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Milling a slot

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  • #31
    The slot drill looks like a two flute end mill. The face or end flutes are offset so plunge milling is possible.

    With standard two flute end mills the flutes are symmetrical but meet in the center providing a cutting edge for the entire face.

    The slot drill just looks like a proprietary grind (offset flutes on the face) from one manufacture (Dormer).

    Does any other end mill manufacture make slot drills?
    My old yahoo group. Bridgeport Mill Group


    • #32
      I confess to the same results as Geo. Thomas and end up cutting the slot with a narrower cutter and finishing cuts of 10 thou or so on each side, using a bit of air so the chip are getting squashed in seem to matter whether its 4there. btw, when doing so it doesn't matter if its 2 or 4 flutes.

      this is a also a better approach as I find the the end mill will tend to get defected off course a little bit from the cutting force so the finish cut on each side cleans things up and restores accuracy.

      I never really paid attention to the two vs four - if you use a slot drill, can you expect to get an accurate neat cut without all the about hassle?

      [This message has been edited by Mcgyver (edited 06-18-2005).]
      in Toronto Ontario - where are you?


      • #33
        Let me try to expain about end mills and slot drills. Many people have their own description of these but I'm afraid no one is right any longer - even me !!!
        First off lets go back in history and see what we had. There were 4 flute end mills and 2 flute end mills. Some could plunge some couldn't. Confused? well you will be.
        The two flute ones were called slot drills in the UK and were ground with one cutting edge over centre so they can plunge cut vertically down and then traverse, hence the name. These are the ones on the right in JCHannum's picture.
        The 4 flute end mills usually had a hole in the centre for clearance when grinding and so can only cut on the sides of the tool. Trying to plunge with one of these will leave a central pip that will break the cutter when you try to traverse.
        Now when we got towards the end of the 20th century things started changing. We had better methods of producing cutters with fancy 5 and 6 axis CNC grinders. We started to see 3 flute cutters getting popular as a compromise between rapid metal removal and chip clearance. We also started to get the 3 and 4 flute cutters with one lip ground over centre like the two flute in the picture. This means that these can also plunge.
        To cap it all the manufacturers put paid to any standards by calling their cutters all sorts of different names. Where a 4 flute cutter was called an end mill it can now be centre cutting and be called a 4 flute slot drill.
        If you look in any cutter catalogue nowdays you will find that they call a certain type of cutter by one name on one page and another manufacturer calls it by a different name on another page! The manufacturers have moved the goalposts. The cutter descriptions we all grew up with in Chapmans and Moultreich <sp> has gone out the window with the advent of grinding techniques.
        I took a 20mm solid carbide 4 flute end mill [ non centre cutting ] in for regrind last month and when it came back it was 4 flute over centre slot cutting cutter. What do I call this now?
        The main thing to look for when buying cutters is the number of flutes you require and whether they are centre cutting or not.
        I can see the time when the old 4 flute centre pipped type will become obsolete as most cutters are ground up from blank material nowdays.
        I had a load of cam track slots to do the other week at 7.2mm wide. I had a choice of doing two passes with an undersized cutter or having a cutter ground down to 7.2mm
        I decided to go with the special cutter and asked the local T&C grinders to supply and regrind an 8mm cutter down. Instead they just ground the new cutter straight onto a 8mm solid blank, 3 flute centre cutting. It was on the machine for all of 3 minutes.

        John S.

        [This message has been edited by John Stevenson (edited 06-18-2005).]

        Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


        • #34


          • #35
            I prefer to use side cutters like woodruff keyseat cutters or slotting or slitting saws for this work. A 3/16" keyseat cutter probably won't get 3/8" deep cut tho. The setup would be to clamp the part directly to the mill table and indicate down to the center and slot.
            If milling I would use a 2 Flute center cutting end mill by whatever name. I would take light cuts and mill the full length. The 2 flute end mill will have less tendancy to walk than a 4 flute. At least that is my experience.
            I would also run the 3/16" end mill at around 1100 rpm or better. Small mills and drills should be ran faster than larger ones.

            [This message has been edited by happy02 (edited 06-18-2005).]


            • #36
              I'm just a dummy, but I gotta say I have done as mochinist says..... cut the slot with an end mill. Any end mill that was smaller than the slot.

              But, doing it in one pass has not been good, two passes or better three has been best with small-diameter end mills. They do deflect at the 0.125 size, and while the slot may look pretty straight, a piece of keystock may say they aren't.

              example being cut. Its an arbor for the mill. I see I was using a 2 flute cutter, but I had used a 4 flute for the smaller keyway on teh near side. A 1.250 arbor, needed a 0.187 slot and a larger one, both.

              Would have used a regular milling cutter, but needed to stop at the shoulder, and reach to it.

              [This message has been edited by J Tiers (edited 06-18-2005).]
              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......


              • #37
                I don't mind the squabbling at all, its a whole lot more polite than on some of the boards I frequent and a whole lot more informative. I think I've learned more about milling from this thread that I learned from a couple of the books I've bought.

                I'm definitely going to try the 2 flute cutter. I don't have a 1/8", only a 3/16" and 1/4".

                I will say that for all the frustration I've gotten trying to mill these slots, its really awesome working with metal again.

                If theres any life left in this discussion, I sure will keep up with it. I'm glad I found this board.


                • #38
                  O2, I am sure that John is right- as ever!

                  Unquestionably, he is like the man who pee on weighing machine, does business on big scale. His comments bring milling into the new century.

                  I'm just an "old fashioned millionaire"- and a bit of a stick in the mud. Nevertheless, I feel that my advice is to use what we call slot drills in preference to end mills for slotting. If there is something better- as John rightly suggests-
                  it is worthy of consideration.

                  Actually, I was sitting with the old book on tool and cutter grinding from the Clarkson factory- and the date was April 1968.

                  Guilty as Hell, me lud!



                  • #39
                    Don't give me that luddite crap Norman.

                    The slot drill such as the one I have shown is not just a Dormer proprietary grind. It is a superior tool for cutting a slot, especially a blind slot. John as usual has illuminated the situation with black light...

                    The slot drill as made that I use cuts a slot that is accurate to a thou or so in one pass. You can see that it is clearly a very clean slot.

                    As I said before, it seems that the US doesn't always have easy access to the best technology. The reasons have nothing to do with what works best for the job but are usually tied up in politics or backward economics, just like the Roberson screw.
                    Free software for calculating bolt circles and similar: Click Here


                    • #40
                      For once, Evan, on this fine English Sunday morning, I was reading St Paul- the tent maker fellow.

                      In Ephesians, he says
                      "see that ye walk circumspectly"

                      and in Thessalonians , he says
                      " Prove all things; hold to that which is good"

                      and Shakespeare writes for those screwcutters

                      " This is the top, the height, the crest or crest unto the crest"
                      King John.

                      For those who tilt at windmills?
                      Cervantes quotes little Sacho Panza:-
                      "All men are as God made them, and very often worse"

                      And Luddites to you, matey!I've never broken a machine yet- but slot drills and end mills? Well, modesty forbids.


                      [This message has been edited by NORMAN ATKINSON (edited 06-19-2005).]


                      • #41
                        Norman, it is just barely Sunday here too. I too have never broken a machine intentionally.

                        This is apropo of nothing but it is one of my favorite poems.

                        Once upon a midnight dreary, while I pondered weak and weary,
                        Over many a quaint and curious volume of forgotten lore,
                        While I nodded, nearly napping, suddenly there came a tapping,
                        As of some one gently rapping, rapping at my chamber door.
                        `'Tis some visitor,' I muttered, `tapping at my chamber door -
                        Only this, and nothing more.'

                        Ah, distinctly I remember it was in the bleak December,
                        And each separate dying ember wrought its ghost upon the floor.
                        Eagerly I wished the morrow; - vainly I had sought to borrow
                        From my books surcease of sorrow - sorrow for the lost Lenore -
                        For the rare and radiant maiden whom the angels named Lenore -
                        Nameless here for evermore.

                        And the silken sad uncertain rustling of each purple curtain
                        Thrilled me - filled me with fantastic terrors never felt before;
                        So that now, to still the beating of my heart, I stood repeating
                        `'Tis some visitor entreating entrance at my chamber door -
                        Some late visitor entreating entrance at my chamber door; -
                        This it is, and nothing more,'

                        Presently my soul grew stronger; hesitating then no longer,
                        `Sir,' said I, `or Madam, truly your forgiveness I implore;
                        But the fact is I was napping, and so gently you came rapping,
                        And so faintly you came tapping, tapping at my chamber door,
                        That I scarce was sure I heard you' - here I opened wide the door; -
                        Darkness there, and nothing more.

                        Deep into that darkness peering, long I stood there wondering, fearing,
                        Doubting, dreaming dreams no mortal ever dared to dream before
                        But the silence was unbroken, and the darkness gave no token,
                        And the only word there spoken was the whispered word, `Lenore!'
                        This I whispered, and an echo murmured back the word, `Lenore!'
                        Merely this and nothing more.

                        Back into the chamber turning, all my soul within me burning,
                        Soon again I heard a tapping somewhat louder than before.
                        `Surely,' said I, `surely that is something at my window lattice;
                        Let me see then, what thereat is, and this mystery explore -
                        Let my heart be still a moment and this mystery explore; -
                        'Tis the wind and nothing more!'

                        Open here I flung the shutter, when, with many a flirt and flutter,
                        In there stepped a stately raven of the saintly days of yore.
                        Not the least obeisance made he; not a minute stopped or stayed he;
                        But, with mien of lord or lady, perched above my chamber door -
                        Perched upon a bust of Pallas just above my chamber door -
                        Perched, and sat, and nothing more.

                        Then this ebony bird beguiling my sad fancy into smiling,
                        By the grave and stern decorum of the countenance it wore,
                        `Though thy crest be shorn and shaven, thou,' I said, `art sure no craven.
                        Ghastly grim and ancient raven wandering from the nightly shore -
                        Tell me what thy lordly name is on the Night's Plutonian shore!'
                        Quoth the raven, `Nevermore.'

                        Much I marvelled this ungainly fowl to hear discourse so plainly,
                        Though its answer little meaning - little relevancy bore;
                        For we cannot help agreeing that no living human being
                        Ever yet was blessed with seeing bird above his chamber door -
                        Bird or beast above the sculptured bust above his chamber door,
                        With such name as `Nevermore.'

                        But the raven, sitting lonely on the placid bust, spoke only,
                        That one word, as if his soul in that one word he did outpour.
                        Nothing further then he uttered - not a feather then he fluttered -
                        Till I scarcely more than muttered `Other friends have flown before -
                        On the morrow will he leave me, as my hopes have flown before.'
                        Then the bird said, `Nevermore.'

                        Startled at the stillness broken by reply so aptly spoken,
                        `Doubtless,' said I, `what it utters is its only stock and store,
                        Caught from some unhappy master whom unmerciful disaster
                        Followed fast and followed faster till his songs one burden bore -
                        Till the dirges of his hope that melancholy burden bore
                        Of "Never-nevermore."'

                        But the raven still beguiling all my sad soul into smiling,
                        Straight I wheeled a cushioned seat in front of bird and bust and door;
                        Then, upon the velvet sinking, I betook myself to linking
                        Fancy unto fancy, thinking what this ominous bird of yore -
                        What this grim, ungainly, gaunt, and ominous bird of yore
                        Meant in croaking `Nevermore.'

                        This I sat engaged in guessing, but no syllable expressing
                        To the fowl whose fiery eyes now burned into my bosom's core;
                        This and more I sat divining, with my head at ease reclining
                        On the cushion's velvet violet lining that the lamp-light gloated o'er,
                        But whose velvet violet lining with the lamp-light gloating o'er,
                        She shall press, ah, nevermore!

                        Then, methought, the air grew denser, perfumed from an unseen censer
                        Swung by Seraphim whose foot-falls tinkled on the tufted floor.
                        `Wretch,' I cried, `thy God hath lent thee - by these angels he has sent thee
                        Respite - respite and nepenthe from thy memories of Lenore!
                        Quaff, oh quaff this kind nepenthe, and forget this lost Lenore!'
                        Quoth the raven, `Nevermore.'

                        `Prophet!' said I, `thing of evil! - prophet still, if bird or devil! -
                        Whether tempter sent, or whether tempest tossed thee here ashore,
                        Desolate yet all undaunted, on this desert land enchanted -
                        On this home by horror haunted - tell me truly, I implore -
                        Is there - is there balm in Gilead? - tell me - tell me, I implore!'
                        Quoth the raven, `Nevermore.'

                        `Prophet!' said I, `thing of evil! - prophet still, if bird or devil!
                        By that Heaven that bends above us - by that God we both adore -
                        Tell this soul with sorrow laden if, within the distant Aidenn,
                        It shall clasp a sainted maiden whom the angels named Lenore -
                        Clasp a rare and radiant maiden, whom the angels named Lenore?'
                        Quoth the raven, `Nevermore.'

                        `Be that word our sign of parting, bird or fiend!' I shrieked upstarting -
                        `Get thee back into the tempest and the Night's Plutonian shore!
                        Leave no black plume as a token of that lie thy soul hath spoken!
                        Leave my loneliness unbroken! - quit the bust above my door!
                        Take thy beak from out my heart, and take thy form from off my door!'
                        Quoth the raven, `Nevermore.'

                        And the raven, never flitting, still is sitting, still is sitting
                        On the pallid bust of Pallas just above my chamber door;
                        And his eyes have all the seeming of a demon's that is dreaming,
                        And the lamp-light o'er him streaming throws his shadow on the floor;
                        And my soul from out that shadow that lies floating on the floor
                        Shall be lifted - nevermore!
                        Free software for calculating bolt circles and similar: Click Here


                        • #42
                          What a delight to read a nice bit of verse.
                          It must be the little brown Celts- Evan Williams- look you! The Bard of Borland Street. They have, my Welsh Wizard, the Gift- or as we say- are Fey. The gift of the Second Sight.

                          How on earth did you choose the bit on the Raven? I married a Liddell of Ravensworth Castle. My lodge is Ravensworth and Alice of Alice in Wonderland is actually Alice Pleasance Liddell- or Hargreaves on marriage.

                          You will be able to solve the riddle of Why is the Raven Like a Writing Desk.

                          How amazingly perceptive.



                          • #43
                            I can't believe that for 35 years I have been milling slots wrong, Tomorrow I am throwing away all those useless endmills
                            and getting slotting drills.
                            Two pages about how to do a five minute job.
                            Non, je ne regrette rien.


                            • #44

                              Sorry, folks!

                              It was Edgar Allan Poe- The Raven.



                              • #45

                                1/4" X 1/8" deep slot, plunge milled one end, one pass at 1/8" depth, 1147 RPM, WD40 coolant. Weldon made in USA two flute center cutting symmetrical end mill, Cat. No B 8-2. Finished slot width 0.2500". Material 6061 aluminum T-6.

                                Total time to complete, 2 minutes, one of which was spent in finding and installing the end mill.

                                No matter what some may think, slot mill is just another name as John says. The Dormer end grind is not proprietary, and gives no advantage other than advertising hype. It is not some vastly improved technology that America has not embraced.
                                Jim H.