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Permalink Reply by Ron "Oily" Sprague on July 17, 2014 at 6:06pm

Whoa. Stop. Wait. Consider.

You have two acoustic guitar necks. I presume they are fretted. How many frets? At what fret did the necks connect to the now-broken bodies? Do you still have the broken bodies? You need an estimate of the scale length, which means you need the location of the bridge / saddle on that body, and the distance from the bridge to the nut. which you can calculate by measuring from the nut to the 12th fret, and multiplying by 2, so you can toss the broken bodies. Measure the same scale length using the necks and suitable boxes, e.g, locate the position of the bridge / saddle on the box top ( about 1/3 to 1/4 of the way in from what you determine to be the tail end of your box). Now, you need to attach the neck to the box. Typically acoustic necks are glued using a dovetail joint into a block of wood set into the body of the guitar. You will have to either duplicate that block, with the dovetail joint cut into it, inside your box, or put two heavy screws through the wooden block that you have glued and screwed inside your box, into the heel of the neck. You also will notice you may need a little bit of neck angle back toward the headstock. This way, your action won't be ridiculously high, your frets will intonate properly, and your instrument will actually sound in tune and playable. Otherwise, you can just bolt the neck onto the box, without regard to scale length, the string tension from 6 strings (you could just put 3 strings on it, a la Seasick Steve) will collapse your neck joint and box, and you will be unhappy / out of tune. Michael Fred Johnson here at CBN has numerous photos of how to do a proper neck set block and dovetail joint.

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Permalink Reply by Ben on July 21, 2014 at 7:48am

Many thanks for your explanations! My english is not too bad but I'm having difficulties
with the tech-lingo parts. Don't wonder if I ask you to repeat or clarify certain parts that you find mundane.

How many frets?

19 each

At what fret did the necks connect to the now-broken bodies?

13

Do you still have the broken bodies?

Yes, I included some pics in my profile (+ the boxes that I got hold o)f. At least one of the guitars was between 70-75 years old and was made by a small guitar maker. Sadly, both the saddles and bridges are missing. 

The boxes are round on the left and right sides which may (or may not?) pose problems.

you need the location of the bridge / saddle on that body, and the distance
from the bridge to the nut...

From the blank space that is left visible on the bodies to the nut is
64,6-67cm (I measured to both the left and the right end of the blank
space) and 62,5-65,9 cm for the other.

measuring from the nut to the 12th fret, and multiplying by 2,

30,9*2=61,8 and 30*2=60. I'm slightly confused. Which of these measures do I have to use for the location of the saddle/bridge on the box?

Typically acoustic necks are glued using a dovetail joint into a block of wood set into the body of the guitar...

The lone neck was simply glued to the top and side of the guitar IIRC. The option with the screws sounds appealing. Would you recommend any particular type of screws?

Once again, thanks for the advice. I'm glad to get advice from the experts.
If you guys have anything to suggest/complain etc., please do! 

One more thing: May I ask additional questions in this topic, related to my project here or do I have to open a new one (I haven't seen any rules or moderators so far?).

cheers

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Permalink Reply by Thumper on July 22, 2014 at 4:22am

I used auto upholstery screws. They're chromed, come with washers built in and in several lengths. Got them at a local hardware store

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Permalink Reply by JL on July 18, 2014 at 1:03am

What "Oily" said

your junk guitars' bodies are likely much bigger than your cigar boxes, so you will have to add an extension to the box so that you can keep the same nut-to-bridge length and still have the bridge on the cigar box.

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Permalink Reply by The Phrygian Kid on July 18, 2014 at 1:34am

In my opinion making a neck from scratch is easier than repurposing one. You can reuse the frets, the tuners...
Maybe have a go at getting the fingerboard off and reusing that on a fresh thru neck? This can be hit or miss with cheap Chinese guitars, but you've got nothing to lose...

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Permalink Reply by Thumper on July 18, 2014 at 4:37am

All I can say is, "ignorance is bliss". I wanted to make a 6 string resonator CBG And went ahead without asking for opinions but chose from several options before starting. 1st of all, I'm no woodworker, so using and existing neck was a  given for me. The one I settled on was an old Peavy bolt on. I added a length of hard wood to it to go to the far side of the box. In order to get depth for the res cone, I used spacers after figuring out the finger board (and neck) depth. By doing a spacer on the attached board I had clearance a-plenty, a spacer would also give you room for your piezo and allow the top to vibrate freely and possibly give you a richer tone. BTW, the brass parts were from Old Lowe.

Attachments:

• 010.JPG, 48 KB
• 012.JPG, 61 KB

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Permalink Reply by Thumper on July 21, 2014 at 11:31am

Thanx Wayfinder, it was pretty much "cut & paste"...looks like more work than it was, but it play's sweet!

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Permalink Reply by Ben on July 23, 2014 at 7:38am

Thanks, "Oily" and the others.

This clears a few things up.

However, I noticed that the correct (scale) length is not feasible as the box is too short (or the neck too long).

Now I see 2 options (?) to solve this problem:

#1 Extending/attaching the neck with another slat, thus creating a neck-on-top CBG as the end of the fretboard extends over the top of the CB. Not my favourite as it would look ugly.

#2 Adding (How? Gluing? Screwing?) a block of wood that extends or "closes" the gap of the heel 'til the end of the fretboard (and possibly goes into the box) which attaches the fretboard directly to the left end of the box?

Or am I just seeing CBG-Demons that want to distract me?

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Permalink Reply by Mike M. on July 26, 2014 at 3:58pm

My license plate resonator uses a neck block similar to a set neck acoustic closer. I am running 4 strings (A,D,G,B) over a 25.5 inch scale. The neck was a 1x3 red oak piece ripped down to 1 5/8" wide. The neck block inside is just the cut off pieces of red oak from the neck, stacked and glued together. I took a piece of mesquite and shaped it by hand as the heel that is glued to the front of the box and the underside of the neck.
It works great save for a couple design flaws.
1. I used .25" poplar for the body. That isn't thick enough for such a soft wood. Either a stiffer wood or thicker stock is needed. Both would be better.
2. The neck is also to thin. It bows to the point that the action, while OK at the nut, is very high. The guitar is currently a slide-only instrument. Just like #1 a thick piece of lumber is needed. I'll probably start with a 2" thick piece of mesquite next time.
3. Might go shorter scale next time but with a stiffer structure I don't think I need it. I could also join the neck to the body closer than the 19th fret to relieve some of the tension.

I'll link some pictures when i have my laptop out later. Other than some iffy finishing, in very happy with this guy my first CBG.

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