surface plate reconditioning
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  1. #1
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    Default surface plate reconditioning

    i have a 3' by 4' plate that needs at least a sixteenth removed. Local metrology companies do not have the equipment to do this. I was thinking of approaching a granite counter top mfg to do the initial removal of material then have the finishing done by a service. What do you guys think of this approach? Or do any of you know of a firm that has that capability in the north east Pennsylvania area or north New Jersey.

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    If I may ask, how did you determine that 1/16" needs to be removed? That is a MASSIVE amount of material to be removed, in terms of a surface plate. Is it damaged in some way? One of the advantages of granite is that, if something is dropped on it, the granite will chip out, and not leave a raised area, whereas a cast iron surface plate will leave a "bump" of material above the surrounding surface, in addition to the "dent" below the surrounding surface. The raised portion MUST be removed.
    I think the cost of removing that much material, in addition to having the surface plate re-finished and calibrated may make it more economical to go with a new plate. Your mileage my vary...

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    I could not do flat much better than 1/16" with a coarse disc but with a 5" wet grinder takeing 1/16" of a 3x4 granite is not going to even take a hour, Diamond cuts granite pretty dang quick. With just a bit of practice, the finer discs let you make a surprisingly flat surface too.

    One word of warning though, most counter top places will not be set up to handle such a lump of stone and a fair few have no sheet polishing at all and just buy in pre polished sheet then and only then cut and hand polish the edges.

    If you can ID the high spots, then a copper bond wheel around the 200 grit range or finer would be able to get you down into hand lapping back to tolerance rage pretty easily. Its a very wet and messy process though and you need the measuring gear to ID the high spots as you go, cost wise it would make way more sense to go buy a good plate than do this. But honestly if you had the mesuring gear and were local, i would be up for trying on a warm day, Simply mark the high spots and take em off just like scrapeing. Get up into the 1000 grit pads and your not going to remove much more than a few tenths a minute. Realy depends on what you can measure too and how near you want it prior to start the true hand work, but would be fun to try!

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    Some one really misused this plate. There are many little chips from the surface, also when you run your hand across it it feels rough. A 1/16th is best guess based on a visual of the dings in it.

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    It may be more economical to keep an eye on ebay/craigslist/whatever for one in a better condition. OK, shipping distance is a big problem, but it does take man-hours (=$) to lap a wrecked plate down to some semblance to flatness. If the counter-top/grave stone shops in the area can grind 3'x4' stones, then you should be able to get within a few thou. At which point a surface plate re-surfacing/calibrating company should be happy to take your money.

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    Quote Originally Posted by roll maker View Post
    i have a 3' by 4' plate that needs at least a sixteenth removed. Local metrology companies do not have the equipment to do this. I was thinking of approaching a granite counter top mfg to do the initial removal of material then have the finishing done by a service. What do you guys think of this approach? Or do any of you know of a firm that has that capability in the north east Pennsylvania area or north New Jersey.
    Not worth it. There are plenty of surface plates in our area that turn up at auction, so either work around the dings, or get another one, unless you have more time than brains, (something I have been guilty of so, ok I am a hypocrite!)

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    A Blanchard shop can grind it near flat..but likely charge 2 hours for the job..Yes I'm just guessing.

    You don't need to bottom every ding full depth to make it useful.

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    Additional question. How much is the maximum material that a calibration service can remove by lapping without the labor getting out of hand.

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    Went through all this a few months back. IMO any granite plate smaller than 3' in any direction with visible damage is an expendable piece. Bigger will often be worth the effort. From my research, most shops are less concerned with what needs to come off and more with what tolerance (B, A, AA) you want it to be. That and the size are what makes up their cost. We looked at resurfacing a 3'x6' plate to A specs. Was about $1000.

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    if there are dings, small divots in your rock...it does not necessarily mean it's not flat or flat enough. any kind of fixturing or height gages, etc.. would straddle or simply cover those dings and would be supported by the material around those defects, right? but if you are checking larger parts and need to satisfy tight tolerances using most of the rock at the same time...then yeah, it might be a problem.

    Does any work you do require that your rock is "certified" by a calibration service? does it need to be laboratory grade (AA)? inpsection grade (A) or even shop grade (B)?

    We have a large rock that has some nasty looking dings in it, but it still just barely not ideal, but that'll do until we can have it resurfaced next go around on our calibration schedule.

    I agree with the other posters that resurfacing is expensive and likely not worth it.

    Our cal service did tell us resurfacing our two small rocks was not worth it if we needed to do it. And one of those is a 3'x4' or close to it. so if you think your rock really is too beat up, get a new one or a newer used one.


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