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From: Frank Krygowski <frkrygow@sbcglobal.net>
Newsgroups: rec.bicycles.tech
Subject: Re: RE: Re: Machine Shop
Date: Wed, 5 Mar 2025 16:07:39 -0500
Organization: A noiseless patient Spider
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On 3/5/2025 2:01 PM, cyclintom wrote:
> On Tue Mar 4 12:03:42 2025 Frank Krygowski  wrote:
>> On 3/4/2025 12:44 AM, AMuzi wrote:
>>>
>>> For a typical dent, this Waterford for example:
>>> http://www.yellowjersey.org/wfd12a.jpg
>>>
>>> the tube is rolled to reform the greater part of the deformation:
>>>
>>> http://www.yellowjersey.org/wfd12b.jpg
>>>
>>> then the remaining low spots are filled with polyester bondo or with
>>> metal (brass, silver, lead. I use lead):
>>>
>>> http://www.yellowjersey.org/wfd12c.jpg
>>>
>>> and finished:
>>>
>>> http://www.yellowjersey.org/wfd12e.jpg
>>
>> Could you explain what's meant by "the tube is rolled"? As I said
>> earlier, I'd thought the first step would be pushing a mandrel through
>> (if the dent was in the seatpost) to partially push out the dent. Of
>> course, that wouldn't work except on a seat tube, and I suppose would
>> still require filling. Are you skipping that step entirely?
>>
>> BTW, my antique BMW has a slight dent in the top of the gas tank,
>> apparently from something falling onto it. I've heard of "paintless dent
>> repair" for car bodies and wondered about it, but never looked deeply
>> into it. I gather that some skilled body workers can do pretty well at
>> pushing dents back out from the underside.
> 
> 
> 
> 
> Have you got this now? Skilled body workers sometimes find a dent that they push on from the opposite side and the dent pops out. Wait a minute - you are all saying that is impossible.

Tom, if you apply a force in the proper direction, you can move metal in 
the proper direction. Nobody's doubting that. It's usually impossible to 
just push it precisely back to its original shape, because the crystal 
slip of yielding that Andrew referred to normally produces some stretch, 
so it's like you end up with a little extra metal area. (Skilled car 
body workers can use a torch and hammering to "shrink" metal back, but 
AFAIK it's a complicated skill requiring access to both sides of the 
metal.)

What we're all disputing is that your dented tube spontaneously returned 
to anything close to its original shape. That did not happen. It's 
impossible. I think the most likely explanation is that you _imagined_ 
that it was dented, maybe due to some trick of lighting.

Next time a miracle is coming your way, please take before and after 
photographs.

-- 
- Frank Krygowski