Official Luthiers Forum!

Owned and operated by Lance Kragenbrink
It is currently Thu Mar 28, 2024 10:48 am


All times are UTC - 5 hours


Forum rules


Be nice, no cussin and enjoy!




Post new topic Reply to topic  [ 81 posts ]  Go to page 1, 2, 3, 4  Next
Author Message
PostPosted: Fri Dec 14, 2018 12:37 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Tue May 13, 2008 10:44 am
Posts: 6232
Location: Virginia
I'm struggling to figure this out but I need to make this a learning experience and move on. Here are the details:

1) Top is Sitka
2) X-Brace at 96deg and 1/4in bracing Sitka
3) Bridge patch: Flat Sawn Osage Orange laminated to QS Spruce (grain direction of spruce same as top)
4) Bridge is BRW and the x-Brace extend through the lower corner of bridge wings
5) straight bracing, not scalloped

None the less the top is extremely distorted at the bridge corners. I use deflection testing for the top and this top I have made stiffer then most. In fact the last guitar I built deflected twice as much and has no problems and is of the same design.

I double and triple checked and the bracing is definitely not loose.

The only thing I can think of is that the X is twisting. The distortion is right on top of the X-Bracing.

Here is a pic of the bass side:

Image

Here is the treble side, It's harder to see here because it's not as bad:

Image

Here is a shot of the bracing:

Image

This is extremely disappointing and I'm struggling to figure out what the problem here is, any input would be greatly appreciated. I have no other choice but to retop this guitar. But I want to learn from this and never let it happen again.

Regards.


Last edited by jfmckenna on Sat Dec 15, 2018 11:12 pm, edited 4 times in total.

Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 12:51 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Wed Feb 20, 2008 7:15 pm
Posts: 7219
First name: Ed
Last Name: Bond
City: Vancouver
Country: Canada
Focus: Build
Status: Professional
Wish I had an answer for you.

Why do you feel it needs to be retopped?


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 1:00 pm 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Mon Aug 23, 2010 11:42 pm
Posts: 1701
First name: John
Last Name: Parchem
City: Seattle
State: Wa
Zip/Postal Code: 98177
Country: USA
Focus: Build
Status: Amateur
Was the top plate thickness in your normal range? The braces can make the top stiff as read by a deflection test, while a thin top can telegraph the braces and\or stress points around the bridge. I had to retop my 8 string nylon crossover because the top was too thin. It did sound nice though, I did not want it going to a client that way.

_________________
http://www.Harvestmoonguitars.com


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 1:09 pm 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Fri Jan 22, 2010 9:59 pm
Posts: 3552
First name: Dennis
Last Name: Kincheloe
City: Kansas City
State: MO
Country: USA
Focus: Build
Status: Amateur
Flat bridge glued to radiused soundboard with brute force clamping pressure?


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 1:39 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Tue May 13, 2008 10:44 am
Posts: 6232
Location: Virginia
johnparchem wrote:
Was the top plate thickness in your normal range? The braces can make the top stiff as read by a deflection test, while a thin top can telegraph the braces and\or stress points around the bridge. I had to retop my 8 string nylon crossover because the top was too thin. It did sound nice though, I did not want it going to a client that way.

That's exactly the position I am in. This is not deliverable. I don't even really measure thickness. Well, I do and I enter it in my book, but none the less I hold deflection as the more valuable measurement when designing the top. And that's why it's confusing because this top was stiffer then what I usually go for because I was going for a more treble tone.

Ed, The pics don't do it justice. If you run your finger over this you can really feel it. I usually go for a bit of bridge rotation and top belly but in this case there is something else going on.

Dennis, I forgot to mention, both the bridge and the bridge plate were arched to accept the top. The bridge and plate were glued down with an arched caul as well.


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 1:45 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Wed Feb 20, 2008 7:15 pm
Posts: 7219
First name: Ed
Last Name: Bond
City: Vancouver
Country: Canada
Focus: Build
Status: Professional
Yes, I could see that being a problem if it's for a client. Just out of curiosity, did you measure bridge rotation? Is a laminated bridge plate your usual practice?


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 1:49 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Tue May 13, 2008 10:44 am
Posts: 6232
Location: Virginia
meddlingfool wrote:
Yes, I could see that being a problem if it's for a client. Just out of curiosity, did you measure bridge rotation? Is a laminated bridge plate your usual practice?

No it's not a usual practice but I have done it before including the last one which was essentially the same as this one only the top was twice less stiff... Hence my confusion.


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 1:53 pm 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Fri Jan 22, 2010 9:59 pm
Posts: 3552
First name: Dennis
Last Name: Kincheloe
City: Kansas City
State: MO
Country: USA
Focus: Build
Status: Amateur
Hmm, this really is a stumper. How long has it been strung up? How much distortion remains when the strings are loosened?


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 2:16 pm 
Offline
Contributing Member
Contributing Member

Joined: Tue Jan 03, 2006 1:47 pm
Posts: 1624
Location: United States
First name: Larry
Last Name: Hawes
Focus: Build
Status: Amateur
That's a real stumper. Can you please let us know what you discover?

_________________
Thank You and Best To All


Last edited by LarryH on Fri Dec 14, 2018 2:46 pm, edited 1 time in total.

Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 2:32 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Tue May 13, 2008 10:44 am
Posts: 6232
Location: Virginia
DennisK wrote:
Hmm, this really is a stumper. How long has it been strung up? How much distortion remains when the strings are loosened?

Good question. I strung it up for a week now and it slowly progressed to this point and stopped. The distortion almost goes away when the strings are off but it's still there.


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 3:10 pm 
Offline
Koa
Koa

Joined: Wed Feb 17, 2016 8:54 am
Posts: 854
State: Texas
Country: United States
Focus: Repair
Some reason I can't see the pics?


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 3:20 pm 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Wed Oct 08, 2008 11:36 am
Posts: 7241
Location: Southeast US
City: Lenoir City
State: TN
Zip/Postal Code: 37772
Country: US
Focus: Repair
DanKirkland wrote:
Some reason I can't see the pics?
Me either.

_________________
Steve Smith
"Music is what feelings sound like"


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 3:38 pm 
Offline
Koa
Koa
User avatar

Joined: Sun Jun 22, 2014 1:45 pm
Posts: 1445
First name: Michael
Last Name: Colbert
City: Anacortes
State: WA
Focus: Build
Me either


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 4:06 pm 
Offline
Koa
Koa

Joined: Sun Jun 20, 2010 2:52 pm
Posts: 519
Focus: Build
Status: Professional
I also can not see the pictures!


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 4:57 pm 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Mon Apr 16, 2012 12:47 pm
Posts: 2422
First name: Jay
Last Name: De Rocher
City: Bothell
State: Washington
I can't see them either, but they were visible this morning.

_________________
Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 5:07 pm 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Sat Feb 02, 2008 4:01 pm
Posts: 1104
Location: Winfield, IL.
Since I can't see the pics either, I'm going to take a complete stab in the dark.
Is your bridge patch in the correct position? With a hardwood patch I shoot for 1/8" in front and behind the bridge, when doing a softwood laminate I add another 1/8" in either direction.

Steve


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 5:29 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Tue May 13, 2008 10:44 am
Posts: 6232
Location: Virginia
I hate Google Photo's!

I re-posted the images. Hopefully you can see now.


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 5:40 pm 
Offline
Koa
Koa
User avatar

Joined: Sun Jun 22, 2014 1:45 pm
Posts: 1445
First name: Michael
Last Name: Colbert
City: Anacortes
State: WA
Focus: Build
jfmckenna wrote:
I hate Google Photo's!

I re-posted the images. Hopefully you can see now.


I can see the first two. The bracing shot is still missing on my feed anyway.


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 5:55 pm 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Fri Jan 22, 2010 9:59 pm
Posts: 3552
First name: Dennis
Last Name: Kincheloe
City: Kansas City
State: MO
Country: USA
Focus: Build
Status: Amateur
Yep, the two outside photos are showing again now, but not the bracing.
StevenWheeler wrote:
Since I can't see the pics either, I'm going to take a complete stab in the dark.
Is your bridge patch in the correct position? With a hardwood patch I shoot for 1/8" in front and behind the bridge, when doing a softwood laminate I add another 1/8" in either direction.

Steve

I saw the bracing picture earlier, and the bridge patch extends plenty far behind the bridge. The distortion is happening right on the bridge patch, which is part of why it's so puzzling. It shouldn't be possible for such a thick sandwich of material to deflect so much.

jfmckenna, check again that the lower corners of the bridge patch are still glued down. See if you can stick one hand inside the box, hook your finger around to get your nail at the potential gap, and then push down on the soundboard from outside to try and flex it open.


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 6:03 pm 
Offline
Cocobolo
Cocobolo

Joined: Thu Nov 27, 2014 10:35 am
Posts: 356
Location: Hopkinton, MA
First name: Robert
Last Name: Ionta
City: Hopkinton
State: Massachusetts
Zip/Postal Code: 01748
Country: USA
Focus: Build
Status: Amateur
Might there be a void in the bridge patch lamination? Layers separating?


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 6:18 pm 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Thu Feb 09, 2006 2:35 pm
Posts: 2951
Location: United States
First name: Joe
Last Name: Beaver
City: Lake Forest
State: California
Focus: Build
That is strange. The deflection appears to be right over, or at least close to the x, but it doesn't seem to be influenced by the x. Strange indeed.

_________________
Joe Beaver
Maker of Sawdust


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 6:30 pm 
Offline
Koa
Koa

Joined: Wed Feb 17, 2016 8:54 am
Posts: 854
State: Texas
Country: United States
Focus: Repair
So some thoughts and I'm just going to throw these out for discussion sake.

That kind of distorion almost always happens when a brace isn't glued well enough. I've fixed it on numerous guitars. I'm not trying to sound accusatory but are you 150% certain that the braces are glued well enough?

On the bridge. Possible that your glue joint is stronger on the wings than the middle?

On the bridge plate. What's the grain orientation of the osage piece?


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 6:35 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Sun Mar 30, 2008 8:20 am
Posts: 5924
Do you do perimeter sanding? The top might be thin around the edge. If the top regains it's shape when you loosen the strings you could add a tall finger brace (a.k.a. side tone bar) where the deformation is occurring and see if that helps.


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 7:38 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Wed Apr 08, 2009 9:34 am
Posts: 3081
Can't see any but 3 photos JF...


Top
 Profile  
 
PostPosted: Fri Dec 14, 2018 7:40 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Tue May 13, 2008 10:44 am
Posts: 6232
Location: Virginia
I tried posting the pic again.

I know what you are thinking because I had the same thoughts but the Bridge patch is absolutely 100% not coming apart. The braces are not loose either.

I do normally thin the edges but not on this one :D

The osage is flat sawn, spruce is QS along the lines of the top. Nice stiff and light plate it was.

I'm thinking that the X is actually twisting and that a 1/4in X-Brace at 96deg angle is too much. Thoughts?


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 81 posts ]  Go to page 1, 2, 3, 4  Next

All times are UTC - 5 hours


Who is online

Users browsing this forum: Chris Pile, rbuddy and 43 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB® Forum Software © phpBB Group
phpBB customization services by 2by2host.com