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  1. #1
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    Default dent removal in brass

    How could I remove small dents (the biggest is 20mm long x 3mm deep, the others are roughly circular about 6mm diameter and 2mm deep) in a brass trombone tube? Most of these dents are halfway round the curve of the tuning slide and the biggest one is in the bell. Musical instrument repairers charge dearly for doing this work so how could I do it myself? What they do is to roll a rounded steel ball over the inside of the dent and gradually increase the sizes of the balls. These tools are also expensive. Could anyone suggest a different way to do the job?

  2. #2
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    Hi Woolyhead

    Welcome to the MetalWork Forums

    To explore the remainder of the Forums do this

    Goto the FORUM box in the top left hand cnr of the page and click the down arrow. This will bring up a pull down menu that has Forum Home at the top

    Click Forum Home which will present a scroll down page.

    Our rules,the Terms of Service are right at the top ,we encourage all new members and old to read them.

    Below that are all the various areas and sub forums that make up out MetalWork forums.

    Hopefully someone who knows more than I about trombone repair will be along in due course.

    Welcome

    Grahame

  3. #3
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    Quote Originally Posted by woolyhead View Post
    How could I remove small dents (the biggest is 20mm long x 3mm deep, the others are roughly circular about 6mm diameter and 2mm deep) in a brass trombone tube? Most of these dents are halfway round the curve of the tuning slide and the biggest one is in the bell. Musical instrument repairers charge dearly for doing this work so how could I do it myself? What they do is to roll a rounded steel ball over the inside of the dent and gradually increase the sizes of the balls. These tools are also expensive. Could anyone suggest a different way to do the job?
    Hi Wooly,

    Welcome to the forum. I've been here a while, nice set of guys.

    As far as your trombone dents are concerned, you can buy steel balls, whether you can get the size that you need could be a problem. The last time I saw anything like that the steel balls were pushed through the tube hydraulically.
    Best Regards:
    Baron J.

  4. #4
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    melbourne
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    Hit you tube.
    I've had instrument repair pop up in my feed. Looks like diy is doable with a bit of bravery.

    I think the biggest question is what is at risk. Is it a valuable item, what would the consequences of messing it up be, are you wanting to just make it better /more playable, or do it up for sale...

  5. #5
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    Default Dent removal from brass

    Quote Originally Posted by russ57 View Post
    Hit you tube.
    I've had instrument repair pop up in my feed. Looks like diy is doable with a bit of bravery.

    I think the biggest question is what is at risk. Is it a valuable item, what would the consequences of messing it up be, are you wanting to just make it better /more playable, or do it up for sale...
    This trombone is not a very valuable item. About 50 pounds sterling. The consequences of messing the job up are not very much. I just want to make it look better for my own satisfaction really and see whether it sounds better.

  6. #6
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    Default dent removal in brass

    Quote Originally Posted by BaronJ View Post
    Hi Wooly,

    Welcome to the forum. I've been here a while, nice set of guys.

    As far as your trombone dents are concerned, you can buy steel balls, whether you can get the size that you need could be a problem. The last time I saw anything like that the steel balls were pushed through the tube hydraulically.
    And the ones I've seen advertised are expensive. But on the net I found this idea (diagram attached). The idea is to thump the hammer head into the stop so that vibrations travel down to the magnet and make it vibrate strongly. The claim is that the ball then vibrates and thereby hammers the dent out. But the magnet has to be very powerful to make it work. But at least the ball doesn't have to be the exact size. Anyway I can't try this idea out because I haven't got access to a powerful magnet.
    Attached Images Attached Images

  7. #7
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    Quote Originally Posted by woolyhead View Post
    And the ones I've seen advertised are expensive. But on the net I found this idea (diagram attached). The idea is to thump the hammer head into the stop so that vibrations travel down to the magnet and make it vibrate strongly. The claim is that the ball then vibrates and thereby hammers the dent out. But the magnet has to be very powerful to make it work. But at least the ball doesn't have to be the exact size. Anyway I can't try this idea out because I haven't got access to a powerful magnet.
    Hi Wooly,

    That idea is a new one on me ! It should work in theory. As far as the magnet is concerned, a dead hard disc drive out of a computer will provide you with a really strong magnet. I have several kicking about that I use for various jobs.
    Best Regards:
    Baron J.

  8. #8
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    Quote Originally Posted by BaronJ View Post
    Hi Wooly,

    That idea is a new one on me ! It should work in theory. As far as the magnet is concerned, a dead hard disc drive out of a computer will provide you with a really strong magnet. I have several kicking about that I use for various jobs.
    I didn't know computer disc drives had powerful magnets in them. That's useful information. Thanks very much BaronJ. Now I can find myself an old computer disc drive and try the vibrating ball idea out. If this works it will cost a whole lot less than a set of steel balls of the right sizes. Great news. Thanks again.

  9. #9
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    Hi Wooly,

    Extracting the magnets from a hard disc drive is not difficult ! But do watch your fingers, they bite, they don't take prisoners.

    The magnets are part of the head drive motor, there is one magnet on each side of the head drive coil. The bearings are useful as well ! The actual platter spin motor is a three phase one and not much good for anything, I throw the ones that I remove into the scrap metal bin, though I've heard that some people melt them down for the scrap alloy. The alloy frame often gets melted down as well.

    The platters make good first surface mirrors and very good reference flats, but they do scratch very easily, they are often alloy as well but there as some glass ones knocking about. They are usually the 3 inch ones.

    If you can lay your hands on an old 5 inch drive the magnets in those are big, very big and very strong.

    Good luck.
    Best Regards:
    Baron J.

  10. #10
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    Red face removing dents in brass

    Quote Originally Posted by BaronJ View Post
    Hi Wooly,

    Extracting the magnets from a hard disc drive is not difficult ! But do watch your fingers, they bite, they don't take prisoners.

    The magnets are part of the head drive motor, there is one magnet on each side of the head drive coil. The bearings are useful as well ! The actual platter spin motor is a three phase one and not much good for anything, I throw the ones that I remove into the scrap metal bin, though I've heard that some people melt them down for the scrap alloy. The alloy frame often gets melted down as well.

    The platters make good first surface mirrors and very good reference flats, but they do scratch very easily, they are often alloy as well but there as some glass ones knocking about. They are usually the 3 inch ones.

    If you can lay your hands on an old 5 inch drive the magnets in those are big, very big and very strong.

    Good luck.
    That's also useful to me. Obliged. But I did wonder whether the small ball in the tube might dent the original dent the opposite way over a small part of it and not actually remove it. I know that musical instrument repairers roll their balls (!) or slide them from side to side right across the dent and thereby avoid what I fear for what the small ball might do as it hammers straight down on to it. Not that it matters much because a rolling action would smoothe it out at a later stage anyhow. What would you think?

  11. #11
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    Hi Wooly,

    As I said earlier the magnet and steel ball method is something I've not seen before !

    The passing of a steel ball down the tube to force out a dent or crease is the only one that I know of.

    I would have thought that an electro magnet with a shaped anvil with the steel ball inside the tube would be more effective because the electro magnet could be driven with a varying frequency voltage. That would have the effect of a small vibrating hammer and would provide greater control of impact level.

    Beyond that, I don't know. If you know any instrument makers they would be the people to ask.
    Best Regards:
    Baron J.

  12. #12
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    Default dent removal in brass

    Quote Originally Posted by BaronJ View Post
    Hi Wooly,

    As I said earlier the magnet and steel ball method is something I've not seen before !

    The passing of a steel ball down the tube to force out a dent or crease is the only one that I know of.

    I would have thought that an electro magnet with a shaped anvil with the steel ball inside the tube would be more effective because the electro magnet could be driven with a varying frequency voltage. That would have the effect of a small vibrating hammer and would provide greater control of impact level.

    Beyond that, I don't know. If you know any instrument makers they would be the people to ask.
    Yes, you're right BaronJ, on several scores. An electromagnet sounds good but an anvil would have to curve in two directions at the same time. Still. it could be done. But I'll try the disc drive magnet first once I've located a disc drive. I used to have three computers in the shed but we recently took them to a dump so I'm asking around, Someone will have one I'm sure. The trombone was made in 1870 in Paris France by a firm who has now ceased to exist but present day brass instrument makers would know how to remove dents, although their idea of what's inexpensive wouldn't be the same as mine. I'll let you know how I get on. Nice talking with you.

  13. #13
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    Hi Wooly,

    I've been having a think about this based on my previous post ! Dangerous I know

    A steel ball would only be a point contact, so any anvil would not need to follow a curve but would need to have a radius to match the tube and would not need to be very long, only about the diameter of the steel ball. If the anvil were part of the piston in a solenoid the ball could be made to vibrate in sympathy with the magnetic field created by the varying current in the solenoid coil. A bit like a tattooists needle.
    Best Regards:
    Baron J.

  14. #14
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    Smile dent removal in brass

    Quote Originally Posted by BaronJ View Post
    Hi Wooly,

    I've been having a think about this based on my previous post ! Dangerous I know

    A steel ball would only be a point contact, so any anvil would not need to follow a curve but would need to have a radius to match the tube and would not need to be very long, only about the diameter of the steel ball. If the anvil were part of the piston in a solenoid the ball could be made to vibrate in sympathy with the magnetic field created by the varying current in the solenoid coil. A bit like a tattooists needle.
    Yes I suppose so but with a ball diameter of, say, 20mm, the increase in diameter of the trombone's bell (where the dent is located) would be about 15mm. So under a flat anvil, this side of where the ball strikes the other side of the brass, there would be an air gap of about 5mm on one edge of the anvil if it was held perpendicular to the centre line (axis) of the bell. But I suppose I could hold a flat anvil at some other angle so as to minimise the air gap. So when the ball strikes the inside of the bell, the brass where it strikes could balloon out a bit into this air gap. Providing the extent were not too much that wouldn't matter and it could be gently tapped back into place using a small hammer. Brass instrument repairers use some sort of fibre hammer for that. Yes it all sounds good, Thanks for the ideas.

  15. #15
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    I wonder if you could not use a VERY powerful electromagnet (not difficult to make) and use a variable power supply that lets you control the force of the ball to directly push the dents out. A bit like the "paintless dent removers" do manually (look at Youtube to see how that works - fascinating to watch!). I'm thinking of a magnet that can lift 100kg or more. Since the ball inside the tube is only close to the magnet face in one spot, and the rest of it further away, you should be able to move it about the dent slowly but forcefully enough to roll and push it out in a very controlled fashion.
    I might experiment a bit with that idea to get dents out of steel motorbike tanks and the like. Might take a stronger magnet, but that's not too tricky....
    I might start with the secondary coil and part of the core of a microwave transformer I have.... Let's see what sort of force that can generate, at controlled DC input up to where it gets hot..... Vibrating it with square wave pulsed DC might even be more forceful.....
    Anyone else got any good ideas for sourcing a very strong electromagnet without winding one from scratch?
    Cheers, Joe
    retired - less energy, more time to contemplate projects and more shed time....

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