scraping a 10x10" plate flat - starting with a raw casting
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  1. #1
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    Default scraping a 10x10" plate flat - starting with a raw casting

    I'm working on a motor mount for an antique 1hp GE motor patent date 1912. On the machine, it had all kinds of washers and shims stuffed underneath it because the machine's cast motor mount is nowhere near flat. To further complicate matters, the motor is larger than the factory mount so an extension plate must be used.

    I have learned enough to know that if you want an electric motor to run right and run quiet, you need to mount it on a flat level base.

    So I scrounged up this piece of cast iron. It's about 7/16" thick, and it isn't anywhere near flat either. If you bolted it down to a mill table with clamps you'd probably crack it because it has a big hump in the middle, maybe .080" high. Maybe I could figure a way to bed it in pitch or something but I decided what the heck. I'll scrape the auxiliary plate flat on one side and then I can use it to spot the factory motor mount so I can scrape that flat too. Finally, with the aux plate flat on the bottom, I can clamp it down and mill the top to something approaching flat, then scrape it in the rest of the way.

    That was my battle plan, anyway. Well, as someone said, no battle plan survives contact with the enemy army. I realized right away that I'd be scraping for months to get that huge hump out. So I moved to plan B. I'm "scraping" it using a coarse flap wheel on an angle grinder. I'm careful not to let it gouge too deep. In half a day and innumerous trips to the surface plate, it's approaching the point where I can start scraping.

    I believe I heard Richard King say he's used an angle grinder for heavy removal prior to scraping before. That's where I got the idea. Anyway, so far it's working. And if I screw it up, well, it's my time and sweat but very little money so in my book no big deal.

    metalmagpie

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    Lol I will admit I did not run a straight edge over the piece I cut, only over the whole piece of plate I had. I should have. If you find that piece doesn't work for you, I would be happy to cut another piece for you on the house, maybe a different part is a bit more flat. Sorry, I didn't realize you were trying to scrape it.

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    Reading the initial post, it comes to mind the mantra "Perfection is the enemy of good".

    Personally, I would have milled/shaped/planed (depending upon what machines you have available) holding it mostly by pressing/blocking it from the edges, rather than pressing down: mill side A, mill side B (you may start adding downward pressure, since side A is now much closer to be flat), then touch up side A.

    If they have used washers/shims/spacers to mount the motor minimizing the distortion, it looks like the motor mount (and, possibly, the motor base as well) are far from flat as well and would profit of a nice cleanup similarly to the adapter plate.

    Personally I think you are overthinking/over-engineering the whole thing.

    Paolo

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    You might put a 1/8 thick piece of leather under each motor foot. Back in 1912 that was a common practice.

    But fresh new scraping is really pretty and good talent to learn.

    About 7/16 at the start? figure with both sides flat how much will you have left.

    10x 10 makes a very nice gauge table with a small surface gauge and an indicator, like a small bench surface plate.

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    Quote Originally Posted by Paolo_MD View Post
    If they have used washers/shims/spacers to mount the motor minimizing the distortion, it looks like the motor mount (and, possibly, the motor base as well) are far from flat as well and would profit of a nice cleanup similarly to the adapter plate.
    Absolutely the motor mount plate is far from flat. And it's attached to a very awkward part of the frame of this old camelback type drill press. I'm sure if it were practical to machine the motor mount surface Royersford (who made the Champion Blower and Forge castings) would have found a way to hold it and machine it. As it is, the only way to fix it is using hand tools i.e. scraping. They weren't willing to do it but I am.



    Quote Originally Posted by Paolo_MD View Post
    Personally I think you are overthinking/over-engineering the whole thing.
    I get that a lot. :-) In this case, I'm pretty sure that having the motor mount solid, true and level will only help the machine. I don't really make parts and sell them. I mostly work on restoring machine tools. I think three or four days of scraping will be worth it in the end. And if not, I'll probably not choose this method next time.

    metalmagpie

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    Snazzy looking motor mount, good luck with your efforts I am sure they will work better than the original.

    Charles

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    True, you're free of spending as much time and doing whatever you like. But, what about using a coarse file to remove the the largest imperfections and, as suggested by Michiganbuck layer some thick leather?

    Paolo

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    If the mount is then mounted to the other mount, the other mount has to be flat and true too or it's all going to twist right to hell again.

    I would definitely mill it if possible to begin with, but barring that grind or file to get close. When you're within 0.010" you still have a lot of scraping to do but doable.

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    I wanted to post an update. I have finished scraping in one side of my cast iron auxiliary plate. I am now using that to spot the original factory motor mount from this old drill press I'm working on. It was much too bad to scrape even with a Biax (nearly 1/8" out in several places) and it's much too awkward of a part to consider mounting it to be machined.



    To work on the motor mount surface I had to fabricate a bracket to hold the part in my freestanding bench vise as is shown in the picture above.

    I am having success removing high spots with an angle grinder. I have stopped using a hard grinding wheel and am now using 3M Cubitron II flap wheels. These remove stock very fast and are quite controllable. This is what the factory motor mount looked like before I started flattening it:



    Clearly it is a raw casting, never machined in any way. Here's a shot after I got going:



    If you look carefully you can see a large low spot on the lower right corner. Also there is a sort of "canyon" a few inches from the left, and a big scoop towards the upper left below the hole. Here it is farther along, spotted:



    Here the low spots are quite a bit smaller, indicating progress. Also, the even distribution of high spots indicates that I am succeeding in keeping the surface relatively planar while taking it down towards the level of the low spots. You can see some crisscross elements to the sanding pattern, kind of analogous to the method Richard King teaches.

    So that's where I am now. I'm obviously not working on this full time. I've been distracted by a death in the family and hampered by pain in my wrist which is aggravated by the angle grinder. But as you can see the fundamental concept of using an angle grinder to remove high spots works.

    metalmagpie

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    It does look a lot flatter.
    if you had a precision parallel of sorts you might feel around it to see how low your low places are. They may be .002 or .005 who knows.

    What are you using to blue it up with?

    When you get close you might use automotive wet abrasive paper and a backer block to take stock or a honing stone with oil.

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    Quote Originally Posted by michiganbuck View Post
    It does look a lot flatter.
    if you had a precision parallel of sorts you might feel around it to see how low your low places are. They may be .002 or .005 who knows.

    What are you using to blue it up with?

    When you get close you might use automotive wet abrasive paper and a backer block to take stock or a honing stone with oil.
    I do gross checking using a Starrett rule held on edge. There isn't any question of .002 or .005, the low spots are still at least .040" tall. So - long ways to go.

    I have roughly a 10x10" piece of flat cast iron about 7/16" thick that I scraped flat. That was what this posting originally was about. I blue up the plate and then rub it on the factory motor mount.

    When I get close I plan to use the Biax scraper and then scrape it in properly.

    metalmagpie

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    Does the motor mount need to zero 100% flat, or just where the motor sets?

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    Quote Originally Posted by michiganbuck View Post
    Does the motor mount need to zero 100% flat, or just where the motor sets?
    Well, therein is the complexity. The motor is actually longer than the factory motor mount, so I need to bolt a plate to the factory mount and then bolt the motor to the plate. I am scraping the factory mount and the auxiliary plate flat everywhere so they make as solid a mount as possible. On the top side of the auxiliary plate (the plate the motor is bolted to) I could probably get away with scraping just where the motor feet sit but that side will first be milled then surface ground and then scraped so the scraping won't be as arduous so I plan to scrape the whole surface.

    The motor has yet to be rebuilt. When I do, I will take it apart. After I get the motor running true and silently (it has plain bearings that are continuously oiled with slinger rings in an oil bath) then the motor itself will have its feet scraped.

    Is this all overkill? Maybe - but the more planar and solid the mount, the smoother and quieter the motor runs. The old belt driven drill presses aren't that quiet but I plan to try to make mine as quiet as I can.

    metalmagpie

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    Quote Originally Posted by metalmagpie View Post
    Is this all overkill? Maybe - but the more planar and solid the mount, the smoother and quieter the motor runs. The old belt driven drill presses aren't that quiet but I plan to try to make mine as quiet as I can.

    metalmagpie
    And then there are always earplugs.

    Of course it's overkill, but the issue is that you wanted to challenge yourself, get some practice, and see what could be accomplished.

    It can easily be criticized on actual need, cost, time and energy, but doing it because you want to try it is unassailable.


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