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Improving your lathe technique, and not use a center-drill

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  • Improving your lathe technique, and not use a center-drill

    I posted the following on another thread site .but felt it may help those who wish to expand their skill levels.
    I think it is self-explanatory

    You do not need a center-drill when starting a drill in the Lathe
    Center-drills are for making centers in a shaft in order to use a live or dead center, but it's "convenient" for some to use for drilling, but sometimes even center-drills are off . Also they are 60 degrees and not 118 degrees like most drills.
    Use a technique that machinists have done for 100 years, before they had easily obtained center-drills.
    Process
    When ever you want to drill in the lathe, always place the bit in the chuck with the cutting lips/edge of the drill in a horizontal position. (!)
    Bring it up to the work face ...then using your tool bit and cross-slide ,( raise the tool bit up about 1/8 ") and then move it in maybe 1/4" to 1/2 " behind the cutting flutes and push the drill off center about .010" ( the above depends on the size of the drill-) . Now this is a two hand operation advance the drill so the divot in the work piece is about 1/2 the drill size and when that point is reached -keep feeding the drill in and at the same moment retract the cross-feed !
    Now you have a perfect centered hole start !
    Technical Data explanation
    So here is what is happening . Pushing the drill away from you makes it cut only on the far side cutting lip( it becomes like a boring bar in miniature) The result is a conical shaped hole with a tit in the middle and is a true centered machined surface ( like a boring tool). Now what you want is a cone length longer than the tit length - when this is reached ( 50 % to 90 % diameter) and the drill forced in (without side cross-feed pressure !) the hole forces the drill lip inward as the force needed to cut the tit is less than allowing the drill lip to cut the cone .
    A few notes
    Doing the above saves setup time . The machinist immediately goes to his drill , no swapping chucks or using the Jacobs key.
    With Aloris Tool Posts , it easy to raise the tool bit and then drop it back into place as I suggested here, but when the old guys used Lantern Posts, they just made sure the tool bit's cutting edge did not touch the cutting flute of the drill bit and used the "Heel" of the toolbit when touching the drill bit.
    In fact, the old guys did not even "face the end" of the work before drilling, and used the above method to "mini-face" the saw cut stock with the drill a small amount before proceeding as noted.
    All the above is for those who wish to expand their skills .
    It also adds to satisfaction at using your skills in new ( or old ! ) ways

    Rich
    Green Bay, WI

  • #2
    Hmmm. Have not tried that.

    I have found that just using a slow advance and allowing the drill to operate as a boring bar will do much the same thing. You advance slightly until the drill wanders slightly, then stop and let the drill stabilize. Do again until a good cone is established.

    Probably both ways can work fine
    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


    • #3
      It takes about 5 seconds to change the bit in the Albrecht so I'll probably stick with that.

      Not all "centre" drills are created equal, some may look like centre drills but are spotting drills.

      Drilling is not a precision operation, it's for effective stock removal so centre drills are perfectly adequate for the task.

      Comment


      • #4
        Center drills for starting a drill are not very good.... spotting drills are superior.

        The center drill, if advanced untl the 60 deg cone is cutting, forces the following drill to start contacting the work "up" on the edges of the drilled cone, with the center of the drill's cone point not involved at all. That leads to chatter and drill whip, potential drill edge breakage, etc.. Yes, YOU can DO that, but.....

        If you stop when just the clearance is drilled, and no part of the cone, then a center drill is probably OK, as most following drills will be larger and it acts as more of a "point clearance" drill. That's if you pick an appropriate size center drill.

        Spotting drills are not too critical as to size, same with spade drills, so long as the follow drill has the same angle, commonly 118 deg.
        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


        • #5
          My father used that method years ago. And I learned it from him. I used it for years too.

          I found it didn't always work ideally. But in reading your post I realize now that I didn't always set the cutting flutes horizontally and that I may not have made the divot deep enough all the time.

          It's also not always realistic to use this trick on the smaller sizes. It relies on contact very close to the end of the drill or the drill can simply flex into a curved shape. So on smaller sizes we need to do the pushing with the tool right near the point of the drill.

          Plus I found when using this method on really small the smaller sizes liked to dig in when pushed away and would sometimes catch the point and rotate upwards and over onto the top of the tool bit being used as the pusher. And if the drill bit didn't snap at that point it at least needed to be re-set for another attempt.

          As a result I think I'll try it again for giggles on sizes from around 1/4 and up. But I think I'm going to stick to using my center drills for the sizes under 1/4". And really I know I'm going to stick with the center drills anyway other than to try it.

          When I use my center drills for spotting like this I don't use the whole length of them. I spot to about 1/16 to 1/8" with just the end. No need to go all the way to the 60° portion.

          ….. and I really should order up some spotting drills anyway.

          Chilliwack BC, Canada

          Comment


          • #6
            I have what looks like a centre drill, but instead of the 60 degree to match a centre, it has a 90 degree which is better for starting drills. I also have a solid carbide spotting drill with a 120 degree tip, which would make a better lathe drill starter than its original purpose. This flatter angle used for spotting has the disadvantage of obscuring the tip somewhat and I prefer the 90 degree spotting drills.

            Comment


            • #7
              OK, simpleton question here. If the drill is hand sharpened is it going to align in the same manner? Because I've seen hand sharpened drills that could not cut a round hole if it's life depended upon it. I'll have to try this method.

              TX
              Mr fixit for the family
              Chris

              Comment


              • #8
                Originally posted by grim_d View Post
                It takes about 5 seconds to change the bit in the Albrecht so I'll probably stick with that.

                Not all "centre" drills are created equal, some may look like centre drills but are spotting drills.

                Drilling is not a precision operation, it's for effective stock removal so centre drills are perfectly adequate for the task.
                Yeah, I read through the OP's description a couple times and still didn't completely understand it. While he's screwin'
                around getting his hole started I'll have used the centre drill, drilled my hole, deburred the edge and moved on to the
                next operation. A spotting drill is a good idea for some situations but you can also get pretty close with a stub length
                drill.

                A drilled hole is just that, a "drilled hole". Never perfectly accurate but accurate enough for 99.9 per cent of the jobs
                performed in a "working" shop. If you want perfect concentricity you need to bore the hole...
                Keith
                __________________________
                Just one project too many--that's what finally got him...

                Comment


                • #9
                  Originally posted by Mr Fixit View Post
                  OK, simpleton question here. If the drill is hand sharpened is it going to align in the same manner? .....

                  TX
                  Mr fixit for the family
                  Chris
                  What difference does it make what holds the drill to be sharpened if the grind is correct? The holder is not the important part, it is getting the angles and centering right.

                  Now, some sharpening methods do make correctness much more likely, of course. Hand sharpening of smaller bits is not one of those, but it CAN be done.
                  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


                  • #10
                    Reminds me, need to get new spotting drills.

                    Comment


                    • #11
                      I use a similar method when I end up with a bent drill to hold it straighter.

                      Comment


                      • #12
                        Boy, the nay-sayers have quick triggers on their typing fingers.

                        If the method Rich describes is good enough for him it's probably more than good enough for me, and I'm gonna give it a serious try.

                        Comment


                        • #13
                          Thanks Rich. I will have to try this.

                          Comment


                          • #14
                            If I'm machining the face first, even on feed, I'll wind the tool in briefly at the centre to avoid a tit, before I wind it out. I can start a 1/8" drill into that tiny depression with no wobble.

                            If the surface is sawn or otherwise rough, I'll hit it with a spotting drill. I don't like to subject the narrow point of a centre drill to the vagaries of a rough surface.

                            You can hit it quite hard with a spotting drill and get on with it. Not deliberately hard, but slide the tailstock up a little too fast kind of hard. No problem for a sturdy spotter, but this can easily cause a centre drill to decide it wants to look more like a spotting drill and shed its point.

                            I like RC's method, but a DIckson QCTP doesn't lend itself to a quick raise of the tool. A nice little pusher tool to mount in a toolholder, with height adjustment by a lever, would be a possibility.
                            Richard - SW London, UK, EU.

                            Comment


                            • #15
                              I've been using Richs' method for some time now- it's an interesting technique and requires some getting used to, but it works. I use it all the time.

                              Something else I use- I cut a short section of flat bar and cut off some meat so it would fit in my tool post. Milled the edges, etc for a good solid fit. Then mounted it and brought it up to the chuck, which has a very short drill bit mounted in it. With pressure from the tailstock I drilled the hole. Now I can mount this 'control bar' and guide a drill bit mounted in the tailstock. This prevents drill wander when you're trying to get a clean and centered dimple established. You still use the technique of positioning the cross slide to control the end of the drill bit.

                              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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