soundboard bracing

[jmuller92]

hey everyone, just a quick query

the books i have are a little sketchy on this topic, when curving the braces for the soundboard, can i use the same curve template for all of the braces that need to be curved? Or do they all have different offsets?

also, i guess its too late if i have done this wrong (as i have already glued finger braces and bridge patch), but i didn't curve the finger braces. Should I have? And are the lower face braces only curved at one end?

cheers

[Dennis Leahy]

I have no idea, but if you post a pic here, one or more of the builders that do know can help you with this.

I will say that there are a number of "tried-and-true" soundboard bracing patterns, as well as bracing profiles, and then there are also a bunch of builders that stray (a bit, or far) from those designs. I don't think you need to worry if you have done something a bit different from the "norm", as I believe that once you have met the functional/structural criteria to keep the box together, there are quite a variety of ways to successfully brace a top. Others may disagree with me strongly - especially if they have had some bracing experiments that yielded poor sounding instruments to their own ears.

Dennis

[Allen]

From your question, I'm guessing you are talking about the radius on the face of the brace that gets glued to the soundboard, that gives the sound board it's dome.

If this is the case, then if all you do is put the radius on the X-Braces, then you wont go wrong. The tone bars, and finger braces can have the radius on them, or not. Many builders do it one way or the other with good results.

One thing that will make things easier down the track with neck set, is to make sure that the Upper Transverse Brace, (the large one above the sound hole) is flat. In fact, if you are doing any bracing above the sound hole, it's a good idea to keep this area braced flat, unless you have a specific reason in mind not to.

[graham mcdonald]

Soundboard braces are usually shaped to a curve of around 25' radius, which is about 1/16" / 1.5-2mm arch over the length of an X brace. You want the gluing surface of the two X braces and the lower soundboard braces ( assuming you are using a Martin type bracing pattern) to be shaped to that radius. You should be fine with the bridge plate and the finger braces flat, and as Allen says keeping the upper transverse brace flat also helps with neck angle and getting the bridge to be the right height.

cheers

graham

[Mark McLean]

Hi Jake
Like Allen said the X-braces are the only ones to worry about radiusing. That is assuming that your top is going to be domed? Are you using a radiused dish to shape the soundboard?. If so you have a couple of ways to get the same curve onto your braces on the side that will glue down to the soundboard. Do it after cutting out the braces but before you glue the X-joint.

One way is to line your radiused dish with sandpaper (use double-sided sticky tape) and then rub your X-braces in this. Only the ends will be touching the paper in the beginning but as they wear down the centre will eventually get down to touch the paper. Once you are scraping wood off the entire length it is done. But this method takes a long time, uses lots of sandpaper, makes your wrists sore, and you breathe spruce dust. A faster method is to remove most of the material with a block plane, on a shooting board.

Did you use a shooting board to prepare the centre join of your top and back? If so, you know how to do this already. In that step you were trying to make a dead straight edge on each side. To plane a curve onto the bottom of your braces you put them on the shooting board and start planing the bottom of the brace (the side that will glue onto the soundboard), Start a few inches from one end and make a pass to the end of the brace. You have removed a shaving from the end few inches. Start the next pass a bit further towards the centre and run to the end. Keep doing this and by the 4th or 5th pass will be starting at the centre and running to the end (producing a shaving that is half the length of the brace. Turn it around and do the same for the other end. This way you remove more wood at the ends and very little in the middle and get very close to the final radius that you want. It only takes 10 minutes. Then finish it off in the radius dish like I said above. Some people do the pre-shaping on a bandsaw but I find I am more likely to stuff it up that way.

Another tip when cutting the brace wood is to keep the pieces for your X-brace joined together until the end. In other words cut out one piece which is a bit more than double width. Curve the bottom and rough-cut the scallops into the top (if you are using scallops) and then slice it longitudinally when you are finished, to get 2 identical pieces.
cheers
Mark

[jmuller92]

hey everyone, thankyou for the great response!

I do plan to slightly dome the soundboard, but dont have access to a radius dish nor the time, unless its totally necessary. My back and soundboard pieces were already joined by Tim so i dont have a shooting board either. Forgive me for my ignorance if so, but I planned purely to clamp the x braces to the soundboard (not secured to the bench) to hold the curve. Is this a bad idea?

Relieving to hear i haven't made a mistake with the other braces. I think i will purely curve the x braces, making a curve template and using the spindle sander.

One more question, about the head block. Does anyone cut the mortise in the headblock before attaching it to the sides? I was thinking it might be easier and less chance of error compared to routing?

Thanks

[J.F. Custom]

I do plan to slightly dome the soundboard, but dont have access to a radius dish nor the time, unless its totally necessary. My back and soundboard pieces were already joined by Tim so i dont have a shooting board either. Forgive me for my ignorance if so, but I planned purely to clamp the x braces to the soundboard (not secured to the bench) to hold the curve. Is this a bad idea?

One more question, about the head block. Does anyone cut the mortise in the headblock before attaching it to the sides? I was thinking it might be easier and less chance of error compared to routing?

Thanks

Hey Jake,

Clamping will work though care needs to be taken to apply an even pressure along each brace and avoid the brace moving out of alignment with each clamps pressure. You also want to be very careful not to bruise/dent your spruce as it can be damaged very easily. However, your assertion about the lack of time, if I understand you, is not correct. Go decks with radius dishes for glueing bracing is surprisingly fast and easy. In my opinion, much faster and easier than any other clamping method for bracing. Worth considering the time involved in making one long term.

With respect to your second question, I'm not sure I follow you. How did you intend to cut the mortise with or without sides on if not with a router? Routers do make quick and accurate work of the job, but having said that, can also make a quick and easy mess of it if you're not prepared! I'm not personally aware of anyone using this method though I'm sure they exist. Your sides would still need trimming down to the mortise line post glueing should you go this method however, which would seem to double your efforts so possibly not as efficient. Plus you'd need to clean up any glue squeeze out in the pre-cut mortise. With both of these considerations, the result may not be as 'clean cut' and fitting. I'm sure others will express different opinions - there are many ways to... I'd say "skin the cat" but being a vegetarian and lover of animals, I'll say... "peel the potato" Guess it doesn't have the same oopmh, but you get the gist

Cheers,

Jeremy.

[Dennis Leahy]

...I planned purely to clamp the x braces to the soundboard (not secured to the bench) to hold the curve. Is this a bad idea?

I think i will purely curve the x braces, making a curve template and using the spindle sander.

One more question, about the head block. Does anyone cut the mortise in the headblock before attaching it to the sides?

Thanks

Hi Jake,

I misread your first post, and went off on tangents...

I planned purely to clamp the x braces to the soundboard (not secured to the bench) to hold the curve. Is this a bad idea?
I know builders that "fake" having a radius dish by shimming up the perimeter of the soundboard prior to clamping. Some use a small wood wedge under each brace and clamp over that. Others cut a piece of 1/8" (3mm) sheet cork to the same shape as the finished soundboard, and then remove all of the cork interior leaving a 1/2" (12mm) gasket/strip the shape of the guitar. To keep it where you want it, it can be glued to a very thin sheet of stiff plastic, or light-duty cardboard (like a cereal box is made from.)

I think i will purely curve the x braces, making a curve template and using the spindle sander.
I think that will work perfectly. The width of a brace is so narrow (especially the soundboard braces) that the gluing surface / footprint of a cylindrically curved brace is probably within a couple of thousandths of being exactly the same as a radially curved brace.

May I recommend that you create just one single curved template/jig (radiused sanding block) at the correct curve for the top (typically either a 25 foot radius or 28 foot radius), and make one single curved template/jig at the correct curve for the back (typically either a 15 foot radius or 16 foot radius.) Then, cover the concave face of that with sandpaper glued on. Now you have a single sanding jig for each radius, so the braces will all have a consistent radius. You can also use those as marking tools, by tracing the shape onto your rough brace wood. Then cut them close to the line on a bandsaw, and finally shape the exact radius using you new handy-dandy radiused sanding blocks.

One more question, about the head block. Does anyone cut the mortise in the headblock before attaching it to the sides?
Yes, that's how I was shown to do it. You have to be fussy about the alignment during glue-up, so that the neck points to the center of the guitar. Then, once you have glued the rims (sides) on to the blocks (covering up the mortise hole), drill a hole through the rims into the mortise, large enough to get a router bit with a bearing at the tip, and simply run the router around the pocket, re-opening the mortise. Finish the corners with a file.

You can also create the neck block and its mortise by stacking pieces of wood and gluing, leaving a gap to form the mortise. After it is dry, then make a small piece to fill-in the bottom of the mortise where it will meet the back.

Dennis

[Allen]

Jake, I cut the mortise on my head block with a dado blade on my table saw, before gluing the sides. In fact I cut the top and bottom angles on the head block as well. The dado goes all the way through. Not stopped like you can do with a router. You can glue in a small piece to make a stopped taper afterwards if you like,

You need to be fastidious about alignment doing it this way. My body mold os attached to a work board that has the center line marked. I also mark the center of both the neck at tail blocks so it's easy to see where they line up.

The work board is flat, as is the top edge of my sides at this point Top edge goes down and touches the work board evenly all around. Spreaders go in to keep sides snug and square to mold. Then neck and tail blocks can be aligned and glued in.

The top edge of the neck block has a 1.5 degree taper cut on it for my guitars. Others builders may vary, but most are in the 1.5 - 2.5 degree range. The bottom of the neck block has a much greater taper on it. Depends on the style of instrument, and the difference between body depth at neck at tail.

Because I pre-shape my sides, the bottom of the neck block will align with the sides as you are looking down on them. The taper with the longer side will be to the inside of the guitar. Viewed from the side, the taper is almost perfectly shaped to accept the back when it's ready. Just a light touch up in the radius dish. I chalk the edge of the sides and blocks so its easy to see when everything has been sanded. I then place the radius dish over the sides that are still in the mold and on the work board. Then move the radius dish in a back and forth circular rotation to true them up. Check progress regularly, as it doesn't take much to get everything just right doing it like this. Then i glue in linings on the back.

I then remove sides from mold and flip over so back is down, then fit them back in, but this time I need a spacer block that is placed between work board and bottom of neck block that acts as a shim to help keep the neck block square. Size vary depending on your design. A final check at this point is that the sides should be protruding evenly all away around your body mold.

For the top, there will be approximately 1.5 to 2 mm bit of side material that needs to be removed starting at the upper bout to meet up with the taper that has been cut on the neck block. I use a plane to get close, then the rest is done in the same manner with the top radius dish, that has had 80 grit sandpaper glued to it. I use a 25' radius on my tops.

I do all this, because I find it far faster and accurate to build like this, with far less sanding dust to breath.