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Aluminum Tone Ring (Science Question)

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Jul 22, 2020 - 8:29:02 AM
370 posts since 3/26/2015

Just got a batch of aluminum tone ring castings in along with my usual batch. I had read some former threads regarding people having some luck with them. We are going to put a few on some rims for a test drive soon. The finished ring came it at just over 12oz. It will be a nice weight saver, but moreover I am doing these in aluminum so I can experiment with some fun custom anodizing and vibrant colors.

Anyone currently have one in a banjo that would like to chime in?

We are going to try a batch of aluminum flanges too for custom anodizing. I will be curious to see if turned to typical flange specs, they have the strength to hold up to the force of head tension and not distort...

Question for the scientists: With nickel plating over tension hooks, do you think there will be a galvanic reaction with anodized aluminum? One way to find out for sure.

Photo (Aluminum ring on right)




Jul 22, 2020 - 8:51:54 AM
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rmcdow

USA

852 posts since 11/8/2014

Colored anodized aluminum typically has a thickness of the anodized layer of from less than a mil up to about 5 mils. The thicker the coat, the more of a green tint comes into the color the anodized layer is dyed with. The anodized layer is aluminum oxide, and is very brittle. If you use anodized aluminum for the tension hoop (I'm not sure if you were referring to that or to a flange, Gibson style), the contact point between a hook, washer, or nut is going to crack the aluminum oxide. There would then be a galvanic reaction between the hook and the aluminum, in the presence of moisture. One way to get around this is to use teflon washers, spacers, or shielding where the metal comes in contact with the anodized aluminum. The teflon serves two purposes. It is a mechanical buffer that can distribute the pressure over a larger part of the aluminum, and can possibly keep the aluminum oxide from cracking. The second part is that it is non-conductive, and there won't be any galvanic reaction without an electrical connection between the metals. This method is used in various places in the aircraft industry, which heavily relies on aluminum in the construction of aircraft. Teflon is available as very thin sheets, from .001" to .020" thick, that washers or spacers can be punched out from or cut from. As a note, the aluminum oxide coating itself is non-conductive, so if you can keep it from cracking from pressure from a dissimilar metal, there won't be a galvanic reaction. However, it is also porous, which makes this a pretty difficult task, making a teflon or other strong non-conductive and flexible barrier a better bet.

Jul 22, 2020 - 8:55:50 AM
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499 posts since 6/2/2011

I believe Rob Bishline is usuing aluminum flanges on his super light banjos. I am not sure what tone rig if any he uses on these models. I saw a set up video where Jerry Rosa of Rosa String Works installed an aluminum tone ring on a master tone banjo,

Jul 22, 2020 - 9:10:36 AM
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453 posts since 10/17/2006

I have a Kayuga (I think that's the name) with an aluminum tone ring, flange, and tension hoop. I've added aluminum coordinator rods and an aluminum armrest. I replaced the wood rim with a good 3 ply and it sounds very good. Extremely light. I polished everything with a scotchbrite buffing wheel and like the looks and sound of it.

Jul 22, 2020 - 9:17:04 AM

RB3

USA

762 posts since 4/12/2004

What was the composition of aluminum that was used for the tone rings?

Jul 22, 2020 - 9:56:39 AM

10820 posts since 10/27/2006

The suggestion to use teflon as an insulator is a good one. During the prototype stage, plumber’s tape will work nicely. When you go into production, you can work out something else.

Jul 22, 2020 - 10:12:52 AM

2924 posts since 2/18/2009

4 years ago I made a canoe trailer to pull behind my bicycle. I used 6061 aluminum angle and tubing, and galvanized steel bolts, and while I was warned about the threat of galvanic corrosion I have not seen any signs of trouble yet, even though my trailer has spent a few weeks hidden in the woods in various places in the Adirondacks, getting rained on from time to time. Given that the banjos will likely not be left out in the rain for days at a time I would think that it's not likely to be a problem, but I don't know for sure. I have used aluminum tension hoops with steel hooks with no problems yet that I know of, but those banjos were all sold before I had them for years to see what might happen.

Jul 22, 2020 - 10:26:53 AM

370 posts since 3/26/2015

All great ideas, thanks for the input. Currently using a basic cast 319 aluminum. Machines and polishes wonderfully. Been doing research on heat-treated al-mag for tensions hoops. We will see where it goes.

Nice idea on the Teflon washers!

More to come!

Jul 22, 2020 - 11:16:39 AM

jrdew

USA

1417 posts since 11/25/2007

When I first started playing, I had a 1977 or '78 Iida banjo with an aluminum tone ring in it. It was not lacking for volume or tone. I had that banjo for about 12 years and it held up fine.

Jul 22, 2020 - 11:16:52 AM
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1062 posts since 5/19/2018

What RMCDow said above.

The reaction he is speaking about just looks nasty over time. I do know it takes some time, but it happens all the same.

I know that Stelling experimented with an aluminum ring sometime back in the late 70’s or early 80’s.

The late Harry Lane, who I would consider a master builder also constructed banjo components from aluminum. I only played one. It was eerily light and a very good sounding instrument.

Aug 4, 2020 - 6:24:21 PM

219 posts since 5/13/2009

See the link. Don't see them offered at American Made Banjo.

https://bluegrasstoday.com/dannick-introduces-aluminum-banjo-tone-ring/

Aug 4, 2020 - 7:51:16 PM

3869 posts since 5/1/2003

quote:
Originally posted by SamCy

See the link. Don't see them offered at American Made Banjo.

https://bluegrasstoday.com/dannick-introduces-aluminum-banjo-tone-ring/

I had one of these rings rings my Kel Kroydon when I first converted it. I liked it ok but it was a big improvement when I switched to the HR 30.


Aug 5, 2020 - 8:38:52 AM

219 posts since 5/13/2009

I think the density of the metal makes a difference. Years ago Ode introduced aluminum rims with a cast-in arch-top tone ring. But later versions added a brass rolled rod. The brass is more dense than the aluminum.


 

Aug 5, 2020 - 12:53:57 PM

Enfield1858

England

19 posts since 8/1/2020

A factor that needs to be allowed for is that the material we refer to as 'aluminium' is very rarely pure aluminium (which is very soft);  it's almost always an alloy, with the other metals and their proportion chosen to give the required characteristics.  In other words, much the same as brass and stainless steel - in both of which there are more different blends than you could shake a stick at!

Another point crossed my mind when reading this;  the fact that, even in cold climates, there are always traces of sweat on our skin - which makes an ideal electrolyte for a galvanic reaction (which is effectively a battery).  Imagine what it's like near the coast of Florida in late summer! A table called the anodic index gives a guide to the voltage which would be generated by two dissimilar metals;  the higher the voltage difference, the worse the corrosion is likely to be.

I quote: "For normal environments, typically there should not be more than 0.25 V difference in the Anodic Index.   For harsh environments, such as outdoors, high humidity, and salt environments, there should be not more than 0.15 V difference in the Anodic Index."

Castings have a voltage of 0.9 Volts if made of an Al/Silicon alloy, 0.95 Volts if other alloys.  Nickel has a voltage of 0.3 Volts - a difference of at least 6 Volts looks like trouble.  To put it in context;  boats with steel hulls use sacrificial anodes made of zinc - so in water, the zinc is eaten away and is electro-plated onto the steel hull.  The anodic index difference between those two metals is only 0.4 Volts - but it's enough to do the damage shown in the attached photo.

HTH
Jack


 

Edited by - Enfield1858 on 08/05/2020 12:55:59

Aug 5, 2020 - 3:58:46 PM

Enfield1858

England

19 posts since 8/1/2020

quote:
Originally posted by Zachary Hoyt

4 years ago I made a canoe trailer to pull behind my bicycle. I used 6061 aluminum angle and tubing, and galvanized steel bolts, and while I was warned about the threat of galvanic corrosion I have not seen any signs of trouble yet . . . 


But in that case, the aluminium was in contact with zinc, not with nickel (galvanised steel is steel plated with zinc), so the anodic voltage difference is 0.3 Volts - only half what it would be if you had aluminium in contact with nickel;  secondly, the metal which would be eaten away by any galvanic action would be the zinc coating on the steel bolts, not the angle or tubing.

With best regards,
Jack

Aug 5, 2020 - 4:17:44 PM

55423 posts since 12/14/2005

I seem to remember that outboard motors had a little hunk of SOME kind of metal, designed to somehow sacrifice themselves, to draw the current and/or corrosion away from the good bits.
Any way to work that principle into a banjo?

Aug 5, 2020 - 5:09:22 PM

Jbo1

USA

953 posts since 5/19/2007

Corrode the banjo tune until just the good bits are left?

Aug 5, 2020 - 5:32:01 PM

nakigreengrass

New Zealand

5181 posts since 5/16/2012


I would be more inclined to use zinc ( perhaps tin ) plated mild steel hooks.....that combination is close on the galvanic scale.  It does depend on the Aluminum composition...but  Aluminum... will likely act as a anode when in contact with nickle if there is any damp around. ( corrosion under hook ) 

I've played around with casting aluminum for resonator spiders, and have found the grainy heavier grades of Ali are the best. (old pistons sound great )    Not so much for the tap tone, which I don't think means much, but because, the ring needs enough mass to compete with the timber dampening effect.  I would guess a light weight timber rim would work best with an Ali tone ring.

PS.  Lanacote..... is the very best product that you can use to stop galvanic corrosion between metals....us off shore sailors swear by it.

Edited by - nakigreengrass on 08/05/2020 17:42:23

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