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Top to thin?
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=26867		 Page 1 of 1
Author:  Dave_E [ Tue Apr 06, 2010 12:49 pm ]
Post subject:  Top to thin?
Hi All,

Long story short, my Jet 10-20 sander gave me some uneven sanding of my top plates and after glueing them together had to do some serious sanding to get it flat. oops_sign I ended up with a thickness of .103. It's for an OM, unbraced it tapped to a "G". I've never built a guitar with a top this thin. Should I continue or scrap this one? Your experience and advice as always are much appreciated! [:Y:] Thanks.

Dave
Author:  Colin North [ Tue Apr 06, 2010 12:55 pm ]
Post subject:  Re: Top to thin?
What kind of wood, how stiff?
How does it feel now?
My latest top is German spruce about that thickness off the sander, but was very stiff.
I've used Sitka at 0.11" that was a bit too floppy, my first at class (lacked top end harmonics)
Author:  Dave_E [ Tue Apr 06, 2010 1:03 pm ]
Post subject:  Re: Top to thin?
Hi Collin,

It' Sitka spruce, what Alaska Specialty called "head stock", (base of the tree). It feels fairly stiff to me, but I've only built 10 guitars and don't do any density or stiffness testing and 4 of them were classical's with cedar tops.

Dave
Author:  Tom West [ Tue Apr 06, 2010 1:07 pm ]
Post subject:  Re: Top to thin?
David: I have 3 guitars I'm putting the finish on at the present moment. One is approximate similar to an OM and the top is thinner then yours,the other two are dreads and they are approximately the same as yours. As you no doubt know it depends on stiffness and how you brace and how you expect the end result to sound.As long as you have a nice stiff top and you don't scallop the braces to pieces I think you'll be fine. Remember if you do over build a bit you can always do some work on the braces through the sound hole. Have fun and good luck.
Tom
Author:  Dave_E [ Tue Apr 06, 2010 7:31 pm ]
Post subject:  Re: Top to thin?
Thanks for the reply guys! [:Y:]

Is the stiffness testing and hardness testing thing hard to do? Is it worth the equipment and $ to invest in? I guess I'll go ahead with this on. I remeasured and my averave is .105.

Dave
Author:  Parser [ Tue Apr 06, 2010 7:55 pm ]
Post subject:  Re: Top to thin?
I hope you have a good glue joint! I think joinery & craftsmanship becomes much more critical when you get this thin.

You could always string it up first with light gauge strings and see how it behaves. You could also brace the heck out of it. It's thinner than I would want to build with...but I'd probably finish it out just to see what it does. I would go ahead and make it a guitar, but I'd put it on a nice cheap set of wood.

Some tops are stable enough & stiff enough to get away with this...and some aren't! Unfortunately, you don't learn anything until something breaks.. :D

Trev
Author:  Jim_H [ Tue Apr 06, 2010 8:57 pm ]
Post subject:  Re: Top to thin?
Dave,

Is the rosette routed and sanded yet?
Author:  Dave_E [ Tue Apr 06, 2010 9:29 pm ]
Post subject:  Re: Top to thin?
No Jim,

No hole, or rosette, just the cut out periphery.
Author:  truckjohn [ Tue Apr 06, 2010 10:52 pm ]
Post subject:  Re: Top to thin?
Use it.
Don't listen to the folks who say it will implode -- it won't if you do your job making good glue joints.

My Esteban Retop Dreadnought has a Sitka top that started at about 0.103" before I did any levelling (And it was *Rough* before levelling... I thinned it out a bunch.) .... I put Cumpiano book bracing on it.... and I still had to do a bunch of brace shaving below the bridge before it would sound right with Medium strings and a "Standard Martin" factory setup action height on it.... I haven't had any problems overdriving it... even with medium strings and heavy flat-picking.

Sure, it has some belly -- but well within "Martin" factory specs for such.

I will give you this advice:
Make sure there are no gaps between the sides of the bridge plate and the X-legs.
Make sure your X-brace joint is tight, and well capped.
Make sure you have adequate soundhole reinforcement
Make sure you have a "Standard" amount of top dome.. I personally wouldn't go flat or with too much dome either.
Leave the bracing "Parabolic" and "Straight" or "Tapered" above the bridge -- no scalloping between the Bridge saddle and the UTB.
Use a "Standard" profile bridge with wings overlapping the X-brace legs

Thanks

John
Author:  David Malicky [ Tue Apr 06, 2010 11:22 pm ]
Post subject:  Re: Top to thin?
For what is "too thin", I think it depends on what you would consider to be a "problem". Somogyi's book says his "steel string guitar tops will usually be significantly less than 0.100" ", but (paraphrasing greatly:) he doesn't consider settling in (telegraphed braces) to necessarily be a problem, and may actually be good for tone. Personally, I like the "responsive" approach, but it does have some risks. I finished my first thin topped (0.100") guitar 3 weeks ago -- it has been fine so far.

The older Taylor GAs were 0.110" thick; if a factory can do that w/o testing the wood, 0.105" should be fine so long as your top isn't a complete noodle.

Here's a simple way to do stiffness testing w/o a jig or dial indicator:
- Get two 1/2" thick x 16+" long sticks and place 18" apart, on a flat board or table.
- Place the top on these lengthwise.
- Place a ~1x2x16" across the top at the halfway point.
- Use sticks of various thickness to measure the gap; this measurement corrects for bow in the top. Try to measure to within +/- 1/32".
- Find 5 lb worth of weight and place on the 1x2, distributed evenly across the top.
- Measure the new gap with various thickness sticks.
- Subtract the measurements for the deflection.
- Turn the top over and repeat. Most builders take the average of the two readings. In my experience, if the two #s are much different, it's because the top was heavily warped and not resting evenly on the supports (I would resticker in that case).
- I gather that many builders shoot for 0.20" to 0.25" deflection (5 lb weight, 18" span).
Author:  Corky Long [ Wed Apr 07, 2010 1:59 pm ]
Post subject:  Re: Top to thin?
One more vote for "build with it"!

I'm also at a point where I dont' have enough experience to know what's "too thin" based on feel. Good argument to start deflection testing all your (and mine :P ) tops and keeping good records.

If your careful with the final sanding on the soundboard I don't think you'll have any problem - I'd simply voice the top once the braces are on it with the awareness that the top is a bit thinner than usual.

Another vote on the extra care on joints and fit - we should all be doing this anyway, but....

Also - if you generally string your guitars with mediums, you may need to use lights on this one.

Good luck.
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