Booger McGee - Posted - 02/26/2010:  08:52:39

Hi all,

After reading Bill Rickard's blog, I began wondering

1) How are spunover rims made?

2) Why are they called "spunover"?

3) How do builders get the wooden pot to fit so snugly inside the metal pot?

4) Is there a noticeable tonal difference between a banjo with a spunover rim and a banjo with a plain wooden rim? If so, how would you describe the tone?

Thanks!

Booger

Axeman79 - Posted - 02/26/2010:  09:23:38

Spun metal is worked on a lathe and the metal is "spun" and pushed over a mold. Here is a short video that shows the basics of the process:

http://www.youtube.com/watch?v=uhJ3...ture=related

One way to ensure that it matches the wood shape is to spin the metal over the wood blank.

Axeman

Booger McGee - Posted - 02/26/2010:  14:58:14

That was a cool video and explained a lot! What about tonal differences? Does a banjo with a spunover rim sound noticeably different from one without? If so, how would you describe the tone?

Thanks!

Booger

vernob - Posted - 02/26/2010:  17:05:54

On my two banjos, the spunover metal becomes the "tone ring" as it bends over the top of the rim. One of my banjos sounds like it has a tone ring. Plenty of pop and ring. The other is plunkier. Less volume. They are not all created equal.

Will1717 - Posted - 02/26/2010:  23:30:00

Booger:

What a topic + where do you start??
1.) First how are spunover rims made? Being a metal guy, I've spent years on the topic of spunover banjo rims and finally come to following conclusion. Very few banjo rims are truly spun rims at all. There were two types of spunover rims built originally and today. The most common construction method has nothing to do with spinning at all. Basically you calculate the circumference of the rim your building + the depth of the rim desired and shear a piece of flat brass to this size. Next you form over the edges of each side over a piece of wire. Another common way to do this is you bead over the edges with a set of beading rollers. You now have a long length of brass approx. 2.5" wide x + or - 38" long with each edge beaded over. Next you roll the length of brass (supporting the beaded edges in the roller dies) into say an 11" dia. circle. Next you silver solder the ends together and re-roll the part into a nice clean 11" rim. So far you've not spun anything but you fool everyone by saying that it's a spunover rim! This is how the majority of lower cost spunover rims were originally built and what appears to be the construction method of choice today.
Next comes what the high end banjo builders did, and this is true metal spinning. If you examine closely many old original spun banjo rims you will find that some have evidence of a metal joint at the neck area, and the higher end rims have no joint what so ever. To build a truly spunover rim you have to start with a solid round disc of brass approx. 16" in diameter x 20 to 22 gauge material. This is placed in a spinning lathe and the side of the rim is first spun down over an expandable mandrel form (11" dia. for an 11" rim). You next trim the outside edge to size and spin in an inside bead using an 11" ring x 3/16" diameter wire to form the lower rim edge, Next you cut out the opposite end while still in the spinning lathe and insert another 3/16" wire ring which ends up being the opposite edge of the rim. Because this was all spun on a expandable mandrel you next reduce the mandrel size until the rim slides off the mandrel. I've probably lost everyone by now as the process is real difficult to explain verbally or in written form. Two excellent You Tube videos explain the spinning process right through the use of cnc spinning machinery. If you watch both of these videos it should all make 100% sense to all. I've also attached a video that shows true manual spinning. The big thing to remember is that the cnc method of spinning is quite new and only realistic if you wanted to build say 10,000 banjo rims! Everything that is spun on a cnc machine was first done on a manual spinning lathe by hand tools. For building banjo rims using a manual spinning lathe is the only way to go in my opinion. Once your set-up it takes approx. 30 minutes to complete a rim. The tooling costs are the biggest concern and usually why the majority of builders don't build a truly spunover rim.
Have a look at these sites and you'll become an expert within 30 minutes, or at least fully understand the complete process. Just keep thinking banjo rims as you watch the videos and don't get side lined by all the cnc crap! I've attached the videos below.

2.) Why are they called spunover? The answer to this is in the videos but as per my above comments, to the best of my knowledge only the best of the original high end banjos really used a truly spunover rim. After that it all became terminology, such as a Fairbanks electric banjo having no electricity etc. Another way to look at it is that the term is really true banjo hype! Can't really say for sure but a truly spun rim does sound different when compared to a beaded and rolled rim. To me I feel that a truly spunover rim is close to being a tone ring in itself if that makes any sense,

3.)To install the wood inside the rim I originally spun the rim over the wooded rim but found that it damaged the edges of the rim during the spinning process + you can't nickel plate the rim after the wood insert is glued in place. The easy way is to roll a single ply insert with a scarf joint. After the spunover rim is nickel plated you just collapse the insert to fit it in the spun rim, and expand it again once it's in place. I normally use a wood panel glue to hold everything tightly together on completion. In the end if you build a fully spunover rim it ends up being extremely strong or stiff in all directions and very suitable for steel strings.

4,) This is a real hard or impossible one to answer in my opinion. A truly spunover rim sound different from a rolled a beaded metal rim and different again than a wooden rim. They all have their own sound and it ends up with the golden question. Do you like the sound? Is it for you? It's like comparing a M. Benz to a BMW, or Audi, or Buick. They all do the job and all have their followers and supporter!

Hopefully this puts some light on the topic. But it's just my perspective and could certainly be challenged. All in all, working with metals and spinning metals is an extremely interesting topic! As they say, "So many things to learn and so little time"

Bill Rickard

Edited by - Will1717 on 02/26/2010 23:36:09

VIDEO: Turn To Metal Spinning - Part 1 (click to view)

VIDEO: Turn To Metal Spinning - Part 2 (click to view)

VIDEO: the art of metal spinning (click to view)

Bisbonian - Posted - 02/27/2010:  00:32:28

Wow. Excellent answer. That's why we're here.

vernob - Posted - 02/27/2010:  03:01:45

Leave it to Bill, eh?