I've carved out the old self bar on this bass I've been working on for YEARS. I'm finally ready for the bass bar, I think. I'm looking for thoughts on length(?), width(21mm?), and positioning(?) of the bar. All I'm going on for now is the Treager book and the blog of Roger Hargrove's bass build. I would welcome any thoughts on shape too. Also, am I right to do the bar first and soundpost patch after, or should i do the patch first?
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The rule of thumb is that you want it to be 7/8 of the length of the top and 20-24 mm wide.
It's not math, it's resonance. I haven't done a bar in a bit but my sieve-like memory tells me you want the tap tone of the finished bar after it is glued in and shaped to ring a fifth above the tone of the top alone.
The highest point of the arch should be below the bridge foot, and the bar should be offset 10-15 degrees depending on how the top is carved, to add strength and discourage cracks along the grain.
I fit the bar to the top, glue it in with the top of the bar square and then shape as necessary. I've had success fitting the bar in a way that, when the bar is glued in, the ends of the plates rest on the neck and bottom blocks but the top hovers 1/4" over the center of the C-bouts.
EDIT -- Incomplete thought now complete.
It's not math, it's resonance. I haven't done a bar in a bit but my sieve-like memory tells me you want the tap tone of the finished bar after it is glued in and shaped to ring a fifth above the tone of the top alone.
The highest point of the arch should be below the bridge foot, and the bar should be offset 10-15 degrees depending on how the top is carved, to add strength and discourage cracks along the grain.
I fit the bar to the top, glue it in with the top of the bar square and then shape as necessary. I've had success fitting the bar in a way that, when the bar is glued in, the ends of the plates rest on the neck and bottom blocks but the top hovers 1/4" over the center of the C-bouts.
EDIT -- Incomplete thought now complete.
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On pre-springing opinions differ. Interestingly, I too used 6mm on my latest BB, but I believe the current majority view is not to pre-spring.
On your question of the patch: if you need such a big patch (for instance: to reinforce a ply top), I'd do it below the BB, and be symmetrical over the top. So first patch, then BB. But with such a big patch you're really changing the top's resonance characteristics, and a normal repair should not extend that far.
On your question of the patch: if you need such a big patch (for instance: to reinforce a ply top), I'd do it below the BB, and be symmetrical over the top. So first patch, then BB. But with such a big patch you're really changing the top's resonance characteristics, and a normal repair should not extend that far.
When you say 7/8's the length of the top is that the whole top, including the small upper tabs that go around the neck pocket? Or is it just the vibrating area of the top?
Vibrating area, I believe. Last time I fitted a bar was almost five years ago so if somebody corrects me, listen to them.
@Ortsom I'm not too hot on sprung bars either. In addition to the possibility of top deformation a sprung bar must be harder to fit accurately because it obviously won't sit flush to the top absent adhesive and tension.
@Ortsom I'm not too hot on sprung bars either. In addition to the possibility of top deformation a sprung bar must be harder to fit accurately because it obviously won't sit flush to the top absent adhesive and tension.
Here's an interesting read on this topic from a guy that knows a thing or two about a thing or two...
Jeff Bollbach Luthier, Inc.: Luthier Rant
Jeff Bollbach Luthier, Inc.: Luthier Rant
On the BB fitting: indeed, it does not fit over the entire length without some encouragement. But 6mm = 1/4" is not much, and some weight on the top to deform it (as you described) solves the problem. That was a rather flat/low relief top, with more relief near the ends of the BB, and a flatter central part. After consideration I choose to have some preload from the BB, cognisant of the issues, while not forcing the lower edge of the top to be flat. (The top is fitted stressless, but not flat: in the C-bout area it is higher than at the blocks. Other than size-wise, this is not a standard instrument.)
If not by pre-springing the BB, how did you get the centre to hover 1/4" above the C-bouts, with the ends resting on the blocks? Was the lower edge of the top flat without the BB?
If not by pre-springing the BB, how did you get the centre to hover 1/4" above the C-bouts, with the ends resting on the blocks? Was the lower edge of the top flat without the BB?
To clarify, the top, with the old integral bar removed, sat flush on all six blocks without tension.
With the new bar fitted the top sat 1/4" above the C-bouts while flush with the top and bottom blocks.
After the top was glued down and string tension applied I was confident the ends of the bar were not under enough tension to deform the top.
Ironically, the guy who bought the bass from me brought it to my mentor for a checkup and he gave my work a thumbs-up.
The sprung bars I've replaced because they came loose from the top were under much more tension than the bar described above. One let go from the bridge area down to the end, and the end was separated from the top by almost an inch.
There was so much tension there I was able to rearch the sunken ply top simply by clamping the free end of the bar down and applying gentle heat over several days.
With the new bar fitted the top sat 1/4" above the C-bouts while flush with the top and bottom blocks.
After the top was glued down and string tension applied I was confident the ends of the bar were not under enough tension to deform the top.
Ironically, the guy who bought the bass from me brought it to my mentor for a checkup and he gave my work a thumbs-up.
The sprung bars I've replaced because they came loose from the top were under much more tension than the bar described above. One let go from the bridge area down to the end, and the end was separated from the top by almost an inch.
There was so much tension there I was able to rearch the sunken ply top simply by clamping the free end of the bar down and applying gentle heat over several days.
I think we agree: 1/4" is not much, but it is a little (so not 0).
"the top, with the old integral bar removed, sat flush on all six blocks without tension": so without load the bottom edge of the top was flat, or at least conforming to some consistent shape.
"With the new bar fitted the top sat 1/4" above the C-bouts while flush with the top and bottom blocks." So installing the BB pushed the centre up by 1/4". Hence the BB was sprung, and probably by more than 6mm (my 6mm are between the ends of the BB and the top, before glueing, but that gives clearly less than 6mm deformation, as both BB & top bend, and meet somewhere in the middle, when joined).
Then pushing-down the centre to make the top fit at the C-bouts increases the load towards the ends of the BB and, over time, might encourage a fig.3-like deformation, referring to Mr. Bollbach's story. I say 'might' as it is by no means certain to happen. What happens over time depends on the arching (relief, both directions are important here), wood quality, graduation, ..., . In a situation like figure 4, some (= 'a little') load by the ends of the BB may be carried well by the arching near those ends, and will not lead to deformation on the long term, but instead helps to enhance the top's carrying capacity a little. Furthermore, some pre-load from the BB will enhance a gentle arch in the top, in the middle section (right where the bridge sits & where the BB is deepest), further enhancing the carrying capacity (well, unless you push that bend back of course).
Yes, once again, there are far stronger pre-sprung bars around, and the pre-springing does not really help but instead can give substantial problems.
Carrying capacity comes from the geometry, not from elastic forces in a bar. Yet some judicious elastic pre-load can help a little, depending on circumstances. (IMHO, YMMV, ..)
"the top, with the old integral bar removed, sat flush on all six blocks without tension": so without load the bottom edge of the top was flat, or at least conforming to some consistent shape.
"With the new bar fitted the top sat 1/4" above the C-bouts while flush with the top and bottom blocks." So installing the BB pushed the centre up by 1/4". Hence the BB was sprung, and probably by more than 6mm (my 6mm are between the ends of the BB and the top, before glueing, but that gives clearly less than 6mm deformation, as both BB & top bend, and meet somewhere in the middle, when joined).
Then pushing-down the centre to make the top fit at the C-bouts increases the load towards the ends of the BB and, over time, might encourage a fig.3-like deformation, referring to Mr. Bollbach's story. I say 'might' as it is by no means certain to happen. What happens over time depends on the arching (relief, both directions are important here), wood quality, graduation, ..., . In a situation like figure 4, some (= 'a little') load by the ends of the BB may be carried well by the arching near those ends, and will not lead to deformation on the long term, but instead helps to enhance the top's carrying capacity a little. Furthermore, some pre-load from the BB will enhance a gentle arch in the top, in the middle section (right where the bridge sits & where the BB is deepest), further enhancing the carrying capacity (well, unless you push that bend back of course).
Yes, once again, there are far stronger pre-sprung bars around, and the pre-springing does not really help but instead can give substantial problems.
Carrying capacity comes from the geometry, not from elastic forces in a bar. Yet some judicious elastic pre-load can help a little, depending on circumstances. (IMHO, YMMV, ..)
