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  • The alignment tool article- a question

    As I read that article, I was puzzled by one statement that drives a design choice made.

    The statement was that five contact points were required for a v-way and a flat, with 4 on the V, and one on the flat. Now, I agree that the original Kingway, which I made a clone of, does have 5 points, I do not think that is a requirement, it seems that it is actually "overconstrained". I thought about a version with just 3, but ended up making it per the original (it is basically the "100" size).

    Four contacts on the v-way is kinematically redundant, one can be removed without affecting the alignment. Why then the need for all four? It seems as if it would actually be more trouble to get all 4 into contact, since 3 define a contact plane that cuts both surfaces of the V. It seems that the four should contact in the same contact plane as 3 would, and they would always have all of the points effective... a 3 legged stool is always solid, but a 4 legged chair often is unstable because one of the 4 is the wrong length.

    Is there something I am missing here?
    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.

  • #2
    Originally posted by J Tiers View Post
    ... It seems that the four should contact in the same contact plane as 3 would, and they would always have all of the points effective...
    It may simply be a matter of balance. If one of the contact points was the peak of the V and the other 2 straddled opposite slopes of the V, it
    would be balanced and stable. But I suspect the peak of the V is not a valid reference point. And simply removing 1 of the contact points would
    allow you to rock it.

    ... a 3 legged stool is always solid, but a 4 legged chair often is unstable because one of the 4 is the wrong length. ...
    A 3 legged stool is solid if the legs are 120 degrees apart. A 3 legged stool with the legs orientated at 90, 90, 180 degrees would lack some
    stability. Removing 1 leg from a 4 legged stool does not make a good 3 legged stool.
    Location: Long Island, N.Y.

    Comment


    • #3
      A three legged stool is not stable if sitting on two planes 90 degrees from each other. Its what I thought the tool needed, how the kingway was built and how I built mine. ymmv.
      Last edited by Mcgyver; 03-10-2019, 10:49 AM.
      in Toronto Ontario - where are you?

      Comment


      • #4
        The point about a 3 legged stool on a plane is good BUT the V was is two planes the,(more or less equivalent) would be 3 points on the two planes with the one being about midway on the opposite side of the V . EX. take 3 ball bearings nested together and lower onto the V, 2 on one side 1 on the other, that defines the stability criteria. IF the single is off "somewhere" beyond the pair (longitudinally) then it's NOT stable.
        ...lew...

        Comment


        • #5
          I've mused about the KingWay in that context. Rich makes a frequent and valid point about mounting parts on three points, not just for stability but properly placed they can minimize deflection. With the tubular component of the Kingway there are four points and perhaps the saving grace is that since they're fairly long, they average out the variations of scraping strokes that might plague small contact points, either three or four.

          I'd wondered about the small contacts in the article, but of course that could be easily managed with feet on the pins (sort of). If four really was a problem there could be provision for one towards the center of the angle. Michael's actual experience using it could be some guidance for others and might come out in the subsequent parts of the article.
          .
          "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

          Comment


          • #6
            The 3 legged stool thing seems to have been wildly misinterpreted.....

            My thought, and I believe it a good one, was that two points would be on one side of the V, and one on the other. (I do not understand the idea of one on TOP of the V). That way, they all HAVE TO be touching the V, and the location relative to the V is just as stable as it was, with zero chance that one of the contact points is not touching.

            Anyhow, I see that there was no special reason for the 4, you did the same thing I did, and basically copied the Kingway setup. OK.

            I like the idea of using a standard level, although it makes the unit need to be rather larger than my "100 size", yours is more like the larger Kingway. I may have to figure out a way to mount my Hilger and Watt level, which is a bit smaller but has a different arrangement of feet.


            BTW, the 3 legged stool with legs at 90 deg is just as good as any other.... (every 3 legged stool in the world is made like that, it's all in how you draw the lines). What you are really saying is that the load has to be put inside the triangle of three feet, which is absolutely true.
            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


            • #7
              My local bookseller didn't have the latest issue(s) of any of the VP magazines.
              Who was the author?

              Comment


              • #8
                Originally posted by J Tiers View Post
                The 3 legged stool thing seems to have been wildly misinterpreted.....

                My thought, and I believe it a good one, was that two points would be on one side of the V, and one on the other. (I do not understand the idea of one on TOP of the V). That way, they all HAVE TO be touching the V, and the location relative to the V is just as stable as it was, with zero chance that one of the contact points is not touching.

                Anyhow, I see that there was no special reason for the 4, you did the same thing I did, and basically copied the Kingway setup. OK.

                I like the idea of using a standard level, although it makes the unit need to be rather larger than my "100 size", yours is more like the larger Kingway. I may have to figure out a way to mount my Hilger and Watt level, which is a bit smaller but has a different arrangement of feet.


                BTW, the 3 legged stool with legs at 90 deg is just as good as any other.... (every 3 legged stool in the world is made like that, it's all in how you draw the lines). What you are really saying is that the load has to be put inside the triangle of three feet, which is absolutely true.
                Three points would still let the thing rotate on v-way even if all of the points are in contact.
                Location: Helsinki, Finland, Europe

                Comment


                • #9
                  Originally posted by reggie_obe View Post
                  My local bookseller didn't have the latest issue(s) of any of the VP magazines.
                  Who was the author?
                  Michael Ward, Mcgyver here on the forum.
                  .
                  "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

                  Comment


                  • #10
                    Originally posted by MattiJ View Post
                    Three points would still let the thing rotate on v-way even if all of the points are in contact.
                    ??????????????????????????????????????

                    No different that it would with four. You are referring to the support(s) on one side sliding up the V-way, and the support(s) on the other side of it sliding down, producing a rotation. But, so-what?

                    The anti-rotation comes from the support over on the flat way, it is the exact same with either 3 or 4 contact points on the V.

                    That's the point. The behavior is the same with 3 points or with 4 (if they all do contact), so one of them is not required.

                    Just to clear up some confusion, the three points on the V-way would be similar to this (yes I already had the lathe bed model for a different project):

                    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


                    • #11
                      JT, your picture in #10 helps greatly in my understanding the contact points, and I believe that having only three on the vee may have a problem. If wear occurs unevenly, particularly to the left front contact point, the saddle will tend to rotate slightly on a horizontal axis, loosing the precision when facing cuts are made. I think the problem of wear would be lessened by having two contacts on the inboard side of the vee opposite the outboard ones.

                      Comment


                      • #12
                        Originally posted by J Tiers View Post
                        ??????????????????????????????????????

                        No different that it would with four. You are referring to the support(s) on one side sliding up the V-way, and the support(s) on the other side of it sliding down, producing a rotation. But, so-what?

                        The anti-rotation comes from the support over on the flat way, it is the exact same with either 3 or 4 contact points on the V.

                        That's the point. The behavior is the same with 3 points or with 4 (if they all do contact), so one of them is not required.
                        In general, why is the flat top of the V way not used as a stable horizontal reference point?

                        Comment


                        • #13
                          I don't see that there's much difference. Three points will always touch regardless but in practice the four points would always touch on a vee because the ball on the flat way is not constrained at all.

                          If the end touching the flat way (that is usually a ball end) was bearing on both the top and the rear shear then it could hold up one of the four points on a spot where one vee shear was more worn than another, but since it's not then it won't.
                          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


                          • #14
                            Four points do not have to all be in a plane. Three points DEFINE a plane, so four can be like an uneven 4 legged chair.

                            Mr Wade's device is adjustable, and my question to him was why he felt (as he stated in the article) that he "had to have" 4 points. That has been answered, basically that he, like myself, followed the original design which has 4 points set up the same as mine below.

                            it seems as if 3 would be entirely sufficient, and might be more reliable, especially as things wear. I did not think too hard about it when I made mine, nor apparently did Mr Wade. I think that if I make another it will have three.

                            Originally posted by old mart View Post
                            JT, your picture in #10 helps greatly in my understanding the contact points, and I believe that having only three on the vee may have a problem. If wear occurs unevenly, particularly to the left front contact point, the saddle will tend to rotate slightly on a horizontal axis, loosing the precision when facing cuts are made. I think the problem of wear would be lessened by having two contacts on the inboard side of the vee opposite the outboard ones.
                            It's not a "saddle".... it is a measurement device..... Similar to this one that I made, only Mr Wade made a larger unit with provisions to mount full size levels on it. In mine, there are 4 contact points where there is a section cut out of the round portion in foreground, you can maybe see the fatter parts of the cylinder at each end. Mine is made just like the original "Kingway" tool. Mr Wade used the same principle, but went at the contacts a bit differently, making them adjustable independently.

                            In mine, I think that even if it were uneven, the cylindrical part could be turned until the 4 points touch, although the rod might not be vertical. In the article, the 4 being adjustable means they can be made to touch. In either case, the points do not "automatically" all touch, which 3 would have to.

                            Last edited by J Tiers; 03-10-2019, 04:47 PM.
                            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
                              Originally posted by reggie_obe View Post
                              In general, why is the flat top of the V way not used as a stable horizontal reference point?

                              It might have been dressed to remove marks near the chuck, or is at least likely to have burrs from dropped parts. If you could PROVE it against other non-working faces such as the flats between two ways then you could be reasonably sure of it, otherwise you're making a risky assumption.

                              I just had my South Bend ground and the grinder deliberately cleaned up the vee way tops just so they could be used as such for levelling.
                              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

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