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| It Broke Again http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10101&t=53502 |
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| Author: | Ken Nagy [ Tue Sep 08, 2020 8:32 am ] |
| Post subject: | It Broke Again |
Last night we were in the living room, and we thought something fell in the closet, and hit the door. This morning I found the source of the noise: Attachment: IMG_0085.jpeg This time the bridge snapped too. I don't think I messed up on the sting sizes. Maybe I did. They don't seem too tight at all to me. They are nylgut, .48 for the g, .6 for the d .72 for the Bb, .48/.96 for the F and .62/1.25(loaded string, 1.0 dia.) for the low C. 540 scale. They should have 4/3.3/3.4/3/3 kgs per string for about 73 pounds of pressure. I guess it's probably just the glue joint. In noticed when I got the plans for the Voboam guitars, that the guy has the solera made with a space carved out for the bridge. Apparently he makes sure the bridge is able to be clamped. Would have been nice to know before I had it all glued up! This is what it looks like up close: Attachment: IMG_0087.jpeg I glued it very quickly. A brush of glue on the body; another on the bridge. Squish them together. I held it for a while, but I probably need to hold it for a longer time, or find some way to put some weight on it. Maybe the glue was a little too thick? I used thin glue before, so I might have went too far the other way? I have rosewood, or ebony, or katalux to make a new bridge. All would be stronger than the Cherry. Maybe that was a bad idea. |
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| Author: | bcombs510 [ Tue Sep 08, 2020 8:47 am ] |
| Post subject: | Re: It Broke Again |
That’s a bummer. Do you have access to or know anyone with a vacuum clamp setup? Maybe you can get a better bond than a rubbed joint? Hope you figure it out! Would love to hear a sound clip. A couple years back the local art museum had a history of guitar exhibit. This guy would fit right in.  Sent from my iPhone using Tapatalk Pro |
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| Author: | jfmckenna [ Tue Sep 08, 2020 9:34 am ] |
| Post subject: | Re: It Broke Again |
Maybe just go to a single hole design? Looks like the glue joint held but the wood failed. What was the grain orientation of the wood? |
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| Author: | Ken Nagy [ Tue Sep 08, 2020 10:51 am ] |
| Post subject: | Re: It Broke Again |
The bridge was perfectly quartered, and I think that the grain was front and back, like a violin bridge showing dots and lines. Ahh, here's a photo. Attachment: 20200425_160447.jpeg The design does seem to make the bridge much weaker. The strings are adjusted for height and supposedly even intonation at the angled side using a tied loop. You'd have to move them around before they get too tight. The knots take up a lot of space, they don't tighten like string or thread, so maybe thru holes with a pocket below them. Just thinking. At least it wouldn't want to flex so easily. |
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| Author: | wbergman [ Tue Sep 08, 2020 11:12 am ] |
| Post subject: | Re: It Broke Again |
I am not sure what you are doing, so forgive me if I make nonsense. If you are attempting a rubbed hide glue joint, it is my understanding that you have to rub it. That is, you have to slide it back and forth the long way until the glue starts to grab. This causes excess glue to move out without making a gap. As the glue starts to set, it seals so that the bridge should not pull away. It almost acts like a vacuum to pull the bridge and top together. Other posts in the past have pointed out that bridges should not be exactly vertical grain, because that makes potential fracture planes in just the wrong places. But, I cannot tell if your bridge broke on those planes. |
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| Author: | Ken Nagy [ Tue Sep 08, 2020 11:35 am ] |
| Post subject: | Re: It Broke Again |
I thought about the rub joint, and I did rub it originally. The second time, I did rub it SOME, because one mustache came off with it. For this one, I was going to make it 1/8 or 1/4" short or so, and put pieces on both sides after it is glued. I glue all my tops with a rub joint. If you don't feel it stick; it didn't stick. I guess a violin, or even an arch top bridge has different forces on it. A flattop bridge is all tension. The other two have some compression as well. Ten small holes will undoubtably be better than 5 triangles cut into it. I thought about double wide holes, and passing the loop through the hole, and having the knots on the bottom. I'd have to make a mockup and see if that would work before doing it. It seems like it would look neater anyway. Too bad Strad didn't have a telecaster style bridge. That would be simple. Easy adjustments, screw it on. |
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| Author: | johnparchem [ Tue Sep 08, 2020 12:06 pm ] |
| Post subject: | Re: It Broke Again |
One other thought. I have been looking at the picture of you holding up the part near where it glues on. I suspect the the right side as in the picture was not glued down well. You have the parts and see better. But I am wondering if the lower right of the bridge was sitting on the finish and you ended up with a film of glue instead of wood to wood contact. Once this started to lift, the torgue of the string pull snapped the nicely glued part of the bridge in half. I suspect this as the spruce is clean there and there is a film of glue on the bridge feet. |
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| Author: | TimAllen [ Tue Sep 08, 2020 12:48 pm ] |
| Post subject: | Re: It Broke Again |
I have never built a baroque guitar, but it does seem like ten holes instead of triangles would be stronger. I have some pictures of the Rawlins Strad guitar, and it _looks_ that one has triangles cut out, but it's hard to see. jfmckenna (John, I think) points out that the wood broke; your photo shows that the wood you used looks perfectly suitable, but possibly another piece would be stronger. (I think Strad reinforced with carbon fiber, but the formula of the Cremonese carbon is now lost along with the varnish.) (Sorry.) |
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| Author: | Alan Carruth [ Tue Sep 08, 2020 1:31 pm ] |
| Post subject: | Re: It Broke Again |
A skew cut would give higher shearing strength. I've used apple and pear wood for that sort of bridge with good results. They do seem to be a bit tougher than maple of similar density. Drill holes if you can. You want as much material as possible along that line to resist the shear. |
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| Author: | Ken Nagy [ Tue Sep 08, 2020 2:07 pm ] |
| Post subject: | Re: It Broke Again |
John, I do think that you are right about the joint being better on the bass side, I think the glue might have been a little thick, an the rub didn't go all the way across. The first one seems to be a starved joint. Tim, part of the varnish secret seems to be a pre treatment on the wood using nitro made from rabbit urine! Really. Alan, I wasn't thinking about the forces. I've used skew cuts on ribs, and the only downside(?) I noticed is less tendency to split on the curl when bending. Yes, you can lose some figuring too. I think that Strad DID put the loops through the bridge, and have the knot at the back. I haven't seen any pictures showing that though. It will be much easier to adjust. He did the triangle instead of a slot, because his high speed mill was dedicated to doing fancy inlays for sale on eBay. I drew out my plan of attack. I'll have to see if it ends up with ten ovals, or 5 slots. Attachment: IMG_0088.jpeg
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| Author: | Ken Nagy [ Thu Sep 10, 2020 1:35 pm ] |
| Post subject: | Re: It Broke Again |
Ahh. Twice I've done that now. Add the photo, and remember it wasn't sized. Instead of letting it go, and letting the system say that you were a big dummy. I hit cancel, you know cancel what I just did. Not CANCEL THE WHOLE POST. Next time I'll remember. Right. The bridge is ready to glue, but I need to make the rosewood parts to blend in the mustaches; it is a little shorter. I even chalk fit it. The glue did pull some off the spruce. I had to figure out the hole spacing. 3Xs the string diameter minimum, so the string fits through the loop. Ended up using a 1/16" 5/64" 3/32" and a number 36 drill. For the low C, I drilled two 1/16 holes, and used my tiny saw blade to make an oval hole. It looks MUCH CLEANER this way than the other way. It seems like I can almost break the other one, so I think it might have been cracking. Attachment: IMG_0089.jpeg
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