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My First Attempt at Scraping

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  • My First Attempt at Scraping

    ... has resulted in many questions

    So, as luck would have it, in this lot of goodies I purchased there happened to be an old Anderson scraper, several pieces of scrap cast iron and some oil stones.

    Between Lazlo's advice and PCarpenter's chip breaker, I made myself a scraper a while ago but didn't have a chance to put it to use. I decided today to give the Anderson one a try first, as I'm a little intimidated by the carbide. I didn't want to bust it and I don't have a diamond wheel for sharpening. I do have a diamond block and I roughed out the shaper with a silicon carbide wheel, so I could make it work if I was a little more "ballsy"

    Anyhow, the Anderson scraper worked beautifully. I sharpened just like Connelly described. At first, I honed it with about a 10-15* angle from vertical and that was way to aggresive. I was impressed at how well it dug in and how well it cut. I then honed it to more of a 30* angle and have been getting along fine, in that regard. I have only stopped to hone the edge every now and then and I've not needed to take it to a grinding wheel. I find that it stands up the this cast iron very well.

    The first piece was some knick-knack - no idea what it was originally for, but I flycut the bottom and was going to scrape it flat. There were some inclusions and some hard spots that were almost like semi-steel, but not too bad, really.

    The first couple of cycles were basically useless. I would cut the high spots really low and then cut the next set of high spots really low so I was, in essence, maintaining the originally pattern but reducing the thickness! I eventually got the pressure figured out so I could make a little progress.

    The trouble I'm running into is with spotting. These two pictures are at the same point in the scraping cycle. That is, the first picture shows the work piece after being spotted by rubbing it longitudinally on the surface plate (observing Connelly's recommendations). The next picture is showing the same piece after cleaning off the bluing and rubbing it transversly.

    I ended up spotting it by rubbing it three times in one direction and three times in the other before removing it. This way I got "spots" instead of streaks until finally I was left with this:

    I wasn't concerned with the bolt holes or the edges, but how is the center area between the bolt holes looking ... It's not really what I expected, to be honest.


    Anyhow, it's pretty obvious that I've no idea what I'm doing. Any advice is appreciated! I guess my trouble lies mainly with the spotting and then interperting the marks.

  • #2
    Your pix don't seem to show up. Sounds like you have too thick a layer
    of bluing on the reference flat and it is smearing out. Try a thinner layer
    to check the spots. You probably need a 4-6" rubber roller to thin out
    the bluing enough.
    Steve

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    • #3
      I sure wish I could get those damn pictures to show up... I'm having some issues with my computer. Hopefully I'll get them posted...



      Originally posted by sch
      Your pix don't seem to show up. Sounds like you have too thick a layer
      of bluing on the reference flat and it is smearing out. Try a thinner layer
      to check the spots. You probably need a 4-6" rubber roller to thin out
      the bluing enough.

      I actually just purchased a rubber roller today for that very purpose. I feel like I got a very thin layer.

      Comment


      • #4
        Technically, they're called brayers and I think they're pretty essential to the process. One thing I recall from the Forrest Addy class I took is that he said the bits you scrape off should look like coffee grounds. And you really need to stone the surface and wipe it down well before taking it to the granite.

        After a time it will all present itself to you - a light will come on, and you will then be in control of your piece. In the beginning though it's more likely you'll make some nasty divots and trenches that you will have to clean up

        And if you're like me you're going to enjoy finding the precision surface hidden under all those coffee grounds you're scraping off.

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        • #5
          Here's a thing I wrote some tme ago:

          Frequently in my scraping classes I'm asked: "How much blue to put on a surface plate?" I always give a non-quantitive answer: "enough so the blue is vivid but not so much that you can't see the texture of the plate through it." Not real clear is it? This is a critical question. Too much blue gives false indications a neophyte may not immediately detect. Too little and the indications will be sparse and hard to interpret. Either way it wastes time when the transfer medium film thickness isn't optimal.

          Tonight it struck me how to quantify the blue; bonehead math. Taking 50 millionths as a starting point, multiply the plate area by the film thickness and that will give you the blue volume required. For example: 18" x 24" plate area X 0.00005" = 0.022 cubic inches. The typical nerdle issued by the tube of blue is about 3/16 dia. The area of 3/16 dia is 0.035 square inches. Dividing: 0.022 sq in / 0.035" the nerdle length is about 5/8" long. Hereafter, it's an eyeball estimation game but you get the picture. At a guess, I would think you'd need about 1/2 the blue volume for a refreshment.

          You who like to experiment feel free to post your separately wrought conclusions. Comment on the figures which seem to work for me. By the way, the figures above are for an initial charge for starting a scraping job. Less will be required to refresh the blue depending on whether you want it thicker or thinner. How much blue to apply in a given situation is still dependent on your requirements but the math gives you a place to start.

          I don't want anyone to load blue into graduated syringes or weigh out blobs of blue on little pieces of paper on a lab scale. Do as before: dab the blue on the plate estimating the amount by eye alone. Got it? Eyeball measurement but this time using simple math to arrive at the desired quantity.

          If I hear of anyone actually measuring a blob of blue with a 6" scale I'll use my frequent flyer miles to track you down and whack his hand with a ruler. OK? OK.

          Finally spread the blue by a means that doesn't contaminate it with fuzz, crumbs, or fluff. That leaves out everything but bare fingers. There's another better, quicker way to spread blue: use a rubber ink roller from an art supply store. I usually bring 1" dia x 3" long "breyers" - ink rollers - to my classes. They spread the blue quickly and it saves the finger joints wear and tear for blue is hard to spread. The roller also tends to pick up contaminants and holds them next to the rubber so that's a second advantage. You can easily pick them off with the corner of a rag. Roll briskly lifting the brayer at the end of each stroke so the roller spins. This randomizes the roller position and multiplies spots of blue adhering to the roller.

          Want a breyer of your very own? Look at your local artist's supply house. If you're web obsessed, here's only one of many suppliers:

          http://www.misterart.com/store/view/...ber-Brayer.htm
          Last edited by Forrest Addy; 12-24-2009, 04:40 AM.

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          • #6
            ok but forrest, I got my scale and was wondering how much pressure to roll the dye out with... j/k
            Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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            • #7
              Ok, so I have a question...

              I have an old van norman 12, and the gibs need to be replaced...but in order to replace the gibs, I need to take the curve out of the dovetail (wore in the center, as is evident by the fact that I can no longer tighten up the table stop)

              Do I need a straightedge the full length of my table, or can I get by with a 12" section of straigtedge and some common sense (that the table is wore in the center and I should start by working that area down, then work in to the center)

              I've never tackled a scraping project before, and it's a bit intimidating. My first project would be scraping in the straight edge that I'd have to salvage from something found in the scrap yard...but that's besides the point right now.

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              • #8
                Originally posted by Forrest Addy
                Want a breyer of your very own? Look at your local artist's supply house. If you're web obsessed, here's only one of many suppliers:

                http://www.misterart.com/store/view/...ber-Brayer.htm
                I looked at the website, but naturally came away with another question. They offer hard and soft rubber, does it matter? I tried my hand at scraping a little, but I used a piece of old shoe leather to spread the ink, not so easy.

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                • #9
                  Mike: Soft rubber. Less work. Better distribution.

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                  • #10
                    Originally posted by Fasttrack
                    I sharpened just like Connelly described. At first, I honed it with about a 10-15* angle from vertical and that was way to aggresive. I was impressed at how well it dug in and how well it cut. I then honed it to more of a 30* angle and have been getting along fine, in that regard.
                    Tom, I'm guessing that's a typo -- you mean 3°, right? Connelly shows 3° rake angle. When I first sharpen the scraper I grind the end square (90°), and then add a 3° bevel on each side.

                    I haven't built a power lap yet either, so I rough the blade on a diamond wheel, and then hone it by hand with a DMT diamond dipstick sharpener.
                    "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                    Comment


                    • #11
                      Post #136 may help Forrest's explanation about the amount of bluing.
                      http://www.practicalmachinist.com/vb...-146913p4.html

                      I wouldn't recommend a 12" straight edge to spot a surface much longer than 20". Even at 20", you're going to have to scrape the 1st 12", then the next 3-4" and so on. It's a RPITA, and can be very risky. Read the entire topic I linked to above, I used a 48" long straight edge to spot and scrape 3 60" long bed way faces, and did the same thing to an 84" long bed several years ago. It isn't easy.
                      Harry
                      Last edited by beckley23; 12-24-2009, 03:25 PM.

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                      • #12
                        Well the pics will have to wait...

                        I keep getting a semaphore timeout error when I try to access my SD card using the desktop. No problems when I link the camera to my laptop, though. Only, I left the cable at school, so the pictures will have to wait about a week ...

                        Robert - That wasn't a typo, although I maybe wasn't very clear what I meant. I was referring to the "honing angle" that Connelly describes. He mentions that 10* is suitable for roughing cuts and semi-steel, while for finishing cuts or softer material, the honing angle is generally greater than that. 30* was probably an exageration, but it was certainly farther from vertical than my initial attempt. (I think this is discussed on page 26 or something like that...)

                        Forrest - thank you so much for that description! I finally settled on a layer of blue that just barely shows the granite surface plate texture, as you described, but I still wasn't sure I was doing it right. It really helps to be able to pop on here and see if I'm headed in the right direction or not...

                        Thanks DP! Instead of a "brayer", I bought a rubber "J-roller" for gluing countertops and the like. They are available from Menards, although I couldn't find one at either HD or Lowes. They have a medium rubber roller and seem to work great for rolling out the bluing. I think it is identical to a brayer, for all practical purposes.

                        Beckley - I'll check that out. Were you the fellow working on restoring a 10EE? I seem to recall and excellent thread over on PM that detailed scraping the ways...

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