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Is there a range of angles that are ok to use when cutting the headstock angle? 10-15 degrees range ok? I made a scarf joint truing jig, thought I had marked 15 degrees but actually marked 13.

13 should be ok for a wide range of things but multiple variables are involved in the definitive answer.

Slothead vs. paddle
head and veneer thickness
fingerboard thickness
tuner post length
even fret height

It's probably easiest to draw out the profile to be sure, but I think you would have to deviate pretty far from norms in the list for 13 not to be workable.
10 degrees on a paddle and you have to start paying close attention to make sure you get at least a 5 degree break angle over the nut.

I use 14 for everything. I don't think 13 would be an issue.

_________________
Steve Smith
"Music is what feelings sound like"

the Martin standard is 15 degree I don't see your being a problem

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I would like to add one variable to David's list,

Classical or SS

The norm for classical is around 12 degrees and 15 for SS.

13 should be fine for either, in my always humble opinion.

Edit: one other thought, if the scarfed head stock is thick and needs to be thinned then you may be able to plane a little more angle into it by taking it from the top. More angle can't hurt.

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Joe Beaver
Maker of Sawdust

I use 13 as standard... no problems at all.

FTL

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www.leddingtonguitars.com

Although largely an academic reply here I'll add a variable as well.

Player attack.

Some of the guitars that we set-up are on the cusp of needing neck resets. As such the saddle has already been taken all the way down, string ramps may have been milled into the bridge depending on what's appropriate for the instrument... and these days bridges are rarely shaved as this practice can be, at times... frowned upon. Again for bridge shaving it's what's appropriate for the instrument. An important term in our business.

Anyway David's 5 degree minimum is a great number and I would consider that as a minimum or near minimum. A player with a light attack will not drive the string as much as a player with a moderate or heavy attack. Or, at times, a player with a light attack who drinks too much.... But without digressing too much the vibrating wave confined by the boundaries of the "speaking length" of the string may breach the saddle and/or nut slot if the break angle(s) is not substantial enough. Hence the question here although seemingly an astetic question is really a physics question.

After all head stock set-back angle is important to the physics of vibrating waves or back to that 5 degrees that David cited.

Some years back I privately approached a builder here who was building electrics with only 2 - 3 degrees of break angle over the nut. My concern was that this would not be enough and his design for his head stock would need to be augmented with string trees. He didn't agree and even though I was trying to be helpful I think that I pissed him off. It was also a private, PM exchange because I didn't want to embarrass anyone.... This never made it to the general forum. Oh well, the best laid plans..... and so on and so forth...

Anyway Frank Ford is fond of splitting the difference of say a 14 - 15 degree headstock for the nut slots or 7 to 7.5 of break angle. This works great by the way and is my go-to standard when possible. But it's not always possible especially in the Fender bolt-on neck world where a Strat's G string may have only 3 degrees of break angle due to Leo not understanding guitar physics regardless of his mastery of manufacturability. An additional string tree or many more winds on the tuner can greatly improve this. By the way there is a tip for you guys. You can increase break over angle at the nut by employing more string winds on the tuners. I sometimes use very nearly the entire, uncut string on Strats for the G string to improve things.

Lastly the reason why your head stock set-back angle matters although it does contribute to our perception of what a guitar should look like is far more important than just another pretty face.... plate.... We are setting the stage for the physics of break angles for strings to be possible.

Break angles matter because after all guitars are tools for musicians.

Hesh said,
"Break angles matter because after all guitars are tools for musicians."

Not exactly sure what that means but, since Hesh said it I agree!

_________________
Joe Beaver
Maker of Sawdust

Sorry Joe I had something on my mind and that was how some guitar designs put the appearance before the physics. If a guitar was a wall hanger it wouldn't matter but for Pete Townshend doing a windmill insufficient break angle will make the kids..... not alright..... so-to-speak