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Dec 7, 2018 - 6:53:22 AM
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1636 posts since 2/7/2008

I enjoyed the video by desert banjo on steam bending. While I was watching it, I was also thinking about bending guitar sides. A growing number of guitar builders use heating blankets to provide the heat to bend sides. They also bend at much higher temperatures than steam could generate.

Could heating blankets be the next big breakthrough for banjo rim bending?

lmii.com/bending-heating/2509-...atts.html

Dec 7, 2018 - 9:14:22 AM

49862 posts since 12/14/2005

If memory serves, the boiling point of water is 212 degF.

I can't imagine anybody snuggling up under an electric blanket which is designed to get hotter than that.

Dec 7, 2018 - 9:49:39 AM

85 posts since 7/14/2017

I make ukuleles and the odd guitar (though I bend the sides on a hot pipe, not using a heat blanket). These heat blankets go to 300 F or above, rather warmer than in that picture!

But this kind of heat bending requires very thin wood. Even 1/8 inch thick is likely too big to bend nicely in many wood species. Anything much thicker requires long steaming.

So probably not the future of banjo building, especially as heat blankets have been available for years so you'd expect them to be common knowledge here if they were useful for rims.

Dec 7, 2018 - 10:05:36 AM

11231 posts since 6/29/2005

quote:
Originally posted by Quickstep192

I enjoyed the video by desert banjo on steam bending. While I was watching it, I was also thinking about bending guitar sides. A growing number of guitar builders use heating blankets to provide the heat to bend sides. They also bend at much higher temperatures than steam could generate.

Could heating blankets be the next big breakthrough for banjo rim bending?

lmii.com/bending-heating/2509-...atts.html


You'd have to rewrite the conventional wisdom about the "three-ply".  Much energy has been expended over the years to vilify multi-ply rims as being " cheap Asian stuff".

I think that just as good a rim as a three-ply can be made with many more plies, and I really like the old Vega 7-ply ones, but there has been such a mountain of propaganda built about the superiority of the three ply, that it would require some serious re-education to reboot perception.

Having tried several methods, I prefer laminated rims to other construction methods, and think an excellent rim could be made with 9 or 10 plies, but I make mine 3-ply because that's what people associate with high quality and perception is reality in a situation where there is no objective standard.

As for the guitar makers, they are discovering that stiffness is really important in guitar sides (which are the equivalent of banjos rims), and are making laminated sides now, which are stiffer and allow a mix of wood species (just as in laminated banjo rims), and you don't even need a steam blanket - just forms. No doubt they are going through a phase of having to convince people that this is just as valid and good a method as solid wood sides, but it's an uphill battle.

Edited by - Ken LeVan on 12/07/2018 10:06:34

Dec 7, 2018 - 10:32:03 AM

1636 posts since 2/7/2008

"But this kind of heat bending requires very thin wood. Even 1/8 inch thick is likely too big to bend nicely in many wood species. Anything much thicker requires long steaming"

This is the thought that caused my initial curiosity and that is: would a blanket bend a thicker piece of wood? Is it plausible to think that a 1/4" thick piece could simply be soaked before using a blanket?

Dec 7, 2018 - 10:35:33 AM

1636 posts since 2/7/2008

"As for the guitar makers, they are discovering that stiffness is really important in guitar sides (which are the equivalent of banjos rims), and are making laminated sides now, which are stiffer and allow a mix of wood species (just as in laminated banjo rims), and you don't even need a steam blanket - just forms. No doubt they are going through a phase of having to convince people that this is just as valid and good a method as solid wood sides, but it's an uphill battle."


I have a guitar that has what were called "double sides" and a "double top". The sides are simply laminated, the top is a sandwich of two pieces of redwood with a sheet of nomex in-between. It's one of the best sounding guitars I've ever heard, but I might have dismissed it as being a "plywood" guitar if I wasn't aware of the technology that went in to it.

Dec 7, 2018 - 3:50:54 PM

krw2dbw

USA

33 posts since 3/4/2013

Gibson steam pressed thin strips of resinous hardwoods together for their sides for years. They added no glue and just allowed the resin in the wood to make the bond. Made some pretty stable sides. They were thin but would not split.

Dec 7, 2018 - 4:11:38 PM

6974 posts since 1/7/2005

quote:
Originally posted by Quickstep192

"I have a guitar that has what were called "double sides" and a "double top". The sides are simply laminated, the top is a sandwich of two pieces of redwood with a sheet of nomex in-between. It's one of the best sounding guitars I've ever heard, but I might have dismissed it as being a "plywood" guitar if I wasn't aware of the technology that went in to it.


You're probably referring to the guitars of Greg Smallman, or one of the many other luthiers that have adopted his design. Not only are his sides laminated, but the internal bracing creates a heavy structure where only the live area of the super-thin top are able to vibrate. The result is a very loud guitar with strong overtones. Kind of reminds one of a banjo head. 

https://www.thisisclassicalguitar.com/wp-content/uploads/2015/02/lattice_020.jpg

DD

Dec 7, 2018 - 9:13:12 PM

4481 posts since 6/3/2011

quote:
Originally posted by Quickstep192

"But this kind of heat bending requires very thin wood. Even 1/8 inch thick is likely too big to bend nicely in many wood species. Anything much thicker requires long steaming"

This is the thought that caused my initial curiosity and that is: would a blanket bend a thicker piece of wood? Is it plausible to think that a 1/4" thick piece could simply be soaked before using a blanket?


You could do that but it would not go above 212 F until the water was boiled out.  Use a heat blanket on both sides of a 1/4 inch might work.

Dec 8, 2018 - 5:40:44 AM
likes this

11231 posts since 6/29/2005

quote:
Originally posted by Quickstep192

"As for the guitar makers, they are discovering that stiffness is really important in guitar sides (which are the equivalent of banjos rims), and are making laminated sides now, which are stiffer and allow a mix of wood species (just as in laminated banjo rims), and you don't even need a steam blanket - just forms. No doubt they are going through a phase of having to convince people that this is just as valid and good a method as solid wood sides, but it's an uphill battle."


I have a guitar that has what were called "double sides" and a "double top". The sides are simply laminated, the top is a sandwich of two pieces of redwood with a sheet of nomex in-between. It's one of the best sounding guitars I've ever heard, but I might have dismissed it as being a "plywood" guitar if I wasn't aware of the technology that went in to it.


I have a laminated one as well, and actually bought some Nomex thinking it might have some usefulness in making banjo resonator rims or resonators, but they are different than guitar tops. To me, multi-ply bent laminations are a very sound method of making engineered structures for a multitude of uses.

Anyway, referring to laminated instrument parts as "plywood" has been the standard method used by naysayers to dismiss them for quite a while.  We hear this frequently on this forum; "cheap plywood rims". The other thing you hear is an attempt to vilify glue joints as somehow compromising the sound, and of course, glue joints go hand-in-hand with laminations. I'll readily admit that at one time I bought into that stuff, but have now gone beyond it.

Dec 8, 2018 - 7:06:57 AM
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Players Union Member

rudy

USA

13156 posts since 3/27/2004

The prejudice against multi-ply rims has no basis is fact.

I strongly suspected the parroted opinions about "too much glue" and "cheap construction" indeed were more wishful thinking by those who owned banjos constructed using other methodology, and some of the best banjos I'd personally heard were old Vegas using multi-ply rims.

Somewhere around half of the conversations relating to difficulty of rim construction focus on three ply rims and how to produce them without gaps.  It's well documented that many of the three ply rims produced by Gibson had gaps large enough that they cut channels over the open joints and added wood strips to fill the areas where the gaps would have been pointed out as defective construction.

The proof in the difficulty is only a search away here on the Hangout, and I initially went down that "rims gotta be three ply" road.

Then I remembered all those Vegas and the light went off.

From my practical experience building "plywood" rims made from 1/8" laminations makes it much easier to produce rims that have uniform well-fitting laminations that have minimal glue, no gaps, and most important to me, have little residual tension in the completed rim assembly.  Wood laminations want to return to the structure that represents how they grew, so anything we can do to minimize that results in a more dimensionally stable rim.

The efficacy of using thin lams to reduce residual stress can be easily tested by bending 3 or 4 feet of 1/8" into a loop and then doing the same thing with 1/4" thick material.

I somewhat documented my search in the "Goldilocks Rim Laminations" topic.

Thin laminations are easier to bend, easier to form into gap-free structures, have less internal stress, are more resonant, are more dimensionally stable, and can be made using less expensive highly figured wood for internal layers and using highly figured wood for the visible layers.

Vega most likely used multi-ply rims because they were easier to produce and resulted in a reliable and stable rim structure.  That sounds like the proverbial "no brainer" to me.

Oh, as a side note, I'm all about easy.  wink

What about block rims?

Outside the focus of this topic, but block rims were obviously developed to get away from all the problems of making hoop rims.  Many of the same comments I made about multi-ply rims also can be applied to block rims.  It's a personal choice, so for me I just don't care for the look of block construction.

Edited by - rudy on 12/08/2018 07:12:31

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