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Internal grooving in small bore diameters..

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  • Internal grooving in small bore diameters..

    I'm looking for some suggestions on how I can achieve a more repeatable and rigid clamping system for internal grooving in small bore diameters. I'm using a micro 100 internal grooving tool clamped in place w/ the set screws in one of the "aloris" type toolholders (boring ones w/ the v groove)for the quick release toolpost. At present the shank is 3/8" w/ the lockdown flat. I could always switch to a round shank. I need the tool to reach inside approx 1.1" in a bore diameter of .312". I need to hold the tolerences within .00025" over a 50 thousandths depth of cut. Are there any toolholders made that would achieve a better more rigid /repeatable clamping of the grooving tool...ie, collet system, bushing system. etc. Any help would be appreciated. I noticed that Sandvik has a coroturn XS system for small parts (grooving, turning, threading). Anyone own one of these??

    Thanks in advance....Krems

  • #2
    .00025 positioning Tolerance ?
    First, are you doing this on a hardinge?
    Do you have DRO to read this ? or are you using a stop?
    Are you using a "real" Aloris or a improv?
    Is it a wedge style holder?
    What is Spindle play ?
    How wide a cut ?

    When you talk about that kind of tolerance, you need good equipment.
    There are some great minature tooling makers, but they slip my mind as far as names.
    We had some made by a firm near Chicago (starts with a "R") that was customed, but really worked.
    I don't need the answers to the above, just that all sorts of things occur when requiring that tolerance.
    Rich

    You will probably want a custom Carbide boring bar..no inserts..you need rigidity !

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    • #3
      Rich,
      I've been making custom moulds for a while. I need the grooving tool to reach inside to cut the grooves. I have been using solid carbide grooving tools w/ a custom grind. Accuracy wise less than .0005" depth of cut is more realistic. Width of cut is not important. I'm cutting a .100" wide groove to a max depth of .065" TIR. But I need to be able to reach in 1.25" into the hole. I've been using the wedge type Aloris clone for a toolpost. There has got to be a better way to hold the carbide bit than the wedge toolholder w/ the v groove in it. Maybe one of the wedge toolholders w/ the round step down boring bar bushings. Any thoughts??

      Krems

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      • #4
        As Rich says, special needs require special tools. .050 DOC? Is that the depth of the grove or the actual DOC you're trying to take per pass?

        Another option is to grind the grove in.

        Comment


        • #5
          CC, The total groove depth is .065"" or ..0325"" depth of cut. Sorry If I confused anyone. I'm cutting 3 seperate grooves inside the bore. The max tool depth is 1.2" . I just want to be sure that I have a rigid clamping system so that the first and third grooves will be the same. I am trying to eliminate any tool flex. Thanks again

          Krems

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          • #6
            You're reaching 1.25" into a 5/16" bore, right?

            Then trying to cut a .100" wide groove with a diameter of .3125+.065, right?

            And you want to maintain tolerances within .00025" (.000125"+/-).

            What's the material?

            How will you even check the parts for accuracy?


            Is this a joke?????

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            • #7
              It sounds like maybe you want this tolerance in order to produce tight tolerance molded parts ??

              I've designed some precision deep bore parts for optics but never this tight. Several thoughts though ... put a tiny geometry (small radius) in that tool to minimize deflection in the finishing pass, use a very fine feed, sharp tools, high speed. You did say width was not critical?

              Or, use something similar in concept (don't know that they even exist) to an expanding reamer. It would have to expand, in place, after positioning at the required depth. The expansion would have to have a hard stop with the OD of the tool ground at that stop.

              Comment


              • #8
                krems, I think the only advantage you would have by going to a bushing type boring bar holder would be that the bar would be supported all the way to the front of the toolholder. With the type you are using now you are losing a little support because of the distance from the front of the tool holder to the set screw that holds it down. As far as the type of tool holder that you are using now allowing your tool to move any at all causing inaccuracies in your work, I highly doubt that. What little bit of rigidity that you will gain by swithching over may not be much but every little bit counts when working in a hole that size. My question is how are you measuring your groove to verify the tolerances stated?
                Jonathan P.

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                • #9
                  Are these lube grooves for lead bullet molds? Aluminum or steel? I assume you are clamping the two halves and boring simultaneously>

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                  • #10
                    Sorry about the terminology confusion. I'm new at talking the language. I am indeed making bullet moulds. Aluminum and iron. Mostly reboring existing ones. 4 jaw chuck, both halves clamped together.. I've probably made 100 moulds or more for myself/friends. I am a lead bullet long range target shooter. I grind my own tools for this...razor sharp.

                    I'm trying to get all the driving bands cut to the same depth so that when the cast bullet is made all bands will have the same finished diameter. I can get them to within .001" but I'd really like to see the finished diameter to within .0005". I think my cutting technigue is good but I'm getting a little flex on the tool as I reach into the cavity further. I realize it's hard to measure on a cast bullet because of all the other variables associated w/ casting ..alloy/temp/shrinkage. etc. I can't measure the mould cavity itelf I have to measure on a cast bullet. If you measure enough of them you can tell what type of job you did on boring the cavity.. A bullet can't be round enough. I'm looking for an alternate clamping system for the boring bar that is more rigid than using the wedge toolholder w/ the v groove in it. Maybe the bushing type holders or the 5c collet system that Dorian tool has for their quick release toolposts. I may be unrealistic in my expectations but am always looking for improvement.

                    Krems

                    Comment


                    • #11
                      The depth of the bore will have no effect on the flex of the boring bar so long as the length of extension remains the same.

                      If the desire is more for uniformity than actual dimensional accuracy, use the same extension of the boring bar for all the grooves, and allow the part to revolve for some uniform period of time at the final depth of cut to compensate the spring.
                      Jim H.

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                      • #12
                        The wedge type holder shouldn't be flexing any at all if it is working properly. Especially with the kind of load you are putting on it making an internal grooving cut. If it was, there is no way you would ever be able to make any kind of heavy turning cut with it. If you are holding the ring size to withing
                        .001, I would leave well enough alone. I doubt you would ever be able to prove that holding them to .00025 was helping any more than holding them to .001 anyway, so why bother. I'm not trying to tell you not to do accurate work, but you have to have some tolerance when machining, and trying to hold a tolerance that you can't even measure seems a bit crazy.
                        Jonathan P.

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                        • #13
                          JC,
                          I never thought of it that way but you're right. I'm making the same cut w/ the boring bar clamped in the toolholder for every cut. My ignorance is showing again. Sometimes the obvious is hard to realize. I may have to change my machining technique to dial in the acceptable tolerence level. I may have differing shrinkage rates going on when the metal is cooling. The mould is hotter at the sprue plate than at the front driving band inside the bore. Quest for accuracy...isn't it fun.

                          japcas: I suppose I'm unrealistic in what I'm trying to do. I havn't bought a commercial bullet mould that was better than mine yet in terms of roundness and consistancy. I should be glad for that achievement and leave it alone. Too many variables come into play here. Yea it's crazy but always worth trying.

                          Thank again..........Krems

                          Comment


                          • #14
                            You could always have a form tool made,(or make one yourself) with the requisite number of cutting edges to form your grooves. That way they'd always be in relation to each other. Personally , I'd use a toolholder that uses a bushing or a collet.

                            Comment


                            • #15
                              Do you not use a sizer on your cast bullets? Usually the cast size is a lot less critical than the sizing die, the bullet can be in a diameter range several thousandths wide and the sizer takes care of the size.

                              Holding diameter to .00025" an inch away from support on a small diameter tool is pretty close to impossible, the only way you might be able to cut to your spec is if you made a tool that would fit the bore and advance a cutting bit out the side to a stop. But since most bullet molds weren't made that way maybe you could make a center closing fixture and use a 'cherry' as the larger makers used. Otherwise you could just hold .001 and be happy that you're doing better than most makers.

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