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Drill Sharpening: An Introduction

Discussion in 'Machining and Fabrication' started by Racey, Aug 4, 2010.

  1. Racey

    Racey Maxwell Smart-Ass

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    The wizdom section has been lacking some love, i decided to put together a quick little tutorial on sharpening your drills. Hand sharpening drills is not as difficult as one would think, and in many cases my hand sharpened drills will out-perform the 'out of the box' sharpening job that comes on the drill.



    I blunted a drill to show your worse case scenario for sharpening. Take note of how the spiral has a flat edge on the cutting side. and is rounded on the trailing side

    [​IMG]

    [​IMG]

    When sharpening drills you are dealing with 2 separate angles, the first angle is the cutting angle, or knife angle, the second angle is what i refer to as 'the compound angle'. In most cases the knife angle should be just shy of flat, this gives the most edge strength at the tip of the drill. The compound angle is more commonly adjusted (Normal drills are 118degrees, hard material drills have thicker center webs are normally 135 degrees, blunt flat is 180 degrees), the sharper the compound the better the drill will center itself, or spot holes, but the harder the drill will work to cut holes. The blunter the angle the better the drill will work on hard materials because the cutting edge will be shorter meaning less contact between the cutting edge and the material being drilled, less cutting per rotation, hence less torque load on the drill.


    [​IMG]

    [​IMG]



    the first cut you make is a combination of both your knife angle, and the compound angle, this will form the cutting edge of the drill bit. You are looking for the cutting edge to be just about knife sharp, if you run your thumb across it, it should feel very sharp like a knife.

    [​IMG]

    [​IMG]



    once you have both sides of the drill matched with the first cut (equal grind on both sides, the point should meet perfectly in the center of the drill) You will make a second cut at the same compound angle, but with a slightly steeper knife angle, this cut will start just behind the cutting edge and extend the rest of the way back down the drill. This cut provides an open path for the chips to escape from the following cutting edge during drilling.

    [​IMG]

    The final cut you will make is center chip relief and 'zero point' cut, in this cut you will use the edge of the wheel and at a steep angle cut into the trailing edge as shown below. Be careful not to touch the knife edge of the opposite side to the wheel, the closer you can get these 2 cuts to come together the better the drill will work at drilling a hole without a pilot (the center of the drill will provide easier cutting). If you notice this grinding wheel sucks, it no longer has a sharp edge, so this isn't the greatest example of a center cutting drill, This is why you try to keep your wheels square, then you can get these two points to meet much sharper, and cut better.

    [​IMG]

    [​IMG]

    [​IMG]
     
    Last edited: Aug 4, 2010
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  2. rivermobster

    rivermobster Club Banned

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    Dude, thats cool!!!

    Sounds stupid, but I cant wait to get home to try this.

    Thank you!

    :bowdown:
     
  3. RitcheyRch

    RitcheyRch Currently Boat-Less

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    Some excellent information. Thanks.
     
  4. Flat Broke

    Flat Broke Well-Known Member

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    That's some solid info. I'd love to see more stuff like this in general. I never thought to take the last step that you showed, mainly because I'm usually in a hurry, but also because dad got me using center drills at the begining of almost any drilling operation.

    As an aside, I think Dave needs to find a way to incorporate more stuff like this (maybe a little bit more boat-centric) onto the "main page". Do this same thing, but lay it out to have it look like an article that prints off nice and easy.

    Chris
     
  5. RiverDave

    RiverDave In it to win it

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    I will work on that next week..

    RD
     
  6. Racey

    Racey Maxwell Smart-Ass

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    I always use centering drills in the mill to spot and start the hole, but with a nice zero pointed drill you can eliminate the need to drill a complete pilot hole in a lot of cases. If i'm drilling something by hand with a hand drill i'll still use a full pilot most of the time (usually an 1/8")
     
  7. Crazyhippy

    Crazyhippy Haters gonna Hate

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    Any thoughts on heat treating (or lack there of)?

    In my experience drills out of the package last 2-3 times longer under normal abuse than those "drill doctored". It could be friction coating on the cutting edges, but I assume it's a heat treating/hardness issue.

    Great article. Never sharpened them by hand.
     
  8. Racey

    Racey Maxwell Smart-Ass

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    I've never worried so much about heat treating, i have the grinder handy so if i need to drill something precise i'll clean up the sharpen job as needed. If you don't overheat the drill grinding it you won't have to worry about losing the heat treat. it has to get well beyond 'cherry red' to anneal.

    However, if it suits your taste many drill bits are made from oil hardening stock, you can heat them to 'cherry red' and drop them in a bucket of oil and they will re-harden. never had a need to do that myself, but Mr. Dunsmore Sr. has told me it works well. :thumbsup
     
  9. obnoxious001

    obnoxious001 Engine building character

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    I would guess that not many people normally "doctor" drill bits as well as Racey has described.
     
  10. Crazyhippy

    Crazyhippy Haters gonna Hate

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    Like I said, my experience is limited to using a "drill doctor". It's a little plastic sharpening doohickey. Makes the bits feel sharp, cut sharp (for a little bit) but then dull quickly.

    Granted, I am hard on drill bits. I turn them faster than I should, and don't use enough pressure on anything bigger than 3/8 or so. Add in the lack of lubrication, and I meet the FBI's definition of torture:skull I might be taking the temper out of the bit before it is re-sharpened and blaming the doctor.
     
  11. Racey

    Racey Maxwell Smart-Ass

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    Maybe my next thread should be on spindle speeds and feed rates :skull :thumbsup
     
  12. Wheeler

    Wheeler Well-Known Member

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    I have often wondered why would you lubricate something you are trying to cut?
     
  13. Racey

    Racey Maxwell Smart-Ass

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    a drill, end mill, or other toolbits purpose is to 'peel' material away, so that ribbon of material that is being peeled is relieved far better with some form of lubricant to reduce metal to metal friction/heat, the oil also helps cool the cut as a bonus :thumbsup

    The same reason you don't shave your face dry, you use water, soap, or shaving cream.... ;)
     
  14. Crazyhippy

    Crazyhippy Haters gonna Hate

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    Knowing where they are, and using them are 2 different things...

    And weak ass hand drills dont help:grumble:;)
     
  15. Wheeler

    Wheeler Well-Known Member

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    What type of gauge are you using to keep the angles equal?
     
  16. Racey

    Racey Maxwell Smart-Ass

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  17. racerden

    racerden Boat #197

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    Very, very cool! Thanks bruddah
    ________
    NEW MEXICO DISPENSARIES
     
    Last edited: Apr 13, 2011
  18. lebel409

    lebel409 Well-Known Member

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    What size drill bit is too small to do? I drill a lot of small holes (#43) in nickel/brass and with those sizes I can get it OK on a drill doctor, but by hand is just silly...
     
  19. Crackerbox

    Crackerbox Well-Known Member

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    Excellent thread Racey. I'm glad I stumbled across it. A tip on eyeballing the angles to see if they are even is to hold your hand up with your index finger and thumb making a circle and holding the drill tip up centered behind it so you are looking through the "hole" and you can really see if it's close.
     
  20. RiverDave

    RiverDave In it to win it

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    Sorry about that spam.. deleted now.

    RD
     
  21. GeorgeM

    GeorgeM Well-Known Member

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    nice job sharpenning the drill by hand. Ive worked in a machine shop my whole life (for the old man) I remember when i was a kid watching my dad do it and I thought it was easy. Took me a while to learn now I can do it with my eyes closed (well not really lol) its funny when we get new machininst and they see me do it they try it because they think its easy haha, they always end up grinding their fingers. usually High speed drills for us atleast last much longer after we sharpen them, Im talking like double the life. Doesnt work the same with the carbide drills tho and those are harder to sharpen by hand.
     
  22. Racey

    Racey Maxwell Smart-Ass

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    I guess these pics got lost somewhere along the way, gonna see if i still have them and post them up. I got this bitchin Darex industrial drill sharpener a while back so i don't have to sharpening them manually anymore :p
     
  23. Roger 1

    Roger 1 Well-Known Member

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    How about posting a picture of your new sharpener ?
     
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  24. RiverDave

    RiverDave In it to win it

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    Fuck that, post the original pics! :D

    RD
     
  25. Racey

    Racey Maxwell Smart-Ass

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  26. Roger 1

    Roger 1 Well-Known Member

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    I have an old black and decker that works real well on bits up to 1/2 inch. I need to learn how to do the larger ones.
     
  27. Roger 1

    Roger 1 Well-Known Member

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    Well Racey, after studying your pictures and reading your instructions, I was able to pull my 7/8 drill bit out of the fire. I'm still going to need a lot of practice but I'm on the road to learning a much needed new skill. Thank you so much!

    Roger
     
  28. Roaddogg 4040

    Roaddogg 4040 Well-Known Member

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    I really like the Darex 3000 It is a little pricey for the average home handyman ($4,600.00) but I'm sure it works great...:D It really is the cats ass in sharpening tools but I almost fell off my recliner when I saw the price. I knew that these things were big bucks but this one floored me. It is used on aircraft type projects. They do have more reasonable priced models too. Now back to reality. Thanks for the sharping tips. I will give them a try tomorrow and see if I can actually get one of my self sharpened bits to actually drill a hole in something in stead for just smoking up the shop:)...

    Steve
     
  29. bocco

    bocco Well-Known Member

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    On a similar subject I would love to learn about all the different types of drill bits available. Which ones cut better and last longer. I've got some Black and Decker bits that are great for particle board and balsa wood but not much else. What's better titanium or cobalt? I would love to get decent set of drill bits that can be used more than once without going dull.

    A neighbor that is a retired machinist gave me a 1/4 drill bit that was courtesy of his former employer. The only marking on it is PTD and 1/4. The business end appears to have 2 hardened cutting pieces on it. It cut through steel like butter. I can't find them anywhere.
     
  30. RiverDave

    RiverDave In it to win it

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    I am not sure the third cut is necessary.. When I was in mold shops almost everyone would sharpen there drills on a disc sander.. You'd do a compound angle for your first cut on both sides and then just a standard chip relief cut. Those guys drill tool steel all day long and if you sharpen it right it will last as long or longer then out of the box. There's all kinds of weird tricks to drills though.. You can make them drill slightly undersize, really close to dead nuts, and even oversize depending on how you use them.
     
  31. Wheeler

    Wheeler Well-Known Member

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    Ok Dave, this is worthy of an explanation. I understand the oversize hole but how do you get an undersized hole?
     
  32. RiverDave

    RiverDave In it to win it

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    When you are drilling you will generally drill pilot holes to get it up to a size.. If you have all three drill indexes (letter, number, fractional). People will generally get 3:4 the way there and then drill the nominal size.. If you slam the drill into the hole it will drill slightly oversize.. If you keep going with your pilot drills and get them within .020-.030 and then are careful with the drill you can land the holes just shy of reamer accuracy. If you get the hole even closer and have s dull drill bit and a lot of oil it will actually cut a hole just slightly (and I mean slightly) undersize.. The drill will do more rubbing then actual cutting.
     
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  33. rivermobster

    rivermobster Club Banned

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    I've found out when going by the drill chart, the hole ends up Too big, and the threads come out kinda crappy.

    I had to frame mount and electric fuel pump, so I drilled the hole one size too small, and lubed the tap Real good.

    I went Real slow, and the Threads came out perfectly. Bolts went in real nice.

    This was all by hand of course. I would guess with a drill press or lathe, it would be a different story.
     
  34. RiverDave

    RiverDave In it to win it

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    Great how too.
     
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  35. Racey

    Racey Maxwell Smart-Ass

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    Can't believe this thread is nearly 10 years old :p
     
  36. rivermobster

    rivermobster Club Banned

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    Beat me to it...

    I use my cheese ball Harbor Freight belt/disc sander these days. A light touch and they come out great.

    The grinding wheels around the shop are too trashed to make a nice edge.
     

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