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Technical Drill bit recommendation

Discussion in 'The Hokey Ass Message Board' started by Phil P, Jan 2, 2019.

  1. noboD
    Joined: Jan 29, 2004
    Posts: 8,456

    noboD
    Member

    I worked in a machine shop most of my life. The only drill bits I buy are screw machine length cobalt brand name bits. The only thing cheap bits will do is wear out your drill motor.
     
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  2. stanlow69
    Joined: Feb 21, 2010
    Posts: 7,348

    stanlow69
    Member Emeritus

    screw machine length. ?
     
  3. 32 hudson
    Joined: Mar 5, 2005
    Posts: 778

    32 hudson
    Member

    Cobalt drill bits. I only buy 5 /6 different commonly used sizes when needed.
     
  4. noboD
    Joined: Jan 29, 2004
    Posts: 8,456

    noboD
    Member

    Yes, all the name brands have them. They are shorter and have a thicker web. When was the last time you drilled a hold with a 1/2 bit that needed to be 6 inches deep? A screw machine length might be 3 1/2 inches long which is plenty for most uses.
     
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  5. TRENDZ
    Joined: Oct 16, 2018
    Posts: 386

    TRENDZ

    I commonly am called on to drill things that have been attempted by others first. As mentioned previously, materials, speed, and heat combine to make a work hardened nightmare. Once you get material to that point, ideally, I would to prefer to use a carbide bit in a mill or drill press. If you need to attempt drilling something with a hand drill once the material gets to that point, you need to custom cut a standard bit to cut. The nice thing is, you can use the bit that caused the damage in the first place. Slow speed, high pressure. You grind the cutting edge of the bit with a more blunt edge. I know it seems contradictory, but it strengthens the cutting edge. DB7A26FC-1551-4260-8CA1-0D7AFB8BB9AC.jpeg
     
  6. Rynothealbino
    Joined: Mar 23, 2009
    Posts: 396

    Rynothealbino
    Member

    I may have to look into into these screw machine length drills for home use. My only experience with cobalt drills are cheap ones which tend to be pretty good up until the moment they snap due to user error. Seems like when they break you lose a big chunk. HSS bits generally get a small chip taken out of them which can be resharpened more easily.

    My experience as a toolmaker says that it is hard to go wrong with a quality (Cleveland, Chicago-Latrobe, or Precision) HSS drill bit. Pick whatever length and finish you want, bit try to stay to the short side. I don't bother with specialized coatings because once you re sharpen it's gone off the top anyways. 135° Non split point is the easiest to sharpen on a belt sander or bench grinder. Other angles and split points can be nice for certain applications bit it's usually not needed. Split points can be done by hand but it takes a wheel with a sharp corner and a lot of practice to do right. Throw the Drill Doctor away and learn to do it by hand. We have a multi thousand dollar drill sharpener at work but most of us still sharpen by hand.

    One common mistake I see is people stepping holes oversized excessively. In general your pilot drill (if you even need one) should be around the same size as the center chisel potion (the web between the flutes). A drill will always follow the path of least resistance even if that means flexing sideways or wandering around. Too big of a pilot and the outsides of the bit will grab and wander around / chatter due to minor differences between both cutting edges. This will lead to the outsides or your drill bit being trashed and holes being wollowed open. If the whole cutting edge is touching evenly (both sides) the easiest path will be to follow the hopefully straight pilot hole. We will drill 1" or bigger holes on a regular basis and will maybe use a 3/16" drill bit as the pilot.

    The other thing I will touch on is speeds and feeds. Without getting into the math (pointless on hand tools anyways) there is a lot we can do with our eyes. One trick I learned is called "the blur factor" and applies to HSS bits in mild steel. The premise is that if your drill is spinning so fast that you can't see the flutes you will have too much surface speed. If you can clearly see the flutes then you are spinning too slow. You want to spin fast enough where the flutes just start to blur together. In harder metals or with cheap bits this will likely be too fast. Aluminum can be drilled at 2-3x this speed. Cobalt bits can go spin somewhat faster, but the point it this will get you in the ballpark and not waste too much time or tear up bits.

    Feed rate wise we need to remember a drill is a cutting tool. It is meant cut out a chip, not wear filings out of a hole. Ideally you can get 2 even chips out of a hole. Take a caliper to the chip. To simplify things greatly your chips should be all least a couple thousands thick in most applications. Thinner than that and you are just wasting time and putting excessive heat into the work. Too thick and you better have a rigid setup and keep a close ear and eye on things. I generally don't like to see much color in my chips, maybe a slight bronze color to them. If they start to turn brown, blue, and purple I think about slowing down or adding coolant / cutting fluid, or an air blast. Yes, these colors are ok, but in a non production environment usually it's just easier to slow down a bit.

    Moral of the story, buy quality tools, learn how to care for and use them. Hopefully my ramblings are useful to someone.
     
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  7. noboD
    Joined: Jan 29, 2004
    Posts: 8,456

    noboD
    Member

    Amen, to all you said. Coatings are a waste of money for the most part. Especially with a cheap make of bit that has junk metal underneath. The coating wears off in a few second from the cutting tip and then you just have a cheap drill bit. Buy quality.
     
  8. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 4,214

    ekimneirbo

    Sorry Beanscoot, but I have to disagree with you that holes need to be drilled at finish size rather than in steps, or that it is an accepted industrial practice. Holes are often drilled in steps as the finished hole sizes get larger. Thats why we have the term "pilot hole". Its also done and then followed up with a "core" drill for a straighter and rounder hole. In industry they may try to save production time by reducing the number of drilling steps they use on N/C machines, but its common practice to use more than one drill size to put a hole thru something. Another thing to consider is the thickness.......or should I say "thin ness" of the material being drilled. Its often difficult to get any semblence of "roundness" when drilling thin metal with a large two flute drill bit. Drilling to finish size may be fine with smaller bits, but it still doesn't hurt anything to drill a pilot hole and lessen the pressure needed to make a hole the finished size with a second bit. :D
     
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  9. Elcohaulic
    Joined: Dec 27, 2017
    Posts: 2,212

    Elcohaulic

    I first get comfortable or I'll be hurrying to get it over with. Use cutting oil and run the bit reasonably slow..
     
  10. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 12,286

    Bandit Billy
    ALLIANCE MEMBER

    I ran out of cutting oil the other night and went searching for something else to use and I found a tube of that rotobroach crap that you use on your spot weld cutter. It worked quite well and I could keep it in my hoodie pocket for easy access.
     
  11. seb fontana
    Joined: Sep 1, 2005
    Posts: 8,442

    seb fontana
    Member
    from ct

    Pakistan boys use water at times! They just use a 2x4 and some chain for more leverage. Really!
     
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  12. leon bee
    Joined: Mar 15, 2017
    Posts: 798

    leon bee
    Member

    Man, I loved that Pakistan video.
     
  13. WB69
    Joined: Dec 7, 2008
    Posts: 1,958

    WB69
    Member
    from Kansas

    I purchased a set from "Winters" several years ago and have had great results with them. Have drilled through everything imagineable.
     
  14. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 4,214

    ekimneirbo

    The purpose of the chain is not to pull the drill toward the hole but to keep it from twisting if the drill bit bites and grabs. The drill has a reduction gear in it and they can be quite difficult to hold on to when they break thru the other side while drilling a hole. I have one that I have had for 40+ years, and it was old when I got it. Guarantee you it has tried to make pretzels out of my arms more than once. I seldom use it anymore unless I need a big hole in something that I can't put on the drill press.
    I saw a fella buy one like mine at an auction. I went over and told him that he needed to be extremely careful when using it.......especially if he was drilling anything high enough to be near his teeth....;)
     
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  15. Harv
    Joined: Jan 16, 2008
    Posts: 974

    Harv
    Member
    from Sydney

    My father owns one of those drills. Heavy cast aluminum body, trigger lock and monstrous torque. The handle on his one has been replaced with 4' of water pipe. I once assisted him in drilling a hole at knee height, him holding the drill and me holding the pipe. The 3/4" drill bit into the material, and spun the drill. Threw him and I both, and proceeded to cartwheel around the workpiece. Didn't stop until it had wrapped the cord up and pulled the plug out of the socket.

    Always entertaining working with Dad :)

    Cheers,
    Harv
     
    ekimneirbo likes this.
  16. PickupNut
    Joined: Feb 24, 2019
    Posts: 37

    PickupNut
    Member

    Look up The Drill Mug on the internet. Been using these for ten years.Excellent quality, easily sharpened.Fair and cool container keeps easy track of bits.
     

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