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I usually put in a very thin shim if either end is slightly loose. Mark Blanchard recommends routing the channel slightly deeper than the rod and gluing a thin filler strip. You can clamp it with spring clamps so it puts some pressure on the rod and level flush after.

I think that’s a good idea. Just a little belt and suspenders protection against a rattle and I had one in an earlier guitar with the LMI two way and no filler strip.

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

Building the the Bolt-On Bolt-Off neck joint requires two or three routing operations on the truss rod slot. First, the routing of the slot in the neck blank, with the slot being used subsequently as a locator for drilling for the bolt bar, etc.. Then, after the loose top tenon has been glued in (which requires shaping of the heel first) the truss rod slot is re-established through the glued-in tenon. A fence either side of the neck blank is required for this operation. Then, if the truss rod has a bulky adjuster, clearance for this has to be routed using a larger diameter cutter. (Details of all of this are in the Build book, now available again). All of these cuts have to be exactly centred, so a quick, repeatable set-up technique is required.

I came up with this pivoting parallelogram arrangement (not in the books), which centres a neck blank exactly and repeatably regardless of its width. The hex bolts are pivots and the socket head cap screws are used for adjusting for neck blank width. The socket head cap screws are locked up when the two fences are swung in against the neck blank. You may notice that the router cutter is not exactly centred in the cutout in the table. That's because the pre-drilled holes in the table either side didn't align appropriately when I bought it (decades ago), so I just offset the router beneath. This is only an issue if you use router bushing on your router table (which I don't). If I'm using bushings, it's in a hand held router. The slot I cut is 5mm wide with a round bottom. A solid carbide spiral metric bullnose cutter (needs a metric collet) cuts a slot that exactly fits sheathed 3/16" truss rod material and will do it in one pass.

If you have one of the fancier, more modern router tables (like some of the pics in this thread) which doesn't encourage drilling and tapping into the table itself, a fixture can be built on a sub-table with a sized hole in the right place to centre the fixture on the router (using a dummy bit) whereupon it can be clamped to the router table proper. It's simple and the pics should be self explanatory. Note: the neck shaft blank needs to have accurately machined, parallel sides.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

I had to re-read it a couple of times for it to soak in; that is a most elegant design.
I'm glad I don't have to explain WHY it works....

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Measure Twice,

Karl Borum

I managed to get Mr. Stock to take some time off from airplane work to take a few pictures of the jigs used at Greenridge and as mentioned in the earlier post above. This solution is handy for one-offs and for situations where the side of the neck blank is an unreliable guide.

1. Lay out the centerline of the truss rod on the neck and mark the nut end termination of the rod slot
2. Apply some thin, high-tack double-stick tape to the reference surface (XFasten works quite well)
3. Align the jig with the scribed centerline of the plastic insert; remove the insert when ready to rout (use the insert scribed-side down to eliminate any parallax error). Set the nut end of the slot 1/16" past the marked termination of the slot.
4. Mill the slot with a 1/4" carbide bull nose from heel to nut end (the depth is set per the marking on the jig... rout a bit shy of depth if in doubt)
5. Dry fit the truss rod and mark the end of the wider/deeper adjuster portion of the slot
6. Use the already cut slot to align the router jig for the wider/deeper portion, and mill with the same 1/4" bullnose after resetting for depth.
7. Ease the transition from adjuster section to truss rod section with a 1/4" chisel

The jigs are just scrap 1/2" ply designed to be used with 3/8" OD bushings and 1/4" carbide bullnose bits. A bit of tape will fine-tune the fit as needed. We marked the required depth directly on the jig to make things easy, with the thickness of the double-stick tape already factored in. A simple set of jigs for low-production or custom shops. On darker neck blanks, a strip of the white low-tack signmaker's tape applied before marking the neck centerline makes aligning the jig a bit easier... not needed on maple/other lighter woods.

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A constellation only takes shape when one maps the whole.
- Beth Brower

I use a similar jig for extending the truss rod slot onto the body or the extension of an archtop. I have a 1/8” one for extending the carbon bar reinforcement onto an archtop extension. Mine uses a fence instead of being designed around a router Collet.
Nice jig Woodie!

IMG_1888 by Terence Kennedy, on Flickr

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

Thanks, Dr. Kennedy... we should have anticipated you had more interesting and extraordinarily clever, useful jigs to share with us!

Your comment reference using the truss rod slot to guarantee jig alignment over the body once the truss rod slot is milled: it makes sense to use that slot to align any other jigs for adjuster, carbon fiber rod slots, further joinery, etc. This reduces or eliminates the potential for alignment measurement error due to a mistake such as use of the wrong layout line (please don't ask me how I know that) or bad arithmetic.

Every direct measurement requires conscious effort to avoid measurement, layout, marking and recording errors, as well as a variable error in tolerancing for assembly (Eek! Tolerance stacking!), so eliminating as many of those ‘opportunities’ as possible pays dividends in avoiding in-process repairs or junked components.

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A constellation only takes shape when one maps the whole.
- Beth Brower

Thanks, Karl!


It's just geometry (!) inspired as a sort of inverse of parallel rules. (Coincidentally, the waters of the chart in the linked pic is where I spent way too much time racing sailboats).

The design criteria for accurate centering are that the pivot holes in the table and the router rotational axis all fall on a straight line, with the router axis exactly centred between the pivot holes. The pivot holes in the fences need to be exactly the same distance from their active edges. For those struggling to visualize how it works, it's a simple job to make a mock-up with cardboard and drawing pins.

If you want to rout parallel offset channels (e.g. like slots for the CF rods in Terence's pic) you just slot a packer between the neck blank and the fence. The packer needs to be twice the width of the offset.

It's a huge time saver.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Yep the truss rod slot is a wonderful thing to utilize for jigging and keeping things aligned and centered. I have a ton of jigs that use it as I am sure everyone else does.

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

Got one of these yesterday after seeing Bob's post. So simple and solves a problem I've wrestled with for years. I do a lot of veneer center laminations on necks, and this gizmo centers the truss rod slot no matter what kind of bit I'm using. Can't believe I hadn't thought of that, but then again I'm old and not that bright!

Dave

Centerline bit is awesome too for bridge saddle slot ..... extends the CL of the collet/ bit right into the slot. You can locate/ adjust your fixture, centerline, angle/ bit travel....

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Measure Twice,

Karl Borum

Also super useful for marking XY0 on a CNC.


Sent from my iPhone using Tapatalk Pro

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