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From: Frank Krygowski <frkrygow@sbcglobal.net>
Newsgroups: rec.bicycles.tech
Subject: Re: Machine Shop
Date: Sun, 23 Feb 2025 10:39:40 -0500
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On 2/23/2025 9:52 AM, AMuzi wrote:
> On 2/22/2025 4:21 PM, Frank Krygowski wrote:
>> On 2/22/2025 4:06 PM, Jeff Liebermann wrote:
>>> On Sat, 22 Feb 2025 19:58:29 GMT, cyclintom <cyclintom@yahoo.com>
>>> wrote:
>>>
>>>> On Fri Nov 8 14:03:46 2024 Frank Krygowski  wrote:
>>>>> It doesn't exist, Tom. You can't pop a dent out a bicycle frame 
>>>>> tube by
>>>>> riding the bike. Thinking you can is a sign of insanity.
>>>>
>>>> If you have a slight dent in high performance steel. the tubing can 
>>>> revert to its natural shape under stress.
>>>
>>> Tom.  The only steel that might do that is spring steel (1095, 1060,
>>> 1075, 1080, etc).  Bicycle frames are not made from spring steel.  If
>>> they were made from spring steel, they would ride like the proverbial
>>> wet noodle.
>>>
>>> So, what's the SAE/AISI number for such a spring steel bicycle frame
>>> and who is selling such bicycles?
>>> <https://www.azom.com/article.aspx?ArticleID=6151>
>>> Since you claim that you fixed the dent on YOUR bicycle, could I
>>> trouble you for the maker and model number of this bicycle so I can
>>> determine steel alloy that was used?  Some photos of the dent, before
>>> and after, would also be nice.
>>>
>>> Note that I'm not talking about shape memory metal alloys:
>>> <https://en.wikipedia.org/wiki/Shape-memory_alloy>
>>>
>>> I'm also not talking about hydroforming, which doesn't work at
>>> removing dents in steel tubing without high pressure hydraulic
>>> assistance.  It's commonly used for bending aluminum frames.  You
>>> obviously don't have the necessary equipment in your garage workshop
>>> because you claimed that the dent popped out after simply riding the
>>> bicycle:
>>> <https://www.bikeforums.net/bicycle-mechanics/919494-ding- removal.html>
>>>
>>>> Where the hell do you get off not knowing the properties of tempered 
>>>> steel and commenting on it?
>>>
>>> Frank, he's all yours now.
>> Sorry, I'm going to disagree with you about spring steel. AFAIK there 
>> is _no_ steel that would spontaneously cure a dent in a bicycle tube 
>> from riding stresses. If the steel is dented, it's been stressed in 
>> that location beyond its yield point. There's no practical way for 
>> that to spontaneously reverse itself.
>>
>> While Andrew knows much more than I about the applicable shop 
>> techniques, I think you might be able to partially remove a dent in a 
>> tube if, like a seat tube, you had access to an open end. Perhaps 
>> forcing in a series of mandrels of increasing diameter could gradually 
>> force the dent outward. (Something similar is done to repair dents in 
>> the tubing of brass instruments like trumpets.) But I doubt it would 
>> give a perfect result, and I think cosmetic repair (maybe Bondo?) 
>> would be needed to get it really pretty.
>>
>> What Tom is describing is his usual mix of lying and fantasy and 
>> ignorance.
>>
> 
> Methods to form, or re form, steel are irrelevant here.
> 
> The principle is that once you're beyond the elastic limit, the piece 
> will have measurable deformation. That's a crystal slip, i.e., the 
> structure of the material has changed.
> 
> Regardless of human decisions after that (re form, cosmetically cover 
> such as lead fill or bondo, replace the damaged piece, throw out the 
> unit) the material has changed; it's not going to spontaneously pop back 
> to pre-strain shape.

Yes, that was the main point of my first paragraph. My second paragraph 
was my speculation on how a dent might actually need removed, absent the 
type of magic Tom pretends to have witnessed.


-- 
- Frank Krygowski