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  • grinding drillbits

    where can i find real instructins on how to sharpen drill bits? Books sowing angles relief and whatnot do not tellme how to grab the bit or how to address the bit to the grinding wheel.

  • #2
    Ya need to find an old geezer that has been doing it since the dawn of time. Myself I use my Drill Doctor or my el cheapo General Tool.

    Comment


    • #3
      Instructions for grinding a drill bit are sort of like instructins for riding a bicycle; you need to do it and figure it out yourself. Actually, it's not quite that bad; if you can find somebody who can show you how to do it, then it gets a lot easier.

      How would I describe it.... I'm not particularly good at sharpening drills by hand, but here's what I do (I think). First, it helps to start out with a fairly large drill so you can better see what's going on. Rest the drillbit on the tool rest, holding it so a cutting edge is horizontal and parallel to the face of the grinding wheel. Drop the tail end of the drillbit down enough so, if you pressed the drill against the grinding wheel now, you'd grind the cutting edge of the drill at the proper relief angle. So: press the drill against the grinding wheel and at the same time sweep the tail end of the drill down, so you grind back along the full area behind the drill cutting edge. Repeat for the other cutting edge.

      (Anybody else who can sharpen a drill by hand; does that make any sense whatosever?)


      [This message has been edited by SGW (edited 09-03-2004).]
      ----------
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      • #4
        Not that I fall in the category of "anyone who can sharpen a drill bit"..., but I'd add that simultaneously while dropping the shank end you sort of rotate the business end that's bearing against the wheel, so that the relief grind is kinda swirled around the tip. But not so much that you hit the other cutting edge.

        Comment


        • #5
          Hey Mike, I resemble that remark!

          SGW and Lynnl have it right. It takes practice. The hard part is to grind both sides the same amount so that the cutting tip is centered and the bit cuts straight. It only needs a quick swipe and then a dip in some water before the next swipe. You don't need to take much material off unless you are rehabilitating a bit with the corners knocked off.

          The more difficult part is sharpening drill bits that are split point. For that the best is to have a very fine wheel dressed to a sharp 90آ° corner. It helps a lot to use a magnifier lamp or similar.

          I've been getting lazy about it lately and am considering building a jig for my Unimat to sharpen bits.
          Free software for calculating bolt circles and similar: Click Here

          Comment


          • #6
            <font face="Verdana, Arial" size="2">Originally posted by Byron:
            where can i find real instructins on how to sharpen drill bits? Books sowing angles relief and whatnot do not tellme how to grab the bit or how to address the bit to the grinding wheel.</font>
            Lindsey publications has a nice little booklet reprinted from an old one published by Cleveland twist drill company listed in their catalog. I have one, and there is more info about drill bit geometry, and sharpening, speeds and feeds etc, than anyone really has any business knowing. I was a foreman in a machine shop before I got tired of dealing with the managers incompetence, lol, and one of my requirements when I hired a machinist was the ability to do one thing, sharpen a drill bit by hand with a drill gauge so that it cut two evenly formed chips. I didnt care how long it took,, but that's basic trade school 101. You'd be surprised how many two year trade school graduates don't have clue one how to do it.

            [This message has been edited by pete913 (edited 09-04-2004).]

            [This message has been edited by pete913 (edited 09-04-2004).]
            Pete

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            • #7
              Byron,

              Here's a link that might help, scroll down a little.

              http://www.tpub.com/steelworker2/121.htm

              -Mike

              Comment


              • #8
                Interesting link. I note they warn about not quenching bits in water. If you dip the bit after each swipe the bit is not hot enough for significant hardening to take place upon quenching. The bit should never get that hot while grinding anyway.
                Free software for calculating bolt circles and similar: Click Here

                Comment


                • #9
                  There used to be an RCM denizen with the nom de plume of "Teenut" who wrote
                  what I consider to be the best written description of how to sharpen drill
                  bits. It's long but worth saving and passing along when this question pops up.

                  ------ Teenut's instructions -----

                  Anyone who wants to learn this skill should start large - and I mean
                  1/2 inch and above. This is a great way to make long drills short.

                  I believe I learned on a 3/4" taper shank drill..it is a lot easier to
                  see all the angles and begin to understand how they work and interact.

                  By the way..we had a handy little doohickey to help get the drill lips
                  level. I have never heard it described before..

                  For the Morse taper shank drills from 1/4" up to about 1" diameter, we
                  had a piece of 2" by 1/8" hot rolled steel strap..about 14" long. One
                  end was bent at right angles, about 2" from the end to form an L shape
                  with one 12" upright and a 2" horizontal. In the geometric center of
                  this short leg was affixed a "dead" center..not a lathe tail stock
                  center!!...more like a 1/2" bolt, 1/2" long, turned or ground to a 60
                  deg point (Approx...no great precision required) and screwed in from
                  the under side. That's IT..toolmaking over!

                  In use the inner face of the upright was coated with whitewash (Never
                  SAW marking blue 'til I got in the toolroom!) The drill was ground,
                  freehand, on the FACE of the wheel (not the flat side)...care being
                  taken to keep the POINT angle as equal as possible on both sides..I'll
                  tell you how to do THAT in a moment..

                  Lets do that now in fact..

                  Jim, You are dead right about not being able to grind a drill without
                  mechanical help! Well here's how you create your own "6 Million
                  Dollar Bionic Darex" ;^)

                  Let's assume we are going to sharpen a 3/8" diameter, 2MT shank
                  drill..it is about 8" long (these figures are arbitrary..I just want
                  every one to have the same mental picture of what I am describing. We
                  approach the wheel, which has been dressed on its face, dead straight
                  across with no grooves..(Ve SHOOT anyone ve catch putting grooves in
                  ze drill wheel!!..No Pity..No Prisoners..Ya! Verdammt!)

                  (Sorry)...

                  The drill shank is held firmly in the RIGHT hand...ALL the movement
                  and control is imparted by the RIGHT hand. For the purposes of drill
                  grinding, the left hand could be...with benefit..a LUMP OF CLAY!!

                  It is from this "lump of clay" that we fashion the "Bionic Darex".

                  Place your left hand thumb and forefinger tips LIGHTLY together..Relax
                  the other three fingers and let them naturally curl against the palm
                  of your hand. Let the drill flute drop into the vee between thumb and
                  forefinger and let the tip of the finger "Find" the curve of the flute
                  where it fits comfortably. The tip of the thumb rests on the sharp
                  junction ot the land and the flute, about an inch back from the drill
                  tip.

                  Now...SQUEEZE HARD!!! YOUCH!...I said it would be easier if it were
                  clay! 8^) Lift the drill from your fingers...see the GROOVE?...Drop
                  the drill back in..it locates within a thou or two! Magic?..Bionic at
                  least! Squeeze again to set the groove. You have created a
                  customized drill guide that fits better than that on any machine ever
                  built! You can relax your grip now..feel how smoothly the drill will
                  ride back and forth, guided by the groove you have created for it.

                  Place the knuckles of your left hand, LIGHTLY on the ginding wheel
                  tool rest, and swing the drill shank, from left to right (using ONLY
                  your right hand) and push the drill lengthways though that groove in
                  your fingers back or forth using the groove to make the drill twist or
                  "rifle" in your fingers. Do NOT move your left hand in any way..it is
                  made of clay remember!

                  UNTIL....

                  A) The drill axis is "eyeballed" to be at half the required point
                  angle to the wheel face...You can scribe or chalk reference lines on
                  your grinder benchtop to help you line this up..at least until it
                  become almost second nature.

                  B) The drill axis is dropped JUUUst below horizontal. This will
                  ensure that your soon to be ground drill lip will start with a
                  "smidgin" of cutting clearance.

                  (Ideally, and certainly for a beginner, the grinder rest should be set
                  dead radially to the wheel center and about half the drill diameter
                  below the true center of the wheel)

                  C) The two cutting edges of the drill..the straight, sharp bits,
                  formed by the junction of the flute and the back face (the only bit
                  you grind), should be horizontally disposed..with the edge uppermost
                  on the side closest to your left hand..the other sharp bit of course,
                  pointing downwards (Jeeze this would be a lot easier with a sketch
                  pad)

                  This I will call the SET or START position!

                  NOW, move your left hand for the first, last, and ONLY time during
                  this whole exercise. GENTLY ease the cutting edge towards the
                  spinning wheel, carefully maintaining all the angles and orientations
                  of the SET position..until the cutting edge is JUST shy of touching
                  the wheel. If you listen carefully you will hear the tone of the
                  entrained air, whistling through the narrowing gap. You will hear a
                  subtle but distinct change of tone JUST, I mean Just...a couple tenths
                  of a thou BEFORE the edge touches the wheel. STOP!!! FREEZE!! DO
                  NOT MOVE!!

                  Now, press the knuckles of your lump of clay..sorry, your left hand
                  FIRMLY down onto, into and around the grinding rest..establish a
                  "Groove" on the back of your hand as well as between your fingers.

                  We are now ready to grind, Your left hand locked to the drill and
                  grinding rest is otherwise quite relaxed..letting the drill slide,
                  twist and tilt wherever your right hand and the groove in your fingers
                  tell it to go.

                  The actual grinding is a bit of an anticlimax.

                  You have previously studied a new drill point, you have read about
                  clearance, and cutting angles, and rakes and......

                  With the RIGHT hand in control, gently, kinda, lean forward... bending
                  or squeezing your arms hands and body..rather than actually moving
                  them..untill you take up that last couple of tenths and the wheel
                  begins to cut. Let it cut..don't force it, and don't rush it..it
                  really won't hurt anything if you take a full minute per pass per
                  face. YOU and your "Bionic Darex" are totally in control of that
                  drill and the wheel..Forget the times when, close to panic, you swung
                  the drill wildly past the wheel, hoping to get "the dirty deed" over
                  with as quickly as possible.

                  Take your time, enjoy the moment, THINK about the shape you are trying
                  to generate. Just the one face is left to "Interpretation"...every
                  other aspect,angle, facet, what have you...Has ALREADY BEEN TAKEN CARE
                  OF!! and is locked in place under your control!

                  The right hand should perform a "Lower Quadrant sweep" for want of a
                  better term. An observer behind you would see your hand move from
                  about 17 minutes past the hour on a clock face, to roughly 25 minutes
                  past. But it isn't a smooth arc of a circle, more a sector of an
                  elipse..You see, as your hand starts to drop slowly, you are also
                  rotating the drill in "the groove"..the first third of the turn needs
                  to maintain that very slight clearance angle on the cutting edge, and
                  not increase it too rapidly.

                  You need the clearance to cut..But too much at that point will WEAKEN
                  the edge, and cause the drill to snatch and chip...So the first part
                  of the rotation is ALMOST but not quite, just as though you were
                  grinding a straight cone point on the end of your drill. Only as you
                  approach the second third, does your right hand start to noticably
                  drop..kinda "Catching Up" on the rotary motion...increasing the
                  clearance as it does.

                  In the last third of the rotaion the right hand drops quite
                  rapidly..Thogh not enough to catch the OTHER drill lip on the
                  wheel..that lip is coming around quite rapidly by now.

                  Above all, take your time, if it helps, move the drill one degree at a
                  time, and think ahead what shape or angle the next degree of cutting
                  face needs...Remember, you have control, and IT ain't going nowhere
                  'til you decide.

                  After a pass on one face, flip the drill in your "Bionic Darex" DO NOT
                  MOVE THAT LEFT HAND!!, return to SET position and repeat, the pass on
                  the other face.

                  Having done a couple of passes on each face..it is now time to check
                  the results on our homemade "Optical Comparator"

                  Rest the center hole in back end of the drill shank, on the center
                  point of the "Comparator" and use, first one and then the other drill
                  lip to scribe a light line on your whitewashed (OK blue or red dyed)
                  surface.

                  You will readily see if the lines coincide..if the lips are even..or
                  not, as the case may be.

                  Lets assume they are..Now look directly DOWN on the end of the drill
                  to check the clearances. HUH? How can you check radial clearance by
                  looking it staight in the face? Surely you need to look at it
                  sideways?

                  Well no you don't...for once all those interacting and confusing
                  angles and faces and clearances are going to work together in YOUR
                  favor and make what could be a tricky bit of metrology..quite simple.
                  While we are looking at the end of the drill, we will also check that
                  the POINT ANGLE is correct too!!!

                  (Ok guys, leave quietly..teenut has finally lost it!!)

                  No really, trust me. IF you look straight down on the point of a well
                  sharpened, standard drill, you will see the two cutting edges, joined
                  by the CHISEL edge which crosses over the web of the drill. The angle
                  fromed by the chisel edge to each cutting edge should be ABOUT 50
                  deg...anywhere between 40 and sixty is ok for a first attempt. (I can
                  hear the purists and theorists screaming and lighting up their flame
                  throwers.) But believe me, get it in that ball park and your drill
                  will CUT. If the angle is too steep..you don't have enough
                  clearance...negative clearance will give you an angle event greater
                  than 90 deg. Too MUCH clerance and the angle will appear too shallow!

                  While looking at the end, check the point angle, How? Look down the
                  axis of the drill at the cutting edges. Are they straight? If so,
                  your point is pretty close to the right angle (As designed for that
                  drill, by its manufacturer when he set the helix angle and the cross
                  section of the flute) If the edges appear CONCAVE the point is too
                  flat and if they appear CONVEX, the point is too "Pointy"

                  If your drill passes all these tests, which take but a second or two
                  to perform, THEN IT WILL CUT..pretty close to size, without
                  chattering, chipping, overheating, wandering or seizing. I guarantee
                  it!

                  Hey, thats a pretty good start for the first drill you ever ground!
                  All it takes now is a bit of practice for it to become second nature
                  and almost as easy with a little 'un or a big 'un!

                  Hey guys!

                  My apologies for "goin'on" but If it helps just one person to pluck up
                  the couragre and go hand sharpen his (or her) first drill, by hand...

                  Then I hope you will bear with me.

                  It is late, I am tired and I am not even going to proof or spell check
                  this,

                  'night all

                  teenut
                  -------------------------------

                  Regards, Marv

                  Home Shop Freeware - Tools for People Who Build Things
                  http://www.geocities.com/mklotz.geo
                  Regards, Marv

                  Home Shop Freeware - Tools for People Who Build Things
                  http://www.myvirtualnetwork.com/mklotz

                  Comment


                  • #10
                    I learned on my own...Its tough to teach someone..I practiced, practiced and practiced until I got it right...

                    Took a lot of drill bits and a lot of time at the beginning...

                    good luck
                    brent

                    Comment


                    • #11
                      Klotz,that has to be the single longest post in HSM bbs history!Congrats

                      Well in simple terms,hold the bit with the index finger of your right hand under the bit and your tumb on top,bring the angle of the point parallel to the grinding wheel with the cutting edge horizonal,touch the bit to the wheel with the edge up and the shank tilted down at about 5-7*,then roll and push in gently at the same time,the object is to make the cutting edge higher than the area imeadiately behind it.

                      Don't over grind!Remember its a precision cutting tool and not lawnmower blade
                      I just need one more tool,just one!

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                      • #12
                        Drill Doc, watch the video and your ready to sharpen.

                        Comment


                        • #13
                          Plus you won't shorten your drill by 1" while you try to get it right.

                          Comment


                          • #14
                            <font face="Verdana, Arial" size="2">Originally posted by jfsmith:
                            Drill Doc, watch the video and your ready to sharpen.

                            </font>
                            Use a drill Doc, get a bad grind, it's the law.

                            Ain't worth crap, gotta diddle with them forever to get good grinds, video or no video.

                            Inconsistent hunk of junk. No wonder Darex wants their name far from those machines...even though they USED to be associated.

                            They are inherently made wrong, or at least mine is. So loose that the drill tip can move almost 0.060 when the collet is in the sharpening tube, with no force applied.

                            And they said mine was one of the best lots they had made....
                            1601

                            Keep eye on ball.
                            Hashim Khan

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