I posted a question about this instrument a few years ago and it was discussed briefly.  I have decided it is time to open it up and fix it and I was wondering about two possible options.

I have a 1936 Black face K-1 and is is excellent shape except that about 10 years ago it developed the dreaded top sag under the bridge disease.  -- a common ailment in these under built instruments. 

I did not play it long after it happened so the problem a this point the sag is "reversible".  That is when string tension is slack off the top rebounds to its proper carved contour.  I have looked at Frank's repair of the 1920 K-2 mandocello on this site and propose to open the back and make a similar repair on this instrument. 

I will not have to do all the heroic efforts that Frank did to return the top board of the instrument to proper shape however nor will I have to do any work on the end blocks.  So this is a much easier repair I hope.

So my question is this what do folks think of using an X-bracing for the top rather than the second transverse brace under the bridge that Frank used?  The X-brace idea is stolen from Bruce Weber's discussion of a oval hole Weber mandocello that he built a few years ago.


My goal is to stabilize the top and yet make a minimal impact on the K-1 tone/sound.  Would anyone want to wax eloquently on the pros and cons of these two approaches.

Bernie Daniel

Views: 1367


Reply to This

Replies to This Discussion

In my opinion, there is another option to this problem, if the top isn't too bad like you say. Basically, it's an abbreviated X brace. I've done this on a few Gibson mandolins with quite good results. Tonally, the results where quite good as well. One example, when I saw it last, has been 11 years and counting with no change since the work was done to the top. I think if you just scale the helper braces up to mandocello size, it should work. This is the least invasive way (that I have come up with) to deal with this problem.

This first image shows the result of a sinking oval hole top. The top shape changes but the bridge foot does not, resulting in the dented Spruce at the bridge ends. The helper braces are positioned below the bridge ends to restore a curved top there and stabilize it that way.

This image shows the helper brace arrangement, forming a triangular area of reinforcement together with the original lateral brace. If you continue imaginary lines from the helper braces, it becomes part of an abbreviated X. Since you say the correct curve has returned to the top, you can just put some sticky back sand paper inside the top where each brace will go and sand that profile into your brace material. Definitely use hot hide glue to put them in!

If on the other hand, the entire top has sunken in around the re-curve, then X - bracing would be your best bet.

Thanks for the suggestion Paul! 

This mandocello top does have gouged out areas marking the ends of the ebony bridge.  But the top sag is wide spread across the top.  It is not sagged now but as I recall the flattening did extend all the way across the top, i.e., was not limited to the bridge area.  So by your criteria I am going to perhaps need the full X-brace?   I expect I should have the two bars intersect directly under the bridge?

I was planning to use fish glue.  It seems to have properties very similar to HHG but without the short working times? 

When removing the back plate do you routinely have a lot of trouble getting the glue to release at the neck block and tail blocks?

Bernie, some sagging on these old oval holes is to be expected and not necessarily a bad thing if it remains stabilized when it gets there. It may be worth your while to string the instrument back up to pitch, then measure the action and write it down. Do this over the course of at least a month, checking the action measurement periodically. If it flattens some but stays there, I wouldn't worry about X bracing.

I have not X braced one of these and don't want to venture any information on how to best configure it. If no one here chimes in, go to the Mandolin Cafe and ask there. Generally speaking though, the upper legs of the X brace should be configured under the bridge ends, like I have done with the mini braces.

I have used fish glue before but hot hide is my mainstay. Either way, the trick to more open time is to keep the work heated up. Infra Red lamps work very well.

Neck blocks may have a nail registering the back to the block. You can see the small hole in the image posted. Not sure if they where still doing that in the 30's.

Thanks again Paul.  I did a lot of measuring some years ago on this mandocello. Without strings the contour is exactly right.   When you string it up and tune to concert pitch (CGCA) it looks OK for about 24 hours - - then you can see it start to deform but of course you can compensate with the thumb wheels on the bridge -- these had adjustable bridges just like the F-5 mandolins -- adjust the action.  It continues to sink for at least a week maybe two and you get to the point where you really don't want to run the bridge up any higher.  When that happened I would take the tension off again --eventually I just took the strings off and put it in the case.

I bought the instrument in 1974 ($250) and it was fine for years -- then sometime in the mid-1980's the transverse brace let loose (but I did not know it) and of  course the top started sagging.  The problem was diagnosed and the brace was re-glued. About five years later is started sagging again but this time the brace was still glued down -- so it needs something more now or I guess it is a wall hanger?

I could not see any signs of a nail -- maybe they started using an alignment pin on the inside? I'll have to research that out.

This K-1 might well have been one of the last mandocellos Gibson made.  Production of all K-models stopped at the start of WWII in 1940 and never resumed.

This K-1 is unusual in that it has back binding as well as top.  I was able to work an exacto-knife in under the binding-side junction -- it slide in over the kerfing all the way to the inside -- it took some effort but should be doable

It will be a slow removal because with the binding I can't really be applying much heat either to the blade or by steaming I'd guess.

My personal, unprofessional, opinion is that an X would do the job of supporting the top but I think it would probably change the character tone/sound more than a supporting brace under the bridge would change things. 

I haven't done this on a mandolin but I've converted a couple of ladder braced guitars to X and found that they were stronger and sounded different as well. In the case of the guitars this was what I was looking for. I don't see why this big of a change wouldn't modify things with a mandolin too. If you were not satisfied with the sound you had then maybe the X IS the way to go but, otherwise, I wouldn't risk it. 

For what it's worth I've got a Gibson mandolin. It doesn't need any repair but I don't think I would consider this radical of a change in the bracing if it need this sort of help.  

One last thing to consider is that your mando is certainly worth much more than $250 now. I think there's a good chance that changing to an X would devalue the instrument much more than adding another brace under the bridge. IF someone should ever want to return it to the original form... for some unknown reason, it's doable with by removing the new cross brace.

Thanks for the thoughts Ned. I like your logic!

Actually, I was starting to think along similar lines most of today.

First, the fact that Frank chose the bridge transverse brace for the repair is, by itself, probably a good reason for doing the same thing. 

Second the single transverse brace probably would add less additional mass and perhaps impact the vibrations of the top board less than the X-brace?

Finally by luck I found a video of the K-2 that Frank repaired today and it still sounds awesome really and to my ear exactly like a Gibson K-model should sound! (<:

Here is the link to the video.

I also agree with the idea that a single transverse brace would be easier to remove than an X-brace if a new owner want to remove it later.  In fact, a person might be able to remove it via the sound hole?  However in my opinion that would render the mandocello back to the status of "original, but wall hanger". LOL.

Thanks again.

Bernie, have you seen this site?  There are a few videos on the page so you can hear his instrument.

I found the "" site by accident several months ago and have been thinking that it would be fun to convert a baritone ukulele I almost never play like he did for his first.  IF I do it, and that's a fair sized "if" since I already have a few years worth of projects waiting, I'll probably pull the back and X brace the ukulele. I may find that I need to install a truss rod to support the neck under steel string tension too. ( Writing that makes me wonder if it wouldn't be easier to just build one from scratch.)  I've never tried to play a big mandolin like yours but I've talked to several players that have and they all say they are hard to play cleanly or quickly because of the fret spacing.  I don't know how long the scale is on your mandolin but this one has a 19 inch scale which is easy for someone that primarily plays guitar.  

Hi Ned,

I forgot to comment on this post.  Yes without any doubt a mandocello is an order of magnitude harder to play than a mandolin and a good deal harder that a guitar both to play cleanly and also to chord. 

The mandocello is a complete monster and perhaps an idea that has not been brought to its logical end point yet.  The scale length of most mandocellos is 24.75 - 25" -- but a violin cello is 27".  So the scale length - string gauge - pitch range combination is a mess of compromises and not all of them work well (IMO).  Likewise, balancing intra-course with inter-course distance across the linear distance you have to work with at the nut is like dancing on a pin point. 

Here is the good part -- playing a mandocello will make playing anything else including an octave mandolin seem easy.  I have a nice Weber Big Sky octave mandolin it is the only F-style octave Bruce ever made with block inlays -- I really don't deserve it --  but it is like playing a toy after the mandocello and it has a 21" scale.

As well a mandocello is very hard on your hands and fingers.  I inherited my mothers osteoarthritis in my hands and playing mandocello has killed my joints.  They are hugely misshaped now -- but so what?

Take home is no one should even think about a mandocello -- but then you watch Mike Marshall.... 

I am totally captured by the idea of a mandocello and while I'll NEVER amount to much on one they might some day have to pry my cold dead fingers off of one.  So as Wake Frankfield once said "..that make sense wit you?"  (<:

One more thing, Bernie, how experienced are you at instrument repair?  If we went over this before, please forgive me and I hope I'm not stepping on your toes here. It just that a couple of your questions and comments make me wonder if you are up to this involved of a repair on this valuable of an instrument.

Well that is a fair thought and one never really knows until one tries but here are a couple of pics of what I call a Gibson K-50 mandocello that I made by converting a 1942 L-50 guitar that had a broken headstock.  I did have some help but I have done three of these arch top guitar to mandocellos.  I have also converted an arch top to a cittern (10 course) and build a kit mandolin. 

The only really totally new thing about this job (I think!) will be removing that back board cleanly!  I have an old Harmony arch top here that needs a neck reset and I might open it up first just for practice.

I need to correct a miss-statement, I was typing faster than I was thinking. I said"  Generally speaking though, the upper legs of the X brace should be configured under the bridge ends" and that's not correct. The X should be configured between the sound hole and the bridge.

Ned makes a good point about the value of this instrument, you can likely add another zero behind the $250 you say you paid for it. I also agree with Ned that such a change will change the character of the tone but it's possible that could improve it too. Bottom line here is, if it's not playable, it's not worth much to anyone. I think it would be worth your while to post this over at the Mandolin Cafe. There is a very good chance that you will get responses from a few that have actually X - brace a Gibson mandocello.

Nice job on the Archtop conversion! Did the L-50 come with a truss rod or did you add it? The tailpiece conversion is very clever and I like the bone saddle as well.


© 2024   Created by Frank Ford.   Powered by

Badges  |  Report an Issue  |  Terms of Service