Cast iron laps - correct depth/spacing of grooves? - Page 4
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  1. #61
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    Quote Originally Posted by ballen View Post
    Yes, I do, a friend sent me a number of small bags of SiC in grits from very coarse (sand!) up to very fine (2000). What grits would you suggest? Will this embed in the cast iron or just wash off?



    That's exactly why I am making these laps, I want to correct my 800 x 1200 surface plate, which is concave and 11 microns deep in the middle. I've gotten good enough with my Talyvel now that I can do a reliable 8x12 grid measurement of the entire plate in about an hour.
    1. Some WILL embed in the cast iron. The final lapping with diamond powder will shave them off.

    2. But then why go through all THOSE motions ??????????????????????????????????????????????????
    Identify the regions you need to lower and start rubbing at THEM with whatever heavy thing you've got. Much quicker.
    11 microns is nothing.

  2. #62
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    Quote Originally Posted by ballen View Post
    Yes, I do, a friend sent me a number of small bags of SiC in grits from very coarse (sand!) up to very fine (2000). What grits would you suggest? Will this embed in the cast iron or just wash off?
    I'd start with 400 grit. As Orbital77 says, some of it may embed, but I found that it didn't embed to any noticable extent on my cast iron lap when I used it on my HLV lathe bed after flattenind it by spot-ginding.

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  4. #63
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    Keep in mind, the SC grains keep breaking down and get smaller leaving finer finish, as you go.
    A wet lap cuts fast, as it dries, the grains break down finer, and the action begins work hardening the surface.

    1930s Harley Davidson engine main bearing and connecting rod lapping tools, with cast iron cylindrical heads, and spiral grooves.
    Old but high precision.

    roller bearing clearance was specified to ,0008".
    Last edited by donie; 05-06-2021 at 01:09 PM.

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