About to make another C-extension; any new ideas/great links?

I'm new around here, but did a thorough search of the archives and couldn't come up with more than passing references to C-extensions for doublebasses. I posted a little in a thread about bridge adjusters, but for a slightly better chance at an answer here's my situation in total.

I made my first C-extension about 6 years ago, for a VSO player. It was a 4-capo type, as he wanted access to a lot of natural harmonics for new music stuff, and the odd older composition requires low pedals. The player had asked for a really solid 'lock' at each semi-tone, so I tried bullet catches. They seem to help a little, the ball bearings being pushed firmly into little detents in the stainless armatures. But I found that the springs 'sang' in sympathy with certain pitches, so an injection of silicon grease was needed. Since then, he's been happy. The long slots in the ebony for tuning the adjusters have never been needed. I'd suggested that these were not really necessary, but I suppose my explanation of the 'rule of the 18th' (actually 1/17.835) inspired insufficient confidence. Add in tapped holes with nylon set screws to make little adjustments to the pressure applied by the leather pads' leading edges, a foot to support the wheel end, in case of knocking into doorways - unpleasantly complicated, not to my tastes. Sorry for the fuzzy pictures; just used a little digital add-on to my Pocket PC to copy a couple of snapshots in incandescent light, for use here.




Over the next few extensions things simplified. I tried to see just how maintenance-free and accurate I could make them. Nothing earth shaking, but people seemed happy. Getting a big, slack C string not to buzz is the hardest part, with really consistent and solid feeling capos being second. Here's one of those, made last year for another Vancouver player. She's small, hence the dropped nut for a fairly short scale without moving the bridge out of balance on the belly:




All along though I've felt there must be a better way. Every C-extension is different anyway, so why should they not improve in design, not just execution? Thoughts of hydraulics kept coming to me from players, but I'm not that high tech in the skills department. And levers, springs, cams, they all make me nervous. And I've worked on enough mechanical, piccolo-type extensions to know what a nest of hornets they can be for maintenance. What about using drill rod, little bar stock bent to act as precise capos? A bit of small tubing should make it work, no? And now I see that someone is doing this, but only for the upper capos, not the E. The confines of that region at the nut make the old swinging capo a better choice, apparently. This from the Merchant site:



I have this guy coming on Wednesday, again. He listened to me think out loud for an hour yesterday, and seems to trust my work from having seen enough in repairs and in his cohorts' C-extensions in the symphony, but he also wants more. He's asking me to experiment on his old Italian, to make a proper C-extension. He's used one from another local luthier for about 10 years, but it's wobbly and the only capo on it is not capable of holding a string for long without buzzing. There's not a lot there to work with, no way to add capos, so it's time for a new one. I am seeking ideas, drawing a blank. Can anyone help me with this? Suggestions, cool stuff you've seen somewhere on the web or even have on your own basses? Pictures of anything out of the mainstream would be helpful perhaps in triggering something in the little grey cells. I've seen Barry's sliding version, and it's not what is needed here. Instead I want to make a 4-capo thing he can blindly reach for and have it respond with little fuzz and effort, both applying and releasing capos. What can you tell me? Thanks in advance for anything at all.

 

WOW, Martin, that's some serious brasswork you've got there! I'll study it some, talk to the player, and see what he thinks. I'm a bit leary on the fitting to any configuration of scroll and fingerboard thickness, while allowing for future fingerboard replacements and such... but your design probably takes such things into account. Thank you very much for the images. Good to have for comparison.
Anyone else?

 

You mean sort of like this?

I drew this about 2 years ago. Meant to get the bass done, mostly, then with the roughed-out built-in extension I'd figure out the details. It's one of the grey areas that has got in the way of my continuing with the project. I don't like building failures, nor even partial successes. Since my patience for doing any one thing repeatedly is about zero, I like to get it right the first time, insofar as that is reasonable. Of course, I know, one improves rapidly with actually making the experiments and then seeing what needs improving. But I am also dealing with a frugality issue, both in terms of a desire not to waste wood, and just being broke for about the past 41 years. Mistakes in bassmaking cost a few thousand dollars in materials and a huge bunch of time. I can't afford either, with rent and other bills to pay.
So whining taken care of, what do you all think of this for a new bass? Since I drew it I have changed a few ideas, thinking it'd be better to have a more organic flow, though perhaps not quite so curvy and soft as that Kelischek in cherrywood. The bass outline itself is somewhat agressively pointy. The C's are very long, with corners arcing inwards to a degree impossible to maintain should they come closer to the bowing plane. The upper bouts are rather small, the lower huge, relatively, and the upper ribs twist back to allow for a 3" shorter upper back than belly. Rib height is thickest at the lower corners, with a 1 1/2" drop as it nears the neck, and a 1/2" drop towards the endpin, using a constantly curved gluing plane around the back edge. Belly lies flat. Arch is low, as the inner back curve more than makes up for lack of a steeply pitched arch.
All in all, an odd little 3/4 bass, with a projected scale of 41 1/2". The girl who used to want it, before a pop career and my delays put her off, is very small. I developed it according to her low shoulder height, but in the intervening time I've had many comments from bigger bassists who are keenly interested in a smaller bass for many reasons. I think the volume internally should approach that of a Kay, perhaps 5% less. And with careful plate tuning I see no reason it should howl when needed. The spruce is a glorious piece, something quite extraordinarily perfect and responsive.
An extended C will probably be 'pushing it' for a smaller bass like this, but we'll see. I mean to pay a lot of special attention to designing a bridge to maximize output, with a bar set a little outboard for greater belly movement at lower frequencies (with matching post position of course). I want also to make certain that I have a decent and long lasting capo design before attacking the scroll wood with a saw. Hard to stomach the idea of gluing bits on to make up for lack of foresight.
Any comments on such a design are very welcome! Of course, my current problem is rather different. No opportunities for teflon inserts to the scroll on this old Italian, not grafting in maple to stiffen the wobbly old thing. I have to make the scroll stiffer, without sacrificing a shaving of maple anywhere. Anyone I caught sawing bits out of old scrolls I'd probably slap, risking the arrest. There are few worse crimes in luthiery these days that that, though I suppose some contenders in the krazy glue department.