the longer scale length will move the bridge about 1/2 inch towards the bottom. The net effect will be to shift the bridge about 1/2 inch towards the upper end of the body.You can draw things out on the underside of the soundboard and see where the ends of the bridge cross the X braces. You can then decide to keep things as is, or shift the bracing and bridge plate up (not down) an 1/2 inch.

OK, Here is what I have at the moment. I traced the layout from the blueprint on the back of my soundboard. The top of the blue tape is where the print says to put the front of the bridge. The line just above it is where the new bridge placement is suppose to go. How I determined that line was to use my fretboard (24.9 scale) with the 14th fret at the top of the body. I then used my Saddlematic to calculate where the new bridge should be placed. That comes out to 1 1/8th" higher (toward the nut) than the original placement.

If I shift the X braces up they end up right at the sound hole (and even a bit overlapping).

I know this is critical to the geometry of the top, the bridge must move to account for the different scale length and the difference between the 12 fret or 14 fret but it doesn't seem right that the braces overlap the sound hole.

I understand the concept but I am not confident I am doing this correctly.

Here is a shot that will help explain.

BTW, @John, Nice radius dish... it works a treat!

Figure out where the outline of the bridge will be, and draw that on your soundboard. The X brace arms should go through the bottom corners of the bridge outline.

The original plans have the X brace placed so far forward, you'll probably be able to just leave it where it is.

On a different topic, I think you should add some soundhole braces. No point in having a weak spot there.

Here's how i did mine with 24.9 scale and 12 frets. I actually shifted it back, and as you can see, it's still ended up with bracing 'shifted' forward of standard. You definitely do not want the X braces going through the sound hole!!! In my drawing, you can see the top edge of the bridge corners going through the X where the bottom edges should go. So, assuming you move it up ~ one inch, the X could really stay just where it is. At most you could just widen the angle slightly and call it a day, or move it forward 1/4" or so. It will be obvious with the bridge outline drawn on.

BTW 1 1/8" doesn't sound right. I'd recheck your math. By my calculation, it should end up about (edit) 1.15" different for that scale and 14 frets.

You'll want to move that tone bar up a bit too.

I got 1 1/8". Or more precisely, 1.158". First extend the scale length, which pushes the bridge down by .2". Then move up by the difference between 12th and 14th fret on the 24.9" scale.

Yeah, you're right. Never respond before coffee... But I'd call that 1 5/32"

Much appreciated guys

How I determined the placement was to lay my fretboard out, used my Saddle Matic and set it from the nut to the 12th fret, swapped it over and marked where the front of the bridge should be. I have used the Saddle Matic a number of times so I am confident the placement is correct.

DennisK, I used my digital caliper and you are correct it is 1.158 to the mark.

So am I assuming correctly that all I need to do is make sure the X braces are under the bridge just slightly? I know the bridge plate takes up most of the tension and the bridge plate extends out further than the bridge so I should be good to go.

One thing I am not quite sure of is by switching over to the 24.9 scale and the 14 fret to the body it moves the bridge and bracing forward. With the bridge sitting farther forward what effect does that have on the tone? In my thinking it seems it will produce less bass and more mids since the bridge is no longer in the center of the lower bout.

Is that something to consider or do I just have to build it and see what I get? I know tone woods have a lot to do with it so FWIW, I am using Spruce for the top, EIR sides and back, Ebony Fretboard and Bridge and Oh yes, Spruce bracing.

And one other question:

What thickness should the soundboard be for a small Parlor like this? It is currently 0.120 which seems a little thick. I know to thin the edges a bit to give the top some movement but I am not sure about the overall thickness.

Sorry for the newbe questions but I am the kind of person that wants to be sure what I am doing before I commit.

Thanks again guys,
Bob

keep in mind that the x brace doesn't necessarily have to be 90 degrees. you can close up that angle, move the brace towards the hole, and still meet your bridge wings. also, i don't know how wide your bridge is but i've seen up to 6 inches wide on a size 2.

in general smaller bodied guitars can go with thinner tops -depending upon species of wood, stiffness, etc... that is. strictly for me, using spruce, my comfort zone would be in the .090 to .093 range.

Pretty much. It's hard to describe with words. See below for a detail sketch of 'typical' intersection of the bottom rear corners of the bridge and the X brace (circled). Moving it forward of this a little isn't a bad idea for a small guitar like this IMO. Opening the X angle slightly will do sort of the same thing. If it were my project, I'd open the X a bit, move the tone bar up a little, and leave everything else as is.

IMPORTANT TO NOTE: The Antes Parlor plans are not typical X bracing, and have the X in an extremely forward position, to the point most would consider it wrong. Perhaps they were originally designed for 14 frets. As I mentioned, you may not need to do much if any repositioning.

More than just slightly, I just finished up a 13 fret Gibson Nick Lucas and adjusted my bracing from a 14 fret tracing. it changed the angle and shifted the X forward just slightly. Like others have said establish your bridge location and adjust your bracing from there.