Announcement

Collapse
No announcement yet.

Smooth finish vs flaked/scraped finish

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

  • #16
    Rich King calls it chicken scratching when the marks are there but almost nothing is removed, You need a sharp scraper and a light touch to get something in between that and a regular 1-2 tenth scrape valley.

    I've never tried it, as soon as I have the right coverage in terms of points, area covered, and distribution, I figure I am done. I'n not making surface plates, but scraping ways, so I don't need 40ppi and shallow marks.
    CNC machines only go through the motions

    Comment


    • #17
      My experience shows that the cuts I make when rough scraping with the Biax can be as much as maybe .010" deep. The majority of the time is spent with finishing cuts and those rarely go deeper than .0002".

      My granite is 12 x 18, black, and when I apply the blue it's so thin it's hard to see it even up close. One cannot mark for .0001" or better if the ink film is a significant fraction of that in thickness! Aim small, shoot small.....

      Pete
      1973 SB 10K .
      BenchMaster mill.

      Comment


      • #18
        Originally posted by 10KPete View Post
        My experience shows that the cuts I make when rough scraping with the Biax can be as much as maybe .010" deep. The majority of the time is spent with finishing cuts and those rarely go deeper than .0002".

        My granite is 12 x 18, black, and when I apply the blue it's so thin it's hard to see it even up close. One cannot mark for .0001" or better if the ink film is a significant fraction of that in thickness! Aim small, shoot small.....

        Pete
        10 thou in a stroke? Wow, I can't recall indicating rough work so don't know how deep i'm going, but having 10 thou to rough off something is huge amount of work scraping, many many diagonal iterations, its enough that I start to think of machining it. I can't imagine i've ever got a 10 thou DOC

        as for the .0001, when you are doing the finest work, you are taking the point off that breaks through and is surrounded by faint blue, not the blued area.
        Last edited by Mcgyver; 03-27-2018, 09:19 PM.
        in Toronto Ontario - where are you?

        Comment


        • #19
          Yeesh... 10 thou would be handy to get in one sometimes, it usually takes me a few passes to get to 3 or 4 thou when I want to shovel off material, as when step-scraping to pull a surface that is misaligned. But I don't think I'd want to do the 10 thou much of the time.

          You must be a real gorilla.... I'm just 180 lb or so, and I do not get that sort of digging done.

          Yeah, taking the center out of "bull's eyes".
          CNC machines only go through the motions

          Comment


          • #20
            Originally posted by Mcgyver View Post
            curious how you know - did you take them apart?
            Only "took apart" one - a 4VH box way version - no flaking or scraping any mating surface. I don't remember if the gib had any.

            On all you can see the silky smooth knee top side (obviously) and if you move the bed to beyond the typical extremes (x) you can see the topside of the saddle. A good way to check wear - the extremes of the saddle are the major wear point on a knee mill. In the absence underneath the table, if there was flaking you'd see it on the the saddle.
            Last edited by lakeside53; 03-27-2018, 09:55 PM.

            Comment


            • #21
              Are they like Acra?
              They use Turcite on the upper and lower surfaces of the saddle and that's where it's scraped.
              Len

              Comment


              • #22
                I have some lathes and mills with both. I dont think it matters what process is used but more importantly if it was done in a good fashion.

                I have an enco rf-45 with ground ways. They are not as terrible as I have seen but still not impressive. My old SB lathe has ground (I think) ways and it is rougher due to age and wear.

                I can get around both of those because I like and want both machines. I have an emco cnc lathe that is ground but cant tell the feel due to well, you know. But the way surfaces on that machine look and feel much nicer.

                My bridgeport machine looks to have flaked chrome ways, and they are silky smooth. It has pressure fed oiling as does my enco rf-45. Plenty of lube allows me to keep all the gib strips tight to where I like i.

                My monarch lathe looks to be scraped but it is so difficult to tell I cant say for sure. And that movement is like none of my other machines or any I have used. You go to move the saddle with the smallest of force and in the smallest distance and it does just that. Its weird to say but it feels like a linear movement from my hand to the saddle.

                Again, I dont think it matters much with either, chasing gnats at that point. Use some proper way lube and cut metal JR

                Comment


                • #23
                  Originally posted by lakeside53 View Post
                  Only "took apart" one - a 4VH box way version - no flaking or scraping any mating surface. I don't remember if the gib had any.
                  .
                  that's what I was wondering, could there still be scraping on the mate. Apparently not, at least on those. I should state I'm not on about flaking/frosting; its for a different purpose. I'm more interested in scraping and its current application (if any) in quality machine tool manufacturing.

                  To state the obvious, for anyone who's thought it through, the great challenge is how to make two parts with complex geometry and alignment requirements. Its not simple or easy to grind say the bed and then grind the underside of the headstock, have all three surfaces mate to a tenth over their entire areas and have the spindle perfectly aligned. Its not easy to the point where quality makers didn't try - the scraped the mating part.

                  A bunch of things have changed in the world; we have super accurate million dollar cnc grinders and machine tools aren't made by the same companies in the same plants. otoh no one started making machines in Taiwan because of their superior techniques and quality, do they not scrape because they have the million dollar grinder making it unnecessary, or do they not scrape the mate because they're striving for a lower level of 'good enough'....which may well be good enough, its light mill after all not a Moore jig borer.

                  Up until a few years ago Standard Modern, the last manual lathe maker in NA, scraped everything to the bed. Was this done because of limitations of the equipment (a 20' gang wheel grinder) or because it was it was the way to achieve the best quality? The owner thought the later, but there was no way that business could afford the million dollar cnc grinder. Are all the makers who don't scrape 1/2 of the mating parts in possession of the million dollar grinder? I doubt it. I took a china mill apart once and laughably the dovetail bearing surface was very roughly milled with the clearance surface (that touched nothing) beautifully ground.

                  What about the next level up from Taiwan mills, are they scraped? Do they need to scrape the mate? Anything big and quality is going to be box ways requireing accurate mates, are they easier to grind? I don't know, but I see Richard King reporting the training he does in machine tool factories, I recognize from first hand experience the challenge in getting bearing parts mating correctly AND aligned and have seen the 'grind one side scrape the other within the last, well certainly in the last 10 years, in use. I don't know the answer, but I think one would need a lot more insight into all the places making machine tools to conclude its in the past insofar as a manufacturing technique goes.

                  As Jerry says, its largely academic for us, any work/reconditioning we do is going to involve scraping, but I am curious as to current production techniques
                  Last edited by Mcgyver; 03-28-2018, 09:04 AM.
                  in Toronto Ontario - where are you?

                  Comment


                  • #24
                    I suspect you can take your cue on this from all the other industries......

                    The overall goal seems to be to have a "worker-free" factory. Even the "taxi cab" companies (Uber) want to have taxis with no pesky and expensive driver. Is it any wonder that the whole idea of having "fussy hand work" is hated and despised by factory managers? It's the absolutely worst part of having workers.... having ones who are skilled and essential, who know that, and so need to be paid accordingly.

                    As another point, it goes against the idea of interchangeable manufacturing. It is to a great extent the same issue as the old time fitting and filing when making firearms. That was hated because one broken part meant the piece was useless and unrepairable in the field, where you really want to be able to make, for instance, 4 good ones out of 10 broken ones, and get them back in use. That was far faster than making 4 new from scratch.

                    I agree that the column casting of a mill is not generally a replaceable part, but the idea has percolated over to any production process; a specific time and operation sequence is wanted, and that is perceived, at least, as not existing with hand processes. But, if a fixture and grinding process can be set up to get the same result, or one that is at least "within spec", then you know and can predict accurately, the production time and costs.

                    It really is the end point of capitalism, the inverse of other "isms"... not only do the workers not own the "means of production", there aren't any workers in the first place.

                    Scraping is not even needed for machine repair, as new interchangeable parts (produced in the same way) can be put in, restoring the machine to new spec, and allowing it to resume producing accurate parts for the product. Newer machines are designed such that scraping is not required, and they are more accurate as a result.

                    It is the factory owner's dream come true. No workers, just a few "on-call" repair contractors.
                    Last edited by J Tiers; 03-28-2018, 10:03 AM.
                    CNC machines only go through the motions

                    Comment


                    • #25
                      doesn't really address the questions......is it still used in high end machine tool manufacturing? You know or is it just speculation? Is it not necessary to scrape if you have a million dollar grinder? Who is Richard teaching to scrape - do they see it as a superior technique or can't they afford the million dollar grinder? Short having the million dollar grinder, is a manufacturing faced with either scraping or turning out low quality machines?

                      Those low cost lathes that keep cutting as you drag the tool back over the work are an example, they are obviously not scraped and obviously have poorly fit matting surfaces. At the other end of the spectrum, the best machine tools have perfectly fit ways.....how?
                      in Toronto Ontario - where are you?

                      Comment


                      • #26
                        Originally posted by Mcgyver View Post
                        doesn't really address the questions......is it still used in high end machine tool manufacturing? ........
                        Kinda did actually.... No scraping unless it is the only way to make spec..... where it is not avoidable.

                        Many CNC seem to use round rail linear bearings/ball races.... all grinding, no scraping. Some older lathes (LeBlond?) used replaceable hardened and ground slideways, which at least theoretically could be just bolted into place ( I have heard that it ain't really quite that way).

                        Error correction software can fix a lot of things that used to need precision manufacturing because the precision was all mechanically set. So the absolute precision wanted does not necessarily require precision scraping.

                        I think Richard King answered the question about high end, that yes, they are still scraped in certain areas, although mot necessarily on the ways, maybe more for fits of non-moving parts, and for fitting the Turcite undersides of moving parts.

                        What's "low quality"? If it consistently makes the spec, it isn't low quality, it is a high quality but looser spec machine, maybe. So for looser spec, you might get away with machining only, no grinding. A cut up from that, ground, but not as high precision. Above that, tight spec grinding on your million $$ grinder.

                        Scraping maybe for parts that do not FIT on that grinder.... or for the grinder itself, which is maybe too big to fit on any other grinder to be precision ground.... Again, scraping where not avoidable, otherwise ground.

                        If it were not required, he would not be teaching it in industry.
                        Last edited by J Tiers; 03-28-2018, 10:52 AM.
                        CNC machines only go through the motions

                        Comment


                        • #27
                          No scraping unless it is the only way to make spec.
                          that has always been true. You're giving economic reasons that might drive it which imo are obvious. I'm more interested in the technical "how its currently" done for what class of work which I doubt either of us really know. As for linear bearings, afaik its only lower priced smaller cnc's that use them, big stuff and quality stuff is box ways.

                          It would be good to have the insight of someone who actually knew re current manufacturing practices. I suspect the reality is better grinding equipment has dramatically shrunk the sweet spot for scraping, and an acceptance of low quality fits and low prices has further cut into into, but its logical speculation not industry knowledge. We also don't know the extent of Richard and others training work; an enigma from years gone by, or are their currently many Richards (who don't post so we don't know them) training people all over Asia and Europe.

                          One fact we do know is Biax still has a pulse, it would interesting to know their sales to manufacturers vs re-builders.
                          Last edited by Mcgyver; 03-28-2018, 11:55 AM.
                          in Toronto Ontario - where are you?

                          Comment


                          • #28
                            Yep, neither of us "know", and maybe Rich King does not really know either. But he knows what the purpose of the classes was, repair or production, I assume. Even his data may be out of date, things change fast.
                            CNC machines only go through the motions

                            Comment

                            Working...
                            X