Official Luthiers Forum!

Solely owned and operated by Lance Kragenbrink
It is currently Wed Apr 01, 2020 2:48 pm


All times are UTC - 5 hours





Post new topic Reply to topic  [ 11 posts ] 
Author Message
PostPosted: Wed Sep 26, 2018 9:13 am 
Offline
Koa
Koa

Joined: Wed Feb 17, 2016 8:54 am
Posts: 596
State: Texas
Country: United States
Focus: Repair
I'm certain this has been covered before.

I'm not a fan of scoring a cross hatch pattern on the sole and top of bridges. This past month I've had a total of 4 that have "popped" from being scored and the small patches of the top that are separated gave way and came off. When I first started I did it on 2 guitars and both had come back within a year from the bridge lifting again. The same thing with the top grain being cut was the culprit.

In my mind I can see how this might make sense from a certain perspective to make the glue hold better. Sort of the same thought with a toothing plane from way back. But seeing these consistently come loose has me questioning this method.

From what I understand a smooth surface can get greater gluing area and can also easily be restored in the future should it need to be glued again.

Any thoughts?


Top
 Profile  
 
PostPosted: Wed Sep 26, 2018 9:51 am 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Sat Jan 31, 2009 8:50 pm
Posts: 1814
Location: Seattle WA
Focus: Build
Status: Semi-pro
It's fairly common that people used to score the underside of the bridge. Are you talking about scoring a cross-hatch pattern on the soundboard as well? If so, I've never heard of that and it sounds like a very bad idea.

_________________
Pat


Top
 Profile  
 
PostPosted: Wed Sep 26, 2018 10:30 am 
Offline
Koa
Koa

Joined: Wed Feb 17, 2016 8:54 am
Posts: 596
State: Texas
Country: United States
Focus: Repair
pat macaluso wrote:
It's fairly common that people used to score the underside of the bridge. Are you talking about scoring a cross-hatch pattern on the soundboard as well? If so, I've never heard of that and it sounds like a very bad idea.


Bridge and the top yes. On each one the fibers of the top give way and the bridge starts to peel off.


Top
 Profile  
 
PostPosted: Wed Sep 26, 2018 12:40 pm 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Sun Mar 06, 2011 12:04 am
Posts: 4257
First name: Chris
Last Name: Pile
City: Wichita
State: Kansas
Country: Good old US of A
Focus: Repair
Status: Professional
In 40 plus years of doing repair I've never scored the bottom of the bridge....

_________________
"Act your age, not your shoe size" - Prince


Top
 Profile  
 
PostPosted: Wed Sep 26, 2018 1:39 pm 
Offline
Cocobolo
Cocobolo
User avatar

Joined: Fri Feb 18, 2005 6:18 am
Posts: 265
Location: United States
First name: Frank
Last Name: Ford
City: Palo Alto
State: CA
Zip/Postal Code: 94301
Country: USA
Focus: Repair
Status: Professional
It's a well-documented fact that scoring does not help wood glue adhesion.

Too slick a surface CAN make for poor adhesion, although it's hardly ever and issue with hand worked scraped or sanded surfaces. I recall an issue with a run of factory guitars where the person using a router to remove finish from the top glue surface was trying to "save the company money" by not changing router bits on the prescribed schedule. By using a dull bit, he actually glazed the surface of the spruce, resulting in bridge glue failure on a fair number of instruments.

One argument I've heard in favor of 'toothing" the bottom of bridges has to do with positioning when it's glued. The idea is that the rougher surface may keep it from slipping as it's clamped. I've not noticed any such benefit myself.

Speaking of scoring/cross-hatching - - - It doesn't get any worse than this example:

Attachment:
scoredtop02.jpg


You do not have the required permissions to view the files attached to this post.

_________________
Cheers,

Frank Ford

FRETS.COM
HomeShopTech
FRETS.NET



These users thanked the author Frank Ford for the post (total 2): DanKirkland (Wed Sep 26, 2018 3:57 pm) • dpetrzelka (Wed Sep 26, 2018 3:47 pm)
Top
 Profile  
 
PostPosted: Wed Sep 26, 2018 5:16 pm 
Offline
Contributing Member
Contributing Member

Joined: Sun Feb 17, 2013 4:58 pm
Posts: 1205
First name: Ed
Last Name: Minch
City: Chestertown
State: MD
Zip/Postal Code: 21620
Country: United States
Focus: Build
Status: Amateur
There is another thread active here in the building page called"Brace radius sanding jig" and on page 2 there is a lively discussion of this. On page 3, Don Parker posted this:

https://www.popularwoodworking.com/tech ... -or-rough/

One of the letters following the article states that the FAA (airplane regulators) will not approve sanded joints for gluing, only those cut with an edge tool

Ed



These users thanked the author Ruby50 for the post: DanKirkland (Wed Sep 26, 2018 9:28 pm)
Top
 Profile  
 
PostPosted: Thu Sep 27, 2018 9:15 am 
Offline
Koa
Koa

Joined: Wed Feb 17, 2016 8:54 am
Posts: 596
State: Texas
Country: United States
Focus: Repair
Thanks for the comments and info Frank and Ed.

I actually found out that there's a shop in my area that has been "doing it that way for years" so I have a feeling I've not seen the last of them. Oddly enough it's the same shop that SRV went to back in the day.


Top
 Profile  
 
PostPosted: Mon Oct 01, 2018 8:56 pm 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Sat Jan 31, 2009 8:50 pm
Posts: 1814
Location: Seattle WA
Focus: Build
Status: Semi-pro
I can see the idea that scoring the bridge would help the glue to grab onto it although most people nowadays don't think that's true. Although, it probably would be a good idea if you were using epoxy.

But, scoring the Spruce seems like you would be losing the strength in the wood fibers right where you want it. Sort of like when you score the Finish around the bridge footprint you would be careful not to cut the wood fibers especially in the back of the bridge where all the force is wanting to pull it up.

_________________
Pat


Top
 Profile  
 
PostPosted: Tue Oct 02, 2018 9:37 am 
Offline
Koa
Koa

Joined: Wed Feb 17, 2016 8:54 am
Posts: 596
State: Texas
Country: United States
Focus: Repair
pat macaluso wrote:
I can see the idea that scoring the bridge would help the glue to grab onto it although most people nowadays don't think that's true. Although, it probably would be a good idea if you were using epoxy.

But, scoring the Spruce seems like you would be losing the strength in the wood fibers right where you want it. Sort of like when you score the Finish around the bridge footprint you would be careful not to cut the wood fibers especially in the back of the bridge where all the force is wanting to pull it up.


Odd, I just had one come in on Saturday that was epoxied. Same thing happened, it just ripped the top fibers right off. The scoring did zilch to help it adhere.

I had a long discussion on this with one of the older repair guys around me that I know. He seems convinced that it's the only way to do things. I just left it at agreeing to disagree on the matter. However this recent one with the epoxy makes 5 so far in less than 2 months. I am simply going to fix what I can and leave whomever is doing this to their old ways.


Top
 Profile  
 
PostPosted: Tue Oct 02, 2018 9:58 am 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Sat Jan 31, 2009 8:50 pm
Posts: 1814
Location: Seattle WA
Focus: Build
Status: Semi-pro
I was just referring to scoring the bridge and using epoxy. I can't see how slicing through the fibers of your sound board would ever be a good idea.

Well, at least you'll have a steady stream of work coming in!

_________________
Pat


Top
 Profile  
 
PostPosted: Wed Oct 03, 2018 2:45 pm 
Offline
Koa
Koa

Joined: Wed Feb 17, 2016 8:54 am
Posts: 596
State: Texas
Country: United States
Focus: Repair
pat macaluso wrote:
I was just referring to scoring the bridge and using epoxy. I can't see how slicing through the fibers of your sound board would ever be a good idea.

Well, at least you'll have a steady stream of work coming in!


You're right it's a terrible idea to score the top. I was saying it's odd how you posted that and I just that one roll through. Weird timing really



These users thanked the author DanKirkland for the post: Pmaj7 (Wed Oct 03, 2018 2:58 pm)
Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 11 posts ] 

All times are UTC - 5 hours


Who is online

Users browsing this forum: No registered users and 3 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