[Dog Pants]

Hi all,

I recently repaired a trumpet that had taken a high dive onto a concrete floor. As a result, the bell was mangled, twisted and badly creased.

The school band committee took it to a local music store and were told it was a write off.

Anyway, I straightened it using the Ferree's Trumpet Bell mandrel and the Votaw Universal Dent Soldier.

The school band committee were really wrapped in the result.

I was happy that I got the Trumpet back into shape but The finished work had several "scars" that look like stretch marks on a beer gut.

I used lots of vaseline (petroleum jelly) and grease proof paper and tried to only work as gently as needed to work out the dents. I was worried that the amount of rolling and burnishing required to iron out the dents and re-shape the bell would leave the brass work hardened and brittle.

I've been told by a fellow repairer that these scars are unavoidable and that the only way to get rid of them is to buff them out and re-lacquer the bell. If the metal is already thinned from all the work, is there not a danger of buffing the bell to the point where it is both thin and brittle?

Is there a better method than the one I currently use? Can I hand buff the worst of it by ragging? Is spray can lacquer a worthwhile option?

I ask because not only do I want to improve my work, but as a result of the work I've done for a few school programs, I've been allocated the repair and servicing for another school with a huge fleet of instruments, many of which are large brass and covered in dents.

Thanks

DP

 

[Stephen Howard]

You have to understand the 'anatomy' of a dent. When something impacts the brass it forces the metal out of its existing plane, and in so doing stretches it very slightly. When you try to shift the metal back you stretch it again. If you add this factor on top of local stress hardening and the various leverages in play as the dent gets pushed out, it's no wonder that there's nearly always a visible remnant of the dent.

How successful you'll be depends largely on your skill - but there's an awful lot of luck involved. If the metal's soft, if the dent is shallow, if you place the tool just right on your first run then there's a good chance it'll come out almost perfectly - but more often than not the metal is hard, the dent is deep and angled and the tool just doesn't seem to want to stay put right where you need it.

Sometime you have the chance to improve matters by annealing the metal - and this works very well - but it can only be used in certain, and rare, circumstances.

I've seen 'perfect' dent work - it's easy enough to spot as the exterior is flawless but the interior is marked by the dent tools. This means, in most cases, that someone's filed or buffed the surface, and that nearly always leads to more significant problems in later years. On something like a bell, where it's possible to file both sides of the metal, the results can be disasterous.

My own approach is to leave the 'witness marks' alone. On an unlacquered instrument it's acceptable to do a very light buff to flatten out any small scratches (though a hand polish will suffice), but I wouldn't do any more than that.

Spray lacquer is an option, but you can rarely match the original finish, and I tend to reserve it for patching up small spots after solder work on relatively new horns.

School work is an excellent training ground for dent work - I'm currently working on a school bari that has a bell that's got so many dents it's practically just one big dent. I'll get it into shape but the mark will show - and it'll be back next year with just as many dents in it...but because I haven't removed any metal I'll be able to get them out again...and again...

Regards,

 

[abadcliche]

Well said. Another vote here for leaving "witness marks" if they come up.

If you have dentwork done, you'd rather have the interior of the bore perfect and some witness marks on the outside. Too often, what is perceived as good dentwork due to filing and buffing on the outside is actually a rippled mess on the inside where it counts.

 

[slausonm]

Well said. Another vote here for leaving "witness marks" if they come up.

If you have dentwork done, you'd rather have the interior of the bore perfect and some witness marks on the outside. Too often, what is perceived as good dentwork due to filing and buffing on the outside is actually a rippled mess on the inside where it counts.

Hmmmm... more often bad dent work is just bad dent work. Due to the already thin nature of instrument metal, a dent or ripple on the inside is also on the outside. I would leave the finish scratches on the outside as well.

 

[abadcliche]

Due to the already thin nature of instrument metal, a dent or ripple on the inside is also on the outside.

Yep, I'm saying a lot of time its buffed smooth. And good dentwork can leave marks- a scratch from the impact, crazing of the lacquer, etc. So how it looks on the outside to the untrained eye is not necessarily reflecting its state of perfection on the inside.

 

[slausonm]

Yep, I'm saying a lot of time its buffed smooth. And good dentwork can leave marks- a scratch from the impact, crazing of the lacquer, etc. So how it looks on the outside to the untrained eye is not necessarily reflecting its state of perfection on the inside.

Lipstick on a pig