Seeking advice Re: tin box body - bridge design, reinforcements, sound holes.

I'm building my first instrument. It's going to be a tenor ukulele, which I'm calling a "banjolele" because the box I'm using is a rectangular tin that once held Whitman's candies. It measures 10" x 8.5". I've got all the materials I need at this point, and I'm working on making a nut out of scavenged bone, so that will take me a bit.

As I'm working on things, I've been thinking a lot about that box top. Because this is a through-neck design with a tailpiece, there won't be upward pressure on the lid, but the bridge will be pushing down hard on it. I'm concerned about the whole thing collapsing the first time I put tension on the strings. Because of that, I'm considering some kind of cross-bracing. When I do that, though, I'm worried about deadening the sound. I like the idea of the whole lid vibrating when I pluck the strings. Won't wood bracing keep that from happening?

Then there's the question of the bridge itself. Should I use a banjo-like design to minimize contact with the vibrating lid, or use a big flat bridge to distribute the pressure?

Finally, I'm thinking about soundholes. They will doubtless weaken the lid, so should I put them around the sides of the box instead?

Ideally, I want an arching bridge, no bracing, and soundholes in the lid. I guess wheat I'm asking for is reassurance that it will hold up to the pressure if I do that.

Here's a photo of the tin, if that will help:

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have built a few bicuit tin ukus and three strings and found that a small bit of wood fixed to the   neck under the bridge works well for support and quite load acustic without sound holes

I like that idea. Maybe hollowing it out so it only meets the lid where the bridge does...

All my ideas I have stolen from the answers Jef Long provides on this site. He seems to be the Tin Man.


http://www.cigarboxnation.com/profile/JefLong

Thanks. I might give him a shout. I'm brand new here and don't want to start bugging people with direct messages until I've lurked a bit. :-)

Might do. As I said to ED, I don't want to make a nuisance of myself. :-)

I've made two tin bodied guitars, but that in no way makes me an expert. 

My first build was a a six stringer with a through neck, but with an electric guitar tailpiece screwed directly into the bottom of the neck wood. The bridge is made from a drawer handle placed right at the bottom, this was an aesthetic design choice not something I'd do again. If you look at the photos, you can see that acute angle the strings meet the bridge. This has the effect of increasing the down force on the bridge, and has squashed the tin a little. I reckon that with the bridge placed further onto the lid, the stress would be more evenly spread, resulting in in less bending of the lid and the bridge being closer to a "sweet spot" for resonance.

You can see that I added sound holes, decked out with screened grommets. I also fitted a magnetic pickup, that's screwed to the lid. I think that the minute you cut into the tin, it will lose some of its resonance. The more holes you make, and add-ons you attach, the sound is diminished. I do also think that the handle having only two contact points might not be ideal.

Apart from the slight bending of the lid, the box is bomb-tight. The structure is fine, as all the other stresses are focused on the neck.

My second build was a a little less adventurous. A 3 stringer, without any holes or pickups to effect the lid from resonating. I made the bridge from a piece of hard wood with a bolt resting on it, and placed it further towards the middle of the lid. It works fine in my opinion (check out my videos), although the bottom of the box gave off nasty vibrations. This was solved without any loss in sound, by putting shredded grocery bags into the box, a tip I found somewhere on the forums. I haven't tried other types of bridges, so can't really advise you in that area. However, with only three strings tuned G D G, the lid isn't bowing at all and the structure of the guitar is sound. 

I didn't want to mess up the lid by cutting sound holes, and anyway, I was rather pleased with sound it made acoustically. Just after Christmas I picked up an identical sized tin in a different design, and set about cutting sound holes. I can report that I found virtually no change in the volume. So, I keep the second lid to use when I fancy a design change.

I like your idea of cutting holes in the side of the box, but I'm not completely sold on the benefit of sound holes in tin bodied guitars.

Anyway, I've prattled on for far too long. If you have any other questions, let me know.

What a wealth of info. Thank you!

Since I'm doing a tailpiece and the bridge will be situated about 1/3 of the way from the tail-end of the box, I think stress will be minimized, as you suggest.

I kind of like the idea of soundholes aesthetically, so I think the jury's still out for me on that question. I may see how it sounds and feels fully assembled, and if I feel a need, I can always take it apart and add the holes.

Love that Cadbury tin!

Hi Karl.

If you are just building a tin ukulele then you'll most likely be using nylon ukulele strings, so the string pressure on the bridge and tin sound board won't be that great, especially as compared to a six-string guitar with steel strings. What I would use is a CBG style "bolt-and-nut bridge", but slip a 1/2" wide by 1/8" thick "slat" of wood of the appropriate length between the bridge and the top of the tin. This piece of wood should distribute the downward force of the strings on the bridge over a greater area, minimizing the risk of denting the top of the tin. Forget the 2 point of contact style of banjo bridge and forget the sound holes. You'll still get a good sounding acoustic instrument. If you want "louder", then add a pup (pickup) and amplifier, something you can always add later. As a first-build instrument you want to keep it as simple as possible.

Good luck.

-Rand.

Thank you. Your advice about keeping it simple is well-taken. I've been giving frets a lot of thought today, and wow, are there a lot of factors to consider there!

I do plan to install a piezo pickup, if not right away, then at a later date. I've got the piezo (scavenged from a dollar store door alarm) but I need to get a mono jack.

Nylon strings? No
Sound holes? No
Big tone sucking bolt shit no
Two feet? Yes. Bend a fork
Piezo? Fuq no

I've built a few tin bodied instruments and played a few more so I figure I'll throw in my ten cents worth of thoughts

Don't worry about bracing or reinforcing - tins seem to have been fine for even fairly heavily strung guitars. If it's really heavily strung and the metal is thin then the top might bow inward a little at the bridge but that doesn't seem to matter soundwise. As long as it all settles down to a stable state then you're fine. With a through neck design the neck can provide quite a bit of added strength and rigidity.

eg.

http://www.cigarboxnation.com/photo/tin-guitar-neckbody-join

For soundholes in tins I took inspiration from Ovation guitars and made composite soundholes using patterns of smaller holes. Seems a neat way to make a large(ish) opening without overly weaking the soundboard. I think it looks neat too...
http://www.cigarboxnation.com/photo/tin-guitar-body

But it might be worth building without soundholes to start with and seeing how the thing sounds (some seem to work well without) - if you don't like the result and you want to try holes then you can always add them later...much more difficult to remove them! 

For bridges I'm tending towards lightness - either aluminium if I want something adjustable for height or simple wooden ones

eg.
http://www.cigarboxnation.com/photo/tenor-banjo-tail

For tin-bodied instruments that sound fantastic it's worth taking a look at the work of Jon at Tin Tone. He seems to use simple wooden bridges.

eg.

http://www.cigarboxnation.com/photo/no-10-the-lux-box
http://www.cigarboxnation.com/photo/no-22-the-cesarian

I had a chance to play some of his guitars recently and they sounded really good.

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