Official Luthiers Forum!
http://www-.luthiersforum.com/forum/

Back center strips/ 2 questions
http://www-.luthiersforum.com/forum/viewtopic.php?f=10101&t=40829		 Page 1 of 1
Author:  WendyW [ Mon Jul 08, 2013 10:03 am ]
Post subject:  Back center strips/ 2 questions
Why is it that classical backs are joined typically with the center strip as part of the center joint and steel strings usually have the center strip inlayed after the back is joined?

another question: I want to have a center strip that is ebony with w/b/w/b on either side. In the w/b/w/b I have from LMI, the black is fiber. Is it ok that the joint includes fiber? I will be flooding the joint with CA, so I would think that would make the fiber more solid or whatever.
Thanks, Wendy
Author:  WaddyThomson [ Mon Jul 08, 2013 3:58 pm ]
Post subject:  Re: Back center strips/ 2 questions
I route mine when I put one.
Author:  MikeyV [ Mon Jul 08, 2013 7:03 pm ]
Post subject:  Re: Back center strips/ 2 questions
I'm a sammich-er. I've glued Fiber in the sammich, but not at the edges. I would use a maple strip on the outer lines, at least it's wood. The fiber de-laminates, you can peel them right apart. And I mean one color strip, it'll peel apart in the middle.

Either way, I think the center re-inforcement inside does most of the work.
Author:  Tom West [ Mon Jul 08, 2013 7:46 pm ]
Post subject:  Re: Back center strips/ 2 questions
Center stripe goes in during glue-up for me with steel strings. If it is not a solid strip I use CA glue on both sides after thickness sanding.
Tom
Author:  runamuck [ Mon Jul 08, 2013 8:07 pm ]
Post subject:  Re: Back center strips/ 2 questions
I would not trust fiber unless the center strip is inlayed - CA glued or not.
I've seen it come apart easily when I've used it for rosettes.
Author:  theguitarwhisperer [ Mon Jul 08, 2013 9:55 pm ]
Post subject:  Re: Back center strips/ 2 questions
I like to inlay it, I just feel I get a better joint. Some people do that and forgoe the seam reinforcement.
Author:  Joe Beaver [ Tue Jul 09, 2013 2:13 am ]
Post subject:  Re: Back center strips/ 2 questions
The only problem I have with the sandwich version is making sure the backstrip and purfling are as thick as the back. Using a binding piece that is say .075-.08 when the back is .10 or more seems wrong to me. Other than that I would trust CA flooded fiber as long as it matches back thickness.
Author:  Tai Fu [ Tue Jul 09, 2013 4:33 am ]
Post subject:  Re: Back center strips/ 2 questions
I sandwich them because I don't want to have to worry about routing a slot wrong... way too much opportunities for things to go wrong when routing a slot. However Cumpiano says that the back will be too weak or something, however I think there is a reason why there is a backstrip. As for thickness they are always thicker than .090" so it's not really an issue.
Author:  Robert Hosmer [ Tue Jul 09, 2013 7:42 am ]
Post subject:  Re: Back center strips/ 2 questions
Tai Fu wrote:
I sandwich them because I don't want to have to worry about routing a slot wrong... way too much opportunities for things to go wrong when routing a slot. However Cumpiano says that the back will be too weak or something, however I think there is a reason why there is a backstrip.

Cumpiano advises against the process of "sandwiching" only when using marquetry strips; full-length solid strips and veneer laminates are OK to sandwich.
Author:  WendyW [ Tue Jul 09, 2013 10:45 am ]
Post subject:  Re: Back center strips/ 2 questions
Well, based on all the replies I think I will go ahead and sandwich as planned, but I will cut my own veneer strips instead of including fiber in the mix. Too bad, it would have been so much simpler to just use the w/b/w/b, because now I will have to do all the side purfling strips individually too. It would have been easier to just bend the w/b/w/b with the binding.
Author:  jfmckenna [ Tue Jul 09, 2013 12:48 pm ]
Post subject:  Re: Back center strips/ 2 questions
Either method is fine and I have used both but I have always felt that routing would make a better joint as you are essentially creating a lap joint. In fact on one guitar I built I did a lap joint on the two halves with no back strip because I thought it would be a better joint. It is but it also was a PIA so I never did it again. The sandwich is plain and simply easier and pretty much just as good a joint.

I cannot however even imagine taking a router to closed box. That's a good 30 - 40 hours of work that could be completely destroyed with one slip ;)
Author:  Mike Collins [ Tue Jul 09, 2013 1:38 pm ]
Post subject:  Re: Back center strips/ 2 questions
I agree with jfmckenna;
I've used both methods -but trust the inlaid joint more.

Mike
Author:  Mike Collins [ Tue Jul 09, 2013 2:05 pm ]
Post subject:  Re: Back center strips/ 2 questions
No two back strip inlays are the same on my guitars.
Some can be 6-8mm wide.
Abalone & wood strips.
some 2mm wide.

If I rout a channel I can set the depth so the 2 back pieces are still glued
together & the inlay helps with strength.
Yes the web over the back joint on the inside
will help -but I like the extra assurance of the 2 joints.

I've fixed many guitars with back joint/purf. problems.

Mike
Author:  Michael.N. [ Tue Jul 09, 2013 2:08 pm ]
Post subject:  Re: Back center strips/ 2 questions
There's a lot holding that joint together. The reinforcing strip, the back bars. You would have to be pretty sloppy to have that joint come apart.
Author:  Mike Collins [ Wed Jul 10, 2013 12:50 pm ]
Post subject:  Re: Back center strips/ 2 questions
Michael;
It's usually a low humidity condition that causes
separation.

Mike
Author:  JoeUlman [ Wed Jul 10, 2013 1:53 pm ]
Post subject:  Re: Back center strips/ 2 questions
I've had joint separation on two guitars occurring along several inches of one or both sides within a pre-made maple-rosewood-maple center strip where it was sandwiched between the back halves. The separation was invisible to the naked eye but could be felt with a finger. I don't believe it was humidity as neither guitar experienced lower humidity than the pre-assembly/assembly humidity. I'm inclined to think it may be due in part to the arch induced after joining. At any rate I now inlay the center strip.

BTW, the problem areas were satisfactorily fixed by light dry sanding w/600 grit, flooding with CA, and redoing the French polish in the affected areas.


Joe
Page 1 of 1 All times are UTC - 5 hours
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/