Announcement

Collapse
No announcement yet.

Grinding vs Scraping?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #46
    Peter. cool info. (just thing out loud) I Have a Heavy 10 South bend compound I would like to sparkle up !
    Say I mill the flats of it on my Bridgeport to within .0005 to .001or so (forget the dovetail for now for the sake of the example)
    ......then write a program in my cnc and just drag a carbide scriber back and forth to make a mesh pattern. ( say over .050 each)
    40 lines per inch horizontal ....40 lines vertical = 400 little squares.......for me basic machining. Has anyone done this? The scrapping thing for me is just too much skill. Thank you....Dean
    www.neufellmachining.com

    Comment


    • #47
      Originally posted by dneufell View Post
      Peter. cool info. (just thing out loud) I Have a Heavy 10 South bend compound I would like to sparkle up !
      Say I mill the flats of it on my Bridgeport to within .0005 to .001or so (forget the dovetail for now for the sake of the example)
      ......then write a program in my cnc and just drag a carbide scriber back and forth to make a mesh pattern. ( say over .050 each)
      40 lines per inch horizontal ....40 lines vertical = 400 little squares.......for me basic machining. Has anyone done this? The scrapping thing for me is just too much skill. Thank you....Dean
      Scraping is to gain an accuracy greater than what your CNC can produce. If you just want the "look", why not examine "engine turning"? Not the same kind of look, but perfect for CNC.

      Comment


      • #48
        Originally posted by dneufell View Post
        The scrapping thing for me is just too much skill. Thank you....Dean
        As someone who has made a considerable effort to make it accessible, I would challenged that. There is very little skill involved. Not more, and maybe less, that what is needed to tap a hole. Its not art or magic, its just a simple and useful shop skill. The basic effort of flatness can be learned in a hour. From there to the most complex geometries of machine tool scraping, I'd again argue its knowledge not skill, the former imo being easier to acquire .

        All that is in your way is a bit of knowledge on and some simple tools, neither of which are overly difficult to come by.
        Last edited by Mcgyver; 02-03-2020, 07:56 AM.
        .

        Comment


        • #49
          I have to agree, the only difficult thing to acquire is patience, it's tedious more than anything.
          I just need one more tool,just one!

          Comment


          • #50
            I don't want to add to the arguments whether scraping is better than grinding. I believe they are both just techniques to achieve the same result. I do agree that scraping is more accessible to the home-shop machinist community than super precision grinders. But let me point out that 20+ years ago I was grinding natural diamond to sub-micron tolerances. So I have no problem believing that grinding can be just as accurate as scraping and way quicker.

            Just an anecdote: My Sheldon and most Sheldon lathes produced after WW2 had beds ground then flaked. Mating parts were scraped. Even the plain bearings in the spindles were scraped. So I think that there is a place for either technique. It just depends on the application. Hope this adds to the conversation positively.

            Best Regards,
            Bob

            Comment


            • #51
              Originally posted by Doozer View Post
              The scraping guys talk like this is some magic voodoo thing
              A year or so ago I asked this forum if the magic of scraping lay in the method of metal removal, or the method of analysis. The consensus was that it was in the method of analysis and plan of attack. I.e., constantly retesting against a standard and slowly adjusting the surface to meet the standard.

              At that time people stated that even a small hand grinder could work if you more or less used it in the way one uses a carbide scraper - removing small amounts of metal only in those places indicated by bluing against a reference standard. We aren't talking a DeWalt 4 1/4 grinder with 60 grit wheel... More like a Dremel.

              I think most of the "scraping guys" are a sensible lot if you approach them in a non confrontational fashion.

              Comment


              • #52
                Originally posted by rjs44032 View Post
                let me point out that 20+ years ago I was grinding natural diamond to sub-micron tolerances. So I have no problem believing that grinding can be just as accurate as scraping and way quicker.
                The question is, do you have one of those big enough and universal enough to fit your mill column on? Rhetorical of course...imo, its not about which is more accurate, its about what makes the most sense for job give the available resources. Having both for decades now, it would be very rare that one of the two doesn't leap to the forefront as being the logical best choice for the task at hand.

                Even if you have a massive like new slideway grinder, there are still lots of reasons to scrape instead of grind. For example, a mating part. With a bed reground, it would be tricky job to set up and grind all the mating surface so they were bearing all over and in perfect alignment. Standard Modern, where I spend an intense but brief period time going over operations had a huge grinder, could do 20' beds. But everything was hand scraped into the ground bed because it was considered the only sensible way to create excellent bearing surfaces and alignment with the equipment at hand. Another example is spindly work. A mag chuck imparts force which distorts. Yeah I know there are ways to mitigate that but they are not as easy or effective as scraping which imposes zero clamping force.

                If its hardened, you grind. If it simple shape that fits on the grinder you grind. I can't see scraping instead of grinding (if you have a grinder) but I also can't see grinding the parts I scrape. There's times when a piece doesn't fit either approach in ones shop - like a hardened lathe bed....there outsourcing is probably the way (pardon the pun) to go. Other than that, from the view of one who frequently does both, they're just not that much in competition when head to shop to get something done
                Last edited by Mcgyver; 02-03-2020, 10:03 PM.
                .

                Comment

                Working...
                X