to scribe, or not to scribe

kurt ratering · #1 02-19-2009, 08:21 AM

to the luthiers out there, when replacing a fingerboard does scribing the glue surface of the f.b. and neck make for a better joint? i have done it both ways with great success, and was just wondering what other luthiers do.

Jake deVilliers · #2 02-19-2009, 09:59 AM

You're talking about scratching up the surface, right?

That's never made any sense to me. Unless you're using epoxy all you're doing is lessening the bonding surface. When I'm gluing a guitar top or bridge or a DB fingerboard or neck joint I want as much gluing area as possible. Don't I?

Unless you wanted to weaken the bond.....

vejesse · #3 02-19-2009, 10:06 AM

The U.S. Forest Products Laboratory did a study and determined that scoring the wood does nothing to improve a glue joint. I think these tests were done with hide glue and aliphatic resin but I could see epoxy glue joints benefiting from a roughed up surface.

1st Bass · #4 02-19-2009, 12:32 PM

My first contact with hot hide glue was through a friend who used it to produce obscure glass. He coated a pane of heavy plate glass with hot hide glue, and then slid it into a padded envelope. As the glue dried, one could hear the shards of glass splintering as they were literally pulled from the face of the pane of glass. The result was beautiful, and very impressive-- the entire surface of the glass, which had been as smooth as...well...glass, was completely tranformed into a surface that looked like flaked obsidian. No scoring needed. Glue-1 Glass-0

kurt ratering · #5 02-19-2009, 12:53 PM

Quote:

Originally Posted by Jake deVilliers

You're talking about scratching up the surface, right?

Unless you wanted to weaken the bond.....

yeah, the light cross hatching
job security

forester · #6 02-19-2009, 07:43 PM

the cross hatch seems less common on the cello/basses then it does on violin/violas,perhaps it has something to do with a greater gluing surface on the larger instruments. a lot of times i end up scraping most of the cross hatch away in cleaning the surfaces for a new joint.. i yank a lot of FB's i will in the future be mindfull of which gluing technique is more difficult to separate and if one style is more prone than the other to tear wood.

arnoldschnitzer · #7 02-20-2009, 06:34 AM

Old-timers scratched up glue surfaces because they did not really understand how glue works. They assumed that the glue put out little "fingers" from one surface to the other, and that these "fingers" pulled tight as the glue cured. In reality, glue works via an electro-chemical attraction, and the smoother the surface the better.

I've come across many fingerboards which have been routed down the center. There is a small longitudinal slot let into the ebony, I assume for dripping something down there to facilitate removal. Anybody know more about this technique?

Mark Carlsen · #8 02-20-2009, 08:06 AM

I always thought that channel was to help keep the FB from sliding around when gluing and clamping...Kind of a suction cup effect...

gp_bass · #9 02-20-2009, 08:54 AM

Quote:

Originally Posted by Mark Carlsen

I always thought that channel was to help keep the FB from sliding around when gluing and clamping...Kind of a suction cup effect...

i've had it explained in this way, as well as making it easier to get the surface to make contact at the edges - no high spots in the center so the board can rock around.

in construction, i've seen boards kerfed in this way to prevent cupping due to moisture or dryness. could the routed channel also have this effect?

Jake deVilliers · #10 02-20-2009, 11:26 AM

Quote:

Originally Posted by arnoldschnitzer

There is a small longitudinal slot let into the ebony

Tongue and groove hardwood flooring has rounded grooves in the back to give it a little room to move with the seasons. I wonder if the groove you've seen is an off-shoot of that?

Jake deVilliers · #11 02-20-2009, 11:28 AM

Quote:

Originally Posted by Mark Carlsen

I always thought that channel was to help keep the FB from sliding around when gluing and clamping...Kind of a suction cup effect...

That's one of my favourite characteristics of hide glue - when you put it down, it stays! It was the hardest thing to adjust to when coming over from Titebond but now I love it.

**Matthew Tucker** · #12 02-20-2009, 12:27 PM

No, actually I think that groove is there to allow for glue squeeze-out in the same way that a dowelled joint always needs a small groove or grooves in the dowel to allow the excess glue to escape. With hide glue, as you know well, the less glue in the joint - as long as there is some glue there - the better.

forester · #13 02-20-2009, 02:12 PM

my vote is toward the manufacturer...in an effort to stabilize their product..relieve the tension wood..prevent cup/bow...but wait... i have seen a similar groove in the necks of several violins,stopping short of the nut and the heel...so now i don't know what to think....wood policy or glue policy

er..sorry for everything..