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  • Scraping

    Ok time to let you all take a look and tell me how to improve what I'm doing. It's just a practice piece, it's too thin and flimsy to be worth anything as a secondary reference. I have to hold it down a bit to get it to pick up any marking, and I can't be sure I'm pushing down evenly.

    A couple of questions, how do you keep a nice crisp edge on the work without rounding it over? About what angle is best to apply the scraper to the work (how high to lift the handle)?

    I think maybe I'm not digging in enough, the surface is so smooth that it glides like a hovercraft, and then if there is much bluing on the flat it wrings down.



    Sorry about the size, I resized them and then put the wrong one in PB
    Last edited by J Harp; 06-17-2007, 02:42 PM.
    Jim

  • #2
    Is that spotted?

    If that piece is in "as-spotted" condition it looks like you are low around the left , right, and bottom edge, and above the right hand bolt hole in the photo. Then again that could be the lighting. The best angle, at least for me, depends on what I am doing. If I am roughing down, a steeper angle is good, say 30 degrees, and the strokes are long, up to an inch. If I am past that and scraping for bearing the tool angle gets much flatter and the strokes get much shorter, like 1/4". The crisp edge is tough, practice practice practice!

    Overall the surface looks pretty good for a first attempt, keep at it.

    NOTE: Not being a professional scraper myself, this is worth .0025 cents.
    James Kilroy

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    • #3
      Thanks jkilroy,

      You are right about the low areas on the left and lower edges, with a larger low above the hole, the right edge is an artifact of the lighting. Two scraping cycles before that it was concave pretty much all over the middle. I think this isn't a good piece to practice on because it is so thin and too light to mark under it's own weight. It was .130 and .150 in the two places I measured.

      If someone knows how and can tell me how, I'll try to fix the picture, I know it's an annoyance to have to scroll across the page.
      Jim

      Comment


      • #4
        What material is it?

        Cast iron scrapes nicely, except hard iron. Steel stinks, IMO.

        Thin items squirm and don't scrape nicely either, besides generally being steel.

        Angle sets the width of the scraping mark, low being wider and high narrower, just from geometry.

        If that is 0.130 thick, it also looks small in dimensions. Maybe you meant it was thin and hollow with the 0.130 the thickness of the top of the hollow area.
        1601

        Keep eye on ball.
        Hashim Khan

        Comment


        • #5
          If you are making a scraping flat, you make it with a couple of high points as I posted about before. This helps prevent both stiction and floating due to surface tension so that you get a good rub. You pivot the straghtedge while it rests on the plate as you are scraping it in to find these high points. They should be about a third in from each end before you give up. You have to know where they are as you scrape in this reference straightedg, however. If you apply pressure to the straightedge as you rub it on the plate, in another location, you will be deflecting or flexing the straightedge around those high spots, giving a false rub. These intentional high points will be the points where you apply just a bit of pressure as you rub away your marking on your work when using it to scrape in another surface.

          The ability to put these high points in is one advantage to using a cast iron reference surface over a surface plate. This is really only practical, however for straightedges as you might use in scraping in way surfaces. Cast iron plates with handles do exist for larger areas, but are rare nowdays.

          You can float a Jo block or even a well finished 123 block on a good granite surface plate....you don't really want that for your scraping work. Still many small part including your reference straightedges will be scraped to this plate.

          Edit-- your scraper angle will vary a bit depending on the angle you put on its face. You will also work more vertical when attempting to cut hard and lay it down as you attempt to shorten and lighten your stroke. If you are not getting enough bearing over time, watch to see that you are not flexing it with pressure you are applying...seee above. Also, be sure to stone the surface with a fine stone between passes. Burrs will hold the work up, leaving you to think that you are not "getting there". It may also explain that floating feeling. I like the method I use (rub the marking *off* the work being rubbed to the plate) as it allows you to clean the plate with a bit of alcohol on a towel each time to insure that you are not rolling your work around in grit that might be on the plate. Same with the piece being rubbed to it...you wipe it clean each time and apply the marking agent to it.

          Paul
          Last edited by pcarpenter; 06-17-2007, 08:42 PM.
          Paul Carpenter
          Mapleton, IL

          Comment


          • #6
            Thanks fellows,

            J Tiers, yes it is cast iron and is hollow on the back, guess I should have taken a picture of the back. It has two small transverse ribs, and a couple of small bosses cast into the underside of the top. Also has increased wall thickness around all the holes, the rest of it is pretty thin.

            pcarpenter, my original idea was to make a flat that I could use to scrape a hump out of the top of my table saw. I have already done that, there was a high spot about 3 by seven by more than a thirtysecond high, I figured it was a hard spot, but it scraped down easy enough, it's not that critical if it's a few thou. off, but was annoying being as high as it was.

            I have decided that the thing is too flexible to work down flat. Did a search and read Forrest Addy's discussion of the subject, and was vacuuming, stoning, cleaning with lighter fluid, waiting a minute and handling with gloves when spotting this morning. I knew it was probably flexing when I had to push down when spotting, but didn't think of scraping pressure causing flex, makes sense though. About the surface finish, should I to use a smaller radius on the scraper to make the hollows a bit deeper to avoid the too smooth surface?

            Thank you both, and all the others who have shared their knowledge.
            Jim

            Comment


            • #7
              JHArp,

              What in the HELL kind of table saw CAN you have that is so far out that you want to scrape it.

              You certainly don't have an Oliver or a Delta or a General. I don't think you can even get a Sears with a "hump" in the path of cut, of a 1/32 inch, AND, I don't think you would ever notice it.

              It's WOOD. f'rChrissakes. You don't MACHINE wood to the thou.
              You CAN plane down wood to THIS dimension, today, you don't know what it will be tomorrow. Micrometers are out of the question for wood.

              What kind of wood are you trying to cut to the thou? Long board, and thick?

              Gonna droop over the outfeed. Scantlings?

              Set your fence to clear them without bind. If you ARE getting binding, wedge the cut.l

              Cheers,

              George

              Comment


              • #8
                gmtov: It's J Harp's fix and apparently it worked for him.

                Your said: "It's WOOD. f'rChrissakes. You don't MACHINE wood to the thou."

                Here's reality: Many woodworking operations require close tolerences as for glue joints and part fit-up. I've determined that the dimensional allowance between what's too loose and what's too tight for a mortice and tenon joint is about 0.006" and the skilled cabinet and furniture makers I've interviewed (showing them sample joints for comparison) concur. A 1/32" hump in the wrong place in a table saw may be insurmountable in any class of work finer than milling form lumber.

                While most woodworkers wing it they are well aware of the necessity for accuracy in good joinery. Precison fitting in woodworking is in the end more economical than figuring out what to do with tight or loose joints and while the actual dimensions don't have to be any particular accuracy their fit-up is quite often very precise well within thousandths resolution if not actual call-out. Most are surprised when confronted by how accurately they routinely work when I check out a few of their parts with their own dial calipers.

                Scraping can be a quick and dirty fix if need be. I've certainly scraped in enough valve flanges to remove corrostion pitting and warpage. A square file and a scraper used in combination can be an economical metal removal system far less expensive and time consuming than disssassembly and machining. If I was confronted with a bump in my saw table I'd attack it with a square file, scraper, and the blade of a try-square as a line reference.

                Less outrage and more enlightenment please.
                Last edited by Forrest Addy; 06-18-2007, 04:17 AM.

                Comment


                • #9
                  gmatov and Forrest;

                  Naw I wasn't trying to work to a thousandth with or on the table saw. It's a Ridgid from Home Depot. The hump I spoke about was on the right side of the table, about in line with the leading edge of the blade. When cutting fairly stiff things like glued up MDF it would affect the squareness of the cut edge (on the thickness). The rip fence was also dragging on it, and I just like to make things as near right as I can. Gotta practice on something don't I?

                  Forrest I appreciate your comments, and always enjoy your posts. If you make that scraping CD that someone mentioned, I'll buy it if it's not priced up there with Connelly's book. George is all right, he's just razzing me a bit I think.

                  If you try to make one of these, you sure enough want your table saw lined up as close as you can get it. There are umpteen ways to screw it up without having misaligned equipment, I made one of the sides twice and the center piece three times before getting it to suit. The dovetails are not as tight as I wanted, but it was a first effort and looks pretty good if you don't look too close.



                  Jim

                  Comment


                  • #10
                    The best scraping I have ever seen was done by sir John he was scraping the inside of his wallet too see if he could get an extra penny out typical Englishman Alistair ps we Scot's are always very generous
                    Please excuse my typing as I have a form of parkinsons disease

                    Comment


                    • #11
                      J Harp-- its been my experience that the scraper with a tighter radius is a bit easier to cut deeply with than a wider radius scraper. It makes a more narrow cut applying the same force to a smaller area. This does, however require more strokes per area to get the same coverage. A bit of a lateral motion in the stroke, will, however widen the mark back out a bit and imparts a bit of a slicing action to the shearing work the scraper does on cast iron. My mentor, a very nice fellow named Gary, produced a very different stroke than my own and no two will likely ever be just the same between scraper hands. His resembled a long feather with a width maybe 5/16" wide or more at times. He was just better at the work and could make the metal smoke when attempting to cut deep while still maintaining this wide cut. I would say that you should work toward something you can do consistently and with enough control to hit the right spot and vary the "intensity" as needed. It may not look the same as mine or Forrest's or Gary's scraping stroke, but may well get the job done and feel natural to you.

                      I'm with you...I would love to see Forrest's instructional DVD or whatever came out of his scraping classes. I think you can always learn a bit more by seeing it done yet another way.

                      paul
                      Paul Carpenter
                      Mapleton, IL

                      Comment


                      • #12
                        George, of the 72 pieces (IIRC) of red oak on this table top, the loosest fit was less than .002. It was built around 1986 and still looks great. I have built many similar pieces with an equal degree of accuracy. My miter fence, tenoning jig, and other tools and jigs have been modified for better precision.

                        Comment


                        • #13
                          gmatov, Forrest, et al.........

                          Of course a good woodworker works to thousandths...... as does a metal worker.

                          The difference is that a woodworker doesn't care WHICH thousandth he is working to, within more than maybe a 32nd or 64th inch. The thousandths come in with FITS, the 32nds come in as lengths.

                          That is of course not so with a metalworker.
                          1601

                          Keep eye on ball.
                          Hashim Khan

                          Comment


                          • #14
                            Yes I work to fine tolerences on my wood but not to thou's like metal it's not needed anyway a good old piece of hand made furniture made when we had very skilled cabinet makers in thousands here in the uk they always worked bu ordinary rule and eye.Alistair
                            Please excuse my typing as I have a form of parkinsons disease

                            Comment


                            • #15
                              Thanks Gentlemen, for the comments.

                              pcarpenter, when you say use a lateral motion do you mean push forward with the right hand and to the right with the left hand (assuming you are right handed), angle the scraper handle end to the right and push straight ahead, or push forward and pivot the scraper around the left hand? I'm willing to try anything, and have another of those flimsy pieces of CI that I could use to try to learn a consistent stroke pattern. Do you have pictures of your scraping that you could post?

                              Joel, that's a nice table, I don't think I'll ever reach that level of woodworking. I messed up the finish on that doo-dad tray, followed someones advice and put paste wax over shellac, big mistake, need to strip it and start over, but I expect getting rid of the wax is going to be a bear.

                              J Tiers and Alistair Hosie, yep I have used a caliper when I spoiled the last piece of a given thickness and had to try to duplicate it with the thickness planer. Don't normally get that picky with wood but I do use length stops and try for square cuts.
                              Jim

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