TubeNet

Are the "dent erasers" only available to repair techs? How much do they run and are they ever available "used?" Thanks!

Careful here...

These are still tools that you need practice with to become proficient in their use.

It is very easy to "over-do" it with magnets. They are a great tool, but not magic.

Google "MDRS"

Thanks for the responses guys. My thinking was this: The local repair shop has one of these and the guy quoted me between $300 and $400 for a complete dent removal on my King I've been posting about. I was going to pursue one of a few ideas I had;

1) See if I could "rent" the magnet/balls and time in his shop to work on the horn myself and have him watching and helping.

2) See how much dent removal he would do for only about $100-150.

3) Since this horn was/is a "beater" I considered buying a magnet/ball set myself to get the practice without fear of destroying a several thousand dollar horn. That way I'd have it around for future use after I get the hang of it on my cheap horn.

Anyway, those were the thoughts I had on the matter. Thanks for the search tip Kevin, I found the site and they go for $450 now for the "Apprentice Kit."

Go here and buy two of the biggest magnets you can afford and shove 'em into a piece of reinforced vinyl tubing. http://www.forcefieldmagnets.com/catalog/ I use two of the 1 5/8 dia x 1" for most stuff. I also use a single magnet sometimes.

Then... go to McMaster-Carr and buy solid steel balls in sizes 1", 1 1/4", 1 1/2", 1 3/4", 2", 2 1/2", and 3".

Have fun and don't tear up too much stuff learning what magnets will and won't do.

I own a king 1241 and the magnets will help a bit with the bottom bow that isn't covered by the bow guard. The magnets will also help a little bit on the first branch. There really isn't much exposed tubing that the magnets will tackle in my opinion...

Pm sent

TubaTinker wrote: Have fun and don't tear up too much stuff learning what magnets will and won't do.

Dan:

Before everyone reading this runs out and buys some of these things to play with ...

I'm curious what you can say about potential dangers and reasonable safety precautions with these things. Like ... I presume that if you have an implanted pacemaker or defib (my son does), using these would not be such a slick idea. Do you have any information about their likely effect on implanted orthopedic devices (e.g., artificial joints or various kinds of implanted braces)? I presume the force acts according to the usual inverse square relationship, but if you have an artificial (mostly steel) knee or hip and manage to get the magnet close enough ...??? And then there's the issue that I always run into when anyone wants to do a head/neck MRI on me: If you use a grinder (who doesn't), they always want to do an x-ray to be sure you don't have any ferrous particles that the magnets could rip out of your eyeballs.

What -- roughly -- is their "working distance" (beyond which the force becomes relatively negligible)? Also, how can you store them to reduce the size or strength of the field surrounding them?

Do you have any pointers to literature on this? Most of the stuff I've seen is along the lines of "Look out. These things can be dangerous." Not very quantitative.

Also, I wonder if you've thought about making an electromagnet rather than using the rare earth ones. It would seem to offer some advantages.

ghmerrill wrote:Do you have any information about their likely effect on implanted orthopedic devices (e.g., artificial joints or various kinds of implanted braces)? I presume the force acts according to the usual inverse square relationship, but if you have an artificial (mostly steel) knee or hip and manage to get the magnet close enough ...???

Most implanted metal is titanium (non-magnetic) or stainless steel (also non-magnetic). For example, I have 7 screws and a plate in my right index finger (they are pretty tiny), and they have no effect whatsoever with magnets.

YMMV. Be careful if you have metal implanted.

Also, I wonder if you've thought about making an electromagnet rather than using the rare earth ones. It would seem to offer some advantages.

It is very hard (or nearly impossible) to create the same magnetic field with electromagnets, as can easily be done with permanent (rare earth) magnets. It can be done; but to get over a tesla with electricity requires lots of work. Lab magnets of that strength tend to weigh hundreds of pounds, and require massive power supplies.

Thanks. Useful info.

I did wonder about the stainless steel issue. The titanium issue is a bit tricky since some implanted "titanium" devices are really titanium and some are merely titanium-coated (on a surgical steel substrate). But those too should be non-magnetic (relatively, at least).

Capping with PVC seems a clever approach. I suppose that if you are careful to always cap the same pole you thereby avoid ( or significantly reduce) the danger of magnet-magnet attraction.

Ya gotta love the French ... Here's a video of magnetic dent removal with class -- and background music, of course: http://www.youtube.com/watch?v=LJi_QzGY--k.

K & J Magnetics is another potential source, and they the provide some technical info. The force associated with a steel plate is not exactly the same as to a ball, but you can see the general magnitude of what you're getting yourself into....

After selecting a magnet that interests you, go to the technical info tab for that item and you can select various graphs that show the relationship between distance and force. Example:

http://www.kjmagnetics.com/proddetail.asp?prod=DX8X0


Alan

Getting your fingers pinched at 50+ lbs seems silly, too. along with the inevitable attempts to pry off the stray items/material that will migrate to the magnets?

Looks OK only for a quick & dirty rough-pass, if that is all that is expected. There appears to be a very marginal level of control over the results of the work if you're trying to do a proper job of it.

Maybe experienced users get better-than-youtube results

Re the video:

Really, guys, I just thought that video was hilarious. Way too serious here. Brass repair to lounge music? Too funny. Everybody knows that C&W is the way to go for brass repair. But definitely classical for woodwinds and strings.