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Graham McDonald
Jan-14-2008, 3:39pm
Here are a couple of pics of a new bent-top mandolin. Sitka, walnut, and maple and an ebony board with a zero fret. Rubner tuners

cheers

graham

Graham McDonald
Jan-14-2008, 3:42pm
And a closeup of the body side. Spalted maple binding

Graham McDonald
Jan-14-2008, 3:46pm
And the soundboard bracing

cheers

Eugene
Jan-14-2008, 4:35pm
I like it. Did you arch perpendicular to the cant as well by cutting a wedge at the join behind the cant?

Bill Snyder
Jan-14-2008, 4:51pm
Graham how do you like the Rubner machines?

Jim Garber
Jan-14-2008, 4:57pm
I like it a lot. Nice aesthetics and has a combination of the European and Brazilian vibes.

Graham McDonald
Jan-14-2008, 5:19pm
The soundboard has a 15' transverse arch and a 8-9 degree cant. I did a bit of experimentation with two soundboard halves which I had pre-bent (pre-canted?) and then clamped over curved braces. With a 15' arch the amount of wedge that needed to be trimmed was negligible (sp?), but a more severe arch does need some trimming of the centre join. I decided it was entirely too tricky to put the bracing on one half of the soundboard and then fit the second half and glue the centre join while trying to glue it to the braces as well, as Robert Lundberg suggested a few years ago. With a 15' arch there was a little distortion in the bottom corners when the braces were glued, but nothing that would interfer with the top being glued to the sides. I have some photos of the experiments with the two pre-canted halves which I think I might have posted in a discussion a few months ago in the classical section. If not I can put them up to illustrate.

The Rubner tuners are fine. Perhaps not as smooth as a set of Grovers, but for side mounts it was either them or Schallers and there is a luthier supplier out here who is bring quite a bit of german stuff into the country and the price was attractive.

It is a bolt-on neck with a CF bar glued to the fingerboard extension which also locates in the slot in the neck block. It sound quite pleasant. Rather like a flat-top I made at the same time, but subtly different. Without the hollow honkiness of the larger volume bowlbacks

cheers

graham

JEStanek
Jan-14-2008, 6:16pm
That looks very nice. My Spira bent top mandolin also has Rubner tuning machines that I like. I don't recall how Jack braced his top, I never got that photo during the build, perhaps it's proprietary!! (or not!). Yours looks quite complicated and interesting. I love the binding.

Jamie

brunello97
Jan-14-2008, 8:32pm
Graham,
Let me chime in. # I remember the conversations around the top wedge Eugene is referring to and your earlier experiments. This is great to see bearing fruit. #But the overall fine craftmanship might actually distract attention from the top itself. #I'm reminded of an old Ron Wood solo album "Gimme Some Neck". #This one just makes you want to grab it.

What are your thoughts on the longitudinal braces to either side of the soundhole?

thanks for posting.

Mick

Graham McDonald
Jan-14-2008, 11:23pm
The bracing is very much based on the pics that Lorenzo Lippi posted of his Embergher copy. I figured if it worked for Embergher it might work for me 8-) I think the transverse braces could be a bit lighter and more delicate perhaps, but it certainly works. I think Jack Spira would be quite happy to tell you how his was braced if you asked.

I am a firm believer in as much strength as possible around the soundhole. Deformation by the neck block rotating is the major problem with older bowlbacks and part of that is because cutting a soundhole greatly reduces the strength of the soundboard as a structural element in the whole system. I don't think there is much going one around the soundhole in terms of sound production on one of these instruments, though it would be great to see one of those laser inferometry (that is spelt wrong) pictures of where a soundboard like that has vibrational nodes. Dave Cohen has done it with a couple of Gibson style carved mandos, but I don't know of any other similar work on mandolins. It is all a matter of having the time...

cheers

graham

Jim Garber
Jan-14-2008, 11:27pm
Without the hollow honkiness of the larger volume bowlbacks
Hmmmm... we bowlheads may prefer to describe the sound a little differently... tho I may use that for a future band name http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif

brunello97
Jan-14-2008, 11:40pm
Graham,

Thanks for the feedback. #I added some longitudinal sides-of-soundhole braces to a Puglisi mandola I was 'repairing' last summer and I think it was an Embergher image that gave me the prompt. # #I've had a few bowls and flatbacks that have distorted around the soundhole as you describe. #The top on the mandola was quite thin and had gone through its fair share of distortions. # Hence my thought to add them. #But I am even barely an amateur when it comes to this stuff. #It is helpful to hear some professional PsOV on their application.

Mick

Griffis
Jan-15-2008, 4:33pm
That is absolutely one of the classiest mandolins I've ever seen.

Scratch that--it's one of the classiest string instruments I've ever seen.

Just beautiful.

Eugene
Jan-15-2008, 9:32pm
Dave Cohen has done it with a couple of Gibson style carved mandos, but I don't know of any other similar work on mandolins.
Dave has analyzed one of my Martins and an old Calace as well. He has presented those data, but not published as far as I know.

Of course, such braces around the soudhole are typical to classical guitars.

Dave Cohen
Jan-15-2008, 11:45pm
Also included in the batch that I presented at the 75th anniversary ASA meeting in 2004 was a Vega cylinderback. I've written a chapter on mandolin family instruments for Rossing's book. Have include that and the Neapolitans in it, as well as several vintage Gibson oval hole mandos, one '24 F5, and a coupla mine. Hope it comes together soon.

JeffD
Jan-16-2008, 12:05pm
Hows it sound?

Looks yummy.

Graham McDonald
Jan-16-2008, 6:24pm
The sound is similar to, but different, from a flat-top I built at the same time and quite different from a carved A style that was also built in the same batch. It is very bright and responsive, with some of the characteristics of a bowl back but with a lot less air volume and a wider body still different. All up, quite a pleasant sound, but definately but a bluegrass sound. I want to get a couple of the good local players to give all three a workout and make some comments sometime soon.

Dave C, very interested to seeing that research. Any idea of when the book is coming out?

cheers

graham

David Newton
Jan-17-2008, 9:47am
Good to see this thread come back up to the top (by me, right?) I am going to be forced into making a cant top mandola, by the purchase of a case that doesn't fit anything else. Thanks for the pics Graham.

dougjay
Jan-17-2008, 9:56am
What is the reason for using a zero fret rather than the standard nut arrangement?

David Newton
Jan-17-2008, 2:42pm
Graham, is the top bent with heat only? My old Scott Antes bent-top plans describe cutting a scribe and running glue in there before bending.

Graham McDonald
Jan-17-2008, 4:48pm
The zero fret is there because I could! This and three other mandolins were really built as examples to be photographed and described during the building process for a book I am working on about building mandolins, which should be published by the middle of the year (some preliminary info on the website if you are interested. I put the zero fret on this one, as a semi-classical mandolin to illustrate it. I don't realy think they are any better or worse than a normal nut. Maybe a little less work as the height of the nut slots isn't critical to the setup.

The top is bent by (carefully) sawing a slot on the inside a little less than 2/3 through the thickness. I used a Stew Mac fret saw with the acrylic depth stop and then relieved the edges a little with a file as the top of the slot closed up before it would bend enough. Water sprayed on both sides and bent over a length of propane heated 1" brass pipe. It would probably work better if the heat were concentrated along a narrower strip, like a 1/4" bar or something, but I could think of a simple way to evenly heat one. When it gets hot it will bend the 8 degrees or so necessary. There is a little fracturing of the fibers on the outside, but nothing too noticeable. I think it is best to do it as quickly as possible so as not to affect the glue join at the bend, but that gets covered by the centre re-enforcement strip anyway. If you get a chance have a look inside a cheap bowlback. There is some really rough work in them, but they work, and rarely fail around the cant or the centre join.

cheers

graham

brunello97
Jan-17-2008, 6:33pm
Hi Graham,

You have been generous with your descriptions of the process. If I understand you correctly you did not 'cut wedges below the cant' as Eugene asks.....but bent the assembled two-piece top in two directions, first at the cant and then transvere along the line of the cross-brace.

Did anything become of the bend-cant-first then notch-and-bend-and-join top-halves experiment? You've obviously been successful with your method, but I am wondering about your observations are on the other?

thanks,

Mick

Graham McDonald
Jan-17-2008, 7:13pm
Many years ago I built quite a few bouzoukis/OMs using the glue/bend/brace approach. As I mentioned before, with a modest (15'radius) arching in the bracing it cause a little humping on the lower section of the soundboard once the braces are attached - a mm or so on the outside halfway around the curve from the ends of the cant to the tailblock (does that make sense?) While that humping is not really wanted, that much distortion can be clamped out when gluing the soundboard to the sides and it isn't noticeable once the binding is on.

With a more radical arching to the transverse bracing (probably something like 10' radius), the lower part of the soundboard humped up considerably on either side of the centreline, and it semed that there was entirely too much stress being put on everything. When I clamped the bent, but unglued, soundboard halves to the same radius, the ends of the two halves overlaped by around 3mm, and the rise in the centre at the bridge position was around 5mm (I have measured at least one bowlback with a 6mm rise across the arching). For the purposes of the book, I took the simplest approach of glue/bend/brace, and haven't yet tried to work out a methodology for bending/wedge trimming/gluing/bracing other than what Robert Lundberg suggested a few years ago. There was talk of Lorenzo Lippi running some classes on bowl back building in Italy, and I am trying to work out a way of getting there if they happen.

I would like to have a go at a bowlback sometime in the next year or so, so it might well resurface at that point. Apart from getting the book finished (!) the current project is trying out some more radical ideas with bits of carbonfiber, which I will post in a few weeks (assuming these somewhat whacko ideas actually work)

cheers

graham