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saintjohnbarleycorn

bass bar clamps

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I wonder if instead of using wood to make a clothespin type spring clamp. You could make a double bend that crosses ,so that when you squees the middle they would open. They might be pretty long though. I will try it out when my wire comes.

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Thanks for the explanation, Jeffrey. I certainly had one misconception in my understanding of the geometry (I probably have others!) -- and that was in what was meant by the size of the springing. I thought that a 1 mm spring, for example, meant a 1mm gap on both ends.

I like to know what the tolerances are. So often folks are talking about fractions of a mm for this or that procedure -- such as how flat to get the gluing surface of a top plate! :) It's good to know the crucial from what works. Clearly people spring bars, so it must work.

Still, it seems that if one were to spring a bar with the top attached to a frame, it might be good to have the clamps holding the top to the frame a bit less than perfectly tight. Allow for some movement in the perimeter. With a frame, and an untrimmed, sprung bar, it seems that it would be very easy to crush the wood in the center of the top -- either that or introduce distortion in that roughly 40 mm distance between the end of the bar and the beginning of the rib-plane.

Melvin -- I had guessed that people who sprung bars did relieve a bit of wood from the bar at the ends before gluing, but apparently it is fairly uncommon. Given that hide-glue doesn't have much creep to it (none?), that seems to be the one fixed site in this procedure. Interesting to think of it as lamination.

Thanks, all -- I learned a few things. Good discussion.

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I wonder if instead of using wood to make a clothespin type spring clamp. You could make a double bend that crosses ,so that when you squees the middle they would open. They might be pretty long though. I will try it out when my wire comes.

I'm sure you could. By adding wood extensions to the C configuration, I was mostly thinking about keeping the weight down... particularly weight offset to one side of the clamping point, which would require greater clamping pressure to keep the clamps in place, and also pull the top of the bar to one side (unless you go from both sides like Jeffrey does). Also, anything you do to increase the total length of the wire will reduce the spring rate, so one might need to compensate with thicker wire, or with more preload to achieve the same clamping pressure.

It's easiest to try out ideas with coat hanger wire. (Edit: Looks like that's what you're already doing) The heat treated wire is difficult to cut and bend. For cutting, I ground it part of the way through with the edge of a grinding wheel, then bent it back and forth until it broke.

Coat hanger wire itself is handy for a variety of clamping jobs. One method I use to glue cleats in a cello back with ribs attached, is to clamp a narrow piece of wood across the top of the ribs with spool clamps, and wedge a slightly curved piece of coat hanger wire between that and the cleat. The wire can easily be re-bent to accommodate different distances, but has enough spring to do the job. It's kind of like a tiny go-bar setup. :)

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One method I use to glue cleats in a cello back with ribs attached, is to clamp a narrow piece of wood across the top of the ribs with spool clamps, and wedge a slightly curved piece of coat hanger wire between that and the cleat

Perfect application for using super magnets. In the photo the magnets are the same size as the cleats-these magnets are coated with plastic.

Oded

post-95-1269007409.jpg

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Ken Pollard said:
Clearly people spring bars, so it must work.

Not necessarily. Whatever it is that is working could be working is spite of, not because of, the spring.

Ken Pollard said:
Still, it seems that if one were to spring a bar with the top attached to a frame, it might be good to have the clamps holding the top to the frame a bit less than perfectly tight. Allow for some movement in the perimeter.

I don't think so. The purpose of the frame is to be able to fit the bar to the top with the rim of the top in the same configuration (a plane) that it will be in when it is glued to the ribs. If you allow some movement in the perimeter, you are defeating the whole point of the frame.

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Not necessarily. Whatever it is that is working could be working is spite of, not because if, the spring.

I don't think so. The purpose of the frame is to be able to fit the bar to the top with the rim of the top in the same configuration (a plane) that it will be in when it is glued to the ribs. If you allow some movement in the perimeter, you are defeating the whole point of the frame.

When I wrote 'it' was working, the 'it' was springing the bar, not that it was any benefit to the violin's performance. Sorry for the lack of clarity. As a feeble excuse, I will say that at the time I was still working on my first cup of coffee. :)

As to the frame, if you hold the perimeter of the plate constant, and if the unfinished (large) bar is basically unflexible, then there must be some stretching or compression of the plate, which I was thinking of as different than simple bending of the plate. Perhaps that was what you were trying to say earlier, and I misunderstood.

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can someone share some pic of homemade bass bar clamps. I did a search but under bass bar clamps and clamps but did not come up with much on home made bass bar clamps but did not come up with much. Also a search on the internet did not show up much . thanks kevin

Hi Kevin,

Here are my "clothes pins" they're quick and easy.

Bruce

post-29446-1269033701.jpg

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As to springing bars, is it true that the bar eventually relaxes and is no longer "sprung", namely under tension?

If true, why bother springing the bar unless you cannot make a perfect unsprung bar?

:)

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As to springing bars, is it true that the bar eventually relaxes and is no longer "sprung", namely under tension?

If true, why bother springing the bar unless you cannot make a perfect unsprung bar?

:)

The way I understand springing, so far, is that it pre-loads the top, much as what one might do by pulling the soundpost a bit towards the soundhole. Even that will eventually distort the instrument (relax it). Everything eventually relaxes (strings, arching), but it's a question of how quickly. Entropy, if you will.

Bruce, those are beautiful clothespins. The ones I have, which I bought long ago from someone who should have known better, had much thicker legs. I can see that yours would actually supply some easy pressure to the assembly, whereas mine simply forced things into place. I'd be tempted to make some of those, give the idea another try.

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.. How close to finished height do you go before gluing it in? If I'm figuring this right, the pre shaped bar would really only be flexible enough to move toward the plate significantly quite near the ends of the bar, as it remains more than twice as high as the plate is thick at the quarter points, right? Do you notice much of a difference in how much the center of the plate moves outward when you do this (as compared to installing bar that's not pre-shaped)? You've got me curious.

.........................

Hi Jeff. If I'm springing a bar I will pre shape the bar ( unrounded) to about 1mm more than its finished height.

When fitting the bar I will try to shape the central 50ish % of the bar so it is bending the belly a bit, upwards into the bridge foot. The remaining two 25%'s of the bar towards the ends is bending toward the belly noticeably but the belly will move a bit too I guess. This helps stop the bar dragging down the plate in the bouts which is a major criticism of sprung bars.

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As to springing bars, is it true that the bar eventually relaxes and is no longer "sprung", namely under tension?

If true, why bother springing the bar unless you cannot make a perfect unsprung bar?

:)

.........................................

Hi Michael,

I don't believe this is necessarily the case. In saying this I am not trying to argue for the sprung bar. I normally do not spring bars as a rule and feel that a badly sprung bar does more harm than good.

My feeling is that without the lamination effect of the non creep hide glue layer between the bar and the belly the combined amount of wood would not be enough to offer resistance to the downwards force of the strings with modern set ups (Celli especially) and that the bass side of instruments would collapse much faster than we are already accustomed to.

My feeling is that this lamination effect preserves the integrity of unsprung and sprung bars and contributes to their stability considerably It probably has a tonal effect too.

An experiment that anyone can do is glue together two spare pieces of lining with hide glue clamped to a curved form so they emerge as in the diagram below. The lamination effect will give a strength and resilience to the form that would not be apparent in a piece of the same wood bent or carved to the same final shape and dimension. The act of lamination brings into play forces of compression and stretch along the wood grain. Generally the wood is quite resistant in these directions.

post-23531-1269044518.jpg

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Hi Jeff. If I'm springing a bar I will pre shape the bar ( unrounded) to about 1mm more than its finished height.

When fitting the bar I will try to shape the central 50ish % of the bar so it is bending the belly a bit, upwards into the bridge foot. The remaining two 25%'s of the bar towards the ends is bending toward the belly noticeably but the belly will move a bit too I guess. This helps stop the bar dragging down the plate in the bouts which is a major criticism of sprung bars.

Thanks Melvin!

Will take this offline... but want to "talk" to you about this. I'll send you a message.

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Thanks Melvin!

Will take this offline... but want to "talk" to you about this. I'll send you a message.

Hey!!!

I want in on that conversation.

Who here wouldn't want to listen to a discourse between two highly intelligent people?

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Hey Dean;

Maybe I'll come back and post if there are any good bits... but I had a few rather boring questions for Melvin that I think might be easier one on one.

Thanks for the "intelligent" classification, though. Some days I think I can use all the help I can get! :)

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As to springing bars, is it true that the bar eventually relaxes and is no longer "sprung", namely under tension?

If true, why bother springing the bar unless you cannot make a perfect unsprung bar?

:)

In a conversation I had years ago with Dario D'Attili he believed that a slight tensioning of the bassbar gave a more immediate acoustic results whereas the "unsprung bar" took a little longer to break in. In the long run he did not think that there was any real difference.

I normally use a frame to keep the belly straight when fitting a bar. Some bellys will not move at all when they are off the ribs but others can go completely out of plane to the rib gluing surface. Normally, looking at the inside of the belly with the outside arching resting on your bench, the end block and neck block area will drop down, straightening out the long arch, whereas the outer extremities (the max widths of the upper and lower bouts; farthest away from the center joint) will curl up slightly. Without a frame, to get back to a neutral, or unsprung bar when the instrument is back together, I will have to add enough spring to pull the long arch back into shape it was when it was glued to the ribs. In bellys that move a lot I find this difficult to estimate; therefore the utility of the frame. Without a frame, if I don't do enough springing in a distorted belly, I could even end up with "negative" springing. I remember once when Hans Nebel took me on a quick tour through the Wurlitzer shop, I saw a violin belly clamped to two horseshoe-shaped aluminum plates, like a full frame with the c-bout section removed, to keep the end block and neck block areas in line with their respective bouts.

On your new instruments you can do what you like but on older instruments I prefer a neutral bar fitted in a frame and, if there is any spring at all, it is like Jeff said in an earlier post on this thread of 1/2 - 3/4 mm over the entire length. Better an inperceptible positive spring than any negative spring. Like Melvin too pointed out, so many instruments have been deformed in the upper and lower bouts because of incorrectly fitted or over-sprung bassbars. Bad gluing technique is also a major contributor; "clamp overkill". The bassbar does not have to be forced into the belly as much as "held in place" while the glue sets and dries. The clamping technique of David Burgess is great for this as you elimate the twist that could be caused by heavier clamps and also excess clamping pressure for those of us who do not have "mechanic's feel".

Bruce

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Using a frame assumes that the ribs are as flat as the frame, is this usually the case?

Oded

Hi Oded,

I don't assume they're flat and I sometimes do some shimming between the table and the frame, especially if I feel the situation is forced and dangerous for the belly. The best way for me to measure some basic reference points around the perimeter of the instrument belly/rib gluing surface is to put the instrument, still strung up to pitch, onto a flat surface. The instrument is held above the surface by three closing clamps (tripod, no rocking action). While measuring with a rule or an adjustable machinists height gauge with a heavy base, shims are placed between the ends of the clamps and the flat surface until I get as close as I can to equal heights all the way around the violin. This will show me if and where there is any distortion so that I can shim with paper or cardboard between the belly and the bassbar frame to reproduce the same situation. I do this on instruments where I suspect that there is a significant distortion. I'm sure that there are other ways to do this but this is what I've come up with. As soon as I remove the belly, if it sits flat on a flat surface without tension I don't bother with shimming.

Bruce

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Bruce

What type of wood would be the best to use for making these clothespins. White Oak, maybe?

Thanks

Ernie,

Mine are made of lacewood but only because that is what I had around the shop. It's relatively lightweight and flexy. You can start with the pieces oversize on the outer perimeter and trim away until you get them as light and still as strong as you need.

Bruce

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The way I understand springing, so far, is that it pre-loads the top, much as what one might do by pulling the soundpost a bit towards the soundhole. Even that will eventually distort the instrument (relax it). Everything eventually relaxes (strings, arching), but it's a question of how quickly. Entropy, if you will.

Bruce, those are beautiful clothespins. The ones I have, which I bought long ago from someone who should have known better, had much thicker legs. I can see that yours would actually supply some easy pressure to the assembly, whereas mine simply forced things into place. I'd be tempted to make some of those, give the idea another try.

Ken,

That little old book (50's ?) on violin making has plans for these and other tools. I can make you a copy if you like.

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