DOC and Holding Tight Tolerances - Page 2
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  1. #21
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    I don't like finishing cast iron with any inserts that are honed edge. That would be nearly all of them so I grind the chipbreaker off the top to have a neutral or negative rake sharp edge. It will last a long time and cuts without deflection. Probably allow .25mm to remove for the finish. If the cutter has to enter the rough cast surface, try to chamfer that edge a bit with the U drill before going to the finish tool.

    I have even used top notch grooving tools to finish cast iron and bronze so that I can boost the feed a little and get a smooth surface.

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  3. #22
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    With a through bore you can cheat the nose radius problem by adding SCEA (side cutting edge angle). It also has the advantage of chip curling out in front of the tool and away from the (just cut) bore wall. ASTM class 45 & 50 will make chips (in addition to the free graphite & carbides dust).

    I’m also in the camp of 2 similar (pressure/depth) cuts. They don’t have to be the same tool, but you adjust the semi-finish size (if needed) to try and extend the life of the finish tool which may start acting up with a very small wear land change.

    Finish tool → I’ll assume these castings are in 220-260 brinell hardness condition. ASM & Metcut both agree that for turning & boring this stuff, a 35 minute tool life is the (productivity/cost) sweet spot. This using C2 carbide running between 220-260SFPM and allowing a .010” wear land (you’d have to adjust that for coated).

    That’s a starting recipe anyway, salt to taste

    Good luck,
    Matt

  4. #23
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    depends very much on
    .
    length to dia ratio of boring bar
    finish of hole bored
    tolerances needed
    .
    often cause of length to dia of boring bar i am limited on what maximum it can take for a finish cut and leave a reasonable finish at tolerance needed
    .
    most times if you try to take 0.5mm you get a bad finish and often hole is tapered and or out of round, a boring bar will make a truer hole but if it starts with bad taper and or out of round it usually has some error left from the roughed bore.
    .
    when tolerance is +/-.05mm or .002" (not tight tolerance) often i will take a
    -.003" or .075mm cut and measure hole and adjust for final cut
    many times bore will be within +/-.025mm or +/-.001"
    .
    as for sfpm or rpm rarely has it got anything to do with limit on carbide insert. most times you have to limit rpm and amount you take DOC so you get a reasonable finish and tolerance on bore. obviously i have data of 1000's of feeds and speeds on standardized setup boring bars and got data on what works good and what doesnt work ok. all the longer length to dia boring bars got many settings recorded with vibration finish problems indicating practical limits for repeatable results.
    .
    i save vast hugh amounts of time and am massively more productive by using history to learn from the mistakes of the past. human memory rarely can accurately remember 10,000's of things that happened over the decades. a computer can accurately "remember" millions of things far faster and more accurately than any human. i had a former boss say anybody can make a mistake but what are you going to do to prevent making that same mistake again. usually got to change things to prevent repeating mistakes.
    .
    and vast amounts of data says often humans are repeating mistakes they made before but just dont remember those mistakes being made before

  5. #24
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    Think about it this way. Would you spend (invest) $185 to save $60,000 overall? Consider looking at cost-per-hole & you might see things differently?


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