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  • Smooth finish vs flaked/scraped finish

    I was surprised to recently see that all the way surfaces and the table surface is smooth, almost a mirror finish, on a new ACER 3VSII E-mill.

    Anyone know the rationale? Is it just economics?
    Last edited by jmarkwolf; 03-26-2018, 05:59 PM.

  • #2
    Not at all surprising. New quality stuff is hardened and ground. You don't have scrape/flake marks on a hardened surface.

    It's not just new stuff either. My Sheldon circa 1976 has hardened and ground ways, while my Burke mill of a bit newer vintage does not.

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    • #3
      Not just hardended. For decades even soft BPs were ground; any flaking was cosmetic and in theory... holds oil better.

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      • #4
        yes and no. On quality machines one surface, the long one that you see, might be ground, but its mate was scraped to it. If it wasn't I question the quality, at least before the million dollar 5 axis cnc grinders that would a chance and matting two sets of ways. Thats how standard moderns were done up until a few years ago, and while a very nice lathe they're not at the top of the pile. So I extrapolate from that, and with a bit of knowledge of machine tool alignment is achieved, that it was industry SOP. There is a a view that the flaking helps by providing "oil pockets", its sort of a a traditional passed down thing, there there is an opposing view that the best bearing surface is perfectly flat (more modern tribology books). I tend to favour the later, but see a bit both sides. I thin it would require some controlled experiment to be conclusive on it. Bottom line is with, pump lots of oil in there if you want to avoid wear.

        Keep in mind that while a mottled scraped surface looks like it has lots of topography, its not difficult to scrape and end up with that look, but it won't move the needle on a tenths indicator - you could say they had that look as a by product of the technique, not an attempt to make an irregular surface. Flaking otoh is intentionally deeper, as in oil reservoir logic or lore, as you may see it
        Last edited by Mcgyver; 03-26-2018, 08:42 PM.
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        • #5
          Yep, if you put two perfect surfaces together, perfectly clean, you'll have a blip of time gettin' 'em apart! Oil? That just makes is worse as it's now, truly, a perfect match. Hmmm, can't move the slide on this thing.....;.

          My SB 10K has a very impressive pattern scraped into the bed ways. But if you really look at it the cuts are a tenth deep. Normal for light, finish, scraping. But it holds oil...

          Up facing ground, down facing half moon flaked. Always.

          Pete
          1973 SB 10K .
          BenchMaster mill.

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          • #6
            Dunno, although I DO find that the ground surfaces tend to "grip" more than a scraped (and maybe a flaked) surface. And they can rub down to a pretty thin oil layer, similar to a rubbed glue joint in woodworking.... where the idea is to get less goue and a tighter joint that is stronger. By breaking up one surface, that effect may be reduced, and presumably there is oil in the recesses that will come out and lube better and/or longer.

            For me it is not an issue, I can make a scraped surface of any length I can get a reference for, but have no means for doing precise ground surfaces. So I do not have to choose.
            1601

            Keep eye on ball.
            Hashim Khan

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            • #7
              if there is a complete layer of oil between, whether its perfect or not, they should be just as hard to separate,. but also both should be equally moveable sideways on the thin wedge. If there is not a complete layer, then the scraped should be easy to pull apart. however of there is a not complete layer of oil, 1) they should be - its the design of the machine to have the entire area bearing on the thin wedge of oil, and 2) it likely means stalagmites and stalactites (properly called aseprites) are hitting which = wear. Its also not clear to me if oil is "pulled" from a pocket, how, and what is it replaced with? Really well scraped surfaces properly lubricated last a long time, and scraping does leave as a by product slight surface variance. It's conceivable after generations of this, noticing scraped surfaces are irregular (to a small amount, could by < tenth) and they last VS more crudely made bearings that didn't, that pocket theory is advanced entirely on correlation and with cause. I haven't seen in any tribology book (and I've looked) mention of pockets or anything other than desirability of perfectly smooth surfaces and they undesirability of aseprites and that their contact is what wear is.

              otoh there is a lot of experience and support for the oil pocket idea not to be scoffed at. Its greatest merit for support I think is what happens after a month of none use and all the oil has gone away. Because its resting where the asperites collide there is minimal contact, on movements, the asperites break (wear), but it can move.....vs the potential lock you could have if perfectly flat like you'd get with a gauge block. Then again ground isn't perfectly flat either...as I said, not taking a strong position as I see both sides and haven't the knowledge or info to conclude which makes more sense. Pressed, I think I'd say perfectly smooth is idea but the oil film must be maintained or have a way of being restored.
              Last edited by Mcgyver; 03-27-2018, 07:58 AM.
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              • #8
                Smooth and ground probably goes best with pumped oil to maintain the oil film. Otherwise oil should be rubbed-out of the space.

                Scraping may be less about oil retained in pockets, and more about making it harder to get the "rubbed glue joint" effect. The "rougher" surface (although very smooth) may tend on a micro level to hold the oil, not "in reservoirs", but just hold it between the surfaces, and tend to prevent it being squeezed out as easily.
                1601

                Keep eye on ball.
                Hashim Khan

                Comment


                • #9
                  I've used a bunch of modern Taiwan mills all are ground with not flaking. No issues... I had a quick look around a cnc machine shop yesterday; no signs of hand work or flaking on any of their $$$ VMC or lathes. Of course, some of them are using linear bearings/rails. I think it is it part of the past with a few holdovers.
                  Last edited by lakeside53; 03-27-2018, 10:52 AM.

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                  • #10
                    Doncha just LOVE that easy, dismissive, phrase...... "part of the past"...? Gets rid of the question so quickly without any more discussion.... efficiently, and in a nice "modern" way... You can almost see a person waving their hand back and forth while they say it, as if they were sweeping that "old stuff" away........

                    So how are the ways on the CNC oiled? Just a squirt when someone thinks about it? Or a regular automatic pump? Right.....

                    I think that is the point.... the irregular hand oiling may go better with scraped surfaces, and the ground may go better with regularly pumped oil. Not so much that the oil is "retained in pockets", but more that the oil is not so easily squeezed out of the space between the parts.
                    1601

                    Keep eye on ball.
                    Hashim Khan

                    Comment


                    • #11
                      Originally posted by lakeside53 View Post
                      I've used a bunch of modern Taiwan mills all are ground with not flaking.
                      curious how you know - did you take them apart?
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                      • #12
                        I agree that a pressure oiled bearing behaves differently than static lubrication. With a decent fit, it wouldn't take much volume to 'float' the interface. Just need enough pressure and sufficient oil ports/channels to assure even distribution. I seem to recall that's how the big Mattison grinders are done. Even then, half-moon flaking is used on one of the surfaces and I'm assuming (!!) that it is to assure an even oil film and decent retention.

                        I, like most of us, rely on tradition to guide us on things like this but progress can be made with open-minded discussions. Besides, kicking things around is interesting!!

                        Pete
                        1973 SB 10K .
                        BenchMaster mill.

                        Comment


                        • #13
                          Originally posted by Mcgyver View Post
                          . . .a mottled scraped surface looks like it has lots of topography, its not difficult to scrape and end up with that look, but it won't move the needle on a tenths indicator . . .
                          Oh yes it will! Scraping is an averaging process. If it 'wouldn't move the needle' on a tenths indicator, it wouldn't show 'averaged' blue either when checked. Now, if you meant that a matched surface sliding on a scraped part wouldn't move the needle, ok.

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                          • #14
                            Originally posted by chipmaker4130 View Post
                            Oh yes it will! Scraping is an averaging process. If it 'wouldn't move the needle' on a tenths indicator, it wouldn't show 'averaged' blue either when checked. Now, if you meant that a matched surface sliding on a scraped part wouldn't move the needle, ok.
                            Yes.

                            As long as it shows spots, and not "smears" of blue when the blue is thin, then it has to have bumps and recesses. Usually at least a tenth, although it is likely possible to scrape down to rather small increments possibly under a tenth, possibly with the "alcohol haze" spotting method instead of blue.

                            My scrape marks are generally as small as 1-2 tenths, based on a small ball-end indicator tip. I use blue, and have never tried the "haze" method.

                            Ask Rich King and Forrest about scraping depth, and the best possible scraping as on very good surface plates.
                            1601

                            Keep eye on ball.
                            Hashim Khan

                            Comment


                            • #15
                              Originally posted by chipmaker4130 View Post
                              Oh yes it will! Scraping is an averaging process. If it 'wouldn't move the needle' on a tenths indicator, it wouldn't show 'averaged' blue either when checked. Now, if you meant that a matched surface sliding on a scraped part wouldn't move the needle, ok.
                              No, what I said. It it is not difficult to scrape something flat enough that a tenths indicator needle moving across it won't move. Done it many times. Well, it won't move appreciably, certainly less than a full increment probably not a 1/2 or 1/4 of one.

                              We're talking a over a short distance, the range from high to low. The goal might be 2 tenths over the length a given machine, but what I'm talking is movement less than a tenth from high to low over a short distance, i.e. the height from peak to valley that you'd go through say 5-8 times over a inch of indicator travel

                              I did not say I regularly strive for that or that is necessary to always be a fraction of a tenth, but that it is not difficult to do.
                              Last edited by Mcgyver; 03-27-2018, 08:43 PM.
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