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Top too thin?
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10102&t=15154		 Page 1 of 1
Author:  Wes McMillian [ Fri Dec 28, 2007 2:03 am ]
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Kinda got carried away with the 80 grit on this soft Englemann top. Swapped over to 100 to try and finish it up and, as of now, the top comes out at .093". And I still have some sanding marks.

So, what is the thinnest you will typically go? I know, it varies with the stiffness of the particualr top, etc, but on average. I still have limited experience handling guitar tops, but I confess, this one is feeling kinda floppy to me. IIRC, most folks have a tendency to leave Englemann a little thicker, if anything.

BTW, this is for an OM. My gut right now tells me to join another top and set this one aside. It is a nice top. Maybe I'll decide to do a parlor one day...

What are your thoughts? How thin would you expect, on average, to go on an Englemann top for an OM?
Author:  Hesh [ Fri Dec 28, 2007 2:21 am ]
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Wes buddy as you indicated it is impossible to know without deflection testing but my gut tells me as well that this top may be to thin.

The Engleman that I have worked with needed to be thicker then say the Adi that I work with.

Prior to doing deflection testing and back when I used "a number" I would think that .115 was a safe number for Engleman for an OM sized guitar.

As you indicated you are not done yet with sanding the marks out of this top so you may end up in the .090 area when finished.

Hopefully you didn't install a rosette yet.
Author:  j.Brown [ Fri Dec 28, 2007 2:57 am ]
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I've taken mine to .085 before to get it to flex like I wanted it to. Too hard to say definitively that its too thin without seeing it. Its probable that it is too thin, but possible that its not.
My very scientific evaluation criteria for my own tops is something like this:
Flexible=Good
Floppy=Bad

-j.
Author:  Blanchard [ Fri Dec 28, 2007 3:10 am ]
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The thinnest I have ever gone with Engelmann is .120 under the bridge and .100 at the edge. Usually it is more like .130 under the bridge and .110 at the edge.

.093 might be good for a classical.

Mark
Author:  Steve Saville [ Fri Dec 28, 2007 4:42 am ]
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It depends -
1) on the stiffness of the wood
2) on how you brace to support it

For an OM I would have no problem with that thickness and even down to .080" or more. It does require more support - larger bridge plate and perhaps a lattice bracing that stes real close to the bridge plate on the first braces.
If this is being built for you, go ahead and build it.
Take a look here.
and here.
Author:  Robbie O'Brien [ Fri Dec 28, 2007 6:57 am ]
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Go ahead and build with it. You will be fine. You are pushing the limits for an Engleman top on a steel string but you can compensate with your braces. You are probably on target for a killer guitar! Don't forget to post your results when you are through.
Author:  Mike Collins [ Fri Dec 28, 2007 8:11 am ]
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I agree with Robbie!
mike
Author:  Howard Klepper [ Fri Dec 28, 2007 8:26 am ]
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[QUOTE=Robbie O'Brien] Go ahead and build with it. You will be fine. You are pushing the limits for an Engleman top on a steel string but you can compensate with your braces. You are probably on target for a killer guitar! Don't forget to post your results when you are through.[/QUOTE]

I don't know how anyone could claim to know that this top will be fine, or that it is probably on target for a killer guitar. If overthinning tops and compensating with the braces made for killer guitars, we all would have been doing it long ago.

Engelmann tops are cheap; the work of building a guitar is costly. Put it aside and do it right with a new one.
Author:  Alan Carruth [ Fri Dec 28, 2007 9:04 am ]
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I agree with Howard.

We just don't have enough information to make that decision with any certainty. Each of us builds differently, and has a different sound in mind. The limits will be a bit different for each of us. Not knowing how you work, or what you are looking for, it's hard to say.

With that in mind: I would set that top aside and use it on a smaller box, or even a classical. If it is 'soft' it is probably also low in density, and the Young's modulus (E) along the grain, which, with the thickness, determines the resistance to deformation from bridge torque, is most likely on the low side. The only way to make up for a low E value is to leave it thicker, and you can't do that now. The alternatives are to makea smaller box, since the need for stiffness drops on a smaller span, or make an instrument that wil have less tension on it: a classical. My feeling is that using heavy braces on a light top doesn't give as good sound as making something more balanced. Why go to all the effort to jury rig something, and end up with a result that is less than satisfactory, when you could put it aside and make it into a fine guitar later?   
Author:  Cricket [ Fri Dec 28, 2007 9:06 am ]
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Wes, go with your gut me thinks.


I respect the opinions and lean both directions, gee that puts me straddling the fence.  Hmmmm.


Toss it or double top it, all is not lost. 


If you don't like it that thin, then maybe you shouldn't build with it.


At the very least you learned something.  ONLY thin tops with the finer grade paper. 


I'll bet most folk don't sand tops with 80.
Author:  Hesh [ Fri Dec 28, 2007 9:07 am ]
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Yeah with no disrespect intended - ever - toward my OLF bros and sisters when I consider what good advice may be for Wes and factor in all that we cannot know I try to error in the safe side of the equation for builders who have not developed a sense for the particular piece of wood that they may be working with.  To me encouraging a builder toward a safe, but good sounding guitar is more important to me then what pushing the envelope may yield if it is a success AND if it is a failure.

Bracing for a wimpy top is not jut a matter of taller, more robust braces.   I view an entire braced top as a system and in as much as this view has inherent interdependencies on the old idea of the weakest link being the one that will get you in the end I personally believe that bracing stouter is not the only answer.  Perhaps as Steve indicated a entirely new scheme of bracing is warranted.  As Steve so generously offered lattice bracing is a option but using lattice bracing is an art in and of itself.  Consider Lowden and how his sound holes are stiffened by far more then 3 1/4" wide 1/8" sound hole reinforcements favoring to reinforce he entire sound area with a second layer of a top.

Then we have the issue of how the player will beat on the guitar, stings used, music played, finger style or picking.

So for the advice that I offer to others it tends to be on the conservative side of the equation.

Above all I never, never want to offer ideas to others that have not been time tested to error on the safer side of the the acceptable performance goals of a particular guitar for a particular player.

I fully understand that one of the many things that separate the Luthiers here from the builders here is knowing how to compensate for less then perfect materials.  But can you truly brace a top that is to flexible by bracing stouter and not perhaps redesigning the bracing scheme as offered in the lattice example?  And are we making recommendations that open new cans of works like using composite braces for a builder like me who has no experience with them?

Life is full of situations where we need to make a informed guess to a specific situation and situations where someone one here is counting on us to provide with them with advice that is better then something that "could" work out for them. 

I think that using this top would create a higher then acceptable, at least to me, level of risk for Wes and that is not advice that I am willing to give.  He will spend much effort, have high hopes, and in the end gets only one shot at getting it right.

Those of you who have suggested that with what very little we know about this top, how J braces, desired playing style, string gage to be used, and the end users dedication to take care of this guitar - are we willing really to use Wes's guitar as a test bed for what we think we believe may be true or is it better to steer him in a direction where the majority of the bell curve has had success?

And again - thin tops are not an answer in and of themselves.  They are part of a highly developed style of building that required ultra stiff rims (double rims, reinforced rims, reversed kerfed linings, etc.) and not to be considered an out of context end all to be all.
Author:  Hesh [ Fri Dec 28, 2007 9:08 am ]
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Jiminy welcome to the OLF!!!!
Author:  Steve Saville [ Fri Dec 28, 2007 9:44 am ]
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Wes,
You never said if this is a guitar for yourself or if it is a commission. That makes a huge difference. If it is a commission, I don't think anyone would ever recommend that you experiment with a top significantly thinner than you are used to.
If this is a guitar for yourself, then you stand to learn a lot by trying my suggestion above. Obviously, if you build it with standard bracing, you are looking for trouble. You will learn valuable lessons, even if the top fails. If it does, put on another top. More good lessons.
Do you take deflection measurements of your tops and braces? Now is a good time to start if you don't.
If you use lattice bracing that will support the top like those pictured in the links above, and do not scallop the X braces, you should be fine. There is no need to have ultra stiff rims, but I think it is always a benefit. That's how I build.
Author:  SimonF [ Fri Dec 28, 2007 9:48 am ]
Post subject: 
Wes,
I build very lightly. I am currently finishing up an Engelmann topped OM
guitar. This particular top was a true mastergrade set and is very nice
and stiff both with and across the grain. I had to take this particular top
down to about 0.100" and this number would be just a tad lower around
the rims where I would sand.

My experience with this particular top lets me think that you might be
able to get away with your own top BUT unless it is an extremely stiff
piece of Engelmann, I think you would need to compensate for this in
your bracing design (particularly in the bridge area). From your post, I
gathered that you are probably not experienced enough to know exactly
what to do at this point.   

So my recommendation is just to set this one aside and get a little more
experience under your belt and use it at a later date. It is good to push
the boundaries but I think it is better to play it safe at the beginning. It
takes so much time and effort to build a guitar and I would hate to see
structural issues put a damper on the experience.

All the best,
Simon
Author:  Brad Way [ Fri Dec 28, 2007 10:13 am ]
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If you have any interest in "Double Top" construction then you could save it for that.

I tend to agree with others on here...it seems hard to justify building an entire guitar around a top that isn't perfect.
Author:  Doug-Guitar-Buckler [ Fri Dec 28, 2007 10:32 am ]
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Just set it aside and start over buddy. Otherwise, you might end up like me on so many things- 1/2 time making mistakes & 1/2 time fixing them. Maybe you can make a uke out of it and post the pics on OLF!!
Author:  Robbie O'Brien [ Fri Dec 28, 2007 10:51 am ]
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I am going on my own experience here. I also know that most builders tend to overbuild their guitars. However, perhaps what Allan and Howard and others say is good advice to go on. Whatever you decide, Happy Building!
Author:  Andy Zimmerman [ Fri Dec 28, 2007 11:14 am ]
Post subject: 
It is difficult to say based on the thickness alone. 0.093. If you had a
chance to deflection test it, it might actually be too thick for some of my
guitars!!! So thickness alone is meaningless.

Don't just look at the number. Don't keep it based on the number, Don't
trash it based on the number.   My basically feeling is we WAY overbuild
our guitars. I love light built thin top guitars. I would follow Steves
adviice. If it is for yourself than go for it. Measure it if you can before
you build with it. You just might find that it will make an awesome
guitar.

Another KEY point, is what size guitar is it for.   I thin my tops to a greater
degree of deflection for smaller bodied guitars!!!!

An example my last L-OO was 0.083 (Deflected 300) while an SJ was
0.089 (Deflected 250)
Both Lutz spruce from the same "batch" with similar deflection properties.
Author:  Mike Collins [ Fri Dec 28, 2007 11:17 am ]
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Wes;
what string guage is going to be used on this guitar?

Is it an order for a fingerpicker -or flatpicker?

What's your string height from the top at the bridge?

these 3 questions are the most important in your situation.


Mike
Author:  Wes McMillian [ Fri Dec 28, 2007 2:07 pm ]
Post subject: 
Thanks, all. Lots of great responses!

After making the initial post, I went back out to the shop, flexed the top again, and set it aside. Grabbed another set to join. Quick and easy solution. Like Howard said, Englemann tops are cheap and I have plenty of 'em.

This guitar is a gift for a friend, so I'd rather play it a little safer. Granted, it will be strung with lights, and he is a fingerpicker (to answer Mike), so it MAY be a safe bet. At this stage, I would rather use a thicker top. Now, as I'm also beginning an OM for me, I may try it on that one. It'll probably be set aside for a little L-00 or parlor or something, though. By that point, hopefully I will have had a few more thicknessed tops through my hands and have a little better feel for deflection.
Author:  Terence Kennedy [ Fri Dec 28, 2007 3:17 pm ]
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I think saving it for a parlor guitar is a great idea.  It should be perfect for that.
Terry
Author:  Kevin Gallagher [ Sat Dec 29, 2007 6:47 am ]
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    Top too thin? Yes.

    I would recommend setting it aside an using another for this OM. You can compensate with bracing and bridge plate to and extent, but the entire top is under stress whe strings are pulling on it and some strange things can happen across even narrow spans of unsupported top plate when it too thin.

   Engelmann Spruce can exhibit great stiffness, but the majority of the tops I've seen made from it just don't have sufficient strength to work at a thickness like .090"

   I know it seems like a waste now, but you'll be glad that you did it after the guitar is done.

Regards,
Kevin Gallagher/Omega Guitars
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