Here's Alan's information:

Being the parent of a high school sax player that prefers vintage saxophones, I've had to become a bit of a sax tech to keep him humming along while still paying the mortgage. While dents don't affect the sound at all, they're not very nice to look at, and while the instrument it torn down for service, I found it hard to put it back together without at least attempting some dent removal.

I've learned that it is possible to repair dents with neodymium magnets and steel balls. For the right situation, it is like magic. The ball goes inside and the magnet on the outside. The pull is so strong that the ball rolls out the dent perfectly. The advantage over dent removal rods is that you can't cause an "outie" because the ball can't go past the magnet.

The downside is these magnets are very strong and potentially dangerous.

Here's some before and after pics of a sax dent and the magnets and balls.







That magnet is so strong that moving it 1/8" closer to the balls would initiate a startling collision. The deal with these magnets is that the attraction increases exponentially with reduced distance. So by the time the ball gets 1/2" from the magnet it is traveling fast enough to break a finger or pinch off a piece of skin. You can't just throw it in a drawer. I store mine in the corner of two walls and the ceiling where a metal joining plate must be.

drgary wrote:That's amazing. Thank you! How are such kits listed for purchase?

Kits are available, but they are $4-500+.

You want at least an N50 magnet. You can use this one:

http://www.magnet4sale.com/n50-neodymiu ... h-magnets/

and then buy steel balls of the size you need from Amazon for $10 a piece, give or take. It's best to make a handle for the magnet. Separating it from the ball can be a workout. I use a 1" x 6" piece of steel round bar epoxied to the magnet.

If you find that particular magnet is not strong enough, you can get a 2nd and stack them. Magnetic force doubles with double the thickness up to the diameter. In other words a 2" diameter magnet 1" thick if doubled will double the force. If you add another 1" thick magnet it does not and is a waste. Disclaimer: once you stick them together, you will not easily separate them. Warning: be very careful sticking them together. Sliding one off a table onto the other is recommended. Make sure any body parts that you want to keep are not in between.

Also, I think this process will only work on non-ferrous materials.

Also, it's a good idea to put something on the magnet surface to inhibit scratching. Felt, Teflon sheet, something.


Moderator note: During my rebuilds and restorations I've often gotten stuck trying to fix metal dents. I'm starting this thread so these techniques can be found in one place. During the past few days I've newly learned of a technique for removing dents in musical instruments using magnets and metal balls. With the permission of the Alan (H-B member Almico) I'm moving his description to this thread so it can be easily found. drgary

In an earlier thread I was trying to fix dents on the case of a Cremina I was restoring. I'm linking it here. This is one of those how-to threads where photos are really helpful to those of us learning how to do this.

How to Fix Dents in Metal Case?

Almico wrote: Also, I think this process will only work on non-ferrous materials.

I guess that makes sense. The metal you're trying to undent needs to be non-magnetic, otherwise you'd risk creating an "outie" dent or deforming it when you pulled the magnet away. Right?

I got briefly excited thinking I could use this process on some hail dents on my car, but I don't think it'll work.

I worked for a while at a viscometer company who used these magnets in the design of their instruments.
When these magnets are in multiples the danger was even worse due to the increase in attraction when unlike poles became close. We had to wear heavy leather gloves when handling them.

They were used to support a torque sensor element without friction, greatly increasing sensitivity and accuracy.

They should not be allowed to come near to electronic equipment, particularly those using iron oxides, such as hard drives. Several workers found this out the hard way.

The use for dent removal is an extra nice application of technology, very creative.

*squint's at the axe* Conn?

Holton.

jccavanaugh wrote:I guess that makes sense. The metal you're trying to undent needs to be non-magnetic, otherwise you'd risk creating an "outie" dent or deforming it when you pulled the magnet away. Right?

I got briefly excited thinking I could use this process on some hail dents on my car, but I don't think it'll work.

I think the issue is that the magnet will just stick to the metal you're trying to straighten and you will not be able to move it back and forth to allow the ball to do it's job.

It work on copper, brass, aluminum and maybe some stainless steel alloys that are non-magnetic.