OM Sinking Top

I have an Ozark Octave Mandola - bought in Nov 2020 as a temporay measure whilst I make my own! I needed something to play.
The top has sunk by 2mm. I fitted it with D'Addario EJ72 (14 -49) as the strings supplied were rather floopy in the bass.
On looking inside I notice that there is only one brace, going across the instrument under the bridge. The brace has not become detached.

Has anyone had experience of this problem with this OM - is it a regular occurence with them?

The OM is still under warranty, but returning it would be a hassle and time consuming. Not only that, the replacement might have the same problem.
The OM is easy to play and makes a good sound. My temptation is to remove the back and to remove the original brace, substituting it with an X brace for more support.

Any thoughts or comments would be appreciated.

I think I would be more inclined to just raise the saddle if necessary, 2mm is not huge.

You're correct, an X-brace with a slight induced arch would be more structurally stable. I don't know if I'd be willing to go through pulling the back though. Getting a back reglued and having everything match up is no easy feat, you're likely to have to rebind it.

If you see it as an exercise to practice skills, then go for it. I'd wait until you have your own build done so you have something to play in the interim.

I’d back off the strings. The EJ72’s are better suited for mandolas than octaves. I’d try the EJ80 set before more invasive interventions.

Yes, try the EJ 80 set. They are the heaviest set I would use on any octave mandolin. You might even need to go a little lighter.
The 72's are a very heavy set, and not only will they tear an OM to pieces, they will also wreak havoc with many mandolas.

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Originally Posted by rcc56

Yes, try the EJ 80 set. They are the heaviest set I would use on any octave mandolin. You might even need to go a little lighter.
The 72's are a very heavy set, and not only will they tear an OM to pieces, they will also wreak havoc with many mandolas.

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Thanks for that. The 72's are listed as medium in the D'Addario catalogue. The Ozark arrived with 12 - 46's on it and was rather weak and floppy on the G & D, and buzzed somewhat on the G. I'm not sure what brand the factory fit - maybe the EJ80's will be better quality despite being the same gauge as originally fitted.

I shall also have to play around with bridge height as suggested by Rob Roy - that's a bit of a PITA as it's a non-adjustable bridge. Truss rod will also be adjusted as there is a bit too much relief.

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Originally Posted by Jeremy A

The 72's are listed as medium in the D'Addario catalogue.

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Gauges that are listed as medium (or even light) for a 15.75-16.25” scale length on a tenor mandola can still be awfully heavy for the 20-23” scale on an octave mandola.

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Originally Posted by pheffernan

Gauges that are listed as medium (or even light) for a 15.75-16.25” scale length on a tenor mandola can still be awfully heavy for the 20-23” scale on an octave mandola.

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Aaah, I hadn't realised that - thanks for the heads-up. I shall give real EJ80's a go along with bridge height and truss rod adjustments.

One key piece of information you left out is the scale length. I had to chime in and say something about the misinformation that’s been spread about J72’s. It’s madness to think that the same string set that works on a 23” scale would be appropriate for a 20” scale. The J80 “octave mandolin” set was designed for a 22 1/2 “ scale. When you put that same set on a 20” scale instrument, the tension is way too low for correct feel and sound. That is why a J72 “light mandola” set is a common upgrade on these short scale instruments. Weber puts a heavier set on their short scale octaves than they do on their long scale ones. You can search these archives and see a lot of threads on this topic. The J72 set will not “tear apart” a properly constructed short scale octave. Key term there is “well constructed”. An OM with just one transverse brace is not well constructed. It should X bracing or A frame bracing.

D'Addario may call the J72 set "light" mandola, but by their own tension data they exert 182 lbs. of tension on a mandola, a pound more than a set of J74 [mediums] exert on a mandolin. The J72 set can sink the top on a Gibson oval hole mandola-- I've seen it several times.

At any rate, our friend's Ozark octave mandolin does not seem to like them. If your instrument complains, give it some relief. If you give it relief quickly, chances are better that it will recover quickly without surgery than if you wait a long time.

You might try backing off to 12 and 22 on your first 2 courses, and try 32 on the third course and 48 on the fourth course. If you have enough patience, you can look up string tensions for various alloys and scale length on D'Addario's string tension calculator, but it's a bit troublesome to navigate. For a lightly built instrument, it's probably best to limit tension to about 19 lbs. for plain strings and 22 lbs. for wound strings, or a maximum of 170 lbs. total. Yes, 10 lbs. can be enough to push an instrument over the edge when you're close to its upper limit.

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By the way, phosphor bronze strings have higher tension than 80/20 bronze strings of the same gauge, and nickel has lower tension than 80/20.

Also, beware of the EJ78 mandocello set-- it specs out at 237 pounds, and will ruin an old Gibson mandocello.

Humidity or the lack of it can cause a 2mm change.

Thank you for the very useful info. Sorry I omited the scale - it is 20". Also thanks to rcc56 for your detailed reply. Much food for thought.

So my OM is suffering in two ways - 1. it is not "well constructed" which is not surprising as it is not a "high end" instrument and 2. having a 20" scale compromises the choice of suitable strings. I have always used D'Addario's on my A style Mando and also have a trade account with them. However the choice for the OM seems rather limited.
As suggested I have removed all strings at present to let it rest for a few days. I shall then fit the first three courses from the J80's (12.22.32) and source a 48 from another supplier.
Has anyone had any experience of Newtone Strings? They are fairly local to me and can make wound strings with PB, 80/20 and nickel windings.

Thanks to all again

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Originally Posted by Jeremy A

Thank you for the very useful info. Sorry I omited the scale - it is 20". Also thanks to rcc56 for your detailed reply. Much food for thought.

So my OM is suffering in two ways - 1. it is not "well constructed" which is not surprising as it is not a "high end" instrument and 2. having a 20" scale compromises the choice of suitable strings. I have always used D'Addario's on my A style Mando and also have a trade account with them. However the choice for the OM seems rather limited.
As suggested I have removed all strings at present to let it rest for a few days. I shall then fit the first three courses from the J80's (12.22.32) and source a 48 from another supplier.
Has anyone had any experience of Newtone Strings? They are fairly local to me and can make wound strings with PB, 80/20 and nickel windings.

Thanks to all again

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Jeremy, have you tried looking on the EagleMusic site. They do Puretone strings which, according to what I've read, are the same as Newtone but branded by Eagle as Puretone. I have no way of verifying this, but I can say that I bought their octave mandolin set (12,24,36,48) for my recent build which has a 21" scale. I'm pleased with the set, but maybe the G and D strings might be a touch floppy on a 20" scale. Eagle also do a Puretone custom set in which you choose the gauges, for the same price, which also suggests the Newtone connection.
The phosphor bronze strings(ball end) appear to be very decent quality from them, so it is just a matter of getting the gauges right.
Mike

I like the Newtone nickel .010 - .037 set for my relatively lightly-built mandolin. No experience with their other string sets, but I wouldn't hesitate to try them out.

Thanks for that Mike. I'm expecting a call from them on Tuesdsay so I'll ask about them. Hopefull they will be in stock because Newtone take two weeks to process orders!

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Originally Posted by mikeyb2

Jeremy, have you tried looking on the EagleMusic site. They do Puretone strings which, according to what I've read, are the same as Newtone but branded by Eagle as Puretone. I have no way of verifying this, but I can say that I bought their octave mandolin set (12,24,36,48) for my recent build which has a 21" scale. I'm pleased with the set, but maybe the G and D strings might be a touch floppy on a 20" scale. Eagle also do a Puretone custom set in which you choose the gauges, for the same price, which also suggests the Newtone connection.
The phosphor bronze strings(ball end) appear to be very decent quality from them, so it is just a matter of getting the gauges right.
Mike

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Mike, I spoke with Eaglemusic who told me that they no longer have a link with Newtone and that the Puretone strings are made for them in the USA. I've bought a set of their OM strings to try.

Developments on the actual instrument - Stentor, who supplied the faulty OM, have sent a replacement which I think is an older model ( they have no new ones in stock). All measurements are the same except the sides are 8cms deep against 6.2cms for my original one. Also the replacement has two horizontal braces both front and back. It is heavier than my original one. I shall experiment with strings & bridges, compare the two and go with whichever sounds better.

Interesting info. re the Eagle/Newtone connection. The Eagle custom sets cetainly used to be made by Newtone and it seems that they no longer are.

I’m gradually working my way through my stock of Newtone, ball end, OM strings (13/24/34/52) My OM has a scale length a shade over 21” and, if anything, the E is a little light for me.

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Originally Posted by Jeremy A

I have an Ozark Octave Mandola - bought in Nov 2020 as a temporay measure whilst I make my own! I needed something to play.
The top has sunk by 2mm. I fitted it with D'Addario EJ72 (14 -49) as the strings supplied were rather floopy in the bass.
On looking inside I notice that there is only one brace, going across the instrument under the bridge. The brace has not become detached.

Has anyone had experience of this problem with this OM - is it a regular occurence with them?

The OM is still under warranty, but returning it would be a hassle and time consuming. Not only that, the replacement might have the same problem.
The OM is easy to play and makes a good sound. My temptation is to remove the back and to remove the original brace, substituting it with an X brace for more support.

Any thoughts or comments would be appreciated.

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Regarding removing the back: I have used Randy Wood's method for back removal several times, and it's worked well for me(he uses it on mandolins, I've used it on archtop guitars). Using a very thin small saw, with no set, saw between the binding and the side wood, all the way around the body. The tricky parts are at the neck and end blocks. No binding removal. Do not sand the sawn surfaces before regluing. If done carefully, the visible joint is mostly tight, with perhaps a few very small gaps to touch-up.

I read about his method in one of the Guild of American Luthier's 'Big Red Book of Lutherie'.

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Originally Posted by Jeremy A

I have an Ozark Octave Mandola - bought in Nov 2020 as a temporay measure whilst I make my own!

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Jermey A , Will you build a flat top or will you carve your new octave?

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Originally Posted by Dave Richard

Regarding removing the back: I have used Randy Wood's method for back removal several times, and it's worked well for me(he uses it on mandolins, I've used it on archtop guitars). Using a very thin small saw, with no set, saw between the binding and the side wood, all the way around the body. The tricky parts are at the neck and end blocks. No binding removal. Do not sand the sawn surfaces before regluing. If done carefully, the visible joint is mostly tight, with perhaps a few very small gaps to touch-up.

I read about his method in one of the Guild of American Luthier's 'Big Red Book of Lutherie'.

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Take note that this method will only work on instruments where the binding does not overlap the joint between the back and the sides. It will work on Gibson oval hole mandolins and some Gibson arch top guitars. It will not work on Martin instruments or most Gibson flat top guitars.

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Originally Posted by MrMoe

Jermey A , Will you build a flat top or will you carve your new octave?

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The new build will be carved, spruce front and maple back.

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Originally Posted by Dave Richard

Regarding removing the back: I have used Randy Wood's method for back removal several times, and it's worked well for me(he uses it on mandolins, I've used it on archtop guitars). Using a very thin small saw, with no set, saw between the binding and the side wood, all the way around the body. The tricky parts are at the neck and end blocks. No binding removal. Do not sand the sawn surfaces before regluing. If done carefully, the visible joint is mostly tight, with perhaps a few very small gaps to touch-up.

I read about his method in one of the Guild of American Luthier's 'Big Red Book of Lutherie'.

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Thanks for the suggestion Dave. Sadly, in this case, the back is 4.5mm thick and the binding 6mm so I can't use this method.

Jermy A, If your top continues to sink you could try adding a sound post.

https://www.mandolincafe.com/forum/t...-in-a-mandolin

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Originally Posted by rcc56

Take note that this method will only work on instruments where the binding does not overlap the joint between the back and the sides. It will work on Gibson oval hole mandolins and some Gibson arch top guitars. It will not work on Martin instruments or most Gibson flat top guitars.

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Right: IMO, it only works on instruments with sides that have straight edges(are a consistent width), without taper or curve along the edges. That usually means only carved top/back mandos & guitars. But it has worked for me, on instruments where the binding does overlap the joint: it means one is sawing through the kerfing, not the glue joint, but it still works.
It will work on f-hole, scroll Gibson style mandos too: Randy Wood was re-graduating '70's Gibson F-models, when he came up with this method. Separating the larger blocks makes it more challenging.

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Originally Posted by Jeremy A

Thanks for the suggestion Dave. Sadly, in this case, the back is 4.5mm thick and the binding 6mm so I can't use this method.

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It's only overlapping by 1.5mm, so I believe it would still work(you'd be sawing through the thicker part of the kerfing, and it should glue up ok, upon reassembly).