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OK, so this time going to parallel integrated bracing as compared to integrated X....
I am carving the top thinner than what it would have been with X-bracing...about 3/16 under the bridge, tapering to 5/32 and then down to 1/8 as you reach the edge...

It should still be stiff enough, but I think it will probably be a more powerful guitar that will project well...(the proof will be in the pudding off course....). Idea is that the parallel braces are a bit stiffer because of the direction of the grain, allowing me to carve the top thinner, and hence let it "pump more air"...

I had to modify my model accordingly, but since I can simply change my parameters in SW, that was not too difficult to do....

We shall see.....

Here it is after the initial cut on the CNC...Braces were left well over sized for final carving by hand and tap tuning....as you can see, not much sanding or work by hand to be completed....

curious as to your thoughts?

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My thoughts? That is pretty dang cool.

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PMoMC

Interesting thought....can you define run out better?

If they are just as strong, keep the top from sagging over time, BUT at the same time produce a louder, and more responsive instrument.....why not?

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Chris is right. Maybe you can layer on top some CF to strengthen the integrated brace, but then again doing manual labor in CNC luthiery may defeat the purpose of CNC.
Isn't this an A brace design - rather than parallel ?

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There it is! An assumption that is not completely valid. They are NOT just as strong, although the side-to-side runout is probably not significant in terms of reducing strength. Runout is where a piece of wood is cut at an angle to the grain, so the grain runs out along the face of the piece. The larger the angle, the greater the runout.

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Yeap...more of an A brace..I agree....my method of testing this is not exactly very scientific, since I can only go so far with "thumb pressure" to test stiffness, and deflection of the top...

Maybe some sort of a jig with a dial indicator and some way of applying pressure to the top might be in order here....thought would be to then compare this, with a traditional top which has individual braces glued and fitted....

I did leave the braces a little "taller" than what I would normally carve, and so far, thumb pressure has shown very positive results.....the tap tone is great as well....this thing sustains!

Anyway, all the feedback really does make sense, and thank you all for that.....now I need to go finish it, and see how it will ultimately sound, and how it will survive the test of time...anyone have a time machine I can use?

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Rodger I am asking this purely from ignorance, and Chris V can vouch for my ignorance! Now with that out of the way, what is the end result of using bracing with runout? I have never built an acoustic so I am a brand new sheet of paper to write on. Is there data that proves if you use braces with runout this will be the result? Now I ask this because of the kind of braces these are, or at least that I am assuming they are. Which are in fact part of the top that is not showing much runout, or at least no where near as much as what is seen on the little brace surfaces. If these braces are part of the top, and the runout is acceptable, what will the end result be from the braces being carved at an angle that shows runout?

Chris since you are completely aware of my ignorance, feel free to chime in as well. Here is the reason I ask this question. Is there really data that says a brace with X amount of runout will twist, split or crack over time compared to a brace with with little to no runout? Now if that is indeed the case, does the same data apply to these braces shown here which are still part of the top with little to no runout? Or......you knew the or was coming....is this one of those areas where "we have always done it this way"! Please do not take offense at this as I truely am asking for a better understanding because I have in the back of my mind to someday build a quasi copy of an acoustic LP and I had intended to carve it on cnc with intergrated bracing.

Mike

Mike,

In general terms grain orientation does have an effect on stiffness, but it's much smaller than people think. I don't have links handy but lab tests have shown that for many species, 1/4'sawn and flat sawn doesn't matter that much in terms of stiffness (this has nothing to do with the issue here but thought I'd throw this out there)

It is a fact that wood is an orthotropic material and the cross grain stiffness of wood is anywhere from a little less in some hard woods to a lot less in softwoods. So think of it like this - when you cut a brace at an angle like this, you are introducing a cross grain component to the brace so we know it's going to be weaker.

To better understand it - imagine making a brace from 100% cross grain. It's going to be much less stiff than a brace made entirely from long grain. An angled brace is going to be somewhere in between the stiffness of a fully long grain brace and a fully cross grain brace.

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You may already know, but 2 builders I've seen do something similar, Jaen & McCarthy, although with curved "parallel" braces. Seems a bit heavy to me, although both examples have inlet pickups.

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Dave
Milton, ON

So the stiffer the top the more responsive it will be? I find that to be a bit contradictory but I might be completely wrong....Is it not the idea to actually find a very fine balance between stiffness and response, so that the top "pumps more air" when driven by the strings? I do remember reading someplace, that Benedetto actually carves his tops a lot thinner when he uses parallel braces, as compared to X-braces. Since the run out in parallel braces will be LESS than in X, this seems to make perfect sense....hence the stiffer the top, the more we have to carve, so that it responds well to string vibration....we might be saying the same thing, but heck, that is why we are discussing it right?



I think you are 100% right here!! An archtop by nature and by the simple physics of it's shape (just go see why all the Romans build their aqueducts this way LOL! ), will be able to withstand strings placing pressure on the top way better than a flatop....just look at the rather simple bracing of an archtop, when compared to that of an acoustic....

So far, my experiments have wielded VERY positive results. The previous Archtop I build with this method, used integrated X-braces...it has been a few months since I finished the build, the guitar is sounding great, and I have not noticed any sort of sagging or cracking of the top...in fact, with 12's as the strings, the guitar really drives good sound, tone and sustain....I also even tried going to 9's, where there was a considerable drop in "power" but the guitar still played great...not that I would consider using this very light gauge anyhow, but again, experimenting....

Thank you for chiming in with your expertise, much appreciate it!

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Yeap..completely agree!!

So we have now come to what I guess Turmite was saying earlier.....we know it has always be done this way, but if over time there are no ill effects of the integrated system, then why not? About it being a wolf-tone killer, I am not convinced about that.....some would even argue (not me) that the presence of a wolf-note is undesirable....it all depends I guess....

the thing sounds pretty dang good, with good resonance, but I think way more experimentation is in order here to really determine that...

All good points!

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At the end of the day, while I do think this is an interesting idea, I don't see that there's much if anything to be gained with it - though I'll happily admit I'm wrong if proven otherwise.

I could see this as an advantage for mass production as the braces would be carved at the same time as the top so it would save an entire step of fitting and gluing braces. The other plus would be that with a modal analysis and structural optimization using high dollar software, you could theoretically tweak the brace sizes and shapes to get mode shapes you're after for a particular piece of wood if you could measure and model the properties of the individual piece of wood well enough.

I also had the same idea as John about caping the braces with CF and there might be something to be found there in terms of durability perhaps but, now you've added back in the step of caping the braces. Weight would probably be a wash I imagine.

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So......splain to me how how runout in this type bracing will lower the s/w ratio. The top itself does not have runout and is in my opinion, almost part of the brace, is it not? I suppose I am questioning whether it really makes a real world difference! Like Andy said, maybe some of the high dollar software would model it, but it is still a human ear that is going to hear it and buy it or reject it, and if this is like about anything else involving humans, it is all in the individual tastes!

Mike

Hi Chris,

I know.....but if you lay a template at a 45 degree angle across the plate surface, doesn't that give you lateral runout on the brace? This is in fact my whole reasoning for the questions I have ask. Plate equals no run out, but angled intregal braces equal runout equal to the angle the brace is placed, yet, the top and the brace are still a single piece.......so is it really going to make a difference? Chris, please understand I am asking this to try to remove my ignorance problem!

Mike

Mike,

A thought experiment tool I like to use when trying to understand some of these things is to use extreme examples where we know the outcome. Forget for a moment that in one case we have braces glued and in the other they're carved. Glue lines are usually stronger than the glue itself so that's not where we focus our attention.

We all split our braces to get the long grain as strong as we can get it. It's safe to say that a split brace is going to give us the strongest brace we can get. Like Chris said, it's not the face runout that's causing our problems here - it's runout 90˚ to the plane of face runout (don't know if it's called lateral runout but let's just go with that).

Say we take a brace billet and cut out a brace at say a 20˚ angle to the split face. We know that brace will be weaker than the brace split from the same billet because of the cross grain component we've introduced by the angle. Irrespective of whether the brace is glued to the top or cut from the same billet as the top, that geometric configuration will be weaker because of its angle to the grain. Similarly, the top/bracing combo will be stiffer using a split brace rather than the angled brace whether it's glued to the top or cut from the top (though obviously you can't cut an angled brace into a top without introducing the lateral runout).

Make sense?

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cyborg (real name),

Nice work. I would like to see the arching on the outside just for fun.

The stiffness can be measured easily enough simply (although destructively) by bonking the plate. After carving out the brace, replace it with well fitted brace that is the same dimensions. Tap the glued in plate and whichever if taps higher it is stiffer. I suspect it might be a few Hz higher. That might not be the only difference that might result in two instruments made identically except a fitted and carved brace. Read on.

Stiffness might not be your only concern though as stated by others above, although the sole purpose is in helping cope with stress, downward, on the top. Of course the sound is the ultimate outcome. A glued in brace might be a way therefore to alter the sound of a plate AFTER it is carved. Springing in a brace might be a way to compensate for a brace that cannot be stiff enough without adding too much weight.

Historically this is a very old argument and there really is no one answer. If you relate this to the viol family and subsequently violin family, it was likely that earlier instruments 15th C, did have a carved in bar. It is well known in violin family instruments, that replacing a bar with a new one can help restore or increase sound projection. These instruments were made to be disassembled and repaired. The bar was often, if not always, carve out and replaced with either a well fitted or sprung one with variable change in tone. Often the plate was re-graduated and other bastardizations. But it is well known that thinning a plate results in a definite change in tone, usually increased power in the upper range, more nasally tone, things like that.

The effects of the bass bar alone are not completely understood but a recent acoustic study by Thomas Croen did conclude that the bass bare compensates for the lack of longitudinal stiffness after cutting the f holes, and that a bass bar, installed under tension, causes the instruments high frequency response to increase significantly.

I am not saying don't carve in your brace or change anything. Except maybe to round the transitions so cracks don't travel as easily through the brace. Or perhaps glue a strip of linen on the brace as a crack stopper. If you get the sound you like and the wood is similar you might just hit a home run every time.

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Ken

Andy I follow the split brace analogy, and I understand that type brack will in fact be stiffer that one that has the grain diagonal across the brace. I don't know if I can even ask what I want to ask in a way that it can be understood, at least the way I am approaching it.

Let's forget anything to do with cut or split braces for a moment, since this top does not have them. What I am trying to find out, is will the carved integral braces, as shown in the op's photo suffice for a stiff enough top to allow a good sounding instrument, without the fear of structral (sp) failure later? Meaning, I suppose, will they work? Now, if that same top were to be made with braces that are free of runout and glued in, would it in fact sound a lot different, and that for the better. I know Ken kinda, nearly somewhat mentioned that would be the case. Now for the real question. Would there be enough of a difference in quality of the sound of the instrument that the average user could, or would notice?

Mike

Great question!! Only way way to find out! Build two and compare....most people will argue that an integrated brace will be no good....but how many of those who will make this argument have actually created a guitar on a cnc with the braces that way??? See where I am going with this? The argument that andy and others made here on the runout and structural rigidity I think are very correct....but your question is awesome....will all this matter when it comes to sound?

The archtop I build with integrated x for 4 months now since being stringed up has shown no signs of any structural defects, sagging, splitting etc....and I did not even use the best sitka....so for me, it sounds great and plays great...and no issues so far....

Next will be the parallel brace, and then I will compare the two...will use pretty much all same materials, finishing layers, string gauge etc....then I can even take some spectral samples of the same notes being strung, and compare....

Will the average user notice? Another great question! ...

So, when are you starting the build???

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When I get my new cnc machine built, or my current machine retrofitted. Tired of lost time and materials, meaning money!

I just purchased a new 4 axis industrial controller all self contained that is supposed to be here Monday. New ATC water cooled spindle, some used RexRoth ways and carriages, plus I already had a good bit of stuff collected. Now to decide to build or retrofit. Honestly, I don't think I have a choice since the current machine is not a real good platform, and especially for using tiny bits to get accurate cuts, ie, fretboards.

Mike

An alternative to leaving a full brace in place when machining would be to leave just a flat pad for the brace. That would give the advantage of long grain as well as eliminating the brace fitting. Just a thought.

An industrial controller? Do tell!

The only industrial-grade control I know of that's less than the cost of a mid-range CNC router is the KFLOP, but you said self-contained...did you get a Centroid?

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Bob Garrish
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Now that is an awesome idea, and some great outside the box thinking !!!

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That is indeed a really good idea!

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npalen wrote:
An alternative to leaving a full brace in place when machining would be to leave just a flat pad for the brace. That would give the advantage of long grain as well as eliminating the brace fitting. Just a thought.


Whoever "Archtopguitarkits.com" is has apparently been doing just that for a while. After seeing the assembly guide on that site, I worked up some cad drawings of a top done this way a year or so ago. But I guess I still think in terms of a bass bar on a violin and like the ability to put the braces in under just a bit of tension. I never carved a top from the cad drawings.

Does it make any difference in sound to do the top one way or the other? I have no idea, but not machining in braces or flats for braces does make it a lot easier to do whatever carving and cleaning up is needed inside the top. Fitting braces isn't a big deal anyway.

The violins I've heard with carved-in bass bars never sounded very good to me, but they were usually the real cheap "box fiddles" from the early 20th century and weren't particularly finely crafted--the carved in bar was just a shortcut (as was the lack of corner blocks) in a hastily built mass market instrument. Not a fair assessment of the built in brace idea.

I think the machined in braces or flats is a cool idea--maybe I'll eventually get around to pulling that cad drawing back out and giving it a shot...

Dave

I am curious if you have ever build an archtop with tension in the braces? Reason I ask is that I think over time, the instrument might loose some of it's voice...wood will eventually settle, and I think this is the reason why violins are meant to be taken apart...remove the top, and put new braces....obviously this is not an option for an archtop guitar....Might be an interesting experiment, but also some carbonfiber in the braces with a bit of tension might eliminate this problem....

Would be interested to find out your results when you do this....

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