Scarf joint question

davros

I'm making a les paul neck with a 40mm thick white limba blank. The scarf angle is already cut, but I'm debating on where on the headstock the scarf should be, as this is the first time I've done anything that's not a 1-piece neck.

Because the blank is quite thick, the join is halfway up the headstock. Would that be ok? I know I'd be losing the benefit of strength at the base of the headstock, but I'll be doing a volute.

I could thin the blank at the headstock end before gluing, which would bring the joint closer to the nut but I'd probably need to stop short of the volute, so is there any benefit?

I'll have a headstock overlay, so the view from the front isn't a problem. 

GSPBASSES

That would not be a good place to have the joint, it needs to be much closer to the headstock, and be a different angle to the lean back of the headstock. I'm sure if you go on YouTube you're fine plenty of people showing you the way to do this. 

davros

When you say closer to the headstock, do you mean closer to the nut end? Looking at youtube videos, this is exactly how they seem to be done, except the neck blanks are more like 25mm resulting in the joint being closer to the nut end of the headstock.

Thanks!

ICBM

If you're going to scarf it I would do it the other way, with the headstock piece running up under the fingerboard - it looks like your blank is just about long enough. A 'flat' scarf like you're proposing does nothing to strengthen the weak point, and nor does a volute to any significant degree - you can find any number of broken 70s Gibsons with volutes.

davros

Unfortunately it's not quite long enough. I had the supplier cut the scarf.

davros

I think I'm limited to Method A as described here
https://theelectricluthier.com/what-is-a-scarf-joint-on-guitars-and-how-to-cut-and-glue-it/

davros

I'm not especially looking to use the scarf to increase strength, I normally make a 1 piece neck and have never had a headstock break. It's more that I couldn't easily source a 1 piece limba neck big enough for a 1 piece with 17 degree headstock angle. I'm also using a dual action truss rod with a small truss rod adjustment hole, so not going to weaken that area like a Gibson would.

GluedtoMusic

Veneering the front and back of the headstock will add strength (and hide the join line)

davros

I'll be using an overlay/veneer and debating headstock wings too, although the blank is wide enough not to meed them. I'm not so fussed about seeing it from the back of the headstock.

My main concern is if it would cause any structural problems vs a 1 piece neck.

davros

davros

I think I have a couple of options. Either I glue the scarf based on the existing neck blank thickness (40mm), or I trim it down to 20, 30 or another thickness. This moves the scarf position.

20 would just cut into the volute (may look quite nice), taylor-ish, but would be visible on the shoulders of the headstock. 30 would be covered by wings.

What does the wisdom of the more experienced builders say?

WezV

I've not done a scarf join in years, but I'd go for the 20mm option there, or the 30mm one veneered front and back.

I prefer laminated necks these days.  You can cut a few laminations out of a 1" thick flat sawn plank to give a really stiff quartersawn neck blank once glued up.  It's more economical, sustainable, and gives a stiffer neck.

ICBM

The 20mm option is the best - I think it will look best, as well as being the strongest both because it maximises the gluing area and because the weakest point will then be partly in the headstock piece so the grain direction is correct.

chickenbonejohn

Look at it from a structural engineering viewpoint, i.e.  the loadings which will be imposed on the joint and timber.  As you have got it at  present, the joint will only be taking the furthermost pair of machine heads, plus of course any accidental shocks from being mis-handled, so as such it will be relatively lightly stressed. The further you move the joint towards the nut, the more loading it will be subject to - it may end up having to resist the pull of another pair of machine heads, and the joint itself will have greater leverage exerted on it by any knocks on the end of the headstock. Having said that, it depends on your view on whether the orientation of the grain will have a significant effect on the overall integrity of the headstock - that's why many people prefer to have the joint the other way round, i.e .in the neck itself and thus reinforced by the fretboard, so that the headstock itself doesn't have any grain "run-out",  ie the grain will be running parallel to the faces, but you've said you can't do that. Putting on a relatively thick overlay veneer on the front and back of the headstock can help, as under a bending force, the biggest tensile and compressive forces occur at the faces of the headstock. If you choose your materials wisely, this can really help the overall integrity of the headstock.

Jaycee

I have made a few guitars with this exact joint, one being a 12 string without any issues. I put a 1 - 2mm thick veneer on the front and also veneered the side on  two of my builds which covers the join. 

Having the machine heads through the joint will help to support it.

davros

Thanks for the advice, all. Looks like there are arguments for all the options. 20 gives most gluing area and takes most advantage of grain direction, but the joint is subject to force from all 6 strings and is the most visible. 40 would be least visible (hidden by wings and faceplate and subject to force from only 2 strings, but is no stronger than a one piece neck.

Jaycee

Picture of my 12 string scarfe joint. 0 .5mm veneer on top. I took the strings off last month to do some work on the heel joint, up until then it has been strung up for more than ten years.

https://live.staticflickr.com/65535/53684552300_48ecfe5f6b_b.jpg

Danielsguitars

Reduce your headstock angle imo, no need for 17 degrees, I use 12 on everything.

If you did this you could probably get the headstock cut out and stack the heel end rather than a scarf joint, just thinking out loud.

WezV

I thought the same, 17 degrees is for replicas only.  Anything over 10 degrees works well enough.


The main advantage of doing a scarf is the wood saving, but you don't get that if starting with a thick blank. 

Jaycee

Danielsguitars said:

Reduce your headstock angle imo, no need for 17 degrees, I use 12 on everything.

If you did this you could probably get the headstock cut out and stack the heel end rather than a scarf joint, just thinking out loud.

WezV said:

I thought the same, 17 degrees is for replicas only.  Anything over 10 degrees works well enough.


The main advantage of doing a scarf is the wood saving, but you don't get that if starting with a thick blank. 

I think the headstock angle on my 12 string was 13 degrees,  this would give you more gluing area as well.  This was the build you gave me the Birds eye Maple piece for the heel cap Wez

Danielsguitars

WezV said:

I thought the same, 17 degrees is for replicas only.  Anything over 10 degrees works well enough.


The main advantage of doing a scarf is the wood saving, but you don't get that if starting with a thick blank. 

I'd stack the heel area rather than a scarf but depends on the finish because I don't like the look of a scarf joint on a translucent laquer like cherry etc.

I think he mentioned it was 40mm thick which is OK, i think I can get away with 50mm thick on a one piece neck.