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saintjohnbarleycorn

bass bar clamps

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ON the spring clamps that Burgess' made did you heat the spring to relieve stress, or just bend and use? thanks.

I just bent it and used it. You need to over-bend a little, because there will be some relaxation at the bend points when you first stretch the clamp open, before it becomes stable.

I really like the idea of clamps which can be applied with one hand though, so just now I tried taping some light wooden extensions to the horizontal legs of the wire clamps, and these can be squeezed together to open the clamp with one hand, more like the action of a clothes pin. The vertical dimension of the back would need to be increased so the clamp will open sufficiently before the wood extensions come together.

This picture doesn't have the extensions taped on, so you'll need to use your imagination, with the horizontal extensions going beyond the clamp to the right of the picture.

barclamp2.jpg

Soundpost stock, or light aluminum tubing secured with two zip-ties each to the top and bottom of the clamp should do the job, if you want to be tacky like me. :)

I'll try to think of something more elegant later.

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I glue locating cleats in - but relieve the bottom corner where the glue line is. With cleats tight into the bottom corner of the bar I was finding the glue oozing out aginst the cleat was tending to push the bar away.

I have put them in as opposite pairs - six in three pairs along the length - again, with the bottom corner cut back. That seems to work ok. I also soap the cleat faces. I sometimes put in one end cleat, so I can rub the joint slightly yet still get it set spot on befire clamping.

I trim them off slowly - I've just split a belly being to too gung ho knocking off the levelling blocks.

I'm just doing one now actually - so will maybe get some pics.

Geoff

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I have a slightly different way of guiding the bass bar.

'notched towers corresponding to pointed end of the bar at the ends prevent any twisting or wandering making fitting the bar much faster and more precise. (IMHO)

Oded

post-95-1268924760.jpg

post-95-1268924789.jpg

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Those are nice clamps Jeffrey. Every time you show a photo of your bench I promise myself to do the smart thing and get a piece of carpet. Do you have a small vacuum cleaner for dust and wood chips?

Dean, I have used the short nap "Home Depot" style runner carpet like Jeffrey for years as well. For clean up I have a small dustpan that has a modified hand broom with shorted bristles. That handles the the quick and dirty removal jobs. I have also mounted a small hand vacuum directly under the bench top. When things get too nasty, its quick work to peal the old carpet off an roll out a fresh runner with a light spray of craft bond.

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Dean, I have used the short nap "Home Depot" style runner carpet like Jeffrey for years as well. For clean up I have a small dustpan that has a modified hand broom with shorted bristles. That handles the the quick and dirty removal jobs. I have also mounted a small hand vacuum directly under the bench top. When things get too nasty, its quick work to peal the old carpet off an roll out a fresh runner with a light spray of craft bond.

Well that's it. I'm bumping that to #1 on my to do list. I really like the idea of the carpet.

Oded,

With your anchoring style how effective is your chalking technique? I use side tabs so I can rub the bar a couple of mms up and down the direction yours is fixed. That seems like it would produce errors by moving the bar but the fit is excellent. Without movement my chalk doesn't stick well enough. perhaps a light tap?

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I have a slightly different way of guiding the bass bar.

'notched towers corresponding to pointed end of the bar at the ends prevent any twisting or wandering making fitting the bar much faster and more precise. (IMHO)

Oded

The notched pillars are awesome. I had totally forgot about them.

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To make the Burgess spring clamps I purchase the steel spring (music) wire he prescribes. I forget the details, but it is not expensive and is readily available. I got the music wire from smallparts.com.

Next, I bought from Harbor Freight a wire bending jig that does a professional job in getting good clean bends. It is not expensive and worth the few dollars.

The nice thing is that now I have some extra wire and the bending jig to make other kinds of clamps that I may need.

Mike

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I, too, appreciate all the photos and replies. Lots of good information to be had.

Finally got around to really reading the section in Heron-Allen at lunch today. In the text, he describes the 'clothes-pin' clamps for use when fitting the bar, while on the next page, he shows a screw clamp for gluing. 3-5 needed, according to him. I don't take Heron-Allen as gospel, but it does seem that he used the clothes-pins more as we might use cleats, to keep things straight while fitting. Stradivari could certainly had done differently.

Jeffrey's comment on not being able to spring the bar with the plaster cast really got me thinking. My initial question was 'why not?' So perhaps the philosophy is that one wants to bend the top, rather than the bar. On the other hand, those that use a bass-bar frame, whether metal, wood, or plexiglass are at least holding the rib-surface rigid. If frame-users tension the bar, don't they then press the bar down to the top, rather than the top to the bar?

I don't know. I've fit a handful of bars, maybe two handfuls, and I just try to get them to fit as is, no tension. I thought I understood the philosophy of tensioning a bass-bar, but it appears I don't.

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Hi Dean,

With your anchoring style how effective is your chalking technique? I use side tabs so I can rub the bar a couple of mms up and down the direction yours is fixed. That seems like it would produce errors by moving the bar but the fit is excellent. Without movement my chalk doesn't stick well enough. perhaps a light tap?

I fit the ends a bit loose at first and when I get close to final fit I glue a slip of biz card paper to make it snug. I tap the bar for final fit.

I really like it that there are never any surprises when I glue in the bar and it takes me far less time to do the actual fitting. In addition, there are no hidden areas of the bar.

I cut out a notch for the area at the pointed ends so that I don't end up unnecessarily fitting that area.

Once the ends are made up I reuse them but they usually need a bit of fitting to line them up.

I glue the end towers with some paper so they knock off easily.

Oded

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If frame-users tension the bar, don't they then press the bar down to the top, rather than the top to the bar?

They both bend toward each other. But the untrimmed bar is a lot thicker than the top, hence more rigid, so the top will flex more than the bar.

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They both bend toward each other. But the untrimmed bar is a lot thicker than the top, hence more rigid, so the top will flex more than the bar.

Thanks, Brad - -but even when a frame is being used? Seems the frame would not flex much.

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Hi Dean,

I fit the ends a bit loose at first and when I get close to final fit I glue a slip of biz card paper to make it snug. I tap the bar for final fit.

I really like it that there are never any surprises when I glue in the bar and it takes me far less time to do the actual fitting. In addition, there are no hidden areas of the bar.

I cut out a notch for the area at the pointed ends so that I don't end up unnecessarily fitting that area.

Once the ends are made up I reuse them but they usually need a bit of fitting to line them up.

I glue the end towers with some paper so they knock off easily.

Oded

I really like this approach Oded...thank you!

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They both bend toward each other. But the untrimmed bar is a lot thicker than the top, hence more rigid, so the top will flex more than the bar.

I tend to agree with this thinking. I think that the top will flex much more than the bar. My bar blanks are really tall, and need much trimming down.

But when the spring is only a mm or even two - evenly over the length of the bar - it is difficult to see the effects on the top, or assign them to a specific piece.

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Thanks, Brad - -but even when a frame is being used? Seems the frame would not flex much.

I don't believe that the frame (if it is really rigid - which is its function.) flexes at all.

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By the way, I attach my bars without a frame.

Right, and I have done it with and without a frame but don't (so far) put tension in. I like the 'definiteness' of the frame. I'm curious about the tension.

So I guess I can try again, and then say the heck with it -- for those that do use a frame and do put tension in, it seems to me they are bending the bar. If that's the case, then one could put tension in using a cast, as Jeffrey showed in his previous photo. Once the glue dries, there should be only minimal movement of the plane that was defined by the frame (it seems to me anyway).

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I have a slightly different way of guiding the bass bar.

'notched towers corresponding to pointed end of the bar at the ends prevent any twisting or wandering making fitting the bar much faster and more precise. (IMHO)

Oded

Oded, that's one of the coolest things I've seen. I will definitely try this method.

Thanks for sharing.

Berl

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Thanks, Brad - -but even when a frame is being used? Seems the frame would not flex much.

The frame does not flex, and the frame holds the rim of the top rigidly, but the arching can still flex.

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The frame does not flex, and the frame holds the rim of the top rigidly, but the arching can still flex.

Thanks -- I'm still having trouble imagining the geometry (like where does the flex 'go'?), but maybe I am assuming that the rim is held in place more firmly than it is. I'll have to remember to take a few edge measurements next time I get to this point.

Cheers,

Ken

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So I guess I can try again, and then say the heck with it -- for those that do use a frame and do put tension in, it seems to me they are bending the bar. If that's the case, then one could put tension in using a cast, as Jeffrey showed in his previous photo. Once the glue dries, there should be only minimal movement of the plane that was defined by the frame (it seems to me anyway).

The bar is rather rigid before trimming... so the clamping pressure required to actually "tension" the bar would be rather severe (hurt the fiddle) if it was forced into a top held in a cast.

Outside a cast, no matter if the plate is in a frame or free, building tension "into a bar" actually results in flexing the plate, not the bar.

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The bar is rather rigid before trimming... so the clamping pressure required to actually "tension" the bar would be rather severe (hurt the fiddle) if it was forced into a top held in a cast.

Outside a cast, no matter if the plate is in a frame or free, building tension "into a bar" actually results in flexing the plate, not the bar.

Ok -- and I don't have much feel for the dimensions here, but this would reduce the end-to-end length of the plate, at least by a small amount? as well as distort the plane of the edge, that part in contact with the ribs, cupping it a slight amount?

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The bar is rather rigid before trimming... so the clamping pressure required to actually "tension" the bar would be rather severe (hurt the fiddle) if it was forced into a top held in a cast.

Outside a cast, no matter if the plate is in a frame or free, building tension "into a bar" actually results in flexing the plate, not the bar.

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

Hi Jeff

I am sure you are correct. Your set up looks like beautifully considered best practice to me. Precious historic instruments that need a new bar will thrive in your care.

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

For us makers who are fooling around with our own humble creations there is more leeway to do things a bit wrong. As a maker rather than restorer I don't normally spring bars, but sometimes I do. In these cases I will pre shape the bar. If the bar is pre shaped it will move toward the plate though the plate still moves a bit too.

The way I look at a tensioned bar is not that a slightly bent bar will be able to resist the deformative pressure of the bridge but that the resistance offered is in the form of lamination at the glue joint. It is about pressure along the length of the joint. Some of us might have a modern bouncy chair made of laminated wood...this for me is one aspect of the strength of the bar in general sprung or not. In some circumstances a sprung bar could be a bit more bouncy maybe and this might or might not be required.

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

Hi Jeff

I am sure you are correct. Your set up looks like beautifully considered best practice to me. Precious historic instruments that need a new bar will thrive in your care.

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

For us makers who are fooling around with our own humble creations there is more leeway to do things a bit wrong. As a maker rather than restorer I don't normally spring bars, but sometimes I do. In these cases I will pre shape the bar. If the bar is pre shaped it will move toward the plate though the plate still moves a bit too.

The way I look at a tensioned bar is not that a slightly bent bar will be able to resist the deformative pressure of the bridge but that the resistance offered is in the form of lamination at the glue joint. It is about pressure along the length of the joint. Some of us might have a modern bouncy chair made of laminated wood...this for me is one aspect of the strength of the bar in general sprung or not. In some circumstances a sprung bar could be a bit more bouncy maybe and this might or might not be required.

Hey Melvin. Don't know if you saw it, but mentioned I used to "spring" bars on new instruments, though I'm not sure what I'd do if I made one tomorrow. To make myself clear, there are still some instances when I will lightly "spring" a bar when replacing one... The cast thing is my default for the "old ones". :)

I've never installed a pre-shaped bar... but that sounds interesting. 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.

Ok -- and I don't have much feel for the dimensions here, but this would reduce the end-to-end length of the plate, at least by a small amount? as well as distort the plane of the edge, that part in contact with the ribs, cupping it a slight amount?

Hey Ken. when I do spring a bar, it's not by much. maybe 1/2 to 3/4 mm spread throughout the bar (unless I'm trying to perform some minor correction in the arch, it's fit so it "rocks" evenly. If you push down on one end, you get a 1/2 to 3/4 mm gap at the other).

I don't have keen skills and abilities to perform complex calculations without effort (Don or someone else with these skills can probably illustrate this numerically), but with movement of possibly 3 to 5% of the arching height and .15 to .2% of the length spread across the plate, I believe the reduction of length has to be very, very minimal... probably difficult to measure. I believe it's a bit less, in the end, as the plate/bar assembly will relax a little once the bar is shaped... or in the case of installation as Melvin describes, the bar may take some of the flex at the time it's glued.

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