Ladder-braced parlor guitar
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Dave Bagwill
- Posts: 5951
- Joined: Tue Dec 13, 2011 7:44 pm
Re: Ladder-braced parlor guitar
About Michael Collins, Titebond, and vacuums: It might be a case of the amount of glue that needs to dry at one time. A lamination of even just three layers involves the entire surface area times two, while gluing on several braces involves only a small fraction of a single surface. Thus it may be there is enough leakage out of the bag on the one hand and absorbent wood inside the bag on the other to accommodate the elimination of the water from such a small area. I am going to review his DVD and make sure I am quoting him correctly and get back here afterwards. It has been a couple weeks since I watched it.
About vacuum clamping a whole back or top: Lets say there is about 1.5 square feet of area on a typical plate; at 1800 pounds per square foot of pressure this would be like placing a 2700 pound weight on the assembly, wouldn't it? If the sides were firmly clamped to a strong mold, they should hold, but I would not want to bet on the plate itself since it would be first to absorb the load in order to transfer it to the sides.
However, perhaps it could be accomplished safely by using fewer inches of vacuum. Or by using a clamping caul that included a cover that protected the plate from the pressure and transferred it all to the edge before applying it to the guitar. The caul would look something like a straw hat with a very narrow brim, with a strong top that would not deflect under load, so the force could travel down the hat rim to the joint between the plate and the sides. Has anyone actually tried clamping a whole plate with vacuum? That would provide the definitive answer.
About starved joints: I am certain Michael Collins applies glue on just one side of the joint. He mentions to be sure to use "enough" and that better to have too much than not enough. U-F glue may transfer more effectively than Titebond using the single side technique.
About vacuum clamping a whole back or top: Lets say there is about 1.5 square feet of area on a typical plate; at 1800 pounds per square foot of pressure this would be like placing a 2700 pound weight on the assembly, wouldn't it? If the sides were firmly clamped to a strong mold, they should hold, but I would not want to bet on the plate itself since it would be first to absorb the load in order to transfer it to the sides.
However, perhaps it could be accomplished safely by using fewer inches of vacuum. Or by using a clamping caul that included a cover that protected the plate from the pressure and transferred it all to the edge before applying it to the guitar. The caul would look something like a straw hat with a very narrow brim, with a strong top that would not deflect under load, so the force could travel down the hat rim to the joint between the plate and the sides. Has anyone actually tried clamping a whole plate with vacuum? That would provide the definitive answer.
About starved joints: I am certain Michael Collins applies glue on just one side of the joint. He mentions to be sure to use "enough" and that better to have too much than not enough. U-F glue may transfer more effectively than Titebond using the single side technique.
John
Re: Ladder-braced parlor guitar
OK, Checked both Michael's DVD and book. I have quoted him correctly. He recommends against using Titebond in a "vacuum veneer press" because it does not cure properly, according to him. When he glues braces he uses Titebond and a go-bar deck, so the question of using Titebond with a vacuum bag for that procedure never comes up.
He does talk about using Titebond with his mold + caul method for laminating veneer. He recommends leaving the assembly clamped for a minimum of 24 hours and "longer if you can" versus 6 hours for the U-F glue, otherwise there is risk of delamination. For his mold + caul demo, he used U-F after discussing its advantages over Titebond. That particular demo was for making linings and involved 6 layers of basswood. He likes U-F for laminating veneer, Titebond for just about everything else, though he uses CA, hot hide, and epoxy for certain applications.
Throughout each veneer demo he repeatedly warns to use plenty of glue to avoid delamination and other problems later. He uses a printmaking roller to apply it, and the surfaces look very wet when he is finished with application. U-F seems to lay on the surface more than I would expect from a similar layer of Titebond. Titebond out of the bottle is a little more viscous and a lot more sticky than U-F. U-F is more lubricated looking, somewhat oil like, which may help in the transfer to the "dry" side. It looks like a good glue for lamination, viewed mechanically. Sound-wise, who knows? I will say this, the back I got from Michael taps out very differently than any wood plate I have ever examined. It wants to vibrate in long amplitude movements and produces a low, resonate note. Brazilian and Honduran rosewoods are very vitreous and make a fairly high sustained note, maple a short thud, spruce sustained and in between, and so on. Michael's U-F laminated Indian rosewood and mahogany back is much different, though still woody.
Michael's back came perfectly flat, where in the video he laminates into a radiused dish that results in a radiused back, per what is needed according to his plans. I radiused my back by clamping it, a side heating blanket covered with foil, and a spring steel slat into a radiused dish, heating to 275 degrees for 20 minutes (a long time considering, maybe longer than I needed), and letting it cool down while clamped. I performed this process three times, to heat bend the whole surface of the back. In fact, I have left it clamped into the dish until I cut it out and brace it, though I did not get much spring back.
He does talk about using Titebond with his mold + caul method for laminating veneer. He recommends leaving the assembly clamped for a minimum of 24 hours and "longer if you can" versus 6 hours for the U-F glue, otherwise there is risk of delamination. For his mold + caul demo, he used U-F after discussing its advantages over Titebond. That particular demo was for making linings and involved 6 layers of basswood. He likes U-F for laminating veneer, Titebond for just about everything else, though he uses CA, hot hide, and epoxy for certain applications.
Throughout each veneer demo he repeatedly warns to use plenty of glue to avoid delamination and other problems later. He uses a printmaking roller to apply it, and the surfaces look very wet when he is finished with application. U-F seems to lay on the surface more than I would expect from a similar layer of Titebond. Titebond out of the bottle is a little more viscous and a lot more sticky than U-F. U-F is more lubricated looking, somewhat oil like, which may help in the transfer to the "dry" side. It looks like a good glue for lamination, viewed mechanically. Sound-wise, who knows? I will say this, the back I got from Michael taps out very differently than any wood plate I have ever examined. It wants to vibrate in long amplitude movements and produces a low, resonate note. Brazilian and Honduran rosewoods are very vitreous and make a fairly high sustained note, maple a short thud, spruce sustained and in between, and so on. Michael's U-F laminated Indian rosewood and mahogany back is much different, though still woody.
Michael's back came perfectly flat, where in the video he laminates into a radiused dish that results in a radiused back, per what is needed according to his plans. I radiused my back by clamping it, a side heating blanket covered with foil, and a spring steel slat into a radiused dish, heating to 275 degrees for 20 minutes (a long time considering, maybe longer than I needed), and letting it cool down while clamped. I performed this process three times, to heat bend the whole surface of the back. In fact, I have left it clamped into the dish until I cut it out and brace it, though I did not get much spring back.
John
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Dave Bagwill
- Posts: 5951
- Joined: Tue Dec 13, 2011 7:44 pm
Re: Ladder-braced parlor guitar
Thank you for the information, John. Titebond keep its stellar reputation for most of the tasks we do, but as my experiment showed, it may not be the best for vacuum lamination. Good to know.
I'm still waiting for Franklin to respond.
I'm still waiting for Franklin to respond.
-Under permanent construction
Re: Ladder-braced parlor guitar
Along my personal bumpy woodworking journey I picked up the practice of expecting a small amount of glue squeeze out from clamping pressure no matter what type of adhesive (of course CA and contact cement are different) and simply, if I do not see that, I disassemble and apply more glue.
ken cierp
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http://www.cncguitarproducts.com/
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Re: Ladder-braced parlor guitar
I watched a demo with original Titebond of laminating one layer of Macassar ebony veneer to a carved spruce top. It was successful.
Perhaps the underlying issue is that original Titebond has less "wiggle room" for its use. He was careful not to use "too much" but, as Ken notes, he did get slight squeeze out. He did only one layer, with a thick spruce base that could absorb quite a bit of water. He removed the assembly from the bag after just 15 hours so that the squeeze out would not be rock hard and therefore easier to remove. This might be critical to success because it allowed final evaporation of the water to occur without encumbrance by the sealed bag, yet the glue had already set sufficiently that the bond would not release.
I tend to think Franklin would not make a special formulation for veneer presses if the original performed well as is. Here is the URL to their cold press veneer product:
http://www.titebond.com/product.aspx?id ... 94cc3ae102
Note that it is for porous surfaces and they appear to assume one of them will be thick, with only one layer of veneer on top of it.
Perhaps the underlying issue is that original Titebond has less "wiggle room" for its use. He was careful not to use "too much" but, as Ken notes, he did get slight squeeze out. He did only one layer, with a thick spruce base that could absorb quite a bit of water. He removed the assembly from the bag after just 15 hours so that the squeeze out would not be rock hard and therefore easier to remove. This might be critical to success because it allowed final evaporation of the water to occur without encumbrance by the sealed bag, yet the glue had already set sufficiently that the bond would not release.
I tend to think Franklin would not make a special formulation for veneer presses if the original performed well as is. Here is the URL to their cold press veneer product:
http://www.titebond.com/product.aspx?id ... 94cc3ae102
Note that it is for porous surfaces and they appear to assume one of them will be thick, with only one layer of veneer on top of it.
John