Sideways bend in bass bar?


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Hi everyone, I need the advice of someone more experienced. The last couple of days I have been fitting the bass bar of my cello. It was a good fit, so today I glued it. I had some issues from gluing it out of alignment, so I had to remove it, rinse off the glue with water and try again.
Second try was still a bit annoying to clamp, but seemed to have a good fit. After 9 hours of drying I took off the clamps and discovered a very weird issue... The bar is bent along the length sideways? It still looks to have a good fit, but I don't know what could have caused this. Too strong pressure in the center pushing the middle inwards? The water warping the bar sideways? 

What really bothers me is the fact that I now only have 41,5mm from the center to the outside of the bridge, while I planned 44mm. I suppose this will give a less powerful tone than I had planned for, or is the strength still distributed along a straight line in the center of the curve and therefore effectively further out towards my goal of 44mm?

Obviously I did something wrong and this is a less than optimal bass bar. It's my fourth bar, have done two violins and a cello previously with no issues. How can I prevent this another time? And is the bar just scrap and I have to redo it, or can I use it? I don't have the opportunity to get another bass bar blank and is therefore tempted to leave it, since the joint is otherwise good and there is no visible warping to the top, but the cello is otherwise a very promising piece of work, so I don't want to ruin its chances of becoming a nice instrument by keeping a terrible bass bar

Thanks in advice!

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1 minute ago, Tostra said:

...How can I prevent this another time?...

Clamp the bar, without glue, where you want to glue it.  Glue some temporary locating cleats, touching the bar, to the inside of the top.  Unclamp the bar, apply glue, place the bar in contact with the locating cleats and clamp it.  I put the locating cleats on the side of the bar towards the center of the instruments, because it's most likely to move in that direction.  I use two locating cleats for a violin bar; more for a cello bar.

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Thank you  Brad. This is, however, pretty close to what I did. I have a block temporarily glued about 1/3 towards each end on the inner side which I hold the bar on to have a stable reference when fitting. I could have had one in the center, but I never thought the bar could bend like that

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134951743_187072946446060_5244873028790801513_n.thumb.jpg.9dafdf66d1815370d80be17aaebf8f61.jpg135006355_5449179458432925_4691349483184881484_n.thumb.jpg.6996d621ece25b517b92c10ebc899f93.jpg

Here are some very quick mobile pics. I promise it looked a whole lot better before gluing or I would never have used it. But should I plane off this bar and start over, or is it not as bad as I make it? I do want a very powerful tone, so having the bar further in concerns me.

The little locating blocks were higher while fitting,, I just shaved them down when I removed the clamps.

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You can use cleats as Brad is suggesting. 

I usually clamp 3 guiding cleats without glue at the center and both ends. This ensures the bass bar is straight. During the clamping process I use those three clamps and remove the cleats. Saves the time to remove glued cleats. (As suggested by Brad.) 

Usually bass bars bent or rather slip sideways in the cente with pressures from the clamps.  It is also important to look during he fitting process to the tilt. I mean if it is standing upright, and basically should align with the ribs. If anything it should be rather tilted so that it is stands perpendicular to the top curvature. Looking at the pics it is difficult to say but I'd say the tilt is in the other direction.

 

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Yes, next time I will certainly add a center cleat if that is my issue, be it on this cello or the next one. I have been checking for straightness of course, and it has been parallel with the ribs/perpendicular to the top gluing surface all along.

Still, it sounds like this is not something completely unheard of to you? Maybe you know whether or not it's usable with a bend like this? It's not huge, but definitely a 2,5mm difference from my plan is significant...

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I know that if I went to all the work of a new cello build, that bar would bug me...

Even on a violin, I use 3 cleats on the inside and 2 on the outside of the bar, and the cleats fit fairly tightly to the bar so that the orientation of the bar is always the same every time it is put in place.   As you are fitting the bar, do you press down on top of the bar in various locations in order to make sure that  the bar always maintains the same orientation to the ribs?   If you press down in one location and the bar has a different tilt than when pressing down in other locations, the bottom of the bar doesn't fit.

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The clamping method could also be a contributor.  If the clamps apply pressure normal to the sloped/arched surface, then there shouldn't be much sideways pressure.  However, if the clamping is all vertical (relative to the rib interface), then the steep slope in the middle will want to slide downhill.  And naturally, higher clamping forces will tend to bend the bar more.

I don't make cellos, but I make the bar fit very exactly to the top, use very light clamping, and a heat gun to re-liquify the glue.  I also have tape on the top around the bass bar to limit glue smear during cleanup, so any sideways movement would be obvious and not good.  My "locating blocks" are something else entirely.

I'd make a new bar and do it right.  Annoying to re-do work, but it's really not that much.

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Exactly, that bar is bugging me.
The first try went wrong because the glue gelled. The second was much better and it didn't gel up at all. However, the clamping pressure was all fairly vertical, so yes, it might very well have slid down.

Since I don't have a new blank and can't get one easily, corona and so on... Is it possible to take it out and redo it? I took apart a top joint once, and that was a destructive process. Wouldn't want to do anything like that on a finished top, but if I could get it out somewhat easily, there would be no issue just gluing it again with a third cleat.

The bar isn't very tall in the center, you're completely right. I got it from a luthier who had cut it down to 25mm. I wanted it 24mm in the center, but it ended up 23 I believe. A bit to the short side, but I thought it was fine as long as I kept it a little less tapered in the center.

As you can hear, I have a lot of issues with this bar and is definitely going towards redoing it to some extent. I don't like doing bass bars though, so if I could have used this one which had a good fit (finally), I would have been happy. Sounds like it's not a great idea though?

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Well, I guess I could just order one from Dictum, actually, didn't realize they had bass bar blanks before I checked a second ago. I guess this is really the build that teaches me patience and repetition... I find myself redoing things that don't meet my expectations rather than just accepting them. Of course that should go for the bass bar as well.

Damn it, time to do things properly then. So basically the only thing I need to do differently is add a third cleat in the middle? I should get more clamps too, but I simply can't afford it at the moment.

Don, you say light pressure. I suppose you're not springing them? I think having a slight spring of 1-2mm is best for my setup, but I could probably still clamp a lot less than what I did here, at least in the middle

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54 minutes ago, Tostra said:

Don, you say light pressure. I suppose you're not springing them? I think having a slight spring of 1-2mm is best for my setup, but I could probably still clamp a lot less than what I did here, at least in the middle

No, I don't intentionally spring bass bars.  I think it's easier to get a perfect fit without the spring, and that's more important to me.  I only use enough clamping pressure to see uniform glue squeeze-out, and the heat gun makes sure I'm not trying to squeeze out gelled glue.

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If you are using the typical "V" clamps an extra suggestion (tip) is to trim the top of the bar to minimize lateral deflection and concentrate the clamping force in the downward direction.

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You're probably worrying too much. Trim it down, close the box, finish the job, and have someone who can play tell you how it works. If semi literate Italian and Austrian ruralites could manage, so can you. Worst case scenario, you pop the top and start over on the bar. Shouldn't take you more than a few hours. You've got this.

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I remember now on my first cello, I think I did almost no spring amd found that much easier. Maybe that's my issue than, having to clamp too hard with too few clamps.

Yes I am chalk fitting. Is there any other way to reliably fit the bar?
I'll check it out and see if there's any new klittle tricks for me

I'm not using those, but I have considered making some, and then I'll make sure not to glue it in too tall

I also think that I'm probably worrying too much. I'm sure this will work but I'm worried it might not work as well as I'd hoped. The cello is for myself, and so far I've made sure that it's the best thing I have ever made. Already before I posted this I had the thought of "I can just keep it, and then some day I or someone else will make a better bar", but would I really enjoy playing it like that? I think for my peace of mind I'm better off making it nice from the start and not starting to lower my standards this close to the finish line

Mark, I'm very curious to hear how you did it? Hot opening knife? I'm most likely not going to need it ever, but who knows what repairs I need to do one day...

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Oh... Well I may be mistaken, but I have heard a few places that a wider sound post/bass bar position, ie smaller overstand of the bridge feet, gives a more powerful sound which in turn requires more energy to play. I have seen a similar trend so far in building and repairing, but I'm afraid I don't have much more than a trust in the people who told me so and a gut feeling to back it up.
I suppose I could use a narrower bridge to get the same overstand if I kept the bar, but then again I can't believe it's the overstand that should define such a thing rather than the relation between the body width and the bridge width for instance. So basically, this is what I choose to follow for now, although it might be a flawed model

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10 hours ago, Tostra said:

So basically the only thing I need to do differently is add a third cleat in the middle?

 

8 hours ago, Brad H said:

By the way, reading this how-to on bass bars couldn't hurt.

Basically yes, a third cleat as close to the foot of the bridge as possible, without hiding the line of the mensur that you need to see to correctly position the bassbar.

In the linked article by Hargrave you can clearly see the cleat in the center, he uses 5 cleats but I think 3 cleats on the inside are more than enough because this is the direction towards where the bassbar would slide under the pressure of the clamps during gluing. With the right (low) clamping pressure the risk is less, but the glue is slippery and a cleat near the bridge foot "cuts the bull's head" (I don't know if this Italian expression is also used in the States:)).

If you think about it, the most important point for bassbar placement is at the bridge foot, so it is extremely logical to put a secure reference (cleat) exactly in that area.

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It's not a saying here in Denmark, but I get what you mean. I honestly thought two was enough, and it was plenty for fitting the bar, but I didn't think for a second that the bar could curve sideways. But I guess that was just one last lesson of 2020 for me.

It makes perfect sense to have it supported at the bridge position now I think about it. I do think three will be plenty, even though I've seen five many times. The outer ones don't really do much for me except making my life a bit more difficult when applying chalk.

I also think less tension is going to be very helpful, as I noticed the hard clamping and 2mm spring made it want to open up in some areas between the clamps. I only have seven clamps which are 1) deep enough to reach the bar, some through the Fs or clamping on an extension and 2) not too heavy. Is there a trick to better distribute the force, like having a spring steel strip on the outside of the top or something? I don't know where I would find a spring steel strip, but I imagine it could help?

I'll plane out the bar today so I'm not tempted to keep it. I'm determined to make a great cello out of this, and I regret considering this as the final bass bar. I guess I was just frustrated from all that work going to waste... But I ordered a bar from Dictum along with a madder lake to have a little fun arrive in the package as well. Looking forward to improving it!

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This is a bass bar jig (early) I made a while ago. The design if from Sharon Que, published in The Strad. I also have one for violin and viola.(they look a bit more sophisticated) The two arms move to adjust the bar while the platform holds the plate flat. The bar rests agains the arms at 90 degrees. Make on and never look back.

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Sure looks helpful! Keeping the plate from moving without a frame is difficult, so I have often considered making a sturdy plate for keeping it flat. That design doesn't look bad, is it stable enough?

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