Hello!
I hope I can get some advice 
I’m a local Brixton musician with a bunch of different stringed instruments
One of them is called a Cümbüs, a 12-string fretless Turkish Banjo. It has a neck which has a layer of smooth formica. I have recently had to change the bridge and the strings are not quite right.
The problem is to sand down the formica neck surface slightly (max 1mm) at one end to increase the space to allow the strings to vibrate, as they are a little bit “choked”
I could try some sandpaper (wet&dry), or even try and borrow a hand-sander. It’s quite a palaver to dismantle the instruments (strings, bridge etc.) but at the same time I don’t want to take off too much, so it’s an incremental process.
Anyone have any other ideas about the best way, I would be very grateful
Best
:Lu
Hi Lu.
Not being a luthier or an instrument pro by any stretch of the imagination, it does occur to me, that the fredboard having fromica (plastic laminate) sounds very odd?
Are you perhaps refering to a thick wood veneer (4-8mm wood piece)? Wood veneer can be sanded NP - I doubt you can sand formica (plastic laminate) by 1mm to good effect.
Can you consider raising the bridge? Unless I’m mis-understanding, it sounds like the bridge is now too low and you’re getting string buzz toward the higher frets? If this is the case, lowering the bridge might be much easier than adequately adjusting the neck?
Perhaps if you post some images, it might be easier for instrument-adept folks to give you some better advice?
Could you post some pictures?
Avoid at any cost to use powertools to sand such a delicate instrument. It has to be a patient hand work with a woodblock and sand paper. Being a neck, the keyboard probably has a radius to keep, which you will meed to find. You then will need to find a radiused block, to use with your sand paper.
Is there any way to adjust the angle of the neck on it? Or the height? Without needing to sand away material.
If you need to remove material from the neck it is worth understanding if the fingerboard is dead flat or has a radius. You would want to preserve this with any adjustments that you make. For other stringed instruments, I use a radius gauge to determine the radius and then I have a set of blocks with the various radiuses on which I attach sand paper to. When sanding it is important to remove material evenly across the radius.
If needed, a block with custom radius could be made using the mini CNC or 3D printed.
I was not familiar with this instrument, but it’s pretty cool. Watching this video:
I think I see what your problem might be; I had a similar issue with my (conventional bluegrass) banjo a few months ago, and @Howard and @Oscario88 solved it for me at one of our luthier nights. I can’t tell without seeing how your instrument is constructed, but if it’s anything like the one in the video there is probably some adjustment possible where the neck joins the body. The adjusting screw is accessed by removing the back of the body. Inside, look at what attaches the neck to the body - if it is some sort of screw or bolt, you should be able to loosen it off, then gently move the neck downwards, increasing the distance between the fingerboard and the strings. You will need to slacken the string tension a bit, but you can probably avoid removing the bridge, strings etc. as you understandably are reluctant to do.
This would be a far easier path than shaving off the fingerboard, and better for the sound quality of the instrument. Luthiers (I’m not one) say that such interventions should be the last resort.
Anyway, sounds like it’s time for another guitar/luthier night at the Space; @luthiers ?
Thanks Everyone!
Sorry for delay I was out rehearsing yesterday with it
The neck is flat (i.e., there is no radius) so it’s not impossible to sand it down.
The area to be sanded down is what is know in the trade as “The Dusty End” - i.e. up the neck where fingers tend not to wander much. That is where the “choking” is happening.
I can indeed adjust the wingnut (it’s a very nice design if you think about it) to minimise the choking, but that would alter the “feel”. So that is why I am thinking of a more radical sanding
I might try a test at the very end of the neck, the body end, to see how easy it is to sand. It should be safe.
I’ll post some pix!
Again, many thanks for all your comments and help!
Best
:Lu