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Incorrect dial on my Acra RF45?

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  • Incorrect dial on my Acra RF45?

    Hello to all. Not only am I new to this forum,but I'm new to machining.I just purchased a used Acra RF45 the other day and I have a crazy question. All of the dials except for the quill feed read in inches. The Quill in mm.The crazy thing is that it is graduated in .02mm per hash mark, but the dial reads 270 graduations per revolution! I would have expected a round number like 300mm. After putting an indicator on it, it reads approximately .106" per revolution! None of my math works out for this. Has anyone else experienced something like this? Any help would be greatly appreciated!
    Bob
    Last edited by Bobbiggs; 03-29-2017, 03:07 PM.

  • #2
    Welcome to the board. You will find it friendly here.

    I left a PM for you on that other board, but in case you missed it, here it is below.

    The imported mills have had a long time problem with the accuracy of the quill downfeed scale. It seems that they have been designed as a metric mechanism. For the English models they have taken various half measures to give approximate readings. The most common one was to use 25mm as the basis of one inch, instead of the proper 25.4mm. This produced an error of about 16 thousandths over that distance. I have a Grizzly RF45 type and it actually has an accurate inch scale, but it reads in increments of 0.002". I added a digital caliper for a quill readout and do not use the scale anymore.



    From your numbers it appears that the manufacturers may have actually, finally made an English version of this downfeed and then they had to do a bad job of converting it to metric. It is puzzling why they can't get it straight. Adding a known good scale, like I did, is the best option and it is not expensive. You can get those calipers for $10 or even less.

    Paul A.
    Paul A.
    SE Texas

    And if you look REAL close at an analog signal,
    You will find that it has discrete steps.

    Comment


    • #3
      Originally posted by Bobbiggs View Post
      Hello to all. Not only am I new to this forum,but I'm new to machining.I just purchased a used Acra RF45 the other day and I have a crazy question. All of the dials except for the quill feed read in inches. The Quill in mm.The crazy thing is that it is graduated in .02mm per hash mark, but the dial reads 270 graduations per revolution! I would have expected a round number like 300mm. After putting an indicator on it, it reads approximately .106" per revolution! None of my math works out for this. Has anyone else experienced something like this? Any help would be greatly appreciated!
      Bob
      The problem isn't your math it's their's. Seems they are off by a factor of exactly 2. Cross out the .02mm and relabel it .01mm. My quill
      downfeed is labeled 0.080" per revolution. I measured that once, it was off by 3 thousands.
      Location: Long Island, N.Y.

      Comment


      • #4
        Oddly enough I posted about this in a recent thread. And you're right, it's very confusing how they mark the metric side.

        http://bbs.homeshopmachinist.net/thr...n-our-machines

        It's odd that your quill only has the so called mis marked metric graduations on it. Did you buy it new? If so I'd check the box of extras to see if there's an inch wheel that goes on in place of the metric wheel.

        If you measured .106 on the quill feed I'd suggest that the intent was to have it move by 0.100 per turn of the wheel but you're looking at a .006" error due to how the pinion and rack is machined. It's tougher to make a rack and pinion it would seem. The way around it would be to do as Paul did above or to fit the quill with a 2 inch dial gauge on a positionable rack and use that. In the meantime it sure seems like you could use a new dial with the proper 100 divisions. Because certainly the 127 division metric oddity is pretty much worthless and annoying.

        RichR, for a 127 division "metric" wheel on a nominal 0.1" travel rack the .02mm per division is actually correct. And the 1mm and 2mm points would occur at the "5" and "10" major index marks that occur at each 10 minor divisions.
        Chilliwack BC, Canada

        Comment


        • #5
          I rechecked mine. As I said, it is the Grizzly version of the RF 45, the GO484. It has been so long since I even looked at the OEM scale that I had forgotten the details. It is divided into 75 divisions that are supposed to be 0.002" each. That's a total of 0.150" per revolution or at least that is what it is supposed to be. So, mine is at least one example of the attempt to make one with a quill feed in English units.

          But when I checked it against the digital scale I have mounted on it, it read between 1.002" and 1.006" when that OEM scale said one inch. Better than the older models, but they still did not get it quite right.

          Between the hassle of 0.150" per revolution, divisions that are 0.002" instead of 0.001", and the still remaining error, I figured that the addition of a digital scale was almost a necessity.

          This is a rack and pinion style feed with gearing between that pinion and the hand wheel. And for either English or metric units, it will require a non standard pitch. Perhaps they just used the closest available one and figured it was close enough.
          Paul A.
          SE Texas

          And if you look REAL close at an analog signal,
          You will find that it has discrete steps.

          Comment


          • #6
            Originally posted by BCRider View Post
            RichR, for a 127 division "metric" wheel on a nominal 0.1" travel rack the .02mm per division is actually correct. And the 1mm and 2mm points would occur at the "5" and "10" major index marks that occur at each 10 minor divisions.
            That's nice, but Bobbiggs said his dial has 270 divisions. (270 x .02)/25.4=.2126. Divided by 2 gives .1063 which is what he basically measured.
            Location: Long Island, N.Y.

            Comment


            • #7
              Originally posted by RichR View Post
              That's nice, but Bobbiggs said his dial has 270 divisions. (270 x .02)/25.4=.2126. Divided by 2 gives .1063 which is what he basically measured.
              You're right. I was fixated on the 127 divisions on my dials from the other thread.

              Which is odd again because 127 x .02 is 2.54mm and 0.1" which we WOULD expect from a proper imperial rack or leadscrew. And if his quill rack was supposed to be .1 per turn then it should be marked up to 254 x .01 and not 270. But in his case it seems like the dial was divided to suit the rack and the odd .106 travel per turn. How odd.......
              Chilliwack BC, Canada

              Comment


              • #8
                WOW! Thanks for all of the good advice! Rich R's advice makes sense, the dial should read ".01mm" not ".02mm". I like the setup that Paul did on his Grizzly. I think that is going to be my first project. Thank you all for the help. Oh, and by the way, Thank you Paul for suggesting this forum!
                Bob

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