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Stock material design standards

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  • Stock material design standards

    I hark from the era of drafting tables and slide rules.
    It was impressed on me to always use fractional notation for relatively coarse work, decimals for fine, and of course reference to the tolerance box when it got to the nitty gritty.
    All before metric- there had to be a compelling reason for a variance from the above, say you had to spec a bearing bore, since most rolling element bearings have a metric lineage the callout would be the odd conversion number so the machinist proceeded with his standard tools and inspection.

    My neighbor wanted his Homart (Sears) concrete mixer repaired. Unknown vintage, but everything is stick welded so I'd guess 60's or before.
    The bearings that the spur gear run in are brass, .750 bore x 1.515 OD.

    Any ideas on why this is?
    The shell is steel, a bit egged from the weld but has tool marks in the bore.
    Not standard DOM
    Bar stock for the brass would require turning from next nominal size up
    Doesn't seem the economical way to make the thing.

  • #2
    I work in a screw machine shop and it's common to buy in 1/16 or even 1/32nd increments and turn down to clean up the exterior. Cold rolled stock is probably not good enough for this bearing application during production assembly. Doesn't mean it won't work for a repair but it's bad practice for a shop making lots of parts. Had we made this size, we would purchase 1-9/16" bar (1.5625 - 1.515 = .0475). Then you are taking off almost .025 per side, which is enough cleanup to remove scratches and dings that might be present in the bar and insure that no out-of-round condition exists.
    Last edited by HWooldridge; 11-03-2016, 10:50 AM.