SBO 22 - Ziricote Dream

[Gary_M]

My plan is to put it in a vacuum bag. Unfortunately the ziricote piece for the top was so narrow that I could just fit the two pieces on it, no overhang whatsoever. Before gluing I'll do a dry run in the vacuum bag to see if it presses all the way down. If not, I can still glue something to the edge for leverage or add a clamp with cauls outside the bag.

Do you plan to make some relief cuts on the back side?

 

[TFM94]

Do you plan to make some relief cuts on the back side?

Not sure yet. I'll make cuts if necessary, but not too deep and also well away from the edges. Another option is to use water and heat (clothes iron) to pre-bend it before gluing. Or both. I want as little tension as possible during glue-up.

 

[TFM94]

Update #9: Disaster has struck

Ok. Breathe. Maybe I can fix this.

Here's the story: I wanted to have a maple veneer between ziricote top and mahogany body for contrast. I also wanted to have a ziricote veneer under the maple strip for the same reason. I figured that aligning this (top+veneer) in one big glue-up would be an uphill battle and decided to glue the veneer to the top pieces first, then make the top joints and then glue it on the body.

Sometimes the human brain doesn't work as it should. Of course gluing a veneer to one side of a thin top wood panel will cause it to cup and warp. I glued it up clamped between two straight panels of MDF and when I took it out it sprung back to about 5mm cup. Not the end of the world, it will be flattened when glued onto the body anyways. So I trimmed the veneer around the edges and put it back between the MDF panels when I heard a loud crack. It split in half.

The crack is relatively straight and clean, so I decided to glue it back together with titebond. I hope the glue line will not be too obvious. If it bothers me, I will have to get a new top. Fingers crossed.

For now I am continuing with the top half. Now that I've been veneering the bottom and center pieces I kinda have to stick to this process. My plan is to glue the top piece veneer only partially on for jointing the top, only 1/2" along the edge where it meets the maple center strip. I will keep 90% of the area unglued and squeeze epoxy in there when I glue the top on, so that it can be bent around the arm contour.

That thin veneer layer is not worth all this trouble.

 

[TFM94]

I'm just brainstorming right now, perhaps I can hide this crack at least partially if I front-rout the control cavity and put a tele-style control plate on it, made from ziricote of course.

I just checked the local (european) prices for a replacement top and I'm not gonna shell out 180 bucks for a new piece. I paid less than half of that for the old piece. Holy moly, prices have gone up.

 

[TFM94]

PHEW. I think we are okay.

After gluing the pieces back together I scraped the clue off and sanded the area. While you can clearly see the glueline in the veneer on the back, on the front it is basically invisible, unless you bring a microscope. Can you spot it?

While it can still show up when applying the finish or on the edges/roundover, I think this is good enough for me to continue with this top.

Perhaps it is a good idea to put some relief cuts on the bottom part as well, simply to take some tension out of it.

 

[ctmullins]

I can't see any glue line in your photo - good save!!

 

[RichterScale]

Perhaps it is a good idea to put some relief cuts on the bottom part as well, simply to take some tension out of

I had the idea to warm it up with a clothes iron to soften the glue a bit, then put it on a flat surface, cover it with a flat board and some weight and hope it flattens out while the glue hardens again
But it's just an idea. You'd need confirmation from someone who's done it a few times with success. Seems to work with straightening necks/fingerboards sometimes.

 

[TFM94]

Yeah, heat can soften the glue, but then it might also soften the glue along the crack and open it up again. I'm pretty happy with it now and I don't need a ton of force to push it down on a flat board. I'll keep it as is for now.

 

[Beej]

Nice save! Lutherie is all about problem-solving and then hiding it.

 

[AK4570]

Good save! Without the back story, I'd never have known that was cracked.

Well played, Sir!

 

[GMC]

Neat work! I can just make out the join line, only because I know it's there. Once lacquered....it will be totally invisible!

 

[TFM94]

Update #10: It's a long way to the top (if you wanna rock 'n' roll)

After an unnecessarily stressful day of lutherie yesterday things are back to where they should be. There has been some progress.

First off, I have made some relief cuts with my dremel and a 2mm spiral bit (about 1.5mm deep) and drilled a few holes in the body:

The laminated top flattened out overnight. I assume the warp (and crack) I experienced yesterday was caused by excess moisture from the glue, not the veneer itself. I routed the center joints and glued it up. A bit of sanding later, we got a top that is not too dissimilar to the concept drawing in my first post:

The little ziricote patch is there to show up in the roundover, kind of a Z/M/Z vs M/Z/M thing. The veneer on the top half is glued only about 1/2" along the jointline and the will be glued with epoxy while the whole top is glued onto the body. This way it is easier to bend.

Next up is cleaning up the neck tenon and routing the neck pocket. Stay tuned!

 

[TFM94]

Update #11: Ziricoated

In my previous post I said the neck tenon would be next, but I decided to work on the headstock instead.

I put some weight relief holes in the top section of the headstock and glued the veneers on. To shape the volute on the bottom side I used a curved sanding block that later turned into a clamping caul. I used three screws to hold the veneer in place while clamping. The holes will be covered by tuners later. I also came up with a build-off side competition: "How many clamps can you fit on your headstock?"

The glue-ups (one side at a time) went well, there's no visible gaps. Despite three screws for alignment the back veneer slipped a little bit and there's a small offset between the maple veneer stripe and the center lamination at the volute. I wonder how this is possible, it looked good when dry clamping. It's only a small imperfection, nothing to complain about, really. It's just that these thin laminates are unforgiving and accentuate any misalignment.

With ziricote veneers on the top, back and sides the headstock is almost completely covered, except for the volute area and the endgrain:

There's still a few router marks to be sanded out, but the general trimming is done. I am envisioning a flamed maple trussrod cover to match the center stripe.

 

[smart51]

That is very nice work

 

[ctmullins]

Interesting. I don't suppose you saved the sawdust from the headstock relief holes, so you could find out exactly how many grams you saved?

 

[TFM94]

Interesting. I don't suppose you saved the sawdust from the headstock relief holes, so you could find out exactly how many grams you saved?

Ha! I didn't save the sawdust, but I weighed the neck before and after. The difference is 6g or 0.21oz. Not much, but given the leverage it's better than nothing. I'm allergic to neck dive, so every little bit helps.

 

[ctmullins]

Cool! Every little bit definitely helps.

 

[TFM94]

Before I start working on the neck tenon and pocket, I would like to consult with the LC hive mind.

Here's the deal: It's a set neck with a full width neck tenon. Since it's a DC junior, the end of the fretboard extends only a few mm into the body (the last fret lines up with the edge). Hence, the neck tenon extends further into the body than the fretboard. In my "original" DC build I covered the exposed neck tenon with a pickguard, but here I don't want to hide the ziricote top. My plan is to have the neck tenon underneath the top. In a cross-section it would look like this:

So the neck pocket would be routed into the body, obviously, and into the back of the top as well. DC juniors are notorious for having a lot of flexibilty in the neck joint when pushing the neck forward, and I want to give the tenon as much thickness as possible. The recess will also help with top alignment.

Regarding the procedure, I have two options:

1. Glue the neck into the body first, then glue the top on in the vacuum bag (with the neck already attached).
2. Glue the top onto the body first, perhaps using a taped-off dummy neck tenon in the neck pocket for alignment and to provide support while vaccum clamping. Then remove the dummy block and push the tenon in from the side and glue it.

Method 1 would allow to have a neck tenon that tapers outward like the fretboard, which would make for a stronger joint in my opinion, a gentle dovetail. Method 2 requires a rectangular tenon that can slide in from the side, but it would be easier to finish work on the body (trimming the top, roundover, sanding etc.).

Any recommendations?

 

[ctmullins]

I don’t think the 3mm will make any difference. How is a 32mm tenon with a 2mm top any more secure than a 29mm tenon with a 5mm top, especially if everything fits together nice and tight?

When I did mine (quite a few years ago), I cut the tenon down to the height of the body, so I could leave the top at the same thickness throughout. It rings like a bell.

 

[TFM94]

I don’t think the 3mm will make any difference. How is a 32mm tenon with a 2mm top any more secure than a 29mm tenon with a 5mm top, especially if everything fits together nice and tight?

That's a beautiful guitar, I love the blue top. Note that the fretboard and full-height tenon extends about an inch into the body, which helps a lot.

My thought is this: Having a large step between the tenon and neck to accomdate the top can create a weak spot in the heel area, even if the tenon by itself has sufficient thickness. Like this:

The amount of grain that is actually extending from the tenon into the neck profile (the light brown area) is quite flat and could create a break along the red line. Adding thickness on the top of the tenon would increase the strength of this transition.

It would probably hold ok either way, but I'd like to make it as stiff as possible.