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Adventures in scraping

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  • Adventures in scraping

    I recently bought a benchtop round-column mill (Warco WM15), with a mind to convert it to cnc operation. My plan is to first fit up the x nd y axes with steppers, and keep the round column with manual, then stepper controlled quill downfeed. I will fix the head in alignment by keying the rack to the column. Later I will change the round column and head for a square steel column I have waiting, fitted with linear rails to carry the z carriage.

    Anyway, I have stripped the base to machine for fitting the ballscrews and found quite the horror-story of an assembly. Some faced are scraped quite well and others hardly touched. Some bear all manner of gouges and grinding marks - some of the work has even been done with the edge of a disc cutter blade. I knew these things are supposed to be poor in quality control, but take a look at these pics and see.







    Peter - novice home machinist, modern motorcycle enthusiast.

    Denford Viceroy 280 Synchro (11 x 24)
    Herbert 0V adapted to R8 by 'Sir John'.
    Monarch 10EE 1942

  • #2








    I can't in all conscience continue with the build with what I have here, and have been unable to find anyone local to look at it so I've decided to learn the basics of scraping and try to bring the machine to some semblance of reasonable operation. Right now, the table and cross-slide bind well before the ends of travel unless I back off the taper gib adjuster a long way.

    I've placed a wanted ad for scraping tools, and got some scrapers on the way from that. I have a small 6" surface plate of unknown quality (left by my late father) and a small tube of spotting blue and I'm looking for a larger granite plate. I've also started to machine a piece of cast iron for the dovetail vee gauge which seems to be 60.5 degrees according to my non-vernier protractor.

    So this thread is to document my adventures into the black art of machine scraping. I figure that with only £150 invested in the hunk of Chinese junk, even if I make a complete mess of it there's no great loss. I'll document a much as I can and take on board any advice and criticism with equal enthusiasm.
    Peter - novice home machinist, modern motorcycle enthusiast.

    Denford Viceroy 280 Synchro (11 x 24)
    Herbert 0V adapted to R8 by 'Sir John'.
    Monarch 10EE 1942

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    • #3
      MullerNick has some pretty good youtube videos on scraping...

      John
      My Web Site

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      • #4
        I've watched Nick's videos, and some others John. I'm also working my way through Connely's book but I find it hard going concentrating on a 500-page book when all I want to do is get hold of some tools and just have a crack at it myself.
        Peter - novice home machinist, modern motorcycle enthusiast.

        Denford Viceroy 280 Synchro (11 x 24)
        Herbert 0V adapted to R8 by 'Sir John'.
        Monarch 10EE 1942

        Comment


        • #5
          If you've still got a VHS video player and a telly to connect it to, PM me a snail mail address and you can have my copy of Michael Morgan's scraping video and book.

          regards
          Mark
          Location- Rugby, Warwickshire. UK

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          • #6
            I know what you mean Peter, I have a compound on my Samson lathe that needs some attention and I have the tools, just need to find the time.

            John
            My Web Site

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            • #7
              Originally posted by randm View Post
              If you've still got a VHS video player and a telly to connect it to, PM me a snail mail address and you can have my copy of Michael Morgan's scraping video and book.

              regards
              Mark
              That's very generous Mark. I don't have a VCR in the house but I'll see if I can find one to borrow.
              Peter - novice home machinist, modern motorcycle enthusiast.

              Denford Viceroy 280 Synchro (11 x 24)
              Herbert 0V adapted to R8 by 'Sir John'.
              Monarch 10EE 1942

              Comment


              • #8
                What is a VCR?

                Comment


                • #9
                  A few tips:
                  - You will need a good way to sharpen your carbide scraper. That means diamonds. I started with a diamond lap. The ones with the little dots. It just didn't work. I have since moved to an accu sharp. Just sharpening on the stationary disc on the bench was a huge improvement over the DMT. Silicon carbide (green) grinding wheels don't work. I hear they micro chip the edge of the carbide. I don't know how true that is, but I can tell you that an edge that is beautiful to the eye isn't sharp, so maybe there is something to that.
                  - You don't need a 60.5 degree straight edge. Any angle smaller than that will do. Just use it as a flat on one side, and tilt it up to use it as a flat on the other angle of the dovetail. It is only important that the mating angles fit well. That is ensured by using one side of the slide to spot the other.
                  - The big challenge isn't scraping (though that takes some learning). It is measuring all the big and strange geometry. Be VERY sure your measurements are correct. It's a bad day when you discover one of your measurements was off and you have to scrape your way out of it.
                  - Start scraping something flat that isn't your mill. You will mess it up, and you will appreciate you didn't mess up your mill. Then scrape something to a geometry other than flat (right angle?). That will get you a feel for the challenges of scraping your mill. It only needs to be a few square inches to get a feel for it, so it shouldn't take more time than you need to understand things.
                  - Don't think you can judge the quality of a scraping job by eyeballing it. It can be as crooked as a pretzel and still have pretty scraping marks on it. The worst looking stuff can be straight. You never know until you get the bluing out.
                  - Beware of false bluing patterns. If the surface makes a V shape, when you blue it, you will rock it on either side of the blue, making it look better than it is. Make sure to hinge the part to avoid false blue patterns.

                  Good luck! I'm looking forward to seeing your progress.
                  Last edited by Erik Brewster; 11-02-2012, 05:34 PM. Reason: grammar

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                  • #10
                    Scraping a whole machne tool so all the axes are linear and mutially perpendicular isn't hard but it does require practice, care, and sequential procedure.

                    Scraping, like any machning process, is subtractive: you remove (scrape off) all material projecting above the surface you wish to establish.

                    My suggestion is you develop your scraping skill and collect the basic equipment. The skills you can acquire by taking a class in the basics, finding a mentor who will teach you, or find books and videos you can self teach from. As for the equipment,some you buy, some you make.

                    Care has to do with the standards you set from your self. The temptation is cone you find how easy it is to scrape small areas flat very close limits (tens of millionths) is to try to make the whole machine absolutely perfect. You have to be practical and set a budget for component contributions to overall accuracy. This sounds frightening by it's something that almost takes care of itself if your order and sequence of operations are practical and well-wrought.

                    Focus early in the game on Connely's remarks on the procedure for scraping-in mating dovetail slides and how you check progress. No one check will tell you all you need to know about the fit of a dovetail way bearing to its mate. Most osf the time you need to take several check and follow their indications to final accuracy.

                    If you ensure that all way bearing pairs are closely fitted and linear, the motion of the pairs are mutually perpendicular your re-scrape will be successful. If you get the spindle correctly aligned to the coordinate system represented by the way bearings your CNC retrofit will be far more satisfactory in terms of size holding, rigidity, and productivity than a plain bolt-on kit.

                    The final problem is gib fitting. I see the machine is equipped with tapered gibs. Scraiping may remove more maerial than the gins can adjust for. You can either insert a shim behind the gib (lame but effectve) on make a new fitted gib (PITA and better buy maybe overkill) Gibs are a PITA to make or they are not-that-bad depending on your approach. When the gibs are properly fitted the machine wiil be a dream to operate.

                    The gaping porousity in the photo is a good place to any of the popular filled epoxies. Flush out the oil with and agressive ssolveny, blow dry, dress the sharp edges, and syringe in the epoxy so it fills from the bottom. Do this early in the scraping cycle.
                    Last edited by Forrest Addy; 11-01-2012, 09:33 PM.

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                    • #11
                      pretty rough. Is it new? I would have guessed someone other than the factory did this; ie doubt the factory scrapes, but that is just a guess. I did a mini mill x/y and the bearing surfaces were as the dovetail cutter left them. yuck.

                      the last few issues of the magazine has a detail account & instructions on scraping a mini mill x/y set up
                      .

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                      • #12
                        Some great advice which I thank you all for.

                        Erik - I saw in one of Mullernick's vids he had made a custom vee-way gauge for a strange angle, that's where I got the notion of making one. I am going to make a diamond lap from a spare motor and chunk of iron. I'm also fortunate enough to have some small (4x3x1/2") pieces of cast iron I bought a while back on a whim. I plan to scrape these for practice.

                        Forrest - as ever I place the greatest weight on your comments and advice.
                        I had thought about what I hope to achieve from my work, and decided that if I can get my slides working full travel with an even amount of sticktion and no slop I would be well pleased whatever the apparent finished condition. Certainly, I'm not aiming for tolerance in the tenths right now. If I find that I have an affinity for the work I can always go-over it when my skills are more developed, if not - well I'll just live with the results or pay someone to rectify my mess. I'm sure it won't come to that.

                        Mcgyver - I don't know who did the scraping, I assumed it was factory. I bought the machine used for £150 but I don't think it's used much at all - just been around a while.
                        Peter - novice home machinist, modern motorcycle enthusiast.

                        Denford Viceroy 280 Synchro (11 x 24)
                        Herbert 0V adapted to R8 by 'Sir John'.
                        Monarch 10EE 1942

                        Comment


                        • #13
                          Just revisiting this thread to let you all know I made my first effort at scraping today. I had intended much sooner but had a nasty accident with my hand and cut a tendon and some nerves, so I've been unable until now to use my left hand fo rmuch.

                          So I took this piece of cast iron I had lying around and cleaned up one side with a file and emery and spotted it with some blue on my granite plate. Clearly I need to work on my bluing as it went on too thick, but I figured it was a good enough indicator as it was, so I started scraping it.







                          Last edited by Peter.; 03-04-2013, 08:43 PM.
                          Peter - novice home machinist, modern motorcycle enthusiast.

                          Denford Viceroy 280 Synchro (11 x 24)
                          Herbert 0V adapted to R8 by 'Sir John'.
                          Monarch 10EE 1942

                          Comment


                          • #14
                            Things were quite frustrating at the beginning. I figured that I was holding my scraper at too steep an angle, so I adjusted that. I was also still struggling with the blue. I was applying it with a paper towel - need to get a roller - and it was very sensetive to how much I put on.








                            Peter - novice home machinist, modern motorcycle enthusiast.

                            Denford Viceroy 280 Synchro (11 x 24)
                            Herbert 0V adapted to R8 by 'Sir John'.
                            Monarch 10EE 1942

                            Comment


                            • #15
                              Very hard to get consitant readings with so much to learn at once - you can read up all you like but until you get your hands on a scraper and actually start doing it you don't realise how many things have to work to get a half-decent result. I paid more attention to grinding the scraper without a burr and used it very flat with lighter weight and started doing a little better. I realise these are first tentative steps and I've a long way to go, but it was quite satisfying when I was stoning the burrs off and started to have the stone stick to the work - really made me feel I was getting somewhere.





                              So that's where I'm at now. 3 hours into my first piece of scraping. All critical comments gratefully accepted
                              Last edited by Peter.; 03-04-2013, 08:53 PM.
                              Peter - novice home machinist, modern motorcycle enthusiast.

                              Denford Viceroy 280 Synchro (11 x 24)
                              Herbert 0V adapted to R8 by 'Sir John'.
                              Monarch 10EE 1942

                              Comment

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