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  1. #1
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    First crack at scraping

    This is my first crack at scraping a part – I chose the table top of my mill because it was in need of having the first few 100’s of an inch scraped off anyways. Plenty of material to practice with incase I mess up.

    The beginnings, a rusty neglected milling table <before I bought this mill mind you>.
    The Beginnings

    Time to give it some new life with some Wd40 and steel wool. Alright so far
    Wd40 And Steel Wool

    I lapped the table with 220, 320 and 600 grit sand paper, but still had some deep dings to get rid of. So scraping seamed like the best option here.
    Start Scraping

    4 cut, or 2nd double cut later I have successfully broken up the surface. My technique still needs work because my strokes are too long, but I am getting better at it so by the time I get comfortable with it those deep cuts in the table will be gone.
    4th Cut Done

    A few close-ups of today’s work.
    Closeup1
    CloseUp2

    Disclaimer:
    I do no suggest people start scraping machinery with out proper knowledge, equipment and some experience. Even though this is my first real part I have been practicing on some scrap metal and on a cast iron angle plate. Read at your own risk.

  2. #2
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    A nice start at breaking up the surface but I do wonder what you are using for a reference plane?

    Dave

  3. #3
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    unless you're doing a lot more than you're telling us, you're removing material in an uncontrolled manner and that will hurt, not improve the accuracy of the mill. lapping is done with a lap and is an accurate and controlled process, it is very different from sanding. Scraping is done with references, surface plates, indicators and blue, where the act of scraping is removing material from a specific location identified by the methodology of blue& reference.

    The objective with scraping a table is to get one of the top or two bearing surfaces flat then bring the other into a parallel plane. How are you controlling the removal of material such that the table top stays perfectly parallel to the bearing surface?

    I debated not posting cuz it’s raining on your parade, but decided that wouldn’t be doing you or other readers any favour. The good news is that scraping removes very little material so you may have not done much or any damage….but this is not the way to go about it and you will damage it if you keep going.

    IMO go at a rusted machine surface with steel wool but not abrasives or scraping unless you are following the proper methodology. If the remaining stains on a good old piece of quality iron are too tough to look at, you’re in the wrong hobby the odd bit of pitting is not going to affect the performance of the mill.

  4. #4
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    Well presently I am not scraping for alignment or bearing, I’m rough scraping the part do a desired depth before I being the alignment process. I’m removing material using a standard 45/45 so that each cut is perpendicular to the cut underneath it, to help cancel chador. Some of my initial stokes didn’t fallow this principle very well, but by the second cut I was keeping my strokes on target.

    The lapping I did wasn’t true lapping – I used an angle iron as a sanding block and in a controlled manner moved it from one side to another. Not perfect but was efficient enough to do a decent job.

    Once I am passed the depth I was shooting for I will refine the table and being to scrape for alignment and bearing.

    I have a grade A surface plate I plan on using for testing the alignment of the part using the transfer to technique with a marking medium. Using an accurate dial I can measure the distance between the table top and the ways and use that to help make the table top parallel to the ways.

    Well in a nut shell that is my plan, and I still have a ways to go.

  5. #5
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    sounds like you've a plan, keeping things flat and parallel is the both the objective and the trick. it'll give you arms like steel bars by the time you are done.

    Still, I'd get the surface plate and indicator going sooner rather than latter, if you keep scraping with benefit of a reference you may well be making more work for yourself by taking too much of one area, not enough on another etc.

    Keep in mind those pits or spots where someone's machined into the table might be 20thou or more deep - they make to difference to the accuracy of the table and may have you scraping until Christmas.

  6. #6
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    Well really there is no harm in throwing the table on the surface plate and checking it out after a cut to see where I am going with it, so I might as well do that. Surprisingly my arms are all right so far, but my hands feel like someone was beating them up with a baseball bat. I ran an indicator over the damaged parts of the table a while back and that little mill spot centered on the table was about 0.001” deep, so that’s my target. I’m close to that depth so a few more cuts then its time to break out the blue and start scraping for bearing and alignment.

  7. #7
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    This is of course my perspective but I would do nothing to the table after the first attack of the surface. All you really want to do on the first scrap is to rough up the surface a bit and make sure there are not any significant burrs or other bruises to the table before use of the reference surface.

    The reality is that you can go the wrong way incredibly fast with out the use of a reference. While it is almost always possible to correct any introduced errors, it is far easier and a lot less work to just start out right.

    In any event don't get to concerned. Scrapping is fairly easy and you will get a handle on it pretty quick.

    Thanks
    Dave

  8. #8
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    Well I had some fun in the garage today.

    I did my last breakup cut over the length of the part then I put the table on my surface plate to take some measurements. The center of the table is about 0.0014” high than the right side and the left side is about 0.0005 lower than the right side of the table.

    Took the table off – marked up the plate and did my first transfer. And it looks about right; center is higher than everything else.
    First Markup Angle 1
    First Markup Angle 2

    After my second markup I didn’t have enough energy to do a third so I cleaned up and called it a day.
    All Cleaned up

    Here is a close up of the dings in the part; it’s interesting to see the difference between close-up 2 and this picture. The surface dings that use to be there are for the most part gone and the table reflects a lot more light. I also did a better job getting rid of the scratch marks on the edges of the T slots. It’s not perfect but not bad for an afternoon in the garage.
    Old Closeup
    New Close Up

    Here is a picture of my surface plate, briar, and my dial indicator (accurate to 0.00005”). If I am not using the surface plate it stays in its box – to keep it safe.
    Surface Plate

  9. #9
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    If you are interested in scraping and machine tool reconditioning I highly recommend

    http://www.powells.com/biblio?isbn=1114266612

    This book has over 530 pages on the application of scraping to machine tool reconditioning. This is invaluable for anyone reconditioning a lathe,mill or grinder. Alternatively, it iwould be very useful for building a machine from scratch.

  10. #10
    couldn t you just run a fly cutter over the table , sounds like a lot of work

  11. #11
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    Getting closer to a bearing surface. The ends are not as refined as the center of the table and I still need to make sure this flat surface is paralleled to the reference points I’m using, but other than that things are moving ahead.

    So Far so good
    A little closer
    First Ding almost gone
    Other ding

  12. #12
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    wow, I didn't know you could do that. I'm just a simple violin maker and I scrape wood all the time (a good sharp scraper and I can work to 0.1mm tolerance when I'm being careful). But I didn't know you can do it to metal too.

  13. #13
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    Re: First crack at scraping

    Wow, Thanks< i came here from google
    Last edited by maxalw; 07-06-2020 at 01:50 PM.

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