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Thread: PEG & bowlbacks

  1. #1

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    Hey guys and gals,
    Anyone here build bowlbacks? Anyone have some experience with PEG wood stabilizer? I am curious if this could help a bowlback live a long and productive life into its 300th anniversary under varying humidity without back slat separations. What kind of a weight increase should I expect? Any experience, thoughts, suggestions?
    I'm on my first bowlback and just brainstorming on the possibility at the moment... My thought was the bowl is so dang lightweight already, I thought the extra might not hurt. Plus it is not an active vibrating back style (a big logical assumption) like a flat or carved back, so the weight should have nil effect I'm guessing....

    Thanks!

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    Only US bowlback builder I'm familiar with is Daniel Larson. You might email him. Website www.daniellarson.com

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    Registered User sunburst's Avatar
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    PEG treated wood is difficult to glue and difficult to finish.
    I've read that you have to use epoxy or resorcinol to glue it and the surface must be freshly prepared and clean.
    Also, shellac, lacquer, and some varnishes won't work. You have to use oil or moisture-cure polyurethane-resin varnish. Apparently, PEG suppliers sell specially formulated varnishes.
    PEG is hygroscopic, so you have to heat the wood pretty hot (I don't know how hot) to dry it enough to apply the finish.

    I don't know...sounds like more trouble than I would want to take on, but if you try it, let us know how it turns out!

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    Hello OldTymer
    PEG is`nt suitable for use in instruments. I`ve used it in the past to instantly season wood for turning on the wood lathe. It works at it`s best on freshly felled unseasoned wood. As sunburst says PEG is hygroscopic, it forces out the moisture in wood and replaces it with itself. A block of wet wood suitable lets say for turning into a fruit bowl can be ready to mount on the lathe within a couple of weeks. The surface of the wood after turning will be waxy, so the only finish suitable for such work is wax. To get the best results from this substance the wood needs to be saturated with water, (freshly felled timber, or lumber as you say in your neck of the woods}.
    Bob Deacon

  5. #5

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    Thanks guys. Yep, sounds like more trouble than 'tis worth. My hope was to assemble the bowl of the instrument and coat the interior with PEG, let it soak in and dry, then have a worry-free bowl.... What I gather from everyone's input it first it's probably too dry, second, it'd probably soak through to the other side and ruin the possibility of a normal finish.. Oh well..
    I appreciate the advice very much.

    Happy carvin'

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    Mando-Accumulator Jim Garber's Avatar
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    I must confess my ignorance of what PEG is. However, the most common misunderstanding about bowlbacks is that they are super delicate. The design above all is intended to produce sound with the use of very light strings. What has happened ot many over the years is that most mandolin strings available from your local music store are heavier, bluegrass gauge, not at all appropriate to use on a bowlback.

    I have seen quite a few bowlbacks, tho that were strung correctly over their lifetime and were intact longer than even the most robust Gibson.

    Jim



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  7. #7

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    Howdy Jim,
    My biggest concern was slat separation due to humidity fluctuations over the years. PEG (Poly-Ethylene-Glycol I believe?) replaces water in the wood forever, so it is in effect always at maximum expansion, no room for shrinkage. A veritable freeze in time. My first hearing of the word came from a wood class where the professor mentioned an old water pipeline dug up at Virginia Tech. They used to make the pipelines sorta like barrels, completely out of wood slats and metal rings! (Imagine the work involved in just one mile of it!) When they first dug it up it was fine, but as it slowly dried, the wood just crumbled and fell apart like dust, the water was actually holding this thing together! In come PEG, they restored this piece of pipeline which I believe is still on display somewhere on campus. "Dry" and solid thanks to PEG.

    Back to bowlbacks. I'm curious what heavy strings do to the bowlback to cause it not to last as long. My intention with the current instrument was for _medium_ guage because I am building both a bigger bowl and a much larger top to yield bigger volume for outdoor playing. This bigger assembly will need more "gasoline" to drive that bigger engine. So all my slats are .125" thick, I figured it'd be strong enough. Would that be enough? Should I be thinking fiberglass bowl interior here? Or more simply, a dowel rod from tailpiece to neck joint inside to stiffen? I want this thing to last through Doomsday.
    Thanks!

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    Registered User Bob DeVellis's Avatar
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    I've oftenthought that some kind of plastic bowl would work well. Aluminum was used in years past with some success. The Fluke ukuleles with plastic backs are surprisingly sweet sounding instruments, and quite inexpensive. If someone wanted to build a rugged, weather-resistant bowlback, I'd think the Fluke approach would be worth a try. The back shape could be based on a classic bowlback, of course.

    As for heavy strings, bowlbacks are engineered for light strings. They can produce a huge sound with light strings because they are built so light. To use the horsepower example, they're morelike motorcycles than cars. They're built light and thus don't need the same horsepower to perform well. Although it would work great in, say, a pick-up or big sedan, putting a big V-8 on a motorcycle would be a problem. Likewise, many modern strings are too much "horsepower" for a bowlback. The neck joint is totally different on a bowlback. The ribs fit into a groove on the end of the neck. There really isn't a single joint anything like the dovetail or mortise and tenon on most mandolins. Also, the tops are thin and the bracing is extremely light. Heavy strings just tear them up over the years.

    I suppose you could re-engineer a bowlback with heavier construction to withstand heftier strings, but I'm not sure if it would have the same sound as a more lightly-built one.
    Bob DeVellis

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    Registered User Martin Jonas's Avatar
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    This is fairly common in wooden artefacts that were preserved under water or otherwise shut off from oxygen (e.g. viking long boats and such) -- they saturate with water and will decay within days or sometimes hours after being taken out of contact with water. Not really comparable to a musical instrument which hopefully will not be buried under water.

    Regarding bowlbacks, they typically fail at the neck joint when overstrung. The term "medium" gauge is culturally dependent and means different things to different people. "Medium" gauge bluegrass strings probably means J74s or similar. For comparison, the German Lenzner string I currently have on both my vintage bowlbacks are labelled "medium", but would be called "light" or even "ultra light" in the US (0.09 to 0.34). I think it's a misconception that bowlbacks are quiet - quality bowlbacks can be played very loud indeed, if strung with the right light strings.

    Interesting project, anyway -- I wish you much success!

    Martin

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    Mando-Accumulator Jim Garber's Avatar
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    Hi Brian:
    We have discussed this already off-board. I didn't realize OldTymer was you.

    I think that the excessive tension of the bluegrass-gauge strings either pushes the bridge too much into the top and/or pulls the body from either end. I am not sure of what the physics of it is but that and the ravages of time and dryness causes them to implode.

    BTW in general I have observed that the vintage instruments that still had their original cases seem to not have been as affected by all this. of course, if it also possible that the owners of these took better care of them.

    My Pandini bowlback uses Dogal Calace medium gauge RW92, but I am not sure what the actually string tension is. I think that these strings are still lighter in gauge than J74s for example.

    BTW many bowlbacks are lined with paper. The Pandini is lined with very thin spruce veneer in an almost papier-mache style. I think that the method is to wrap the form with the liner and glue the bend wood slats to each other and to the lining.

    I think that the essense of the bowlback sound is the lightness of the box and not being seriously or technically versed in acoustics, can't really say how a thicker back would affect the sound. I know that canting (bending) the top and judiciously bracing adds strength and changes tone, as it does on any mandolin.

    You might contact Daniel Larson and see if he is willing to give you some tips. I know he has taught a lutemaking workshop.

    I would be glad to give you measurements of my Pandini. It has a great sound is is a joy to play. It is a large-bodied bowlback, larger than the std American style vintage ones.

    It has occurred to me that if the bowlback were just a tad more popular that Ovation would have made a mandolin with their fiberglass bowl. I am not saying that that is a good or bad thing.

    Jim
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    Registered User John Bertotti's Avatar
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    For what it's worth the bowl on my vega resonates quite a lot and the sound of the instrument does decrease when more of the back is in contact with the body. John

    I remember researching lod home building many years ago. There was a company claiming to have logs that the called process 2000 that would never check or shrink or warp. The process 2000 would stabilize the wood cells to prevent this. Is this peg the same thing? If not maybe it is a viable alternative. John

    Just did a search and it is peg they are using also.
    http://www.firesideloghomes.com/woodtreatmentsystem.cfm
    I guess it was worth a try. John



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  12. #12

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    You should also write to Cafe member Dave Cohen. He does not build bowlbacks (and thus will not view you as competition), but he has done some quality research on the acoustic functioning of the bowl and top of a few classic instruments, including my own 1908 Martin. His insight could prove useful.

    Proper, classical bowlbacks are conspicuously absent from the repertoire of US builders (excepting the fine instruments by Dan Larson). I would like to imagine there would be some market for such things; after all, pieces of rather menial quality are still mass produced in Asia and the Czech Republic. What if a company like Martin were to reintroduce a line of bowlbacks somewhere cheaper than a boutique like Larson, but more expensive and of substantially better quality than mass-produced junk? I think their post-1917 style 2 would be an excellent choice: just enough decor and the classic "teardrop" pickguard that reeks of Martin. Give it a 29-fret fingerboard, and it could tackle anything. I would even settle for 24 frets.

    The notion of this project is very exciting. Please keep us apprised, Brian.

  13. #13

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    Let me tackle this one at a time

    As for fiberglass, I'd never build the exterior with it.. No style hehe. My thought was to fiberglass the interior of the wood bowl for extra strength. But now that I think of it, the spruce veneer is quite a nice idea! Not to the natural look, great smell, no need to wear a face mask, atmospheric pollution, the list could go on, hehe. I think I'll try that, shavings should do the trick. Papier mache, I like that.

    The width of the body should come close to 10" finished. It is a perfectly round back, at least in one two dimensional slice, in the other two dimensional slice it is teardrop. Jim, I'd love to know the dimensions of your Pandini. Especially for the body. How would you compare the volume and tone of the larger vs the more traditional size bowlbacks?

    I'd love to keep this bowlback as a part of what I offer. I know I'm small time, but I love the challenge and diversity. I have spent countless hours trying to fgiure out how to do this, think I have it partially down so far. We shall see though. I hope it comes out as expected. The neck joint will most definitely be a dovetail, tall a one as possible to fight the stresses. I may even go so far as a sprung arch of wood internally to counterbalance the string tension of the neck. Just a possibility at this point, but couldn't hurt by any means. I'll post some photos when I get the bowl done.. The neck is coming along nicely too.....

    Talk to ye's soon,
    Brian

  14. #14
    Registered User John Bertotti's Avatar
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    I think you could even use silk as a bowl liner. Alex has posted some benefits of silk but I don't know if they would remain once glued in a bowl. John
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  15. #15

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    Just curious, how did you come across patterns for building this piece, Brian? If you haven't already, you might want to consider buying a wrecked low-end piece of junk on eBay just to pull it apart and see how it ticks.

    A 10" span constitutes a pretty massive soundboard. For comparison, both Martin and Vega mandolins were typically around 7 3/4". Modern German mandolins have considerably larger soundboxes than those of the classic Italian and American traditions; they have smooth, consistent tone, sometimes compared to a classical guitar. They are often strung with flat-wound Thomastik strings. Unfortunately (to my ears and taste) they lack the bright sparkle to tone that I consider to define the classic mandolin. For examples, see links in my second long roster-like post here.

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    I think someone tried useing a "sprung arch" to reinforce bowls. Ended up not being worth the effort. Where I see movement in antique bowlbacks is typically on the top, the area between the fingerboard and the cant (the "bend" in the top in the bridge area). The vectors working on the instrument are trying to pull the neck toward the tailpiece; this results in a rotation around the neck joint.
    Aside from rendering the higher (>17) frets less than useful, and warping the top a bit around the end of the fretboard, it seems to have little deleterious effect.

    As for needing desperate measures to seal the wood of the bowl, not an issue. The wood is finished on the outside, covered with glue and paper (or wood) on the inside, and sealed with glue on the sides of the ribs. None of those areas are big on sucking up moisture anyway - it's the ends of the ribs where the tubules open, and that's where moisture woul;d get in, except they're also glue-sealed.

    I've seen a few (very few) really old bowlbacks (well, a hundred years old, anyway) that had serious rib problems. Usually just a few slight separations between a rib or two, easily dealt with.

    It's the neck joint that is the most delicate part of the instrument. There isn't much wood there, and it has to resist a fair amount of force. It's surprising how well it does so, unless abused by modern strings.

    As has been pointed out, delicacy rather than brute strength is the order of the day with these instruments. Even so, they are surprisingly strong for their graceful delicacy. Think ballerina here. Properconformation and careful use of body mechanics produces uncommon beauty, and exhibits effortless effects that cannot be duplicated bt the Schwartzenegger body type.

  17. #17

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    For the design I just sat in front of a blank blueprint and started at it. I draw things and invariably change it 100 times to get the proportions I need, taking into consideration the size of the soundbox and the desired sound.. The soundbox is going to be a bit larger, sure enough... Here's a photo in progress, I'll have more soon:



    My intention is to increase the neck angle (more pressure on the soundboard than normal to move the larger air volume) while supporting this increased pressure with an induced arch rather than a "bend".. It'll have a moveable bridge.

    The bright sound you're referring to in the Neopolitans vs the Germans... Isn't there a hefty brace right under the bridge in the Neos? I believe it's the secret to brightening the tone. The tighter the brighter. I'll post a soundfile when I complete this one, you can all be the judges if it's bright enough like the classical style..

    What is the normal thickness of the slats in a Neopolitan mandolin? I should probably take one apart and check, but someone helped me be lazy by sending me pictures of exactly what I was looking for once, the neck joint. I believe it was Jim. Thanks again, Jim!

    I checked out your list, Eugene. Nice! I got lots of ideas just scanning through it, beautiful examples.

    Later...
    Brian

  18. #18

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    You know, I just checked out my old Mannello Neopolitan and realized, the body on the one I'm building isn't as big as I had compared it in my imagination when I was drawing it out. That Neo is _deep! ..though narrow. I'd bet the one I'm building has only a tad more volume.. We'll see......

    Bob, I usually brace heavily under the fingerboard, it's "dead" there so it can only help sturdiness... Thanks for the input. I learned from my early mistakes, I had this same sort of sinking right there because of bad construction on one of my first protos.... The fingerboard brace didn't affect the sound. Will do the same here....

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    What I've seen in bracing is usually a brace under the fretboard, and two braces between the soundhole and the bridge. On some instruments they're parallel, on some they widen toward the treble side. Sometimes there are braces oneither side of the soundhole as well. There is usually a wide flat strip of wood supporting the center seam of the top, running from the last brace to the end of the instrument.

    The top is usually arched from side to side. On most bowlbacks the "bend" in the soundboard is necessary to get the string pressure right while keeping the bridge mass low. On Greek bowlbacks the bend is very slight or nonexistent; the bridge is quite high, and the fretboard is quite thick. On the better Italians (except for the Roman models) the fretboard is pretty thin.

    Serious jiggery in that photo, BTW.

  20. #20
    Mando-Accumulator Jim Garber's Avatar
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    I immediately ran to Alex Timmerman's book De Mandoline en De Gitaar, in which he has photos of historic instruments + measurements etc.

    These are two small illustrations of Embergher bracing. Luigi Embergher, a Roman luthier, made some of the finest-sounding bowlbacks. The left is a solo model and the right is an orchestra one. I assume that the solo model would be braced to have a brighter sound.

    I hope that Alex does not mind our using these drawings and would chime in here as well.

    Jim
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    Registered User Martin Jonas's Avatar
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    Quote Originally Posted by (Bob A @ Oct. 15 2004, 20:15)
    On the better Italians (except for the Roman models) the fretboard is pretty thin.
    Just by way of amplification of Bob's statement: I've just measured the fingerboard and bridge on my Neapolitan Ceccherini. The ebony fingerboard is 2.7mm thick and the bridge height (soundboard to top of saddle) is 4.2mm! In combination, this gives me an action of 2.3mm at the 12th fret (from which one can deduce that the top has moved by a couple of millimetres over the last century-and-a-bit; the original bridge height would have been about 2 to 3mm higher).

    Martin

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    Mando-Accumulator Jim Garber's Avatar
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    Quote Originally Posted by (OldTymer @ Oct. 15 2004, 16:09)
    Jim, I'd love to know the dimensions of your Pandini. Especially for the body. How would you compare the volume and tone of the larger vs the more traditional size bowlbacks?
    Pandini measurements:
    Scale: 330mm
    Width of top (at the cant): 200mm
    Depth of bowl: approx. 150mm
    Width of fretboard at nut: 27mm

    Any more? Just ask.
    Jim
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