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Making a CI surface plate

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  • #61
    I did support the prototype plate under each end, pushed down in the middle with maybe 40 lbs of pressure and measured .003 deflection.

    In the past few days I have read so much and watched so many videos about preparing CI straight edge castings by plaining, milling, and grinding my eyes are crossing. I've learned that plaining may be the ideal preparation for scraping a part this size. Whatever I do, I still see stretching a length of belt sanding paper on a plate and "lapping" or "grinding" from let's say .002 to .001 a legitimate option. There's no clamping distortion when doing that.

    I also decided to add stiffness/support (before final surfacing) to my prototype by attaching legs. The end result will be a channel shape with the legs appx 3/8 thick and 3" tall running the length on each side. The legs can be removed for easier machining of the many changes to come (the shape and dimensions of the counterbore will be changed). Since CI stock of this size for legs is not available I planned to use cast aluminum. My suspicion that this may also be a legitimate idea has been confirmed by this:
    https://www.penntoolco.com/a6100/
    A precision parallel/straightedge that uses a cast aluminum "leg" to provide support for a thin CI surface with straightness of .0003 over 36". The fact they are mating these two different materials and expect the complete assembly to remain stable to .0003 ($2500 worth of .0003) is informative. Oh, and they are "ground or scraped".

    The CI plate is at a nearby shop to be machined to accept the legs. Aluminum material for the legs is on the way. I'm working on the walnut mock up legs now which will do until the aluminum ones are done. I ordered my Biax hand scraper starter kit today. And the CI straightedge castings (for practice scraping) are being rough milled at another shop. He claims he can get them to .001 by milling. And I dropped a steel plate yesterday, crushing the small bone and fracturing the middle bone of my big toe. Hence, the marathon of research I've done today on the couch.
    Last edited by rmcphearson; 01-18-2022, 07:38 PM.
    -Roland
    Golf Course Mechanic

    Bedminster NJ

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    • #62
      I got my flimsy flat bar back from the local shop with rabbits milled in each side and 12-24 holes drilled and tapped. My aluminum never arrived so I made the support base out of walnut. I attached the base with countersunk 12-24 screws. This is enough support for demonstrations and experimentations. And I can remove the base for re-machining the counterbore and other future changes.

      https://www.youtube.com/watch?v=Q-goFMrMlwM

      One thing I've failed to explain is that my plate will calibrate a gauge that's not perfectly flat (most of the gauges are not perfectly flat). Using a multistep process with a granite plate and a gauge block under the catch will calibrate a gauge only if it is perfectly flat.
      Last edited by rmcphearson; 02-05-2022, 02:30 AM.
      -Roland
      Golf Course Mechanic

      Bedminster NJ

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      • #63
        Here are the latest videos on gauges in general and my plate
        https://www.youtube.com/watch?v=bvnZdTCzkoA&t=2s
        https://www.youtube.com/watch?v=eQXVoVEMhYs&t=2s

        I scraped the prototype you see in the video by hand and took it to the trade show in San Diego a few days ago. I was happy with the reaction from those who saw it but I have continued making changes to the design. I now realize that it does not need to be long enough to act as a lapping plate for non-flat gauges, actually it only really needs to be long enough to span the contact points (where the two .010 shims are placed) under the gauges, so 18" is more than long enough. And I realize it only needs to be only slightly wider than 2". That's going to change the game. I may just buy solid bars of gray iron (durabar) 2-1/4 wide, and approximately 2-1/2 tall and have the bottom cavity hogged out and milled. Then I will have a large selection of shops to do the surface grinding since it's only 18" long.

        It's been pointed out the me that Snap-On trucks have a calibration tool on the truck for techs to use for their torque wrenches. This product will be very similar. There are a similar amount of mobile techs (trucks) in this industry as there are Snap-On trucks. The retail price of this tool will be insignificant to the dealers to have in each truck. If I can get the retail price down to around $600 I'll get one into a good percentage of each golf course shop too. There are 15k courses in North America and 35k worldwide. I have a few preorders ("send me one, I don't care about the cost"), one of those preorders is from Europe.
        -Roland
        Golf Course Mechanic

        Bedminster NJ

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