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  • #16
    Originally posted by Doozer View Post
    Why ream after you bore ? ?
    Does your lathe cut crooked ?

    -Doozer
    Boring is just to assure the hole is on location. Doesn't matter if you're on lathe or mill - same rule: Drill, Bore, Ream. In that order. On rare occasion you can cheat by boring with end-mill if the hole size is very small. But it depends on application and tolerances. Hope this helps.

    Best Regards,
    Bob
    Last edited by rjs44032; 11-04-2020, 05:22 PM.

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    • #17
      You can bore with greater accuracy than you can ream, or pehaps measuring the bore is too difficult and you rely on the size marked on the reamer.

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      • #18
        The "threads" issue seems to be dead, so let me bury it: even if poor threads can make the wheel wobble, it doesn't affect the that bore is .006 TIR on the arbor.

        I'll make another one & bore the bore - that seems to be the consensus. I'll have to make a small boring bore - I don't have anything small enough to do a 5/16 hole, 1-1/4 deep.

        Thanks for all the replies - I didn't know that a reamer might not center on a drilled hole.

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        • #19
          I bore often with a end mill, in lathe.
          Set it up as to cut on a single flute, I call it snaggle tooth. A 1/4" end mill might get you there for a 5/16 hole

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          • #20
            A reamer SHOULD center, but there are factors that can push it "off". One is forcing it, which is not that hard to do. Another is not facing the surface it is starting at, although that is also almost certain to mess up the drill as well, unless great care is taken.

            I noticed you used a 4 jaw, and "kinda centered" the stock, which theoretically should not affect anything if you turned the final diameter at the same chucking, as it seems you did.

            I give it an even chance that the DRILLING was off-center, and the reamer DID follow the drill hole. Drills wander more than reamers usually do, and mostly that is wandering when starting to drill, while the center of the drill is the only thing cutting. Drills are quite flexible, and will wander around, drill off-center, etc.

            There are drills that are short and stiff, so they can make a good pilot hole. I do not like using a center drill for this, although if you stop when you have just a "pip" and do not start cutting with the conical part, they are usable. I have a carbide spade drill around 3/16 (~~5mm) for the purpose if I am doing something that needs that.

            I don't see any mention of a pilot hole in the original post. Pilot holes usually help a lot in centering, but drilled holes are not really reliable for size, location, angle, smoothness, or roundness. They pretty reliably make a hole "similar to" what you wanted.

            Reamers usually do well on size, finish, and roundness (unless you want the ultimate), but do not do much for location. They can only correct small issues of angle, and even then tend to "split the difference". Some types do better with certain issues, and not so well with others.

            Boring, with a decent boring head, or on the lathe, can be rounder than a drill, can fix location and angle, is pretty accurate on size, but may not be as good with finish (this is linked with size, as the hills and valleys do not have a defined size, really).

            I agree with boring and reaming after, boring to near final size leaving a small amount (few thou) for the reamer, so long as the reamer is sharp. If you need better, then you either need better boring technique, or possibly to finish by grinding, or lapping..
            Last edited by J Tiers; 11-04-2020, 07:10 PM.
            3751 6193 2700 3517

            Keep eye on ball.
            Hashim Khan

            If you look closely at a digital signal, you find out it is really analog......

            Comment


            • #21
              If you can't bore before reaming, even using a short countersink , or stiff big centerdrill, may provide a better start for the reamer..chamfer can be finished at this time.
              if the drill hole was off far enough for 6 thou run out, it probably would be visible with drill still in hole, or you can check that by 're entering hole with the drill you used.

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              • #22
                A start with a countersink is a good idea.

                BTW, drills can drill fairy true for a start, and then wander off. If mounted by the hole, the other end might be way off, farther than it seems. Boring fixes that too.

                We were not told if the 6 thou was TIR or eccentricity.
                3751 6193 2700 3517

                Keep eye on ball.
                Hashim Khan

                If you look closely at a digital signal, you find out it is really analog......

                Comment


                • #23
                  What are the threads holding? The wheel? If so that shouldn't matter anywhere.

                  I see a set screw on the edge of the hub. I'm guessing that's how you tighten it down on the shaft of your grinder.

                  The hole has to have clearance for the shaft, and the set screw loads the shaft to one side of the boar in the hub, so that there creates an off-center issue which could cause vibration.

                  JL ....

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                  • #24
                    Good point.... depends on the amount the hole is oversize. If it is close fit, the off-center will be small.
                    3751 6193 2700 3517

                    Keep eye on ball.
                    Hashim Khan

                    If you look closely at a digital signal, you find out it is really analog......

                    Comment


                    • #25
                      Clarification: the part was faced, leaving no pip. Center drill, 3/16 pilot drill, 19/64 drill.

                      "TIR or eccentricity"? There's a difference? I accurately centered a 5/16- rod in the 4-jaw. Positioned the part on it & measured .006 DI swing on the arbor.

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                      • #26
                        Originally posted by Ringo View Post
                        I bore often with a end mill, in lathe.
                        Set it up as to cut on a single flute, I call it snaggle tooth. A 1/4" end mill might get you there for a 5/16 hole
                        Good idea - I'll try that (though I have a horizontal mill, I do happen to have a 1/4" end mill). Thanks

                        Comment


                        • #27
                          Originally posted by Bob Engelhardt View Post
                          Clarification: the part was faced, leaving no pip. Center drill, 3/16 pilot drill, 19/64 drill.

                          "TIR or eccentricity"? There's a difference? I accurately centered a 5/16- rod in the 4-jaw. Positioned the part on it & measured .006 DI swing on the arbor.
                          TIR is the reading between the two max positions of the indicator... "Total Indicator Reading".

                          "Eccentricity is the amount the one thing is off of true center... so that is essentially half the TIR.

                          Sounds like you measured TIR as 0.006", and so the eccentricity was 0.003".

                          Was that the same at all places along the arbor? If not, there might have been an angle error instead of, or along with the actual eccentricity.
                          3751 6193 2700 3517

                          Keep eye on ball.
                          Hashim Khan

                          If you look closely at a digital signal, you find out it is really analog......

                          Comment


                          • #28
                            I have a solid carbide 6mm Garant boring bar that would go 1 1/4" deep in a hole predrilled to 9/32". I was very lucky to get it cheaply, but had to pay the full price for the rare tiny inserts. If you cannot bore that deep, then bore as deep as you can, and use that bore to hold the drill true for the rest of the depth. That will keep the finishing reamer more concentric than drilling alone.

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                            • #29
                              I worked with an ederly machinist who taught me that holes made only with drills and reamers were unlikely always to betrue and run straight. His recommendation, for the part in question, would have been that the hole should be made first in an oversize piece and that then a mandrel would be turned to a gentle push fit, the part fitted to it and the rest of the features created, that way the hole would have to be true to the rest of the item.
                              It really should not be necessary, IF you and your machines can work in harmony and produce good concentric holes, but if not then it is a good " Work Around"
                              Regards David Powell.

                              Comment


                              • #30
                                That mandrel method is exactly how I got an R8 mill spindle running true. I put an R8 soft ended toolholder in a four jaw chuck and spent some time getting it running exactly true. Then I fitted the spindle on it and held it tightly with a short drawbar. That was checked for trueness before setting up a steady and machining it. The mill spindle is in two parts screwed together and runs within 0.0002" tir.

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