Bracing Design & Other Changes

So I have a fingerboard layout and next on the list is sorting out the bracing design. The original Gibson L-O was "H" braced and that will not do for a MandoCello. So I'll design a more or less standard "X" brace for this.The trickiest part of this is positioning the X and getting the bridge path in the right spot.

I decided to go with and X slightly shifted away from the sound hole, which will give a slightly stiffer lower bout. i was also thinking about using 3 tone bars but this looked like over kill so I went with the more standard 2.

One of the big changes that came out of this exercise was what I had originally envisioned to be a 12 fret to the body instrument ended up a 14 fret to the body instrument. In the 12 fret configuration the bridge just did not end up in the right spot, this was due to using a longer scale than the original instrument and the fanned-fret configuration.. So a 14 fret instrument it is.. Now I guess I really do have to carbon fibre reinforce the neck as well as the truss rod.

More MandoCello Design - Strings

There are several reasons you might make a guitar a multi scale or fanned fret instrument, one is to make the instrument more ergonomic and playable the other is to allow for better string tension on the bass strings, which is my reason.

Since a MandoCello uses relatively large strings on the low C (0.070-0.074”) getting enough string tension at the shorter scale length I want to use (24.75”) is problematic so to help I’m hoping to do a fanned fret design with the treble side (A₃) being 24.75” and the bass side (C₂) being 26.25”.

Unfortunately going to a fanned fret or multi-scale design changes the design of the entire instrument as the saddle, bridge and nut all now need to move around and this effects the brace position.

My first consideration is getting the fingerboard properly designed and picking the strings. Choosing strings is an art in and of itself, there are many options and types to consider. I’ve looked at several types and since I want to do a pin bridge I need ball end strings. So after much thought and a bit of a guess work I’ve settled on stainless round wound strings for everything but the A string which still might be plain steel.

Next the string gauge needs to be determined. Ideally all strings should have the same tension or a slight increase in tension as you go lower in pitch, at least that is what I am aiming for and that tension needs to be high enough so the strings are not “floppy” and low enough so the instrument can be built with reasonable bracing so that it continues to be responsive.

So after some fiddling with an on line calculator (http://www.surveyor.com/guitar/stringtension.html) I’ve ended up with the following, C₂-0.068; G₂-0.046; D₃-0.030; A₃-0.018 which give 24 to 25# tension per string  slightly increasing as they go lower. So around 200# total string tension which is say about what an extra light strung 12 string would be, I think.

Now I need to design/modify the top bracing to accommodate the new bridge location.

Thinking about MandoCello Design

So I'm busy this summer with things other than lutherie, but it is on my mind, things like tonewood and the odd part purchase and trying to design a new Workbench and tool box addition.

In Addition to that I've been thinking about the conundrum of trying to make a MandoCello in a scale length short enough for me to play comfortably and yet long enough for the low C to not be too floppy. Frankly the two requirements are not really compatible.. So How to solve this??

Well it came to me the other day when I was reading a post on multi-scale classical guitars! Make it multi-scale or as some people call it fanned-fret.. Not sure why this did not come to my mind before, perhaps because I have no real idea how to design a multi-scale fingerboard...

Time for some serious reading.. need to figure out the two scale lengths and then where the 90 degree fret will be, I thinking 24.75 and 26.75 or maybe 27 inches for the scales and maybe the 5th fret for the 90 degree fret but that is all wild guesses right now...

I'll probably have to tweak the the X brave a bit too to account for the bridge angle...

Here is a phot of a multi-scale guitar made by Mike Doolin http://www.doolinguitars.com

Designing a Mandocello

One of my summer projects is to finalize the design for the Mandocello I plan to build this fall. I'm certainly not an instrument designer but I am trying to come up with a design that is both aesthetically pleasing and playable. I also have a certain skill level in building that I want to match.. So for now those requirements rule out a caved arch of the A or F style classic Gibson's.

Mandocellos are a bit of an enigma as far as instruments go, although some would say they are enjoying a comeback after years in obscurity they are still what I guess you fringe instrument. Most people have still never heard of one let alone thought of playing one. Designs of modern Mandocellos are all over the map. Ranging from those that closely resemble the classic Gibson'
s to guitar body shapes and beyond.

Historic Gibson K1

Also the tuning of what some people are calling Mandocellos varies some tuned more like an Irish Bouzouki and a Mandocello. I think of a Mandoceloo as still the Cello part of a Mandolin orchestra so still CGDA Exactly the same a bowed Cello.

So my plan is to build a Mandocello that is tuned to the standard tuning CGDA and use a guitar shape with an induced arch top and back. Now there are a lot of other parameters to consider, things like scale length, body size, depth and arch.

One of the big decisions with a Mandocello, at least for me is scale length, A bowed Cello is about a 27" scale length but for me anyway that is too long to play comfortably. The problem is the shorter you go with scale length the harder it is to the the low C string to have enough tension.. A good scale length for my hand size would be 24.25" but that is getting really short for a Mandocello. I will most likely use a 24.75" scale length which is the same as the old Gibson A style Mandocellos.

A modern Ovation Mandocello

You also need to consider the body size, and although I am using an Gibson A style scale length I think the A style body does not have quite enough internal volume for the lower register.. So I am going to use a Gibson L-0 bidy shape.

Next the stress on the body, since I am not using a carved body plates I need to account to the increased string tension of a Mandocello over what a 6 string guitar's String tension would be. The tension on a Mandocello is almost double a 6 string guitar.. I will be reworking the bracing pattern to mimic what would be a 12 string guitar X brace design.. perhaps with carbon fibre  Over the summer I'll be finalizing that design as well.

Gibson L-0 6 String Guitar

Also the neck has to withstand these forces as well so I am planning a Narra neck with a double acting truss rod and I am debating carbon fibre reinforcement.

Lastly aesthetics  Mostly because the last few instruments I've built have been darker tone I'll be going a bit lighter looking for this one.. I'm planning a Oregon Myrtle Back & Sides with a Sitka Spruce top (Sitka will help in withstanding the string tension) The trim on the instrument is planned for Indian Rosewood, I'm still deciding how I am going to do the rosette but it will be some form of segmented wood rosette I think.

So there is the process thus far.. Of course you can follow this Mandocello as I build it.

Celtic Tenor & Summer Plans

So As I said I did change strings on the little tenor I built and the new ones do work better. The guitar is settling in nicely and I quite happy with the sound.. It is an Octave Mandolin sound..

Summer is just around the corner - I hope so I doubt there will be much guitar building going on in the summer. I have lots of plans right now and not many of them involve Lutherie.. I do hope to get a few more jigs built over the summer and perhaps an new tool box made.

The other thing I really want to do is finalize the design for the Mandocello that will be the next instrument I build.. I've got the over all design in my head and just need to decide on all the details.. It is going to be a guitar shape based on the Gibson L-0 from the late 1920's.. It is going to be made of Sitka Spruce, Oregon Myrtle and Narra with most likely Indian Rosewood trim..

It is going to be a short scale instrument (as Mandocellos go) with a 24.75 or 24.4 inch scale length..

I may bet started on it over the summer but I doubt I'll really get into it until September.

And It's Playing Music

The Celtic Tenor Guitar is finished.. it has a coat of blonde shellac French Polish , Schaller gold tuners with ebony buttons and an Allen Tailpiece. Currently it is strung with 0.042, 0.030, 0.020 and 0.012 strings tuned to GDAE an Octave lower than Mandolin. So it's a Tenor Guitar tuned as an Octave Mandolin :-)

The strings are a bit floppy on it so I'm going to replace them with some Mandola strings which as 0.049, 0.034, 0.023 & 0.014 Which should give 21 to 23 pounds string tension across the board.

All in all I'm happy with the results, it has a Mandolin like sound and should be good for playing Celtic pieces.. One I sort ou the strings I'll try and post a sound clip.

Sanding and Pore Filling

Sorry no photos of the exciting task of sanding, but pretty standard, 80 grit with a orbital sander, 80 grit by hand then 150 grit by hand then 220 grit by hand..

After sanding it is on to pore filling, there are as many methods of pore filling as there are luthiers, I'll be using two methods for this guitar. For the back and sides I'll be using Zpoxy brand epoxy. I've used it before and it works well under a French polish. For the neck I'll just be wet sanding with shellac.

The Zpoxy needs to dry overnight then get sanded (more sanding) then probably a second coat and more sanding to insure all the little pores are filled.

Nice thing about Zpoxy is you start to get and idea of what the finished guitar will look like

Back & Sides  First pore filling

Looks good

High tech applicator....