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If I searched more I am sure somewhere here there is discussion of neck centering and a jig for adjusting yaw. But since I just made this jig for myself I thought I would share it with you all. If you are like me, you balk at the price of some of the complicated-looking commercial jigs on the market. And while they may work great and with all sorts of necks, this one works pretty well for me. All you need is a truss rod channel that is formed down the center of your neck. It's pretty self explanatory: clear plastic body, longer is more accurate. Maybe shoot for about the scale of the instrument (25" or so). Form a groove with a narrow kerf blade along the length of the body. If you run it both directions through the table saw it will be perfectly centered, although with this jig its not important. Form two spaced apart holes the same diameter as your truss rod channel (1/4" inch for example) where both holes will be located on the neck. Make the holes exactly centered on the channel. Make two dowels to interference fit into the holes (brass is nice). You are done! The cost is less than a cup of coffee. What do you think?

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Snap!

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Nice jig Steve. Don't mean to steal the thread but have been wanting to show my version for sometime. I built it 10 years ago and considered going into production but decided I would rather build guitars. Anyways, it works using the hardware from a Jorgensen wood clamp consisting of counter threaded rods and posts. I use it often when doing resets. It seems to be very accurate. If anyone is interested I can provide more details.

@Colin and Barry - well done you guys. Thanks for sharing. Every time I think I am sooo clever. lol

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"Building guitars looks hard, but it's actually much harder than it looks." Tom Buck

Yaw had me at hello…

Very cool!
I am going to build one of these....
Thanks!

Yep, pretty much exactly what I use. Works great. Cool stuff.

The truss rod channel is so useful for all kinds of jiggery.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Here's mine. Phenolic instead of acrylic because that's what I had at the time. Pivoting centering things on the neck that can also center on a truss rod slot, and the centerline the rest of the way down. Obviously not yet centered in this shot--neck's not that far off, but haven't used the centering things yet...

Dave

Dave, be aware that the centering part of that jig might be slightly off center if used on a tapered neck.

It self centers on tapering necks--it's been spot on every time.

Dave

Theoretically, the taper should throw it off center a bit, but in practice, it must be that the difference is negligible. That's good to know.

Actually I don't think so. Although it looks like it might I believe the stagger of the alignment points on each side will compensate for the taper.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Our world is a bit different since we don't build but repair. So for us there is typically an already located, for better or worse... bridge in the pic.

So we find the center in four locations on the fretboard and mark with masking tape and a dot. We line up a straight edge with these four dots and the center of the bridge between the D and G and Bob's your uncle.

That seems to be right--you can flip the two centering gizmos either direction and it doesn't move the centerline.

At any rate, I think that the fact that the centering gizmos are short and the taper of the neck is not extreme makes the error Barry described negligible in practice.

Dave

That jig will definitely introduce error by shifting the centerline -- knowing a bit of trig will help calculate the actual offset (using cosine to give you the x value for given angle, if I'm not mistaken). It may be negligible but if I were you, I'd calculate it to be certain and then adjust my jig accordingly if it's more than 0.010"

For what its worth, I just use a flexible Starrett ruler and place thick masking tape along the centerline -- 2 at both ends of the neck and 2 at both ends of the body. I live some room for movement in my mortise/tenon design so that I can adjust accordingly. For me, the biggest thing about the neck joint is ensuring that I get excellent and full contact all along the heel -- absolutely no gaps whatsoever. The heel region on my upper bout is also curved -- so this requires sanding and careful fitting. A lot of guitar body designs are flat here and that simplifies the process and allows you to use jigs to accurately set the neck.

I got to wondering why my jig has been working--Barry is right about the theoretical error. So I tested it on a narrower and more abrupt taper, and it does indeed miss the mark. I think I've just been lucky--my alignment gizmos are short and the taper of my necks isn't extreme, so there isn't any measurable error. But narrow the board, or increase the taper and it's trouble. Thanks for bringing it up!

Dave

I wonder if the same happens with this style of jig? I’m offering these for sale to uke builders and they have the standard uke scale lengths etched into the tool. I partnered with Luthier Suppliers to use their design for a uke version of the tool. Will have to run some tests.



Brad


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No need to worry -- that jig is self centering.

Yeah, unlike mine that one has the pins absolutely perpendicular to the centerline so no error is introduced. Nice looking jig.

Dave

This is why I also designed my jig to register off points on the neck/fingerboard that are perpendicular to the centerline.

The nice thing about a jig is that it takes away measurement error and are really quick to use. A slight error in measurement or even too wide of a pencil mark on the fingerboard is magnified when you extend the centerline down to the body. It may be hard to understand the benefit of a good centering jig until you use one in practice.

I was in talks with Stew-Mac to supply a commercial version of my jig, but l decided it would be more work than it would be worth. The total number that would be sold didn't justify the effort.

Lots of ways to do this with straightedge, truss-rod referenced tooling, etc., but we had to be able to handle just about anything from rough fitting on a commission to resets on weird older vintage stuff. Although there were several jigs to handle the odd ducks like 5 string banjos and some of the Greek and Turkish instruments we commonly saw, we had a couple of Luthier Suppliers Centerline Finders that handled the vast majority of work.

With a 24" straightedge and a Centerline Finder, pretty much everything needed to fix the neck angle during preliminary caving, or to do the final fit prior to glue-up. Fretboard on or off, truss rod slot/no slot, neck still square or pre-carved - does not matter. $90 is a bargain, considering that we billed at $110 an hour when I left Greenridge and the boys just went to $125 an hour to get some breathing room back in the schedule (apparently, the usual Jan 15 - end of the yearly gratis loan period to the IRS did not happen this year).

As a bonus, the Cenerline Finder now has a locking square attachment that gets the bridge nicely squared when getting it on a new or retopped guitar.

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I just put together a thread on how to build my jig over at the MIMF, if anyone is interested.

Centerline Jig