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Sanity check - thicknessing
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10102&t=14275		 Page 1 of 3
Author:  billm [ Sun Oct 28, 2007 3:28 pm ]
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Hey guys -


Thought I'd get some other eyeballs on this - some background, I've built kits previously and am working on my first scratch build.  I've got my top joined, rosette installed, cut out, and today worked on thicknessing it.


Down to .125", this is the amount of flex I'm seeing - this seems excessive to me, thought I'd ask for a sanity check.  Thoughts?


Thanks!  - Bill


Putting a link and image in, in case the image doesn't take (haven't gotten this to work yet)


http://i139.photobucket.com/albums/q319/wmansfield/IMG_1958. jpg?t=1193627974
Author:  Andy Zimmerman [ Sun Oct 28, 2007 3:38 pm ]
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Judging thickness is SOOOOO builder specific. It all depends on the wood
selected. Is yours spruce?
Also I can show 2 pieces of wood of the same time with vastly different
stiffnesses.

At 0.125 with what looks like spruce, it is "probably" unlikely that you
went too far. I have made guitars with tops as thin as 0.082 to .130.
Vastly different woods, but is shows how varied it is. Redwood for
example is longitudinally stiff but weak side to side. Spruce tends to be
stiffer than an equivalent thicknessed cedar.

Bottomline you are probably just fine where you are. I would be a total
shock if you went too far. Go for it. Also bracing is the other major step.

Consider this...most guitars are way over built in my opinion. I love the
sound of a lightly built and braced guitar.
Author:  billm [ Sun Oct 28, 2007 4:00 pm ]
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Yes, sorry - it's AAA spruce from LMI.


Thanks for the input - I guess I just expected it to be more stiff.

Author:  Rick Turner [ Sun Oct 28, 2007 4:14 pm ]
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AAA spruce means nothing other than it's kind of boring and pretty. The grading of spruce is virtually 100% visual, and visual has little to do with tone.   It does enhance the saleability.   Go figger!

Also, many of us here graduate our tops. I often go from .125" to even .135" in the bridge area down to less than .080" at the edges. That's a range that is close to proportionally equivalent to an archtop's graduation.
Author:  grumpy [ Sun Oct 28, 2007 4:14 pm ]
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Methinks you've discovered what some of us refer to as a "floppy top".

I don't like how it flexes immediately, and completely, right where you're holding it, under its own weight. It should have a smooth, even curvature right across, and slight at that.

At .125", I'd most likely toss this one. And just so you don't feel bad, I've seen(and have here, for demonstration purposes) flawless, tight ad even grained red spruce tops worse than this at .150". It happens....
Author:  JohnAbercrombie [ Sun Oct 28, 2007 4:59 pm ]
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I'm with Mario aka Grumpy on this- though I've only built a few (15 or so) guitars. This one definitely looks to be in the 'floppy' zone for me. I just checked in my shop- I've got a few tops that aren't braced- and even at 0.100 an Engelmann top (thin- it's destined for a parlour guitar some day) can pretty well support its own weight. BTW, that Engelmann top is an A/AA top- because it has a couple of streaks of colour in it. You can save money on tops if you don't mind some colour aka 'looks like wood'.

I'd turn it into back reinforcement strips if it were mine, but I don't know much. That decision can depend on how much time/money you have invested in the rest of the guitar- if this is a quick,simple build with sapele b+s, it's a different case than pairing it up with expensive b+s and lots of abalone inlay, etc...

Cheers
John
Author:  Rick Turner [ Sun Oct 28, 2007 5:00 pm ]
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Good old Floppy Tops,

Floppy Tops, Tennessee....

Floppy Tops, Tennessee...


Thanks for a great tune, Felice and Beaudeleaux Bryant.... Dolly sang it wonderfully, but that made me wonder if a couple of other things might be floppy...

http://en.wikipedia.org/wiki/Rocky_Top
Author:  Rick Turner [ Sun Oct 28, 2007 5:12 pm ]
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Hmmm,

Might "floppy tops" be perfect for ladder bracing schemes?
Author:  JohnAbercrombie [ Sun Oct 28, 2007 5:13 pm ]
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There are these pills they advertise all the time on TV- supposed to cure problems like this....
Author:  Rick Turner [ Sun Oct 28, 2007 5:17 pm ]
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Yeah, John, the "V-tops"! All night stiffness, all night tone... There's the marketing slogan! But only when you're ready...
Author:  grumpy [ Sun Oct 28, 2007 5:20 pm ]
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On a sadder note, Dolly's 'ol partner died today.

http://tinyurl.com/2gkspe
Author:  joe white(old) [ Mon Oct 29, 2007 1:57 am ]
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Was it Porter? Gosh, I just read yesterday that they had moved him into Hospice Care to try and keep him "comfortable" A sad day indeed. 
Author:  Mike Mahar [ Mon Oct 29, 2007 2:22 am ]
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The best sounding guitar I ever made had a top like that. I was prepared to route it off if it didn't work and finished the instrument just for the experience points. Sometimes you gotta do something dumb just to see what happens.

If the top is stiff lengthwise, it might still be usable.
I have heard, second hand, that Serge de Jonge doesn't care about lateral stiffness and just adjusts the X brace out wider if the top is too floppy. You might want to splay the X brace out a little bit to compensate.

However, since this is your first "from scratch" build it might be best if you made another top. There are so many variables in the guitar sound equation that I wouldn't mess with a top that was too far to the edge of the bell shaped curve. If the guitar was disappointing you wouldn't really know if it was the floppy top or some other aspect of the build.
Author:  Blanchard [ Mon Oct 29, 2007 3:15 am ]
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That top might be just fine.....

If the density is low and you are putting it on a small guitar and you adjust the bracing angles correctly, it could be great !!

Example:

I built an OMish guitar once with a top that was at least as floppy as that one is. It was very low density so I was able to leave it .145" under the bridge and .125 at the edge without the top weighing more than usual. I also opened up the X brace quite a bit, splayed the finger braces out to almost horizontal and ran the tone bars almost straight across.

The guitar had a luscious, warm yet very clear, tone. I still consider it one of my better guitars.

Mark
Author:  grumpy [ Mon Oct 29, 2007 3:24 am ]
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Yes, it can be made to work, by adjusting this and that, and accepting that the outcome will be different, but it's his 1st....

Too many variables already.
Author:  billm [ Mon Oct 29, 2007 3:40 am ]
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Hey guys - thank you very much for all the input.  Not sure I'll have a chance to call LMI today, but I did send an email to customer support and included the link to the photo.  We'll see what they say.


To answer a few of the questions -


 - Was planning to put it on a guitar with a 16.25" lower bout - so not small


 - Is very stiff lengthwise - can hardly get it to bend at all in that direction actually


Thanks for all the info (plus the A-HA that wood grading is based on cosmetic elements - that'll save me some money in the future).


 - Bill


 
Author:  WaddyThomson [ Mon Oct 29, 2007 3:44 am ]
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This is very interesting.  I thought my top was floppy (guitar top, that is ), but it holds its own weight up from the edges.  You have to physically bend it, but it sure seemed to bend easy to me.  I now see that what I thought was floppy may be stiff, but I was told it was nice and stiff when I bought it, so I was going on that as a guide, but without a solid comparison ...  Maybe I need to join up a bunch of tops and just flex them at varying thicknesses.
Author:  chewy63 [ Mon Oct 29, 2007 3:45 am ]
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 im wondering if u guys check yur tops for stiffness before u cut the shape out? 


 it loods like a very wide lower bout.   which would take more to support.


  also im wondering if u do check for stiffness before you cut the shape u get support from grain in the upper bout. 


   chewy


   go colts


ps looks like u are using the door to pry on the top
Author:  John How [ Mon Oct 29, 2007 5:38 am ]
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I'm not so sure I would reject the top either. It appears that you are pulling the top into that curve though and it's difficult to guess what force might be required to do that. All wood will be much more flexible on the side to side and to me anyway, I like a little flop in that direction just like I like stiff in the other direction. Ya really gotta build a few before you can make that judgment. I'd probably go with it and then redo it if you don't like the results. If your using a bolt on neck, it's not too crazy to think about re-toping if the results don't produce the desired results. It's all about learning from your trials. Have fun!!
Author:  John How [ Mon Oct 29, 2007 5:41 am ]
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[QUOTE=John How]results don't produce the desired results.[/QUOTE]

Oh well, I guess we'll have that button soon enough
Author:  Rick Turner [ Mon Oct 29, 2007 6:34 am ]
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John, you're our ladder braced builder here. Could you comment on using floppy tops for ladder braced instruments? I would think that that would be a good match.
Author:  MikeP [ Mon Oct 29, 2007 6:47 am ]
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what I'm seeing from that linked to image is that the top has been roughly shaped and he's holding it on the edge of the lower bout which means there is not that much of a length of material until it hits the waist...in a nutshell a piece of wood less than 1/8" thick being held by the edge is 'weak' enough, the addition of the rough shape concept just makes the 'problem' look worse than it may actually be..that's a fairly long moment arm with a fair amount of mass being 'held up' all things considered....I also agree with the comment about he's possibly creating part of the 'problem' by the way his fingers are located.....


Author:  John How [ Mon Oct 29, 2007 6:51 am ]
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Hi Rick, As I said I do like a little flop in the side to side direction but as there are no braces along the grain in a ladder guitar I like it as stiff as I can get it in that direction, especially on a ladder braced guitar.
When I graduate my tops, I usually leave them full thickness down the center (.110-.125 depending on the flex) and thin out the wings or sides of the lower bout. If I want a little more bass response then I'll remove a little at the end block too but these little ladder guitars don't require much boom in the bass. Of course this is all done after attaching the plates so you do as much as possible to get it right inside first and then expect to do a little graduating after the box is closed.
After the first couple of ladders were done with good results, I tried going a little thinner on my tops and lost a little of the snap in the upper frequencies so have been going a little ticker down the middle.
Author:  billm [ Mon Oct 29, 2007 7:38 am ]
Post subject: 

Hey guys -


You are right, and I had the same thought looking at the picture a bit later, that I was holding it at the lower bout which certainly emphasises the problem due to the elements already mentioned.  Holding it at the waist, I had a similar effect but certainly not as drastic.  Was not exerting any force, only gravity.  Overall, it feels to me kind of like a vinyl placemat in that dimension.


LMI responded to my email within half an hour - essentially the message was they usually don't replace tops due to stiffness issues because it's so subjective, but looking at photo it was clear that this one should be replaced.  Fantastic customer service!


So - I appreciate all the input!  My takeaway is that we can at least call it questionable, so I think I'll get it replaced.  Hopefully with a little more experience I'll be able to judge better, or be able to intuit how to work around it.


Also - good questions were raised about order of operations - I did cut it out before thicknessing, because I wasn't using a drum sander, and I thought it would make tapping more accurate relative to the final shape - interested in anyone's comments.


John How from Gold Country - checked your web page, we share an area code.  Curious, if I may ask, whereabouts are you?  I'm in El Dorado Hills.


Thanks guys - this has all been very helpful and informative - Bill
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