Using a grinder to 'scrape' a hardened part - Page 3
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  1. #41
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    Heat would be a factor if making burns all over one side of a part..likely that would cause stress in compression and draw the part to wish to relax in concave shape over time..so a softer wheel or disk the better choice.

    On the other hand if the part was full of stress then cool grinding one side might relieve surface stress and make it wish to go the other way,.

    Guess one would have to deal with change if it comes.

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  3. #42
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    Quote Originally Posted by challenger View Post
    I'm not looking to argue the validity of temperature impact on moving metal in regard to scraping. Seems there are plenty here that agree that temperature IS a factor that needs to be watched so this has nothing to do with temperature.
    My question is about you project. These are covers right? In other words these don't need to be precision scraped to a reference and then mated with another moving, or non moving part correct? I guess perhaps they still need to be precisely fit to whatever they are covering but not in the sense that they need to be to the same level of precision AND have other characteristics such as bearing points etc??? If this is the case, and judging by the size of the parts in the photo, it doesn't seem as if they are thick and/or heavy enough to be stable. These look as if they would easily "bend" while handling them during scraping. Seems to me, and this is ONLY from what I've been reading, that the simple act of hinging these on a surface plate could make them change shape???
    These are just questions BTW. I'm not casting aspersions or telling anyone they are doing anything improper.
    Thanks

    Galaxy S4, Slimkat
    If I wasn't married I'd quit fishing

    That one is the plate that can be seen as the top part of the box way for the ram on this picture of the same type of shaper that I've linked to from Tony's site:-



    It is in contact with the ram as it moves back and forth, so must have flatness and bearing suitable for a sliding surface. But in this case, an even better finish is needed initially, since the only way to adjust the fit of this type of way is to remove metal from the mounting face of the main casting until the cover plate can pick up blue from the ram surface (or vice versa) or to remove metal from the ram (or the bottome face that the ram rides on), if one has gone too far. Thus, the plate is being used as a master to check the ways fit. Obviously, the straight edge and surface plate are used to maintain flatness when scraping the main casting or the ram, but the plate is needed as a transfer once the clearance is less than the 1.5 thou that can be judged with feeler gauges.

    A good fit is needed, since on a heavy cut, the ram can be pushed up by the tool and any clearance will produce chatter and/or inaccuracy.

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  5. #43
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    Thanks for the explanation.

    Galaxy S4, Slimkat
    If I wasn't married I'd quit fishing

  6. #44
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    Quote Originally Posted by dcsipo View Post
    It is not just deep beliefs, but also deep gauges . If you ever used a grinder on cast iron, you know how easily it can gauge the surfaces and go all over the place. I just cut up a casting using and angle grinder and it is like sinking a hot knife into butter .

    dee
    ;-D
    Yeah Ive had some experience cutting up CI and agree that progress is quick. But I didnt let that experience stop me from trying it on the lathe bed I linked in the reply to ewlsey. I removed 0.006 in short order with a grinder.

    Beliefs are far more powerful than any angle grinder, we should use them with great care

    Ive an 18" x 18" surface plate coming my way soon that i plan to use as a granite lap. With a bit of luck itll be well wonky, we can have a carve up with a grinder and see whats really what


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