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  1. #1
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    Ueee is offline Blacksmith, Cabinetmaker, Machinist, Messmaker
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    Default Scraping, the spin test.

    Hi all,
    Not having been to one of the scraping classes (yet) i am wondering on the method used for a spin test. I found another forum with a brief note on the item spinning from 1/3 off each end when pushed from the opposite end, but it is all i can find.

    I ask as soon as i put my scraped cheap China level on the new surface plate it felt like it was "floating" on a central point. I spotted it on the very thin blue that is on my little plate and it has contact full length. There is however 2 spots in the middle where stoning has completely removed the scrape marks (2nd pic). They don't pick up any blue though.

    I have shot a vid of a test somewhat akin to R.C's straight edge sag test but i cannot measure any lumps with a 10th indicator.

    I have cut the first 2 min off the video as it was mostly me not being able to get consistent readings.....

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    1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.

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    Hi Ewan
    "and it has contact full length"
    Well I hope you now know why you do a spin test

    How did you flatten your stone?

    Stuart

    p.s. No pictures

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    Quote Originally Posted by Stustoys View Post
    Hi Ewan
    "and it has contact full length"
    Well I hope you now know why you do a spin test

    How did you flatten your stone?

    Stuart

    p.s. No pictures
    Pics added.....

    The stone was flatened with AlOx grit on float glass.
    1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.

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    You can get blue the full length, but how do you know you are not rocking the workpiece....

    That is what the spin test is for, you get blue full length and the workpiece pivots about a third in from each end, then you know what the blue is telling you is accurate...

    Of course this only holds belief for symmetrical workpieces.... If you have say a right angle triangle, then as all the weight is at one end, your pivot points should reflect this weight distribution...

    http://www.users.on.net/~rcre/other%20files/pivot.wmv
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    Hi Ewan,
    Thats not how you do a spin test but RCs video should clear that up.
    I'd use a little more blue than that to start with*. Though I'm not sure I would start scraping with my level(though it shouldnt hurt really I guess lol)

    Stuart

    *though blue is tricky to get pictures of.

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    The level was not very good when new. I scraped it when i got it. The blue is thin, but not as thin as it looks in the pic.

    Thanks for the vid R.C, that explains it, i think it will fail and spin from the center, just going by how it feels. I'll try tomorrow.
    1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.

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    Quote Originally Posted by Ueee View Post
    Thanks for the vid R.C, that explains it, i think it will fail and spin from the center, just going by how it feels. I'll try tomorrow.
    You did pick up from the video, you only push it at each end? Rotating it like you were doing in the video, spinning it from the centre, it will do that every time, even if its perfect, that's just inertia.

    Regards Phil.

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    Thanks Phil, got it now
    I searched for a video but came up blank. Like always there are probably plenty out there but i used the wrong search terms.

    The funny thing is if you sit it across the little plate is moves perfectly, a 1/3 from the end, but on the big plate it moves closer to the middle. I may not have been testing correctly but i knew something was wrong just be the way it moved......
    1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.

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    Default A follow-up question, if I may your worship...

    So every time we check levels we find room for improvement on the factory ground surface. How would you then check the involute groove? Blue up a known true cylinder and check the marks? Or perhaps levelling a shaft is a less fraught procedure where a handful of microns don't matter?

    Greg
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    Greg, I stand to be corrected, but I would suggest inverting the level so that either a ground shaft or dowel pin can sit in it and then use a depth micrometer on some parallels to check that it is parallel to the flat lands either side.
    Flatness and that you have a co-planar relationship between the two ends can be checked with a straight edge or the edge of your surface plate.

    Michael

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    Default

    Great Video here of Wyler doing it. Mandatory viewing.

    Symbiosis high tech and mechanical art (handcraft) - YouTube

    Those fixtures must be mounted to foundations. Seems 6 – 8 blokes working there. It would drive you nuts if they kept moving.

    I’d imagine if you had a really smick cylinder square, you could tune your surface plate up until the level read zero – zero on the flats, then check the Vee on the cyl square on the same place on the table.

    That will only give you line contact, so you would need a prism, or you might get away with smaller parallel’s to scrape the vee.

    Same could be done on the vertical faces of a box or triangular level. Using a granite square and the cylinder square.

    All conjecture, because I've never checked mine. I don’t believe I've ever used a level on a shaft.

    Regards Phil.

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