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| Floppy Top Syndrome http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=25819 |
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| Author: | DannyV [ Mon Feb 01, 2010 12:23 pm ] |
| Post subject: | Floppy Top Syndrome |
G'Day, Thought I might throw this out there. I'm well into doing an OM from Michael P's most excellent plan. I glued up a rather nice Engleman top, put in a rosette and started final thicknessing. I've got it down to .120 and man this thing feels very floppy. Now I haven't flexed a ton of tops in my life but the last guitar I built was Sitka and that top was much stiffer. And of course being Mr. Hasty (it bights me in the bum on a regular basis) I never looked at how well it was quartered. Just went to the pile and said" there's a pretty one and look, it has AAA's on it". Turns out upon further inspection it is more off quarter than I would like. 5 or 8 degrees in the centre to about 15 degrees on the outside. My question is how you might approach this top with respect to bracing? I'm going to use Sitka for the bracing that I think is pretty stiff. On MP's plan all the lower braces and X are 3/4" tall. How might I vary the bracing according to top stiffness? Happy to hear you opinions! Thanks, Dan Always in Way Too Much of a Hurry Vincent |
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| Author: | Rod True [ Mon Feb 01, 2010 12:28 pm ] |
| Post subject: | Re: Floppy Top Syndrome |
Hi Danny, Of course without flexing the top, no one will be able to give you a ![[:Y:]](./images/smilies/smiley20.gif "Thumbs Up") for sure.My guess though would be that you'll be fine. Also 3/4" is VERY high for braces and I suspect that you could even go lower with them and still use this top. I'd keep moving forward with it. Take as many notes as you can and chalk it up to a good learning experience. I really do suspect that you'll be fine with the top. |
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| Author: | Colin North [ Mon Feb 01, 2010 2:06 pm ] |
| Post subject: | Re: Floppy Top Syndrome |
When you say floppy do you mean across the grain? Is the top still quite stiff along the grain? If it is, then you may well be fine as it is, but maybe take it easy if you thin the plate around the edges. |
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| Author: | Colin North [ Mon Feb 01, 2010 2:39 pm ] |
| Post subject: | Re: Floppy Top Syndrome |
BTW, I agree with Rod - 3/4" bracing sound really quite high. I've never build an MJ I admit, but my 3 OM's (16" lower bout) are I think overbraced even at 7mm x 15mm (5/8") german spruce, scalloped to around 12.5 - 13 mm (1/2") on the X's |
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| Author: | truckjohn [ Mon Feb 01, 2010 2:42 pm ] |
| Post subject: | Re: Floppy Top Syndrome |
I was doing the Esteban Retop project... I bought a stack of #3 tops for $6.50 each... 2 were *Way* off quarter -- like 45* off... so those went to the side.. Then, there was 1 that was very wide grained, but otherwise fairly stiff... and 2 others that were fine grained and hard as rocks.. Figuring that it would be best to ruin the wide grain and moderately fairly stiff top... I went ahead with it... During the thinning process (All by Hand Plane) -- it got thinner and a bit less stiff.. and thinner and a bit less stiff... and then I lost track and it got quite a bit thinner and a whole bunch less stiff... like Floppy feeling... This is around 0.100-0.105" thick... Gosh, it feels so floppy.. I think it must be ruined.. Well, says I.. It is a practice top after all... so I may as well put in a Rosette for practice... because I will surely ruin it... Lo and Behold, Against all odds, it went fairly well.... so I.. I may as well go ahead and brace it up.. Just for practice.... Nothing to loose... and that went well.... So I end up with this braced up, rosetted top.... and What the heck.. It's an Esteban... I'm gluing it on! AND It still turned out too stiff... but after some more "Voicing" -- It is great... Loud and Clear with Medium strings on it... Go ahead and try it out. Thanks John |
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| Author: | Tom West [ Mon Feb 01, 2010 5:41 pm ] |
| Post subject: | Re: Floppy Top Syndrome |
Danny: There are lots of old guitars with decent names that have tops with the quarter way off but they still sound excellant.The quarter off by much more then yours. These were guitars built by factories. As individual builders we try to maximize the stiffness to weight issue.I've used spruce with the quarter similar to your and had success and unless you have someone there with you the best way is to just dive in and do it. Leave it at it's present thickness and use 5/8" tall X braces and see what happens.We all have to learn this be doing and adjust for the next one if need be. No one said it was going to be easy.Some of the other folks may give different opinions. Good luck and let us know how you make out. Tom |
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| Author: | Jeff Highland [ Mon Feb 01, 2010 8:41 pm ] |
| Post subject: | Re: Floppy Top Syndrome |
I would not make the braces any taller than you normally do. The problem is the soundboard spanning between the braces. If you had springy floorboard in your house, would increasing the size of the joists help? No you would have to decrease the spacing between joists So you could look at things like narrowing the x angle, shifting the x intersection towards the tail, moving the tone bars closer to the brdge etc. |
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| Author: | DannyV [ Mon Feb 01, 2010 8:47 pm ] |
| Post subject: | Re: Floppy Top Syndrome |
Hey Rod! Good to hear from you. How's life 2 ferry rides away? And John and Tom. I have gone down with the bracing and I'll just keep carving away and see what happens. The "Coach" just happened to drop by just as I started shaping with some sound advice. Colin. It seemed stiff with the grain but I find it a little hard to judge flexing in that direction. It is an OM BTW. I'll take your advice and go a little easy thinning around the edges. I'll let y'all know how it turns out. Thanks, Danny |
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