Official Luthiers Forum!

It was a lot easier and simpler when there was just one log....
This is a subject that has peaked my interest since a few yrs ago when talking first with Greg Maxwell and I learned of a special fiber from a special log. It was a bridge stringer log that I set aside, because it didn't meat the criteria conveyed to us for sell-able guitar tops. Back in 1998 we were supplying another soundboard producer with a container load of sitka guitar block per month. So we set this log aside for double bass fronts. It was by accident, from cutting shorts into guitar tops, and the conversation a few years laster with Greg, when he was looking for specific criteria, that was out of the normal "looks Thing" Aesthetic criteria used by most. Afterwards, with what was left of the 80' by 63" bridge log, Turned out to be what we labeled our "ultra light"sort. And because we cut everything to be a soundboard, the needed stiffness was already there to accompany the light density and a GREAT soundboard. Since then we have targeted density for some of our customers that pay attention to that. Now the time has come to step it up a bit. Over the past yr+ and a couple material acquisitions, where we have cut chunks and long butts and tops of logs to length that a smorgasbord of material was processed into guitar tops. Some log/chunks we noticed to be very light density. And from several thousand guitar top sets, I have gleaned and set aside, what is now a pallet of about 800 sets with various character types of color and texture, etc.., but all are lighter density than the more common 28 pounds per cubic foot density.

So back when there was just the one log and the character of aesthetics of that log, it was one sort. Now we have many character types. Some tops have more open growth lines, and other finer. Some have hard grain lines, some have moderate color variation. But all have a density less than the norm. So I am asking the market how best to sort these 800+ sets, and lots more to come, when we get back to working up the logs these chunks worth of tops came from. But it is limited.. The logs are high defect that will yield at best 40% recovery. So I'll hipshot estimate 4000 tops worth of log of this light stuff. We have log material for over a million guitar tops sets.
Martin, Santa Cruz, Lowden, Gibson and many other customers follow the grading rubric, that most of the industry does.
We already have so many sorts now, because there are so many character types that the forest yields to us, and we are not able to simplify all those different characters into 4 sorts and since we produce for all acoustic instruments, sizes come into the mix as well. which is why we have 460 SKU's from the 4 species of wood that grow in our forest.
Since we don't have warehouse shelf space in our 15,000 sq ft facility for 15 more sorts, I'm trying to figure out how to lean down the SKU's to 3-4. maybe 5 at most for these light weight sets.
But we will also have both flat top and carved top product coming out of this production.
Here is the various criteria of looks;
color, texture[evenness of growth lines, and straightness.] "bearflaw" or not.
strong medularies, moderate or not much which may or may not attribute to stiffness.
And then there is the density with a range of 20.4-24 pounds per cu. foot
Should we even care about the looks, if density and stiffness is the more important?
But so many people buy with their eyes, and already have pre-conceived notion of what "quality" is supposed to look like.
Do any of you folks have an idea of a grading/sorting rubric to use for this?

I would stick to the normal grading system, a, aa etc. I'd say by and large that my clients don't care what the density is, it's irrelevant to them. I will choose varying density for different purpose but it will still be sold to my clients based on what it looks like. That top above looks right in line with what I usually use which is graded as single A.

I guess I'm trying to say that density and stiffness may be all that matters to the function of the guitar, but we still have to sell it to people that generally aren't interested in the nuts and bolts of the components, only the results, of which what it looks like is pretty important.

For some density does matter. A classical maker who wouldn't ordinarily use sitka might consider using a light weight sitka top. You could use the same grading system as used for cosmetics (A,AA,AAA) and add an L to it for tops that are less than 24lbs/cu ft.

I'm just saying density would matter to a builder but not their client. Density matters to me and I sort my tops by density (and therefore stiffness) and choose according to desire result, but it's never part of the conversation with clients.

Density may not be a consideration for the person buying the finished guitar, but for the person building it, it may very well be. Adding a density designation along with the typical cosmetic grading would allow those people who prefer light weight tops (and also those who prefer "normal" density tops) to get more of the type top they prefer. Obviously in a production environment you can't measure each individual top's properties, but having a general indication of grouping of tops might be doable.

Thank you for the input. Since we are professional soundboard producers.. going on 25 years. We see and have seen so much. Unlike some small producers that get a tree or 2 process it and sell it, we have near a million board feet of large diameter old growth log. We see how rare it is to find old growth sitka with these physical properties, and certainly want to do what we can to distribute these desires properties to those that are seeking and see value and benefit, and of coarse capitalize as business folks on the product. Gold miners get more for their jewelry grade nuggets than the ounces of fine placer. And I wouldn’t buy prime cut 45 day dry aged ribeye to make a pot of beef stew. Someone may do that, but they will have to pay the price for the product to do that.. you get what i’m saying right?. Clay has a good idea, building on what Ed stated, with the L classification added to the normal grade lettering. Now I’m thinking maybe L and UL. Normal average old growth high grade sitka is 28 #, and we have 24 pound and then the extra light 20 pound, which is even more rare. I know it’s something special to have fiber the density of red cedar with the hardness, toughness and elasticity that sitka spruce is. It just has me believing it to be an absolutely amazing soundboard material, exceeding all other soundboard product material. Because there are several other species of fiber with generally lighter density[ norway spruce from all regions of Europe, lutz, Engleman and White spruce]. But sitka and red spruce are near the same hardness, An attribute of durability. And elasticity has sitka top dog? One customer suggested to buy all of it. Until learning the qnty volume, Then just the Cream of it, which to me seemed quite unrealistic, and then it just got quiet.

I believe You guys have me thinking on the right path.

Another question, i can understand how material like this would be Great for fingerstyle playing of an instrument. But is it at all a benefit for hard played bluegrass, or maybe even a detriment? Whatcha think?

Given the popularity of red spruce for bluegrass, I'd be inclined to think that good quality spruce with high density (where the Young's modulus increases in proportion with density, as opposed to wood with typical modulus but higher "dead weight" density) would be desirable to some. So perhaps a good structural quality rating would be modulus divided by density. Then low/medium/high density would be preference based on the type of instrument you're building (with low density most likely commanding a higher price, especially if it's the least common).

But once you go mixing in all the bearclaw figures and such, it gets a lot harder to categorize.

Clay, you have a good point, especially as he's selling it to us and not our clients.

I remember the first bits I got from Shane were around .32/m3, getting some Sitka like that would actually be pretty cool.

So categorizing it separate from your regular spruce is a good idea, but I still think it should be graded for appearance/other properties in the same standard as usual.

Brent, I think you're thinking more or less in the right way about it's usage.

If you peruse the AGF then every other week or so it seems there is a thread about wood grading, runout, flash, joint seams, and a whole host of other topics on the cosmetics of guitars. I'd say that there are pretty much two kinds of people, those who don't care one bit and those that demand absolute perfection. Some don't care about runout others won't even pick a guitar up in the shop if they see it. Obviously to all people the guitar can't look like garbage but it's half and half as to weather the natural features of wood bother people or not.

As a builder I'd love to see a more appropriate grading convention that considers the properties of the wood rather then one based solely on it's looks.

But for that other half, the one's that buy with their eyes, you still have to have that sort of grading. So even in your low density offerings you would have low density A and low density AAA the only difference being color, grain uniformity, and other perfect features.

In general, the Young's modulus along the grain of softwoods tracks the density pretty well. I use SI units (kg/meter/sec) in my measurements. In a plot of density vs Elong you can draw a ling from a density of 320 kg/m^3 (20 lb/ft^3) and Elong of 6000 MegaPascals (I don't know the conversion factor off hand) at one end, up to 520 kg/m^3 (32.5 lb/ft^3)and 18,000 MPa at the other. About 60% of all softwood samples I've measured will fall within 10% of that line. This is all softwoods.

In general, late wood seems to add more to density than stiffness. Wood with narrow latewood lines, such as that from higher up in the tree, tends to be 'above the line' more often; to have a higher Young's modulus along the grain than would be predicted by the density. By the same token, heavy late wood lines, whether these are from actual 'reaction wood' or some other cause, add mass without adding commensurate stiffness.

If you build to a pre-determined stiffness and can leave low density tops a bit thicker they will end up somewhat lighter in weight. Weight goes directly as the thickness, but stiffness goes as the cube of thickness.

A light, low density top tends to produce a 'responsive' instrument, while higher density seems to correlate better with 'headroom' all else equal. Obviously you can do a lot with things like brace profile and bridge mass to favor either headroom or responsiveness, but: "Although the battle is not always to the strong, nor the race to the swift, that's the way the smart money goes".

Brent, I applaud your efforts to differentiate tops by relative weights. When you handle as much wood as you do I am sure you develop a feel for the weight of a given piece. Many of the tops I buy sight unseen, even from Alaska Specialty Woods, are heavier than I'd like. Some are just flat out unusable for the way I build. If you can provide an initial selecting of lighter-than-usual wood I think you would be performing a valuable service that no other wood supplier I know of is providing.

_________________
Stay with the happy people.
--Reynolds Large

How ironic. I JUST took a break from reading Gore and Gilet. Yes was on the chapter regarding mass and stiffness!




Sent from my iPhone using Tapatalk

Next question. Lets start with the presumption the tops are cut within 2 degrees of perfect VG with strong medularies present and STIFF. Where would you suggest we draw the line that separates the light or super light density from the normal sorts?
Lets use these measurements of mass 23" x 9" x .36" How many ounces or less should the scale read?
I'm thinking 17.5 oz. would be the line drawn to be Lights. But we have some as light as 15 oz
Most of our tops on the shelves seem to be 19.5-21.5 oz and a few even at 24.5 oz

I tend to reserve tops with a specific gravity of less than about .375 for classicals. That's sort of arbitrary.

IMO cross grain stiffness doesn't really impart any structural benefit in the long run. Over time as the top cold creeps the crosswise stiffness is canceled out. It does seem to make a difference in tone, and I usually reserve the tops with the highest cross stiffness for wider boxes; Jumbos and Dreads. Smaller guitars are usually not much shorter in the box length than large ones, but are proportionally narrower, so they don't need as much cross stiffness. On something like a size 1 you can use a pretty floppy top and still end up with good sound.

Alan, Though I don’t build anything but big piles of saw shreds, chips and dust, I believe what you say regarding “cross Grain Stiffness”. Surely longitudinal stiffness is the real deal regarding strength and the tops usability.. But by feel, and a million boards I cannot detect one from another in length stiffness. Given the perimeters I have dimensionalized most of our top sets to, What does specific gravity of .375 translate to in ounces of weight with an MC at 8-10%?

LOL found conversion tables... The internet has everything. 14.63 ounces. Wow most of my western red cedar is 17 oz+ for this dimension set.

Hi Brent,
Sounds like your thinking is right for the break points - less than 17.5 oz for the lights, and less than 15 for the ultra lights.

Most classical makers won't touch sitka. I think if it's light enough then it's perfectly good for a classical. One of the best classicals I've ever made was a sitka top. Personally I select on density and very low runout. I don't mind wide grain providing it's fairly even across the board. In fact I prefer the look of wide grain but then again I'm probably a bit odd in that regard.
I'd much rather have a supplier who did give an indication of the density. Better to have it than not.

Brent, This topic is one of many where the metric system has its advantages. I have arrived at this method for figuring specific gravity, which is more useful than weight in ounces (at least for me).
The thickness must be constant, so a pass through a sander is helpful (unless your tops come off the saw within a few tenths of a mm). I am not advocating you to calculate s.g. for each and every top. But, if you do several and weigh the final result then you'd have a baseline to do a quick weight test on your rough sawn tops, assuming the final dimensions of your tops are close to equal.
The process is: multiply thickness, width, and length together (in mm) and divide by weight in grams. The figure you come up with is divided into 1. With some moving of the decimal place you will arrive at the specific gravity.
I'm after soundboards that have an initial figure of 2500, which translates to s.g. of .4
I'm no math whiz so if I am incorrect in my method I will not be offended to stand corrected.

_________________
Stay with the happy people.
--Reynolds Large

We surface all of our flat top soundboard products with a widebelt sander. Our older Miller had a manual crank to adjust thickness, with no digital readout of thickness, just a ruler/sticker and a pointer, and we would just run stuff through to "clean it up". We ended up with varying thicknesses from batch to batch. Now we have the 2 head/belt sander with digital readout and we are dimensionalizing everything to particular thickness .185". Because of the volume of product we produce, when we are really going, it's around 400+ top sets per day of a 85%/10% /5% mix between flat top and carved top and bracewood products. Whether we use metric or US Customary, we need to keep things as simple as possible.