Cigar box mandolin - dealing with string pressure

I want to build an 8-string cigar box mandolin but I have limited tools and skills and is currently investigating whether it can be done.

My main concern is the string pressure. To deal with it I think I have to make a neck-through design. That should not be a problem. If I add two internal braces to the box I think that it is going to hold up just fine.

However I don't think I will be able to pull it off without installing a truss rod in my neck. My problem here is that everyone seems to do this with a router and I don't have one and my budget doesn't allow me to buy one for just this task.

Instead I am considering a design like pictured below where a piece of metal bar gets laminated into the neck. This have the added bonus of reducing the metal work part of the build to cutting the bar to length.

Would such a design work out even though the truss rod would be non-adjustable? I know that adjustable truss rods is a relatively new invention and that fine instruments were made without one.

If this approach to the problem is a viable one, what kind of metal bar would I have to get? Would an iron bar be enough or do I have to use (more expensive and harder to work) stainless steel? I can also get my hands on aluminum bars if that would be a better choice.

Are there any other issues with a cigar box mandolin that I should be aware of?

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Permalink Reply by The Phrygian Kid on May 18, 2014 at 12:29am

Mandolins don't need a truss rod. Some commercial ones do have one, sure but it's hardly necessary. (These often have ridiculously skinny necks too IMHO) The string tension is very high on em, but there is little leverage to bend the neck because the scale length is so short.

Instead, you should be worried about the soundboard. I've repaired maybe a dozen mandos in the last ten years, all with the same problem, a collapsed top, and some of the bracing falling out..

Your idea with a steel or alum bar is sound, a lot of guys tap one into a slot they put up the centre with a table saw, should work ok as you've drawn out, as long as your joinery is good..
Have fun, personally I reckon a laminated neck (for example if the beech is twice as wide and you forgoe the steel) will be more than adequate..