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Combination metric and Imperial hand wheel scales on our machines

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  • #46
    Another question about the dials with the gearing between the metric and Imperial. I know 125 to 127 isn't a big amount. But do such setups shift the apparent center of the larger metric ring slightly so the position at the top where the pinion would be that links the dials is even? I know it's not a huge diametrical difference but that would certainly keep the gearing running smoother than having it all on a common center axis and relying on the play of the teeth for the coupling.
    Chilliwack BC, Canada

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    • #47
      Originally posted by BCRider View Post
      Another question about the dials with the gearing between the metric and Imperial. I know 125 to 127 isn't a big amount. But do such setups shift the apparent center of the larger metric ring slightly so the position at the top where the pinion would be that links the dials is even? I know it's not a huge diametrical difference but that would certainly keep the gearing running smoother than having it all on a common center axis and relying on the play of the teeth for the coupling.
      Check over what sir John said.... The teeth are "adjusted" in order to make everything fit. Any resulting "play" is far smaller than a division, and so of no consequence.
      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.

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      • #48
        Originally posted by J Tiers View Post
        Got two of them, need one, or none.... But the gears I may want are small enough that I am not confident of the shaper being accurate enough. They are kinda coarse in action. I know they are fine at 12 or 16 DP, but at 64 DP?
        It would certainly be a wise time to set the machines a touch on the snug side to remove any play.

        Hmmm.... a slightly oversized hardened steel pinion could be used as a sort of shaper run equivalent of a hob. That way it would partially cut two or three teeth ahead of the final cut of the tooth that is radially centered. I'm not sure that would save any work but it's a thought.

        Really the only way to use a rotating cutter for making such an internal gear would be some form of driven head with the cutter in the end that can pass through the ID of the rings while cutting the teeth. Otherwise you'd have to get really crazy imaginative... like 125 and 127 small diameter holes in a pattern on an internal face with pins pushed into all the holes to make an open sided lantern gear.

        For the short throw needed if you don't trust the rams of your shapers what about a plunger unit driven by the ram of the shaper? The short throw could mean such a plunger would be pretty small. Or it could be a hinged arm that is sort of "L" shaped where the short side of the "L" has the cutter on it and it swings through the ID cutting the gear teeth. Yes it would be cutting along an arc of travel. But a long enough "L" with the small width of cut would make the depth of the arc insignificant. Here again this plunger or swinging cutter arm could be driven by the ram of the shaper. But really there should be no need if the dovetail for the ram and the ram are in nice condition and can be tuned to run well over the short amount of throw needed. Even if it means it would bind badly in some other spots you won't use them there. And you can open up the clearance after the gears are cut.

        Whatcha'think?
        Chilliwack BC, Canada

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        • #49
          Someone needs to explore the possibility of using the idea of the cut knurler, or the rotary broach for cutting the internal gear. Such a tool would need to take tiny bites to be useful on hobby machines.
          Last edited by J Harp; 03-27-2017, 10:15 PM. Reason: For clarity, & capitolization
          Jim

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          • #50
            I don't know that it is a case of not trusting the ram, so much as it is the knowledge that a thou or two error in any direction is a huge amount with gears like that. Just the oil thickness is a variable of significant size as far as the gears are concerned. A 64 dp gear has teeth a bit under 50 thou pitch by my rough estimation.
            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


            • #51
              Originally posted by John Stevenson View Post
              The number of teeth on the idler wheel has no relationship to the calculation.
              It's only the 127 / 125 difference that matters.
              Yes. The comment was more to give a rough indication of the size they were and because I'd pointed out that they have a tendancy to wear out over time (thus needing new ones to be made).
              Location- Rugby, Warwickshire. UK

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              • #52
                I had the dilemma of the metric/ imperial with the old imperial Smart & Brown model A at the museum. The cross slide leadscrew was worn in the middle, which made backlash adjustment over the entire range impossible. I stoned the ends with some success, but was pleased when an unknown make of leadscrew long enough to accommodate at least 7" of movement turned up on eBay.
                It was advertised as 8tpi and had two substantial bronze nuts, all unused. It turned out to be a 3mm pitch. I got in touch with the vendor who was very apologetic, refunded the money and said keep it.
                Making a dual scale was way beyond my capabilities, so I modified it to fit and we made a replica scale with 118 divisions instead of 125.
                3mm is actually 0.118110236" or thereabouts, but for our purposes it's good enough for government work.
                Backlash over the entire range is 0.0005".
                Last edited by old mart; 03-28-2017, 01:39 PM.

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                • #53
                  If the travel is less than a full turn, 118 divisions is as good as 125. And if the travel is more than a full turn, it's no more trouble to deal with 118 than 125, they're just numbers.

                  But, IMNSHO, all feed screws should be required, by law, to have 10 tpi so I can do the arithmetric without making so many mistakes.

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                  • #54
                    Originally posted by cameron View Post
                    ......But, IMNSHO, all feed screws should be required, by law, to have 10 tpi so I can do the arithmetric without making so many mistakes.
                    I hear ya! ! ! ! If only.....

                    The new knee mill that I used for the dial picture has 10TPI screws. The lathe has 8TPI overall. That includes the compound.

                    I've gotten used to working around the crossover from 124 to 0 on the lathe. It does cause me to count "one little piggy, two little piggy, three li...." when increasing the cut past the transition. But I've gotten used to it. But it would be easier/nicer if the lathe were all 10TPI even if it did mean having to spin the wheels a few more times.

                    My shaper is the oddball. It uses 6TPI for all the table leadscrews. So 166.6666666666667 thou per turn of the screw. No even numbers for ME! BUT WAIT! THERE'S MORE! Even the tool post holder slide on the ram is an oddball because the dial runs up to 80 then the next decade mark is 0. That's right, .09" per turn. So technically this is 11.1 TPI..... Who in the hell would make an 11.1 TPI screw... other than the Brits! ! ! ! And no, I did check and sure enough. Offering up the pointers from a set of calipers set to 1" shows a thread count of 11 and a little more. So it really is an 11.1 TPI screw.

                    Faced with the oddities of the shaper I have to say that the "blue sky" 0 to 12 +7 metric scale oddity on the lathe and mill pale into insignificance......
                    Chilliwack BC, Canada

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                    • #55
                      If it's really oddball, send it to Chilliwack.
                      Probably using proprietary threads so the user has to buy spares from the manufacturer, you might need a time machine though.
                      The non standard crosslide leadscrew has been noted in the lathe documentation for future users benefit.
                      Last edited by old mart; 03-28-2017, 04:41 PM.

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                      • #56
                        Hmmmm, I know the 'remainder' on these scales is a confusing annoyance but this is a homeshop site and I am sure there are people here who could craft a solution.

                        For example devise some system so the scale wheel automatically advances (or retards) past the remainder zone. It would work like this, with an imperial feed screw and metric markings advance to 125 reading and the scale would 'click forwards' to 0 reading, advance some more and the scale reads 1.

                        Of course if 125 is too awkward you could make the advance point at 100.

                        There is no reason why you could not make the scale manually settable with stops according to the size of the remainder zone.

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                        • #57
                          I am not sure about the 11.1" pitch leadscrew but I suspect it is somehow related to the ligne.

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                          • #58
                            AB, all the wheels on the lathe and mill are settable so if I were working in metric I'd do just what you are saying manually. But I work so little in metric that there would be no point in making a flipper device. Or if I were going to do anything I'd simply buy a DRO or for occasional use rig up a metric ruler attached to the machines or rig up some clamp on rig to hold a digital caliper and use it as a 0-150mm temporary DRO.

                            What really prompted me to post was the reasoning behind the 0-12 arbitrary markings on the dials which were not referring to anything other than some way to count. I wasn't sure if there was some method to the madness or if it is simply madness. The collective appears to agree with me that it's a bit of madness plain and simple.

                            If I do find myself working more and more in metric for some odd reason I'll likely remove the dials and skim away the numbers in a recessed band and re-number the major markings with actual metric values related to the .025mm per division on the lathe and .02mm per division on the mill. So the 4, 8 and 12 on the lathe dials and 5 and 10 on the mill dials would become 1, 2, and 3 mm with suitable decimal amounts for the marks in between. Other than perhaps buying a DRO for the mill that is as far as I'll ever need to go.

                            But then again I've been fine for all 63 years of my life without doing anything yet so I don't foresee any change any time soon.
                            Chilliwack BC, Canada

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