Neck Centering Jig

[Barry Daniels]

I built this jig about 10 years ago but I thought it might be useful to others in getting the neck lined up with the center line of the body. I use it on new builds as well as resets on old guitars. It is built with the hardware from a Jorgensen wooden handscrew clamp consisting of counter-threaded rods and posts. If anyone wants more details let me know.

[Donald Martindale]

I would love to see details.

[Eric Knapp]

I would love to see details.

Me too!

[Carl Dickinson]

I've got a set of the hardware minus the wooden jaws. Looks like I've got the start of one. Show us the details. Thanks!

[Barry Daniels]

Oops, now I've got to step up. Guess I can put together a tutorial. I will assume that you guys are going to build one. It is not very time consuming or difficult. Materials include 1/4" and 1/8" plexiglass and a medium sized wood clamp. We need a clamp that has 5/16-18 threaded rods that are at least 7" long which I believe is the 10" wood clamp. Several places even sell clamp kits which just have the metal hardware so you don't have to sacrifice a clamp (Lee Valley, Taylor Toolworks). The jig is mostly made up of 1/4" Plexiglas (you just need a small amount of the 1/8" Plexiglas). The main center strip of 1/4" Plexiglas is 3" by 36" long. I made the jig this long so it can extend to the bottom of the body, or also be used on a bass guitar. Lay the threaded rods crosswise at points 2" and 13.5" from the top of the long piece. Now a 2" by 6" box of Plexiglas will basically be built around the threaded rods to house them. Here is a top view of the clamp which shows a cross section of the box.

[Barry Daniels]

The cross section shows a sandwich of Plexiglas. I encourage you to click on the pictures to see a blow-up of the different layers.

[Barry Daniels]

One of the outside layers of 1/4" Plexiglas consists of two pieces 1.5" wide that abut the main shaft. There there are two strips of 1/8" Plexiglas (7/8" wide by 6" long) and two same sized strips of 1/4" Plexiglas that sit on either side of the threaded rod. Finally, a layer of 1/4" Plexiglas sits on top of the threaded rod as a cap. All of the Plexiglas is glued with either thin CA glue, or even better, thin plastic cement that is made for this purpose. The CA leaves the joint kind of cloudy whereas the plastic glue is supposed to bond the layers clean and clear. I can find the part # for the glue on MacMaster Carr if anyone needs that. The top and bottom layers get oblong holes routed out for the posts to run in. The holes are 9/16" wide by 1-1/4" long and are spaced 1-5/8" apart. You have to build the box around the metal parts and the main goals are to have the posts fairly well supported by the oblong holes that are just wide enough for the posts to run smoothly, but not so wide that the posts will tilt when the threaded rod is turned. Also, the layers of the box need to be very even at the ends because washers and nylon locking bolts will be placed here to hold the threaded rod in place.

The process of how I built the jig was to lay down the center shaft and then position the four small pieces that abut the center shaft and glue them at the edge butt joint. Let this cure then cut out the oblong holes that span the glued joints. Lay down the threaded rod with the posts properly positioned into the oblong holes. Then start stacking and gluing the other layers. Top off the sandwich with the full sized cross piece of Plexiglas that has the oblong holes already cut out. Let everything cure. Place the washers and locknuts into position to give a snug/slip fit to the hardware. One set of locknuts will need to be lefthand threads. Options to the locknuts are to use normal nuts and CA glue them into place, or cross drill the threaded rod and use a cotter pin. I prefer the nylon locknuts cause you can sneak up on a proper fit.

The final step is to scribe the center line on the flat side of the jig. I did this with careful measurements using a couple of accurate steel rulers of equal width, laying side by side, held against the jig by tightening the threaded rods. Start off just marking the center line with a fine tipped Sharpie. Double check the accuracy by marking the centerline down a straight board to the end of the jig, and then flipping the jig over. Any error will be doubled. Once you get the center line dead nuts, scratch a deep line with a scribe or awl. Fill the line with a bit of red enamel or run the red Sharpie down the groove. Throw on a couple of handles or knobs on the end of the threaded rods, and call it done.

This method of building the jig and creating the centerline, eliminates error from any slop or misalignment during construction, as the centerline is determined by the working parts of the jig that actually contacts the neck. One last touch that I added was dipping the posts into some plastic dip to provide a slight bit of cushion during contact with a finished neck/fingerboard. In use the jig appears to be accurate to much less than 1/64" measured at the very end.

I would like to encourage people to make this jig. It is an easy weekend project, and has turned out to be the most useful jig I have ever made. The accuracy of the jig compared to doing hand measurements and extending the line with a ruler is night and day.

[Bob Francis]

This is great. Thank you

Would there be any advantage in adding a pin hole on the center line below the existing hole?

[Barry Daniels]

I don't quite follow you Bob. Do you mean a hole for marking?

[Barry Daniels]

At one time I made a small plate that attaches to the jig that would set the bridge in the proper location. That is the purpose of the three weird holes in the jig over the bridge.

[Pat Foster]

Brilliant!

[Barry Daniels]

Thanks, Bob and Pat!

[Barry Daniels]

One thing to mention about the jig is that if you place the extra long part of the threaded rods (that will receive the handles) on the same side of the jig, then the clamps will tighten in reversed directions. In practice this is not a big deal. It is just the way the wooden screw clamps are designed to work. To get the clamps to work in the same direction you would have to put the handles on opposite sides of the jig. I decided to keep the handles on the same side and deal with the reverse action.

[Karl Wicklund]

Thanks for sharing this!

[Barry Daniels]

You're welcome.

[Chris Paulick]

Nice, very clever.

[Pat Foster]

Following up on this jig, I got the Lee Vally clamp kits, but they were pretty rough for this application. I had to chase the threads on one of the rods (good thing I didn't have to find a left-handed die!) because a 5/16-18 nut wouldn't go on and the barrel nuts are a bit too loose for my taste. Lucky for me, I was describing this project to a friend of mine who offered me an old pair of Jorgensen clamps in just the right size. Much more accurately made and smoother operation. My advice, get the clamps if you can. I also learned how poorly some TS wood blades cut plastic. I figure by the time this project is done, for the time and cost, I'm about breaking even with buying the jig offered by luthiersuppliers.com, but where's the fun in that? Plus I learned a few things.

[Bob Gramann]

I have been making my jigs out of Lexan (or its generic equivalent) for some time now. It cuts much easier than acrylic plastic on the bandsaw (10 tpi blade). I cut wide of the mark and plane to it (Lexan planes very nicely). And, it doesn’t crack. It’s well worth the extra cost.

[Pat Foster]

I have been making my jigs out of Lexan (or its generic equivalent) for some time now. It cuts much easier than acrylic plastic on the bandsaw (10 tpi blade). I cut wide of the mark and plane to it (Lexan planes very nicely). And, it doesn’t crack. It’s well worth the extra cost.

Lexan is nice to work with. I wish I had a scrap pile of it like my pile of plex. I do like the stiffness of the plex, but wish it was a bit less brittle. Can't have it all, I guess!

[Barry Daniels]

Pat, I am surprised to hear that the Lee Valley parts are so inaccurate. But, am not surprised that the Jorgensen clamp rods are well made. That is what I made my jig from and it seems to be deadly precise.

Yep, a bandsaw cuts plastic very well. Rough edges can be cleaned up with a hand plane if you like. Or just hit it with a file.