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View Full Version : sound board scarf joint vs butt w/ grafts



johneverett
04-21-2015, 03:06 AM
Hi
anyone ever scarf a soundboard together rather than butt and graft?
If so, does it make any noticeable difference to sound quality?

Beau Hannam Ukuleles
04-21-2015, 04:47 AM
no difference to sound quality.

your center line would shift the more you sanded it.

sequoia
04-21-2015, 08:01 AM
I've never done it but I've thought about it. Master guitar makers Cumpiano and Natelson use a scarf joint to join their top plates ("Guitar Making: Tradition and Technology; Chronicle Books, pg 98). The advantages are more surface gluing area for a stronger joint and a sharper edge. You have to think upside down and backwards with your plates when you plane/sand the edge. Beau is right, the centerline would shift the more angle you put on the scarf, but since you still line up the center line on center, it wouldn't make a difference on the show side of the top. On the underside however the centerline would be shifted slightly.

Doug
04-21-2015, 08:29 AM
David Hurd writes about it on his web site. Ukuleles.com.

johneverett
04-21-2015, 09:13 AM
Wow! Lots of great info there Doug. Thanks. Didn't find the section on scaring but I'll keep looking

Appreciate the book reference too sequoia. Thanks

Beau Hannam Ukuleles
04-21-2015, 09:31 AM
Glue line are more visible with a scarf joint- think about it- a glue line on an angled plane is longer over the same distance compared to a normal 90/90 angle. This can be seen on classical guitar headstocks where the bwb ramps are cut- the bwb is elongated.

The angle would have to be pretty large to gain a larger gluing surface.

Scarf joins on headstocks are stronger- but thats a 1" glue join.

johneverett
04-21-2015, 10:02 AM
An inch is about what I was thinking. Approximately 12:1

I understand the offset issue.... center line ect...

Not sure joint is more visible unless not cut well, wavy from differences in sanding, and or poor alignment during glue up. Lots to go wrong for sure.

Sven
04-21-2015, 10:20 AM
One inch? If you thin the edge down like that it will curl when you apply the glue, and it will be much harder to make a clean bookmatch. The edge will lack definition. I would make a complete mess out of it - try it on scrap before you waste good wood. It's much easier to find pieces wide enough for a one piece top if the seam makes you nervous. Prove me wrong and post some pics of it, and I mean that sincerely.

Sven

johneverett
04-21-2015, 11:24 AM
Feel like l amost have to try it now.
:)

Kekani
04-21-2015, 12:22 PM
I predict your centerline will be akin to sanding down ablam, or more specifically, laminate MOP.

Stuffing a Big Block into a new gen Camaro - that's the kind of challenge we'd like to see. All of the engineering required will be a sight to see. But mostly the end result, if done properly, which should be something phenominal.

In this case, there's so much to go wrong with a 1" scarf on a .070" plate. All I need to ask is what I normally do - where do I want to end up? Then backwards plan from there.

The path taken to the end result is nothing like the car example above - increasing degree of difficulty just to say you could, or did? Okay, admittedly, I can see that, but not at the sake of time in process when there's no real improvement that would make it viable.

Here's an example, admittedly, of "because I can" - mortise and tenon bolt on neck v. bolt on butt joint. Increased degree of difficulty in the M&T "because I can". Butt (pun intended), the shift in other processes affected makes it well worth it, for me. Unless you're a builder, you wouldn't understand. So it becomes a "feature" (because I can) rather than a solution (for a problem I never knew existed).

Philstix
04-21-2015, 04:34 PM
I have never seen a top joint which is either scarfed or any type of butt joint. A butt join is end grain to end grain and a scarf joint is that same joint with an angle cut into each piece so that the glue joint is face grain to face grain. Both are used to elongate a piece. Every top I have ever seen is an edge join. What is being called a scarf joint is in reality just an angled edge join. Sorry for being pedantic. That said, there is no need to angle the edge join as a straight join is plenty strong. On the other hand there is no harm in an angled edge join and it is not hard to do well if you are cutting both pieces at the same time. If you are sanding the joint I would advise foregoing the angle as any wobbles will be magnified.

Allen
04-21-2015, 08:24 PM
I can't be the only one who would like to have a bucket of pop corn, a 6 pack and sit down and watch this join be made and glued up.

Like a late night movie. It will be full of suspense, trepidation, horror and disaster......with a bunch of swearing through the entire procedure.

And if none of the other Pro's here are going to say it, I will.

Give your head a shake. You really need to ask yourself what the heck do you think your accomplishing? If it was a good idea, then the pro's would be doing it.

Beau Hannam Ukuleles
04-22-2015, 03:52 AM
I can't be the only one who would like to have a bucket of pop corn, a 6 pack and sit down and watch this join be made and glued up.

Like a late night movie. It will be full of suspense, trepidation, horror and disaster......with a bunch of swearing through the entire procedure.

HAHAHHA.

a normal 90/90 join holds together for centuries under decent conditions- thats good enough for me.

sequoia
04-22-2015, 08:37 AM
Like a late night movie. It will be full of suspense, trepidation, horror and disaster......with a bunch of swearing through the entire procedure.

Good one Allen. I needed a chuckle this morning...Good point too.

jcalkin
04-23-2015, 04:21 AM
No one else here seems to join plates using a 6x48 belt sander, but for me it works perfectly and is super fast. I always try to make a 90 degree seam, but since I do it free hand a bit of tilting is probably happening. It would be a simple matter to tilt the wood intentionally to get the sort of joint being discussed, but I'm positive I could never get a 1" wide joint on wood that thin and keep it true. And like others here, I don't see the point.

I owned Cumpiano and Natelson's book for decades, but the snooty nature of the writing and the jumping around from steel string to classical kept me from reading it much. I was given all the other how-to-luth books for review purposes and found that after reading them I never referred to them again, so last year they all went to ebay to lighten life's load. Video is the way to learn a craft these days. UU also suits me well. I honestly don't expect to learn much that's new, but one never knows, do one? Robbie O'Brien is planning a uke making on-line series (for money, not gratis), and if I was a struggling beginner I'd watch for it. His steel string guitar series and mandolin series are excellent. If Pete goes ahead with his uke videos they will likely be a good investment, too.

RPA_Ukuleles
04-23-2015, 07:31 AM
Hmm, hope you have a microscope and a high quality plane.

So an inch long scarf joint on a say, .075" thick topů that's a loooong thin little wedge you're cutting. Here's a diagram...

78822

I don't think there's room for glue on this one. Better just go ahead and dovetail it. ;)

grenosi
04-23-2015, 08:25 AM
Hi!

A soundboard scarf joint is like fixing wheels to a tomato - time-consuming and absolutely unnecessary.
A joint made in the traditional way (plane and a shooting board) is strong enough, actually stronger than the wood.

johneverett
04-23-2015, 09:21 AM
For Sven,


https://www.dropbox.com/sh/ouxaevskktadiz4/AAAxuwIxE4qBPi1xvbxgAPKga?dl=0

15 minutes to cut (includes time for crude bevel support jig)
glue didn't curl the fine edges (quarter sawn cedar)
10 minute glue up

I can't say whether this joint is necessary or beneficial ....are ukes necessary or beneficial?
I can say it is possible to do this joint relatively quickly and easily.

Haven't decided if I'm going to use the method or not but I satisfied my own curiosity thanks in part to a little push from Sven, who is lucky to live in the land of the wonderful First Aid Kit. Hope everyone is having a great spring.

Sven
04-23-2015, 10:40 AM
Nice work! And thanks for the pics. I did really mean what I wrote, I was curious and not trying to be a smart arse. I gravitate towards one piece tops on all sizes nowadays, since I cracked resawing really wide boards.

Sven

johneverett
04-23-2015, 10:59 AM
Nice work! And thanks for the pics. I did really mean what I wrote, I was curious and not trying to be a smart arse. I gravitate towards one piece tops on all sizes nowadays, since I cracked resawing really wide boards.

Sven

You're welcome Sven.
I didn't think that you were being insincere. Thanks for the gentle nudge. Impressive that you are re-sawing wide planks. Carbide bandsaw teeth?

redyak3
04-23-2015, 06:08 PM
Hi!


A joint made in the traditional way (plane and a shooting board) is strong enough, actually stronger than the wood.

I agree.
The drawings on page 98 in the Cumpiano, Natelson book has me a little confused. I used the shooting board method discussed in the book on two guitars and the tenor in progress. Never paid attention to the drawing till now. Stacking the plates as shown (5-3) and shooting them on the board, how would one get the angled edge shown in fig 5-2? Thought keeping everything flat, square and flush was the whole idea of using a shooting board.

Michael N.
04-24-2015, 01:23 AM
I haven't got that book to hand (I have it somewhere) but I'm guessing that they show the edge joint as being with a slight angle? You then flip one of the boards over and bingo! the joint is a match. Just like the ridiculous scarf joint in this very thread, except that in comparison the angle/scarf is extremely slight. You certainly wouldn't call it a scarf joint though.
This method is or was the normal one for joining/shooting thin plates. It accounts for any very slight tilt or lateral adjustment in the jointer Plane. It makes perfect sense because any tilt (no matter how slight) is going to be magnified when the plates are joined if the plates are not stacked in the correct sequence.
This exact same method of jointing is also shown in the Mcleod/Welford book on Classical Guitar making, a book that predates the Cumpiano by some 15 years or so. It just allows for any slight tilt in the blade, whether intentional or not.

rmaine
04-25-2015, 07:58 PM
For Sven,


https://www.dropbox.com/sh/ouxaevskktadiz4/AAAxuwIxE4qBPi1xvbxgAPKga?dl=0

15 minutes to cut (includes time for crude bevel support jig)
glue didn't curl the fine edges (quarter sawn cedar)
10 minute glue up


How thick was the top plate?

Sven
04-26-2015, 03:17 AM
You're welcome Sven.
I didn't think that you were being insincere. Thanks for the gentle nudge. Impressive that you are re-sawing wide planks. Carbide bandsaw teeth?

No, not even a bandsaw actually. See it here:
http://forum.ukuleleunderground.com/showthread.php?106388-Resawing-by-hand

Hluth
04-30-2015, 07:04 AM
I agree with the comments not in favor of a scarf joint for joining plates. 90 degree Edge joint is the way to go. To take it one step further, you can make your joint in all early wood if the grain is straight enough. That way if the glue shows, it looks more like the other (darker) late wood grain. I attached a photo that has three joints that I made in the early wood of some cedar because the stock wasn't wide enough for what I needed, and it's nearly impossible to find them.

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