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  • Managed to turn a taper so now questions

    For machining today was a good day.
    I have only attempted to deliberately cut a taper one time before and it did not go well, more like metal spinning than metal turning.

    So yesterday I reviewed the “tubalcain” video about turning a simple taper.
    Following the basic points, it went much, much better.

    I randomly chose an angle of 10؛, found some mystery metal I had worked with before that was not particularly good (a bit stringy) and not particularly bad (it was pretty consistent over the entire amount of material w no odd spots or inclusions) though it saws better than it turns. Then just tried to follow the steps from the video.

    The external taper went smoothly and since the whole thing was just an experiment in “how to”, I just kept taking off more material until the amount removed was sort of pleasing to the eye while making mental notes about what happened if the DOC was changed (I am wanting to learn more by deliberately trying to separate between roughing and finishing actions).

    Thought, “OK, how about an internal taper?” As this was not in the video thought in the moment was required which was/is also something I frequently struggle with and want to develop.

    I very deliberately bored well past where I intended to stop the taper to (a) allow some place for the chips to move to as the piece was not bored through, (b) minimize the chances of “crashing” into the back of the blind hole [a project rapidly moving up the “to do” list is some sort of micrometer carriage stop (and DRO) as currently even good estimation can get a little dicey and it always seems to be just enough to slightly chip inserts].
    Not sure if its standard operating procedure but what I basically did was use a boring bar at the same angle as the external taper and started at the point of the internal taper that was the furthest down the bore. I could not think of any other way it made sense.

    It went almost as smooth at the external taper except between the angle, length of compound movement (this is still less than 6x that I have moved the compound via its screw) I slightly miscalculated the amount of room needed and was not quite to the face when I ran out of angle/travel. I think the only option I had was to move the carriage that little bit further towards the headstock and restart the whole repeating process and it seemed to work.

    I ended up with an internal and external taper that are parallel to one another, the finish is OK for roughing and the wall thickness is consistent as best I can measure.

    I have to go back and re-re-reread sections on turning tapers, the differences between degrees and amounts over a given longitudinal amount and, being math challenged, not particularly looking forward to it.


    Questions about internal tapers:
    is there some formula or rule of thumb about the relationship between the size (diameter) of the boring bar, the angle of the taper and the size of the hole you use to access?
    if the part needs both external and internal taper, which gets done first? [I maybe over-thinking this but to me it makes more sense to go from small to large diameter of the taper and if you do the external taper first, to do the small to large internally don't you have to flip the part end for end and if you do that, how do you grip the taper you just turned? Conversely, if you turn the internal first you have to leave excess material to grip in the chuck, enough that you can turn the complete external taper, right?]
    what do you do if the combination of compound movement and boring bar length do not allow you to do the full length of taper you need to do? I assume that if this happens externally, you do a series of steps and then try to connect them, if you do this internally, are you not trying to put the boring bar where material still exists? This also relates to question one above as the smaller boring bars are shorter.
    Last edited by RussZHC; 09-10-2012, 11:00 PM.

  • #2
    Some of this depends on how you turned the external taper. Did you do this with the compound, the set over method (moving the tailstock), or use a taper attachment?

    If you used the compound or the taper attachment one way to "cheat" is to turn a small boss on the end of the shaft and cut the taper between centers. Set the compound or TA so the small end will be toward the headstock and cut the taper. Once it is done leave the compound on the angle, set up the piece with the female taper and drill & bore until the male portion fits properly. As to the size of boring bar, simply use as big of one that will fit.

    If you are trying to match a taper one of your "best friends" will be Prussian blue. You can use it to compare how the tapers are matching and adjust accordingly.

    Which one first? Well that's a chicken & egg question. Really does not matter as long as they mate up correctly.

    BTW, one major advantage of a taper attachment is the ability to use the power feed and obtain a nice consistent finish. If you have starts & stops there will be some lack of proper fit even if the angles are "exactly the same". Another big advantage is in the length of the taper. With the compound rest you're more or less limited to the length of the travel of the CR.

    For short tapers, i.e. globe valve seats & disks, I prefer to use the compound. Just keep in mind the mating surfaces should be 1/2 degree different in order to reduce the width of the contact between the mating surfaces.

    Comment


    • #3
      Whether you do the bore or the plug first is a matter of personal preference
      I personally prefer the bore first as OD work is easier for holding size and so should be last

      If turning matching tapers, try this :
      Rough out the plug , and then remove it.
      Mount your boring bar or endmill ( make great boring tools) parrallel to the Spindle axis.
      Mount the bore piece and bore the taper---do not change anything when done !.
      Now remount the plug and run the spindle in reverse and use the same boring tool on the back side.
      Use the previousely bored hole -if possible---to check your fit, and determine how much to remove.
      Because the tool and tool slide have not been changed, the tapers will match...and its fast

      Rich

      Comment


      • #4
        Right now the plan is to just use the compound method...no taper attachment and unlikely to find one and want to avoid moving the tailstock for as long as possible

        Rich: will try that...sort of the thing I was wondering as I was working (the bit about removing/moving the work piece and leaving tool and adjustments "as is") but could not quite figure out the logical order of ops at the time

        Dr Stan: certainly want to try between centers work;

        Concerning the limits of length using the compound, I have noticed that some Morse taper pieces have a nearly unfinished reduced size gap between two tapered sections, is this related to the length limit or is it more that the fit is better since the tapers do not need to match precisely over what would be the entire taper length [I am not talking cheap copies but stuff from Jacobs and Precision Twist]

        Comment


        • #5
          Originally posted by RussZHC View Post
          Concerning the limits of length using the compound, I have noticed that some Morse taper pieces have a nearly unfinished reduced size gap between two tapered sections, is this related to the length limit or is it more that the fit is better since the tapers do not need to match precisely over what would be the entire taper length [I am not talking cheap copies but stuff from Jacobs and Precision Twist]
          I've seen & used MT shanks such as you describe and really have no idea as to why there is a unfinished undercut section. My guess is that it helps reduce the time required for grinding.

          BTW, I've cut #2 MT's with the compound on my 14 1/2" SB after dialing in the angle using an existing end mill holder held in the 4 jaw. No adjusting was necessary and the taper mated right up.

          Comment


          • #6
            Not all tapers are a perfect match on the first go. If centre section is undercut, it makes it easier to get a perfect fit with a file.

            Comment


            • #7
              Mount the bore piece and bore the taper---do not change anything when done !.
              Now remount the plug and run the spindle in reverse and use the same boring tool on the back side.
              Use the previousely bored hole -if possible---to check your fit, and determine how much to remove.
              Because the tool and tool slide have not been changed, the tapers will match...and its fast
              A bit behind in the tubalcain videos, so watched the more elaborate taper related ones this pm and in one he does something similar by boring with the tool turned upside down on the back (my lathe has screw on chucks and with my level of experience am quite hesitant to run in reverse)

              Comment


              • #8
                Originally posted by RussZHC View Post
                (my lathe has screw on chucks and with my level of experience am quite hesitant to run in reverse)
                That's a good thing to be hesitant of.

                Comment


                • #9
                  If starting your lathe in reverse causes the chuck to come off, then obviously you do not want to do it.
                  The secret to running in reverse is starting the spindle using a clutch ( or belt tensioner) for gradual engagement of speed.
                  I have never had my chuck come off unless I wanted it off, so suggested the method for speed and accuracy .

                  In any shop work, safety is the first step, and knowing your machine is paramont to acting accordingly
                  Rich

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