Path: ...!weretis.net!feeder9.news.weretis.net!news.quux.org!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: Frank Krygowski Newsgroups: rec.bicycles.tech Subject: Re: Machine Shop Date: Thu, 6 Mar 2025 12:10:27 -0500 Organization: A noiseless patient Spider Lines: 52 Message-ID: References: <4edkrj13v11bkgfpmgcr58psf6v64j906f@4ax.com> <6eqkrj5abvkm749g5sbpf4hhinchc2br6k@4ax.com> <7r4lrjhc9opmfm8p252rd3pnmvj7jb7amm@4ax.com> Reply-To: frkrygow@gmail.com MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Thu, 06 Mar 2025 18:10:28 +0100 (CET) Injection-Info: dont-email.me; posting-host="4e6e60d7ec5363b66384a0dead0ef03a"; logging-data="3225448"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18U/k1Xfd4g7hiJ8NYUl05t/FfTFDFPmwQ=" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:j3wTZxTGgb+81tcmq0yQh+krry4= In-Reply-To: Content-Language: en-US Bytes: 4237 On 3/6/2025 9:31 AM, AMuzi wrote: > On 3/5/2025 2:46 PM, Frank Krygowski wrote: >> On 3/5/2025 1:51 PM, cyclintom wrote: >>> ... instead of actually looking into the science. >> >> What a weird idea. I took two courses in metallurgy as part of my >> first engineering degree. I taught basics of metallurgy as part of >> manufacturing courses at two different schools. I'm betting I'm the >> only person here who has used a metalloscope (although Andrew might >> have), I'm sure I've done and observed more heat treating than most >> here, and I'm sure I've done and taught more physical testing of >> materials, including testing for modulus of elasticity, elastic limit, >> yield point, ultimate tensile strength, hardness by at least 3 or 4 >> different methods, etc. >> >> Tell us about your education and experience in metallurgy, Tom. >> Especially, tell us where you were taught that plastically deformed >> metal can spontaneously return to its undeformed shape, and how that >> can happen. Nobody here believes you. >> > > No, I have not observed metallic structure directly but textbooks are > rife with diagrams and micrograph photos along with the text. (cheap at > any used bookstore). > > This is short and clear: > https://www.slideserve.com/angeni/single-crystal-slip > > I think the misunderstanding here is to consider metals as amorphous > like liquids and polymers. They are crystalline, with an ordered > repeating structure like ice not like water. Permanent deformation > exactly describes crystal slip which is a permanent change and can be > removed only by remelting (recycling) the material as Nucor does. Or for > a small area, heating and cooling only a portion (see link at end). > > Because crystal slip inherently makes the material larger by some > degree, any reshaping (such as working a dent or straightening a bend) > will not and cannot return the piece to exactly the same shape. Close > enough for many actual applications, but not perfectly the same by its > nature. > > Short overview of practical application: > https://www.hotrod.com/how-to/0709rc-straightening-sheetmetal/ Interesting. I hadn't heard of the Shrinking Disk. Not that I do any bodywork these days. My last related adventure was using a heat gun to soften a plastic rear fender to allow pushing out a dent. Much easier than metal! -- - Frank Krygowski