The case against scroll "strengtheners"

[Rob Grant]

Dale, I'm not sure what you mean by "half-lapping."

Here's a back view of a 2.5mm veneered F5 headstock with Cooktown Ironwood blending into the three-piece neck centre strip. The reverse face is 2.5mm ebony. This is not a "fragile" headstock. The centre strip of Cooktwon Ironwood that extends out to the point and the extra "beef"(thick veneers on both sides) securing the scroll makes for a knock about headstock that seems to readily take abuse.

[Dale Ludewig]

In furniture type work, there is a joint called a half lap. I can't draw a picture here on the cafe right now, but think of a picture frame, one corner with the two pieces coming together. One piece going vertical, the other horizontal- a right angle. It's not mitered (mitred). Half the depth of one piece is cut away, half of the other. The two pieces' grain are running at right angles to each other and are flush top and back. I'll try to figure out how to post a drawing unless someone beats me to it.

[Dale Ludewig]

Here's a quick try......

[Rob Grant]

Dale,

Perfectly clear. I've always called that a "scarf joint" (which according to Google it isn't). Thanks for setting me straight.

[Ivan Kelsall]

As well as from the 'added strength' point of view,i've alway liked the addition of a rear headstock veneer,even against a dark neck.
A black rear veneer would look very nice indeed against any light coloured wood. I don't know if this is a veneer or stain on the Collings MF,but it's a real attention grabber,& there's nor reason why the (a) veneer shouldn't (couldn't) be thick enough to give the additional support to the scroll.The sideview on the headstock with a black veneer front & back, would also look very good (IMHO),
Ivan

[BradKlein]

Since the grain of any veneer is running the same direction approximately as the grain of the neck/headstock, I don't see that the strength of a maple sandwich is going to be a lot greater than maple with no veneer on either side, for example. Depending on wood choice it might be slightly less (or more) prone to breakage, but short grain is short grain, no?

I no longer have a wood shop, or i'd make up a dozen test scrolls, and have some fun knocking them off.

That said, just the words "Cooktown Ironwood" suggest a veneer that can bar-room brawl with the best of 'em. But overall, I think the OP's point is well taken.

[sunburst]

...overall, I think the OP's point is well taken.

Yes, I think I've made the point I was trying to make (scrolls break if you hit them hard enough, they're harder to repair when there's a "strengthener" present), but just one more point about why those little round cross-grain biscuits can be of little strengthening value.

In order for a glue joint in wood to be as strong as it can be, the two pieces of wood must fit precisely against one another on their side grain surfaces. The end grain of wood does not glue nearly as strongly as side grain (it can be bonded fairly strongly with epoxy). If we look at the situation with a round disc inlaid cross grain into another piece of wood we see that the majority of the joint around the edge of the disc is end grain, either in the disc or the surrounding wood. In light of that, for there to be any strength, the bottom of the cavity and the bottom of the disc must be accurately matching surfaces and they must fit together tightly.
Here are two images, the first one showing the end grain of the disc to each side, and the end grain of the head stock to the top. (There is end grain at the bottom too, but I didn't mark it because most of it is cut away anyway.) The second image shows the fit between the disc and the bottom of the cavity. The fit was obviously better on the other side of the disc, as evidenced by the neck wood that remained glued to the disc, but this hardly qualifies as a good fit.

[Tom C]

So these things fails after 80 years of expanding and skrinking. How about strength when new?
To last 100 years, what differences would you make?
How about carbon fiber binding?

[Ivan Kelsall]

From Brad - "Since the grain of any veneer is running the same direction approximately as the grain of the neck/headstock....". The point i was aiming at is that it doesn't have to run like that at all. There's no reason that if you consider the headstock wood grain to be running 'vertically upwards',then the grain of the veneer on either side of the headstock 'could' run at at an angle to the headstock grain - one direction on the front & the opposite direction on the back.The only thing against doing that, is that you'd have end grain showing at the headstock edges. However,since the top of a 'normal' headstock has end grain showing,it shouldn't be too much of a problem re.finishing - just an idea,
Ivan