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Re: Machine Shop Videos

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  • Bud
    Walter, Thanks for the link....I have downloaded all of the MIT videos and ahve been watching them.....and ordering new tooling as I go. best regards, bud
    Message 1 of 16 , Nov 30, 2008
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      Walter,

      Thanks for the link....I have downloaded all of the MIT videos and
      ahve been watching them.....and ordering new tooling as I go.

      best regards,

      bud


      --- In mill_drill@yahoogroups.com, "Starlight Tool Services Ltd"
      <starlight_tools@...> wrote:
      >
      > http://www.eng.hmc.edu/E8/Videos.htm
      >
      > Here are some more basic Machine shop videos
      >
      > Note the safety infraction by the lathe operator wearing a big ring!
      >
      > Walter
      >
    • Denis
      Walter, Thanks for the video links. I noticed the guy wearing the ring and you can t help noticing the bruise under his thumb nail. That sure is a nice Mill, I
      Message 2 of 16 , Dec 1, 2008
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        Walter,
        Thanks for the video links. I noticed the guy wearing the ring and
        you can't help noticing the bruise under his thumb nail.

        That sure is a nice Mill, I wonder if I can take that one down into
        the basement?

        Denis

        --- In mill_drill@yahoogroups.com, "Starlight Tool Services Ltd"
        <starlight_tools@...> wrote:
        >
        > http://www.eng.hmc.edu/E8/Videos.htm
        >
        > Here are some more basic Machine shop videos
        >
        > Note the safety infraction by the lathe operator wearing a big
        ring!
        >
        > Walter
        >
      • Jack Dinan
        You know, as I am watching these videos and those in the MIT series, I soon find my attention wandering from whatever lesson is being taught and fantasizing
        Message 3 of 16 , Dec 1, 2008
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          You know, as I am watching these videos and those in the MIT series,
          I soon find my attention wandering from whatever lesson is being
          taught and fantasizing that it is really me standing there using
          those big pieces of machinery and not the random instructor. I try to
          pay attention to the message, but can't.
          :-(
          jack
        • jim_dear
          Did anyone notice the narration calling out step drilling as a bad idea that compromises the squareness of holes? I ve seen any number of texts advising that
          Message 4 of 16 , Dec 3, 2008
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            Did anyone notice the narration calling out step drilling as a bad
            idea that compromises the "squareness" of holes?

            I've seen any number of texts advising that when drilling a large hole
            one should spot drill, then use a series of smaller drills to work up
            to the final diameter, then finish ream.

            Cheers,
            jim

            --- In mill_drill@yahoogroups.com, "Starlight Tool Services Ltd"
            <starlight_tools@...> wrote:
            >
            > http://www.eng.hmc.edu/E8/Videos.htm
            >
            > Here are some more basic Machine shop videos
            >
            > Note the safety infraction by the lathe operator wearing a big ring!
            >
            > Walter
            >
          • Jack Dinan
            I noticed it and am baffled. What possible compromise would be made by sneaking up on the final size? jack
            Message 5 of 16 , Dec 3, 2008
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              I noticed it and am baffled. What possible compromise would be made
              by sneaking up on the final size?
              jack



              >Did anyone notice the narration calling out step drilling as a bad
              >idea that compromises the "squareness" of holes?
              >
              >I've seen any number of texts advising that when drilling a large hole
              >one should spot drill, then use a series of smaller drills to work up
              >to the final diameter, then finish ream.
              >
              >Cheers,
              >jim
            • Starlight Tool Services Ltd
              These video s from Harvey Mudd College are the first time I have ever seen this concept mentioned, everybody else I have dealt with, any classes taken etc
              Message 6 of 16 , Dec 3, 2008
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                These video's from Harvey Mudd College are the first time I have ever seen this concept mentioned, everybody else I have dealt with, any classes taken etc recommends drilling in a series of drill sizes, which reduces the overall power required to drill the hole and the final hole is more round.
                 
                I like using Rota-Broaches (annular cutters) myself.  These are common on the magnetic drill presses and are available in a range of sizes and in 1 in, 2 in and 3 in depth of cuts.  Got the R8 Holder from KBC Tools, they have three lengths available and a variety of other shanks.
                 
                Walter
                ----- Original Message -----
                Sent: Wednesday, December 03, 2008 11:53 AM
                Subject: [mill_drill] Re: Machine Shop Videos

                I noticed it and am baffled. What possible compromise would be made
                by sneaking up on the final size?
                jack

                >Did anyone notice the narration calling out step drilling as a bad
                >idea that compromises the "squareness" of holes?
                >
                >I've seen any number of texts advising that when drilling a large hole
                >one should spot drill, then use a series of smaller drills to work up
                >to the final diameter, then finish ream.
                >
                >Cheers,
                >jim



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              • stanley879
                ... hole ... up ... ring! ... small hole to relieve the pressure in the drill point leaving 1/64th in for reaming cheers stan
                Message 7 of 16 , Dec 3, 2008
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                  --- In mill_drill@yahoogroups.com, "jim_dear" <jim314159@...> wrote:
                  >
                  > Did anyone notice the narration calling out step drilling as a bad
                  > idea that compromises the "squareness" of holes?
                  >
                  > I've seen any number of texts advising that when drilling a large
                  hole
                  > one should spot drill, then use a series of smaller drills to work
                  up
                  > to the final diameter, then finish ream.
                  >
                  > Cheers,
                  > jim
                  >
                  > --- In mill_drill@yahoogroups.com, "Starlight Tool Services Ltd"
                  > <starlight_tools@> wrote:
                  > >
                  > > http://www.eng.hmc.edu/E8/Videos.htm
                  > >
                  > > Here are some more basic Machine shop videos
                  > >
                  > > Note the safety infraction by the lathe operator wearing a big
                  ring!
                  > >
                  > > Walter
                  > >
                  > hi I worked in a large machine shop the usual method is to drill a
                  small hole to relieve the pressure in the drill point leaving 1/64th
                  in for reaming cheers stan
                • Michael Parrish
                  I ve seen it done that way before. At the machine shop they would check the size of the point on the drill and start with that. Not a bunch of steps in-between
                  Message 8 of 16 , Dec 3, 2008
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                    I've seen it done that way before. At the machine shop they would
                    check the size of the point on the drill and start with that. Not a
                    bunch of steps in-between though. I have a 1 1/2" twist drill. The
                    point is ~.270 wide. I would want to start that hole with a ~17/64"
                    drill. The 17/64" has a point ~.125" wide. You could start for that
                    hole with a ~1/8", etc. If a critcal final size is needed, the last
                    drill used would be ~1/64" under, and the hole reamed. It didn't hurt
                    that they had hundreds of reamers. Seemed that a drilled hole was for
                    sticking a bolt through. Anything more critical than that, got reamed.
                    It is true that they never "snuck up" on a final drill size though,
                    pilots were only for the points. MIKE

                    --- In mill_drill@yahoogroups.com, "stanley879" <stylestitch@...> wrote:
                    >
                    > --- In mill_drill@yahoogroups.com, "jim_dear" <jim314159@> wrote:
                    > >
                    > > Did anyone notice the narration calling out step drilling as a bad
                    > > idea that compromises the "squareness" of holes?
                    > >
                    > > I've seen any number of texts advising that when drilling a large
                    > hole
                    > > one should spot drill, then use a series of smaller drills to work
                    > up
                    > > to the final diameter, then finish ream.
                    > >
                    > > Cheers,
                    > > jim
                    > >
                    > > --- In mill_drill@yahoogroups.com, "Starlight Tool Services Ltd"
                    > > <starlight_tools@> wrote:
                    > > >
                    > > > http://www.eng.hmc.edu/E8/Videos.htm
                    > > >
                    > > > Here are some more basic Machine shop videos
                    > > >
                    > > > Note the safety infraction by the lathe operator wearing a big
                    > ring!
                    > > >
                    > > > Walter
                    > > >
                    > > hi I worked in a large machine shop the usual method is to drill a
                    > small hole to relieve the pressure in the drill point leaving 1/64th
                    > in for reaming cheers stan
                    >
                  • Rexarino
                    A drill bit guides itself partly by the center web, so the roundest and straightest hole may result by drilling a pilot hole just slightly larger than the
                    Message 9 of 16 , Dec 3, 2008
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                      A drill bit guides itself partly by the center web, so the roundest
                      and straightest hole "may" result by drilling a pilot hole just
                      slightly larger than the web, followed by the full size drill bit.
                      This reduces the drilling effort as you no longer have to 'push the
                      center metal out of the way' with the chisel point, but retains the
                      guidance of the center web.

                      A split point drill takes less effort because it adds a cutting edge
                      to the center web, but it looses the guidance properties of the center
                      web, and can wander if the split of the point isn't equal.

                      To enlarge a hole satisfactorily using the step drilling technique,
                      you need the work to be rigidly held, the drill/spindle combination to
                      be as rigid as possible with little spindle slop, controlled feed, and
                      you need the drill bit to be identically sharpened on both (all)
                      cutting edges. This is tough to achieve on free hand sharpened, hobby
                      drill presses - so some instructors have noted that a spot drill,
                      followed by the final size drill slowly and carefully fed into the
                      work achieves better results. It works that way for me.

                      The out of roundness is particularly evident when drilling a large
                      hole freehand in eighth inch and thinner sheet. I usually get a 3
                      lobed hole, reminiscent of a Wankle cam/piston, when I try this.

                      YMMV
                      Rex

                      On Wed, Dec 3, 2008 at 11:36 AM, jim_dear <jim314159@...> wrote:
                      > Did anyone notice the narration calling out step drilling as a bad
                      > idea that compromises the "squareness" of holes?
                      >
                      > I've seen any number of texts advising that when drilling a large hole
                      > one should spot drill, then use a series of smaller drills to work up
                      > to the final diameter, then finish ream.
                      >
                      > Cheers,
                      > jim
                      >
                    • borusa
                      I recently used the many steps method to drill on the lathe. The results were very good. I think the reduced cutting forces and lessened amount of swarf is
                      Message 10 of 16 , Dec 3, 2008
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                        I recently used the many steps method to drill on the lathe. The
                        results were very good. I think the reduced cutting forces and
                        lessened amount of swarf is a benefit, causing less deflection among
                        other things. Also, a higher feed rate due to the reduced cutting
                        load seems to increase balance between the cutting flanks.

                        Also, with one heavy go, the swarf tends to catch between the flutes
                        and the side of the work. I have noticed that particularly when
                        drilling deep holes.

                        I have used a new drill bit in the place of a reamer to clean up a
                        bored hole too, light cut, but not as slight as a with a reamer.

                        --- In mill_drill@yahoogroups.com, Rexarino <rexarino@...> wrote:
                        >
                        > A drill bit guides itself partly by the center web, so the roundest
                        > and straightest hole "may" result by drilling a pilot hole just
                        > slightly larger than the web, followed by the full size drill bit.
                        > This reduces the drilling effort as you no longer have to 'push the
                        > center metal out of the way' with the chisel point, but retains the
                        > guidance of the center web.
                        >
                        > A split point drill takes less effort because it adds a cutting edge
                        > to the center web, but it looses the guidance properties of the center
                        > web, and can wander if the split of the point isn't equal.
                        >
                        > To enlarge a hole satisfactorily using the step drilling technique,
                        > you need the work to be rigidly held, the drill/spindle combination to
                        > be as rigid as possible with little spindle slop, controlled feed, and
                        > you need the drill bit to be identically sharpened on both (all)
                        > cutting edges. This is tough to achieve on free hand sharpened, hobby
                        > drill presses - so some instructors have noted that a spot drill,
                        > followed by the final size drill slowly and carefully fed into the
                        > work achieves better results. It works that way for me.
                        >
                        > The out of roundness is particularly evident when drilling a large
                        > hole freehand in eighth inch and thinner sheet. I usually get a 3
                        > lobed hole, reminiscent of a Wankle cam/piston, when I try this.
                        >
                        > YMMV
                        > Rex
                        >
                        > On Wed, Dec 3, 2008 at 11:36 AM, jim_dear <jim314159@...> wrote:
                        > > Did anyone notice the narration calling out step drilling as a bad
                        > > idea that compromises the "squareness" of holes?
                        > >
                        > > I've seen any number of texts advising that when drilling a large hole
                        > > one should spot drill, then use a series of smaller drills to work up
                        > > to the final diameter, then finish ream.
                        > >
                        > > Cheers,
                        > > jim
                        > >
                        >
                      • leasingham_connelly
                        ... hole ... If you are using a big high powered drill with powered downfeed then this may be true. If you are hand feeding then it is asking for trouble with
                        Message 11 of 16 , Dec 5, 2008
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                          --- In mill_drill@yahoogroups.com, "jim_dear" <jim314159@...> wrote:
                          >
                          > Did anyone notice the narration calling out step drilling as a bad
                          > idea that compromises the "squareness" of holes?
                          >
                          > I've seen any number of texts advising that when drilling a large
                          hole
                          > one should spot drill, then use a series of smaller drills to work up
                          > to the final diameter, then finish ream.
                          >
                          > Cheers,
                          > jim
                          >

                          If you are using a big high powered drill with powered downfeed then
                          this may be true. If you are hand feeding then it is asking for
                          trouble with some materials such as stainless steel. If you think
                          about the path of the outside edge of a 1" drill it is 3.14"
                          circumference and in order to cut and not rub it needs to be fed at a
                          high rate, 0.012" per rev. (think of a triangle with a 3" base and
                          0.012" side, the slope is not all that great). At the same time the
                          inside edge near the chisel point may be traveling only 0.5" but still
                          being pushed thru at 0.012" per rev. This requires a lot of force from
                          both rotation and feed. It also needs to be continuous all the way
                          thru to avoid work hardening. If you are hand feeding and fail to
                          maintain pressure then as soon as the drill start to rub you will get
                          work hardening on the cut surface. Once this happens your drill will
                          quickly fail and you will be looking for expensive carbide or high
                          cobalt drills to force thru the hard skin to finish the hole.

                          The point is that what is true for a machine shop with a full set of
                          big machines may not be true for a home shop or someone making do with
                          available machines.

                          Walter, we use braoch cutters for mild and stainless steel gland
                          plates from junction boxes, 3mm thick, 16mm, 20mm, 25mm and 32mm
                          diameter. I have watched someone ruin a new broach cutter by peck
                          drilling a 20mm hole in 3mm stainless plate instead of going at it
                          with plenty of force and pushing thru in one go.

                          Martin
                        • kidharris
                          Your explanation makes a lot of sense to me, however I was wondering how come the center of the bit rubbing causes work hardening? I thought work hardening was
                          Message 12 of 16 , Dec 6, 2008
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                            Your explanation makes a lot of sense to me, however I was wondering
                            how come the center of the bit rubbing causes work hardening? I
                            thought work hardening was caused by vibration or flexure. I know that
                            heating to a certain temp and then rapidly cooling causes hardening.
                            Do you mean that the bit rubbing is heating the material and then when
                            you withdraw the bit, as in pecking, that the material cools fast
                            enough to case harden the material under it? Please explain the
                            mechanism by which it hardens.

                            --- In mill_drill@yahoogroups.com, "leasingham_connelly"
                            <martin.connelly@...> wrote:
                            >
                            > --- In mill_drill@yahoogroups.com, "jim_dear" <jim314159@> wrote:
                            > >
                            > > Did anyone notice the narration calling out step drilling as a bad
                            > > idea that compromises the "squareness" of holes?
                            > >
                            > > I've seen any number of texts advising that when drilling a large
                            > hole
                            > > one should spot drill, then use a series of smaller drills to work up
                            > > to the final diameter, then finish ream.
                            > >
                            > > Cheers,
                            > > jim
                            > >
                            >
                            > If you are using a big high powered drill with powered downfeed then
                            > this may be true. If you are hand feeding then it is asking for
                            > trouble with some materials such as stainless steel. If you think
                            > about the path of the outside edge of a 1" drill it is 3.14"
                            > circumference and in order to cut and not rub it needs to be fed at a
                            > high rate, 0.012" per rev. (think of a triangle with a 3" base and
                            > 0.012" side, the slope is not all that great). At the same time the
                            > inside edge near the chisel point may be traveling only 0.5" but still
                            > being pushed thru at 0.012" per rev. This requires a lot of force from
                            > both rotation and feed. It also needs to be continuous all the way
                            > thru to avoid work hardening. If you are hand feeding and fail to
                            > maintain pressure then as soon as the drill start to rub you will get
                            > work hardening on the cut surface. Once this happens your drill will
                            > quickly fail and you will be looking for expensive carbide or high
                            > cobalt drills to force thru the hard skin to finish the hole.
                            >
                            > The point is that what is true for a machine shop with a full set of
                            > big machines may not be true for a home shop or someone making do with
                            > available machines.
                            >
                            > Walter, we use braoch cutters for mild and stainless steel gland
                            > plates from junction boxes, 3mm thick, 16mm, 20mm, 25mm and 32mm
                            > diameter. I have watched someone ruin a new broach cutter by peck
                            > drilling a 20mm hole in 3mm stainless plate instead of going at it
                            > with plenty of force and pushing thru in one go.
                            >
                            > Martin
                            >
                          • leasingham_connelly
                            There are a number of materials that work harden. This means that anything that is done to them mechanicaly such as rubbing or bending causes them to harden.
                            Message 13 of 16 , Dec 8, 2008
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                              There are a number of materials that work harden. This means that
                              anything that is done to them mechanicaly such as rubbing or bending
                              causes them to harden. It is a metalurgical property where the
                              material grains/crystaline structure changes from one form to
                              another in the reverse process from that which annealing carries
                              out. This happens with copper and also with some (but I would not
                              claim all) stainless steels. Try flexing a piece of stainless or
                              copper wire and you will probably find it stiffens up at the point
                              where it is bent. This is why repeated flexing of a piece of wire at
                              the same point causes it to snap, it hardens to the point of
                              brittleness.

                              The rubbing takes place at the periphery of the tool not the centre
                              as the angle of the cut is shallower and is more likely to rub if
                              there is not enough feed. (Plot the triangle formed with a base
                              equal to the circumference and height equal to the feed rate for
                              0.060" feed per rev for 1/4" and 1" drills, see which one is very
                              shallow and more likely to rub, then consider a realistic feed of
                              0.006" per rev) Consider now that in order to get a proper, non
                              rubbing, cut at the periphery of a large drill the feed rate must be
                              higher than normal at the centre where a larger than normal feed
                              rate for that diameter is being applied. This takes more power and
                              creates more heat if you do not have high coolant flow.

                              Recommended speed and feed for stainless drilling for 1/4" and 1"
                              drills is 915 rpm @ 0.006"/rev and 235rpm @ 0.012"/rev. So with a 1"
                              drill the centre is cutting at much slower than recommended speed
                              but double its recommended feed per rev. When you can visualise the
                              triangle of motion for the tool circumference you will understand
                              that larger tools need higher feed rates. This seem the wrong way
                              round to a lot of people, I have had to educate a number of people
                              to stop them from reducing feed when they increase tool diameter. We
                              drill lots of holes in 316 stainless pipe where I work, 2" and 3"
                              diameter is a common hole size to be drilled.

                              An important aspect of this when machining these work hardening
                              materials is that you need to make sure when milling that enough
                              material is taken off at the start of the cut to avoid the tool
                              slipping rather than cutting. So when milling stainless steel if you
                              are taking a shallow cut you may need to "climb" mill rather
                              than "conventional" mill the material to get a good finish and avoid
                              tool wear. Conventional milling starts off shallow then gets deeper
                              as the cut progresses, climb milling starts off deep then gets
                              shallower.

                              Martin


                              --- In mill_drill@yahoogroups.com, "kidharris" <kidharris@...> wrote:
                              >
                              > Your explanation makes a lot of sense to me, however I was
                              wondering
                              > how come the center of the bit rubbing causes work hardening? I
                              > thought work hardening was caused by vibration or flexure. I know
                              that
                              > heating to a certain temp and then rapidly cooling causes
                              hardening.
                              > Do you mean that the bit rubbing is heating the material and then
                              when
                              > you withdraw the bit, as in pecking, that the material cools fast
                              > enough to case harden the material under it? Please explain the
                              > mechanism by which it hardens.
                              >
                              > --- In mill_drill@yahoogroups.com, "leasingham_connelly"
                              > <martin.connelly@> wrote:
                              > >
                              > > --- In mill_drill@yahoogroups.com, "jim_dear" <jim314159@> wrote:
                              > > >
                              > > > Did anyone notice the narration calling out step drilling as a
                              bad
                              > > > idea that compromises the "squareness" of holes?
                              > > >
                              > > > I've seen any number of texts advising that when drilling a
                              large
                              > > hole
                              > > > one should spot drill, then use a series of smaller drills to
                              work up
                              > > > to the final diameter, then finish ream.
                              > > >
                              > > > Cheers,
                              > > > jim
                              > > >
                              > >
                              > > If you are using a big high powered drill with powered downfeed
                              then
                              > > this may be true. If you are hand feeding then it is asking for
                              > > trouble with some materials such as stainless steel. If you
                              think
                              > > about the path of the outside edge of a 1" drill it is 3.14"
                              > > circumference and in order to cut and not rub it needs to be fed
                              at a
                              > > high rate, 0.012" per rev. (think of a triangle with a 3" base
                              and
                              > > 0.012" side, the slope is not all that great). At the same time
                              the
                              > > inside edge near the chisel point may be traveling only 0.5" but
                              still
                              > > being pushed thru at 0.012" per rev. This requires a lot of
                              force from
                              > > both rotation and feed. It also needs to be continuous all the
                              way
                              > > thru to avoid work hardening. If you are hand feeding and fail
                              to
                              > > maintain pressure then as soon as the drill start to rub you
                              will get
                              > > work hardening on the cut surface. Once this happens your drill
                              will
                              > > quickly fail and you will be looking for expensive carbide or
                              high
                              > > cobalt drills to force thru the hard skin to finish the hole.
                              > >
                              > > The point is that what is true for a machine shop with a full
                              set of
                              > > big machines may not be true for a home shop or someone making
                              do with
                              > > available machines.
                              > >
                              > > Walter, we use braoch cutters for mild and stainless steel gland
                              > > plates from junction boxes, 3mm thick, 16mm, 20mm, 25mm and 32mm
                              > > diameter. I have watched someone ruin a new broach cutter by
                              peck
                              > > drilling a 20mm hole in 3mm stainless plate instead of going at
                              it
                              > > with plenty of force and pushing thru in one go.
                              > >
                              > > Martin
                              > >
                              >
                            • Bud
                              Hi Martin, This is very interesting to know...thanks for the info. bud
                              Message 14 of 16 , Dec 8, 2008
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                                Hi Martin,

                                This is very interesting to know...thanks for the info.

                                bud



                                --- In mill_drill@yahoogroups.com, "leasingham_connelly"
                                <martin.connelly@...> wrote:
                                >
                                > There are a number of materials that work harden. This means that
                                > anything that is done to them mechanicaly such as rubbing or bending
                                > causes them to harden. It is a metalurgical property where the
                                > material grains/crystaline structure changes from one form to
                                > another in the reverse process from that which annealing carries
                                > out. This happens with copper and also with some (but I would not
                                > claim all) stainless steels. Try flexing a piece of stainless or
                                > copper wire and you will probably find it stiffens up at the point
                                > where it is bent. This is why repeated flexing of a piece of wire at
                                > the same point causes it to snap, it hardens to the point of
                                > brittleness.
                                >
                                > The rubbing takes place at the periphery of the tool not the centre
                                > as the angle of the cut is shallower and is more likely to rub if
                                > there is not enough feed. (Plot the triangle formed with a base
                                > equal to the circumference and height equal to the feed rate for
                                > 0.060" feed per rev for 1/4" and 1" drills, see which one is very
                                > shallow and more likely to rub, then consider a realistic feed of
                                > 0.006" per rev) Consider now that in order to get a proper, non
                                > rubbing, cut at the periphery of a large drill the feed rate must be
                                > higher than normal at the centre where a larger than normal feed
                                > rate for that diameter is being applied. This takes more power and
                                > creates more heat if you do not have high coolant flow.
                                >
                                > Recommended speed and feed for stainless drilling for 1/4" and 1"
                                > drills is 915 rpm @ 0.006"/rev and 235rpm @ 0.012"/rev. So with a 1"
                                > drill the centre is cutting at much slower than recommended speed
                                > but double its recommended feed per rev. When you can visualise the
                                > triangle of motion for the tool circumference you will understand
                                > that larger tools need higher feed rates. This seem the wrong way
                                > round to a lot of people, I have had to educate a number of people
                                > to stop them from reducing feed when they increase tool diameter. We
                                > drill lots of holes in 316 stainless pipe where I work, 2" and 3"
                                > diameter is a common hole size to be drilled.
                                >
                                > An important aspect of this when machining these work hardening
                                > materials is that you need to make sure when milling that enough
                                > material is taken off at the start of the cut to avoid the tool
                                > slipping rather than cutting. So when milling stainless steel if you
                                > are taking a shallow cut you may need to "climb" mill rather
                                > than "conventional" mill the material to get a good finish and avoid
                                > tool wear. Conventional milling starts off shallow then gets deeper
                                > as the cut progresses, climb milling starts off deep then gets
                                > shallower.
                                >
                                > Martin
                                >
                                >
                              • Curt Wuollet
                                With the stainless steel I have been making corn stove agitators out of, you get one shot to drill them. If the bit stops cutting, you throw the piece away.
                                Message 15 of 16 , Dec 8, 2008
                                • 0 Attachment
                                  With the stainless steel I have been
                                  making corn stove agitators out of,
                                  you get one shot to drill them. If
                                  the bit stops cutting, you throw
                                  the piece away. Repeated attempts
                                  just ruin cobalt drill bits. Yet it
                                  machines well on my little 7x14
                                  lathe and milling flats is not a
                                  problem. Tapping is really
                                  nasty as the hole edges are
                                  hardened by the drilling.

                                  Regards

                                  cww

                                  Bud wrote:
                                  > Hi Martin,
                                  >
                                  > This is very interesting to know...thanks for the info.
                                  >
                                  > bud
                                  >
                                  >
                                  >
                                  > --- In mill_drill@yahoogroups.com, "leasingham_connelly"
                                  > <martin.connelly@...> wrote:
                                  >
                                  >> There are a number of materials that work harden. This means that
                                  >> anything that is done to them mechanicaly such as rubbing or bending
                                  >> causes them to harden. It is a metalurgical property where the
                                  >> material grains/crystaline structure changes from one form to
                                  >> another in the reverse process from that which annealing carries
                                  >> out. This happens with copper and also with some (but I would not
                                  >> claim all) stainless steels. Try flexing a piece of stainless or
                                  >> copper wire and you will probably find it stiffens up at the point
                                  >> where it is bent. This is why repeated flexing of a piece of wire at
                                  >> the same point causes it to snap, it hardens to the point of
                                  >> brittleness.
                                  >>
                                  >> The rubbing takes place at the periphery of the tool not the centre
                                  >> as the angle of the cut is shallower and is more likely to rub if
                                  >> there is not enough feed. (Plot the triangle formed with a base
                                  >> equal to the circumference and height equal to the feed rate for
                                  >> 0.060" feed per rev for 1/4" and 1" drills, see which one is very
                                  >> shallow and more likely to rub, then consider a realistic feed of
                                  >> 0.006" per rev) Consider now that in order to get a proper, non
                                  >> rubbing, cut at the periphery of a large drill the feed rate must be
                                  >> higher than normal at the centre where a larger than normal feed
                                  >> rate for that diameter is being applied. This takes more power and
                                  >> creates more heat if you do not have high coolant flow.
                                  >>
                                  >> Recommended speed and feed for stainless drilling for 1/4" and 1"
                                  >> drills is 915 rpm @ 0.006"/rev and 235rpm @ 0.012"/rev. So with a 1"
                                  >> drill the centre is cutting at much slower than recommended speed
                                  >> but double its recommended feed per rev. When you can visualise the
                                  >> triangle of motion for the tool circumference you will understand
                                  >> that larger tools need higher feed rates. This seem the wrong way
                                  >> round to a lot of people, I have had to educate a number of people
                                  >> to stop them from reducing feed when they increase tool diameter. We
                                  >> drill lots of holes in 316 stainless pipe where I work, 2" and 3"
                                  >> diameter is a common hole size to be drilled.
                                  >>
                                  >> An important aspect of this when machining these work hardening
                                  >> materials is that you need to make sure when milling that enough
                                  >> material is taken off at the start of the cut to avoid the tool
                                  >> slipping rather than cutting. So when milling stainless steel if you
                                  >> are taking a shallow cut you may need to "climb" mill rather
                                  >> than "conventional" mill the material to get a good finish and avoid
                                  >> tool wear. Conventional milling starts off shallow then gets deeper
                                  >> as the cut progresses, climb milling starts off deep then gets
                                  >> shallower.
                                  >>
                                  >> Martin
                                  >>
                                  >>
                                  >>
                                  >
                                  >
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