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I have a few lapping questions, I know little about this subject.

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  • I have a few lapping questions, I know little about this subject.

    Hello forum folk's ... I have been involved on the fringes of a hydraulic
    motor manufacturing company for a number of years. A little production here and there.
    Cutting out nylon gaskets, punching some thin sheet-metal parts etc. Well this comapny has lapped
    a few of the part for this motor. The lapping machine they have was bought 20 years ago and it was on
    it's last legs then. It is a lappmaster 20 (20" platten). it has three ring that are held equaly around the disc.
    the motor "rotors" fit very loosly in these rings. As they were being lapped they had a tendency
    to like swing back and forth inside the rings. My question is, we have an oppertunity to purchase a
    Lappmaster 15 (15" platten). It also has three rings but they are smaller. I can allready predict that this
    pendulation or swinging will be just about completely dimminished. Is this OK, or it this action bennifiacial?
    These machines are not cheap even used. I'd hate to advise this purchase and have the process go south.
    Thank you all agin for your time

    Kind regards

  • #2
    Lapmaster general outfitting

    Common practice for Lapmasters and clones is to place parts in carriers, that is, in snug openings in phenolic disks having a small clearance in the conditioning ring. The parts while free to float in their carrier openings are rotated by the net drag of the lapping face. You can find a ton of Lapmaster related material on Google.

    I'm always a little guarded about answering Lapmaster questions. The damn things look so simple few operators bother to read the manual on how to use them and few shops provide the necessary resources or administration for their efficient use. Operators are new guys on trial or defaulters being unofficially punished. There are a lot of tricks to maintaining parallelism, adjustment and truing, dealing with spent lapping media, abrasive storage and handling, cleanliness and housekeeping.

    For example, the face of the lapping disk never stays flat for long. It has to be tested with a straight edge every shift and the conditioning rings are adjusted in or out as needed to correct domed or dished conditions respectively. The object is to keep the disk flat to 0.001”.

    For another example, a Lapmaster will run forever so long as the table segments and conditioning rings are replaced before worn to nubbins.

    For yet another example, changing abrasive grit is a huge PITA because of the cleaning time and run-in to ensure the old coarser grit is flushed away. It's better to have two separate machines; each with its preferred grit.

    Also the general purpose lapping vehicle sold by Lapmaster is closely approximated by twenty parts de-odorized mineral spirits and one part hydraulic oil.

    Lapping is a very dirty process. Housekeeping is vital for good results, passing OSHA and fire inspections. worker safety and environment, and preventing tramp abrasive from drifting where it will do the most harm. Clean-up is a constant job.

    Essential equipment for the Lapmaster station to be located within the work area includes:
    - An optical flat and a monochromatic light.
    - A hard straight edge to span the lapping disk (used daily).
    - Three sets of feelers for daily tests for flat.
    - Part carriers and carrier blanks.
    - A polishing plate furnished with rolled or sheet abrasive polishing media.
    - Storage for abrasive, clean rags, carriers and vehicle.
    - Spent lapping slurry containers.
    - A solvent wash tank with a cellular bottom grate (grit trap), pump and filter, and a spout with a valve,
    - The wash tank should be placarded: "For Lapmaster use only. Caution: Abrasive Hazard. Use for no other purpose."
    - A fire-rated waste container.
    - Access to shop equpment to machine or bandsaw carrier disks
    - Absorbant ground clay floor dry or equivalent in a plastic pail furnished with a scoop
    - Push broom and floor squeegie
    - Spill kit
    - "No Smoking - No Hot Work" sign
    - Fine extinguisher
    - And whatever creature comforts are acceptable to the management.

    If the Lapmaser work area is subject to airborne debris, it should be located in its own room, a containment, or at least three wall shelter. This is a finish quality issue not operator environment. A single piece of grit from a nearby bench grinder may spoil a whole load of parts - scratch the puddin' out of them.
    Last edited by Forrest Addy; 08-21-2014, 03:33 PM.


    • #3
      For those, like myself, who have never seen one of these machines:
      Paul A.
      SE Texas

      And if you look REAL close at an analog signal,
      You will find that it has discrete steps.


      • #4
        Man there's a bag O' worms.
        I bet you could find 20 of those machines in use around the world, and investigate
        what / how is it being done. I'd be pleasantly supprised if two of them are being used correctly
        by any-one who even remotely understands what's important.

        The other 18 fall into a group practicing . . . attrocities . . . Yup that's the word , attrocities.
        I'd go further to assert that, in 14 of those cases parts come off those machines
        in worse condition than they went on (as regards flattness).


        • #5
          Looks like I have a lot nore to learn than I thought, Thanks for all of your time. I'll keep you posted as to how this turns out



          • #6
            There is a company not far from here that has a room full of these machines, I think precision lapping is pretty much all they do. I had them flatten a set of 6" wafer dicing machine chucks for the place I worked for a few years ago. I don't know how flat they actually were but I could not measure any variation with a digital gauge that read to half-a-tenth. We had optical flats available, but I never bothered to check as it was significantly flatter than factory spec called for.

            It was impressive especially considering that it was not really all that expensive to have done.