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  • Combination metric and Imperial hand wheel scales on our machines

    I have to admit that I've never really looked at this too closely in the past. Early on I saw that the metric scale on the cross slide hand wheel had an odd number of graduations and forgot about it until just now while reading the thread about handwheels on the leadscrews.

    So first off I just assumed that the 12 major graduations were for 1mm each. But then the light dawned that with only 1/8" or 3.175mm of travel that this was not right. So it seems that each major graduation of 10 units should be .25, .5, .75 then 1 and so on up to 3.0 with 7 more small steps more before hitting 0 again. But it's not, it's graduated with 10 small marks of .025mm each then at each of 10 marks there's a major line with a 1 then 2 then 3, etc. So turning in from 0 to get a 1mm depth of cut I need to turn it to "4".

    Is it any wonder that I removed the index marker for the metric scale on the dial early on? I likely said "Self, that's rather useless!" and only re-discovered it just now.

    For those of you with combo scales is this what you have as well? Is there a method to the apparent madness?
    Chilliwack BC, Canada

  • #2
    Don't know why I didn't also look at the milling machine. 10TPI lead screws on that one with the metric scale having the same 127 markings but this time of .02mm instead of .025. But it has the same silly 0 to 12 major numbers at the 10th minor mark. That make no sense to me at all. Do ANY of you folks work in metric with this oddball scale? Are metric only machines actually marked in proper mm's?
    Chilliwack BC, Canada

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    • #3
      [QUOTE=BCRider;1107330... Are metric only machines actually marked in proper mm's?[/QUOTE]

      Of course.

      There IS a way to get both, by incorporating two scales, and two dials, with gearing between them. This HAS been done, works fine. I believe there actually was an article in HSM about making that setup, 10 or so years ago.
      CNC machines only go through the motions.

      Ideas expressed may be mine, or from anyone else in the universe.
      Not responsible for clerical errors. Or those made by lay people either.
      Number formats and units may be chosen at random depending on what day it is.
      I reserve the right to use a number system with any integer base without prior notice.
      Generalizations are understood to be "often" true, but not true in every case.

      Comment


      • #4
        My hardinge HLV has dual dials. There are 10 tpi feed screws with the imperial 0.2" dial having a 127 tooth internal gear on it. The metric 5mm dial floats coaxially with the imperial dial and has a 125 tooth internal gear. There is a single pinion connecting the two together. The pinions have a habit of wearing out after only 65 years and I really need to work out what the DP is, so I can make/buy replacements for the three dials.

        In the meantime one can work in inches or millimetres as desired, and even swap units during an operation. It's almost like having a DRO.
        Location- Rugby, Warwickshire. UK

        Comment


        • #5
          I just had to run into my shop and turn on the DRO on my CX601 mill to check this--One full turn of the X or Y axis handle gives 0.125" of travel. there are 50 graduations on each dial, so one graduation equals .0025" or .063 mm. I knew as soon as I got my mill home that I was going to have to buy a DRO set up for it.---Brian
          Brian Rupnow
          Design engineer
          Barrie, Ontario, Canada

          Comment


          • #6
            Originally posted by brian Rupnow View Post
            I knew as soon as I got my mill home that I was going to have to buy a DRO set up for it.---Brian
            Me too
            “I know lots of people who are educated far beyond their intelligence”

            Lewis Grizzard

            Comment


            • #7
              My Force International 1440 (house brand for a now defunct retailer) has both metric and imperial on all the dials, as well as tables for both metric and imperial threading (and two other types of threads)...

              Comment


              • #8
                Originally posted by J Tiers View Post
                Of course.

                There IS a way to get both, by incorporating two scales, and two dials, with gearing between them. This HAS been done, works fine. I believe there actually was an article in HSM about making that setup, 10 or so years ago.
                I have a geared one here that fits an imperial Bridgeport screw an OEM item I am told.

                Paul

                Comment


                • #9
                  Method to the madness? Well, you start with two completely different definitions of a standard for length. One was originally based on the finger of a long dead English king and the other based on a fraction of the distance from the poles to the equator. Both of these are very difficult to actually measure. They were developed in countries that were often at war with each other so bringing them together was also probably difficult, but the scientists did try.

                  Fast forward to the present or at least to the last 100 years or so. Both systems had been detached from the original finger and half line of longitude and had been embodied in more manageable forms, but there were many copies of these "standards". And more modern methods of comparison had shown that the various copies of each standard did not match each other perfectly.

                  Some time ago those scientists got together and produced a single standard meter that was supposed to be the master and then copies of it for the various countries that needed them. Not perfect, but as good as they could make it. And the inch was not easy to express as any simple fraction of that standard meter. As measurement methods were refined, the decimal places in the translation from meter to inch increased, seemingly without limit. This made for an impossible situation. So, the wise men decided on a single, fairly conversion factor that came very close to the previous standard for the inch/foot/yard. And that number was decided to be the official, new DEFINITION of the inch. It was EXACTLY 25.4mm and no matter how many additional decimal places you wanted, they were all, BY DEFINITION, zeros. 25.4mm IS an inch to a million places of accuracy and many, many more. BY DEFINITION.

                  For better or worse, that was the best that they could do for standardizing the conversion between the two systems without causing a lot of confusion. If they had dropped the 0.4mm from it, then everything measured in English units prior to that point would instantly be in error by 1.57..... percent. That was far too much of an error to tolerate so the 0.4mm remained. It had to remain.

                  That leaves us with a problem if a MECHANICAL conversion between the two systems is to be constructed. 25.4mm in an inch is not a whole number and you can not make a gear with 25.4 teeth. 50.8mm in two inches is also awkward. So is 76.2mm in three inches and so is 101.6mm in four inches. That brings us to 127mm in five inches. This is the first point where whole numbers of the two units will line up perfectly. If you notice, both of these numbers, 127 and 5, are primes. Neither can be evenly divided by any numbers except 1 and themselves: that's the definition of a prime number. So there is no way to reduce the fraction formed by them to lower terms. It is already minimized as far as you can go. (Note: 25.4 X 10 = 254mm in ten inches. But that number is not prime as it can be divided by 2 yielding 127. That is how the number 127 is related to the original 25.4: it is five times 25.4)

                  This means that we can form a gear train that will precisely translate from one system of measure to the other, but one of the gears in it must be either a 127 tooth or a multiple of that number (254, 381, etc.) I can remember reading in an industrial journal around 50 years ago how this precise definition of the inch as 25.4mm made it possible to make such gearing for industrial machine's feed knobs. They said "possible", not simple. They showed an exposed drawing of such a feed knob and it was somewhat akin to a Swiss watch. And at least one of those gears had 127 teeth.

                  It seems that in the years since then many manufacturers have tried to come up with simpler, less expensive ways to handle this problem. Some inexpensive, import machines actually ignore the 0.4mm and translate feeds based on 25mm per inch. Most of the import milling machines use this factor on their quill feeds. The basic quill feed is based on about 125mm of travel and the metric versions of them would show the feed in fractions of a mm. They just slap a 100 division scale marked as thousandths of an inch on a simple change in the gearing that produces 2.5mm of motion per revolution. That gives you a 0.015748..." error per inch of travel as displayed on the inch scale. That can get to be real noticeable.

                  Eight TPI screws are common. Gears cost money and the other parts that contain them are also expensive as they need to be made to fairly precise to keep the proper mesh if the gears have small teeth. You are in the realm of clocks. But 8 TPI screws are a challenge for two scales without gearing between them. As seen in the original post, 1/8" may equal exactly 3.175mm, but that hanging decimal (0.175mm) is difficult to handle. If you ignore it, after eight turns, you are a whole mm off so that is not a good idea.

                  You can use a helical scale with eight turns. Try reading that while making a part. Reject percentage will exceed 80%. So they try to subdivide the mm markings into a number of divisions such that they will come out even at a single turn of the wheel. That means that you will need to divide that 3.175mm by that factor of 127 which gives you, surprise, surprise, 0.025mm. This is where that number comes from. It is precisely the largest size division of that 1/8" distance where the English and Metric scales will come together EXACTLY. So, you have 127 markings of 0.025mm in 1/8" or 3.175mm. And all of this is EXACT. No rounding or approximations.

                  0.025mm is 1/40 of a mm so, in order to keep things exact, you are stuck with that as your distance between the divisions on the metric dial. This is not necessarily bad as one mm equals 0.03937" or approximately 40 thousandths.So the two scales will be comparable in terms of accuracy. 40 X 3 gives 120 such divisions for three mm and that leaves the extra 7 divisions that are just there, past the 3mm mark. If you need a distance of 4mm, then you need to stop 7 divisions short of the 1mm major division on the second time around. In fact, on that second time around, you need to stop 7 divisions short for any number you want to hit. On the third time around that becomes 14 divisions short and on the fourth time around it is 21. It keeps going up by multiples of 7. Simple? Well, yes and no. But that is how it works. And it is exact. That's where those numbers come from.

                  Notice that the 127 divisions for an 8 TPI screw are close to the 125 divisions that give you thousandths of an inch on that same screw. This makes that number more reasonable. More divisions for a metric scale would make the hand wheel larger by whole number multiples. A scale with 254 divisions would need to be twice the diameter of the 125 division scale for inches if it were to be equally easy to read. So that number is a good fit for a 8 TPI screw. Other screw pitches would yield other solutions.

                  You can thank that English king and French scientist, but that's going to be hard as they are both long gone now.

                  I agree that this is one of the best arguments for getting DROs or CNC.



                  Originally posted by BCRider View Post
                  I have to admit that I've never really looked at this too closely in the past. Early on I saw that the metric scale on the cross slide hand wheel had an odd number of graduations and forgot about it until just now while reading the thread about handwheels on the leadscrews.

                  So first off I just assumed that the 12 major graduations were for 1mm each. But then the light dawned that with only 1/8" or 3.175mm of travel that this was not right. So it seems that each major graduation of 10 units should be .25, .5, .75 then 1 and so on up to 3.0 with 7 more small steps more before hitting 0 again. But it's not, it's graduated with 10 small marks of .025mm each then at each of 10 marks there's a major line with a 1 then 2 then 3, etc. So turning in from 0 to get a 1mm depth of cut I need to turn it to "4".

                  Is it any wonder that I removed the index marker for the metric scale on the dial early on? I likely said "Self, that's rather useless!" and only re-discovered it just now.

                  For those of you with combo scales is this what you have as well? Is there a method to the apparent madness?
                  Paul A.
                  SE Texas

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

                  Comment


                  • #10
                    Guys, it's not so much the 127 units on the metric side that confuse me. Nor is it the idea that an inch is 25.4 or that there's a unique relationship. That's all fine. It is the totally arbitrary graduations of 1 thru 12 for the major marks for each ten small marks. This makes no sense at all. So a full 1mm occurs at the index mark labeled "4" on my lathe and "5" on the mill due to the difference in the lead screw TPI.

                    Here's a picture of one of the mill handwheel scales so you can see what I mean. You can see the two scales and the sizes of the increments and each of the 0's. Needless to say the "1" is not 1mm. Yet they number it "1"..

                    Chilliwack BC, Canada

                    Comment


                    • #11
                      One of my lathes has two scales on one dial. It's a 2.5mm pitch but it's fairly close to 10tpi so they just printed a 100thou scale on it too. It accrues .0016" error per turn. I don't find it so much of a big deal since the screw is worn more than that in the middle, I just rough down near to size and then take a measurement just as you would normally. It's a fairly small lathe.
                      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


                      • #12
                        Originally posted by BCRider View Post
                        Guys, it's not so much the 127 units on the metric side that confuse me. Nor is it the idea that an inch is 25.4 or that there's a unique relationship. That's all fine. It is the totally arbitrary graduations of 1 thru 12 for the major marks for each ten small marks. This makes no sense at all. So a full 1mm occurs at the index mark labeled "4" on my lathe and "5" on the mill due to the difference in the lead screw TPI.

                        Here's a picture of one of the mill handwheel scales so you can see what I mean. You can see the two scales and the sizes of the increments and each of the 0's. Needless to say the "1" is not 1mm. Yet they number it "1"..

                        Thats pretty confusing way to mark the wheels. Even my Kerry lathe is way better, I replaced the worn out 10TPI cross slide screw with metric 2mm pitch so now "0.1" takes 0.4mm off the diameter and finest graduation is 0.04mm
                        My guess is that someone made gazillion of these handwheels by accident and now if western marketdroid wants to buy the cheapest possible lathe from Asia they dig up the bastard handwheels from warehouse bottom
                        Location: Helsinki, Finland, Europe

                        Comment


                        • #13
                          My lathe has a metric rack on it, but the dial on front of the apron is marked imperial. Now this is really strange. One full turn of the wheel moves the rack 1.1811". or 30 mm the dial has 59 equal divisions on it. Each division moves the rack .0200" or .508mm. This is kind of a moot point anyways, because the apron wheel gives such a coarse movement I only use it for finishing up the last .050" of a longitudinal cut under power feed anyways. (and I really DO miss the little handle on the end of the leadscrew which was on my previous lathe for longitudinal travel.)
                          Brian Rupnow
                          Design engineer
                          Barrie, Ontario, Canada

                          Comment


                          • #14
                            Considering that the totally accurate solution is made by the thousands and sold for $29.95, this is clearly not rocket surgery.

                            I have several dial calipers, at least one of which cost that, which have the two needles geared at the correct 2.54:1 ratio, so the mm needle turns 2.54 times per each 0.1" indicating turn of the inch needle. No, they do not have double racks, there is just one rack, and the dial mechanism does the conversion.

                            There is no nonsense of error, nor fractional divisions left over, backlash, or any other such crappola. It just works and works well. In fact, the calipers agree completely with the metric and inch mics, and the ratio is at all times correct. Lathes are made with dual dials in the same way, that move at different rates.

                            The dual marked dials, and 2.5mm mismarked dials are just made that way because it is cheap. And because stupid americans will never know the difference because none of them know what a millimeter is anyway,all they know is fractional inches.

                            https://books.google.com/books?id=7e...0lathe&f=false
                            Last edited by J Tiers; 03-26-2017, 11:15 AM.
                            CNC machines only go through the motions.

                            Ideas expressed may be mine, or from anyone else in the universe.
                            Not responsible for clerical errors. Or those made by lay people either.
                            Number formats and units may be chosen at random depending on what day it is.
                            I reserve the right to use a number system with any integer base without prior notice.
                            Generalizations are understood to be "often" true, but not true in every case.

                            Comment


                            • #15
                              It's nice that some of you have those geared hand wheel dials. But I'm not about to change out the lathe to get such a thing. I'll simply do as I've done in my ignorance for the past 25 to 27 years of using this lathe and ignore the odd metric scale it has and work in inches. I'm really only curious about this odd method of marking the metric scale in this way.
                              Chilliwack BC, Canada

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