drill bit sharpening

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  #1  
Old 01-03-03, 10:55 AM
handymam6
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Question drill bit sharpening

I have a variety of dull drill bits. I usually just buy new ones, but I know they can be sharpened. What do you know about the available options? Is it worth it?
Thanks.
 
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  #2  
Old 01-04-03, 06:30 PM
scrapiron
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I see two options: Replace bits as they dull or resharpen them. I prefer to start with a good set and keep them sharp. They can sharpened by hand or with one of the many bit sharpeners available now. Another option would be to visit a local machine or welding shop. Most of them have some type of bit grinder set up and they probably wouldn't charge much. In my opinion cheap bits are a waste of time and money.
 
  #3  
Old 01-04-03, 08:12 PM
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Hello: handymam6

Of course drill bits can be sharpened and should be. The trick is to do it correctly. And the correct method is to use a machine specifically designed to do it.

Hand sharpening, as in without machinery or on a grinding wheel or belt sander is possible. Takes a trained eye to recreate the exact cutting angle and relief angle.

Failure to obtain the correct angles will produce poor cutting quality at the least. At the worse case, the dit will not cut well at all or it can become further damaged.

Hand sharpening using a file or any means mentioned above will not thin the center web either. Nor will it insure the center is centered. Each is required or the bit will walk as it begins to cut.

Walking is it's inability the start where the bit is placed onto the surface to be cut into. A center web that is not thin does not allow the bit to start cutting into the surface in a small area.

Drill bit are like any other cutting tools. They are precisionly made and must be maintained as is. Sharpening must be done accurately to produce quality results.

Sharpening shops are listed in local phone book directories. A visit to one with bits in hand will be well worth the money spent and also a welcomed sight to any shop owner....

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  #4  
Old 01-05-03, 05:58 AM
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Hello, I do all my bits by hand grinding. And I use a drill angle gauge. THis one I picked up at Sears years ago. I'm not sure they even sell them anymore...... The main thing I feel is to keep the lengths of the cutting edges the same and to keep the relief ground back right, too much and it will cause the cutting edge to breakdown quickly, not enough and the drill will rub and not cut.For general purpose drilling 118 degrees is the prefered angle. There are others depending on the material being drilled. One thing I don't do is grind anything smaller than 3/16". I find its too hard to do it offhand. I usually go to the toolcrib and get another one. In a pinch I would do something smaller but not if I can help it.
 
  #5  
Old 01-06-03, 04:16 PM
scrapiron
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In a pinch you can tack weld the flats of two hex nuts together for use as a gauge. This gives you a 118 degree angle.
 
  #6  
Old 01-10-03, 02:27 PM
handymam6
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Drill Doctor?

Thanks for your help.
I was shopping the other day and saw a Drill Doctor.
Does anyone have any experience with these, any comments . . .
 
  #7  
Old 01-10-03, 02:36 PM
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Received one for Christmas; love it. Takes a few minutes to figure out the procedure at first, but after that can get a good sharp bit in under a minute. Got the "500" model that is ac powered and can do regular, split, and masonry at 118 or 135 degrees. Only problem so far is that it doesn't seem to work well on really small bits, but that could be my technique (need to check out the video taped instructions I suppose to see if I'm missing something).
 
  #8  
Old 01-10-03, 07:50 PM
lnmrosen
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I saw the drill doctor demonstrated at a trade show recently. I was impressed.

I usually sharpen my bits with a diamond stone. You don't have to take a lot of the bit to sharpen it. I run it across the diamond stone by hand very carefully and it works for me.
 
  #9  
Old 01-10-03, 09:20 PM
NutAndBoltKing
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Some interesting opinions on the drill dr and on drill bit sharpening in general can be found at:

http://www.practicalmachinist.com/ub...ML/000492.html
 
  #10  
Old 01-14-03, 10:12 AM
kk007
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How much does the drill doctor cost and where can I buy it?
 
  #11  
Old 01-15-03, 10:29 AM
NutAndBoltKing
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I guess there's nothing wrong with buying a machine dedicated for sharpening bits, especially if you have the money, and you break or dull enough bits to warrant a purchase; but I think there's some other things that need to be considered: first and foremost of course is safety and the risk of injury, but the second is the difficulty of learning the art of sharpening bits. No matter what machine you may choose to buy - you, and you alone must sharpen the bit. No machine does it for you.

Brand new bits become used bits just after one use. Improper drilling speed and poor lubrication are the biggest culprits for reducing the sharpness and overall optimum life of the bit. Bits are one of the most misused tools, and even the best regular routine maintenance (sharpening touch-ups) will not keep good bits in a bad mechanic's tool box.

No matter which type of bit; conventional, split point, notched, helical, or etc; after safety and patience, there are three parts to the art of sharpening drill bits: 1). The outer edges, 2). The point, and 3). The web. Each part is learned only through patience and practice as no machine will do it for you.

1). The outer corners are the first to wear. It starts out as a slight "rounding" and moves out toward the margins. (The 'margin' is the cylindrical portion of the land - the 'land' is the part between flutes). This wear reduces bit size, and the worn edges need to be removed.

2). After removing the above worn edges the next step is to address the surfaces of the point - which must be re-ground. The point is where the two leading conical shaped surfaces meet with the face of the flutes. It forms what is called the 'cutting lips' and they intersect to form the chisel edge. The cutting lips must be releived so that the chisel edge will penetrate.

3). The web of a new drill usually increases in thickness from the drill point back towards the flutes, but the above two steps usually shortens it, and it too has to be redressed. It has to have the original thickness or it will generate more heat when used.

The point I hope I've made is that sharpening bits is an art that has to be be learned. Some machines being sold can make the job easier, but they won't do it for you.
 
  #12  
Old 01-15-03, 07:45 PM
scrapiron
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I know that powered sharpeners are good but there is a certain pride that goes with being able to sharpen tools by hand. It didn't matter how well you could program a cnc machine, if you couldn't sharpen a drill bit or grind out a lathe bit by hand my college shop teacher would not pass you. The ability to hand sharpen a knife will probably be one of those lost arts we keep hearing about someday. Just ramblin..........
 
  #13  
Old 02-08-03, 09:33 PM
DeMolet
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Hand Grinding drills

Hey all,

I've ground drills for the last 32 years it's very easy to me and I have almost no patience. We have drills around the shop that are 40+ years old we still use them on occasion.
I have always worked in crummy, small machine shops that do not have fancy drill grinders.
One of the oldtimers handed me a burned up drill and showed me how to grind it over and over til I got it to cut on size. Around there they'll send you down the road if you can't get a drill to work right .
Now I'm the oldtimer and have to show young guys how to grind drills.... most give up before they start. I'm the designated drill grinder now I guess

A drill has two cutting edges and the point (Chisel point) the rest is all support.

The chisel point should be 12% of the drill diameter when you get done. This is done by thinning the web. Make sure when thinning the web that you don't put a negative angle on the "top" of the cutting wedge.

Now, when I grind the ends I use a drill gage (most I've seen are made by GENERAL most machining outlets carry, Sears may also ). I start at the cutting edge, matching the angle, and then you roll the drill a little while tilting the back end down slightly. You roll and tilt at the same time. Keep the drill cool with water because if it starts to turn blue it loses it's hardness.
Grind a little on one side and then the other so you don't get to far out of whack. Both sides have to be the same or it will cut an oversize hole. Don't use the side of the grinding wheel you might need that flat surface for something sometime.

The only part of the drill that you want touching the material you're cutting is the chisel point and the two cutting edges. This is why you have to roll the drill a bit to put clearance behind the cutting edge.

To thin the chisel point use the corner of the wheel. You need a good sharp corner on the wheel. The outside corner of each side of the drill is on center so don't grind there; use that as a guide to bring the top edge down at the center of the drill. In other words both cutting edges should be parallel when you look down at the point. If you look at a new drill you'll see what I mean.
If the cutting edges rise as they go towards the center they are "above center" and won't cut and you'll need to thin it some more.
If when thinning the web you should happen to grind out by the edge, you'll be lowering the cutting edge at that point making it "below center" and it will chatter probably. Thinning the point down smaller than 12% of the OD will make it chatter and buzz too.

If the sides of your drill are wore, grind the point back until you get rid of it, because even if you sharpen the edges it will squeal when you're drilling metal and it'll burn wood.

This is probably not too clear . I'm used to showing people this stuff right at the grinder. Take one of your old drills that you were going to pitch and sharpen it up and try it out on an old piece of metal. Don't use a lot of RPM on metal and use some kind of coolant.
Small drills 1/8 or less have to be ground on a small grinder. They are really too much of a pain to do except in a pinch.
Files and sandpaper won't do for drills. Good drills are probably harder than a file anyway.
Some el cheapo drills are ok for wood but they won't keep an edge for 2 minutes when drilling steel.

I might be able to figure out a problem with a drill from a description of the symptoms.

DeMolet
 
  #14  
Old 02-09-03, 04:03 AM
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Heres a trick that works for me. After I get the angle right and the length of the cutting edges the same, I reverse the grinding procedure from back to front, toward the cutting edge, with a real light pressure. For me anyways, it helps me make sure that the relief is adequate on the heel of the bit, so the bit is certain to bite in and not rub. I feel that it is an art to really getting a drill bit sharpened right. It takes practice to get really good at it.
 
  #15  
Old 02-09-03, 08:50 PM
DeMolet
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Hey Toni,

I sharpen drills from that direction also. Either way. Most of the time I start at the cutting edge. The old boss used to raise hell when he'd watch me doing it that way. "I don't know how in hell you get 'em to cut that way" he'd say. I could make 'em work though. I'll have to post sometime how he used to grind drills. He was a character.

We use these drills from 1/8 or less to 2 inches in Automatic screw machines so they have to drill good holes. I use the drills to run sometimes 1000 pcs or more in 1215 steel.

Grinding them from below the cutting edge and then rolling them up to the edge can help keep the clearance on the ends. You can see the edge grind when it reaches that point. You won't see any sparks at the edge until the edge actually reaches the wheel. Also, when you see sparks at the edge , don't roll the drill any further because you'll lose the clearance. I think I'm starting to confuse things again.

Oh, and if you have to climb up and hang on your drill press handle to get it to drill, you probably don't have enough clearance on the end or your web isn't thinned enough.

Lindsay Publications has some books that show drill grinding. He reprints old time machining books. He has a web site.

I like to do things the old way and try to keep the old methods from disappearing.

Happy drilling, DeMolet
 
  #16  
Old 02-10-03, 05:36 PM
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I'm with you DeMolet and another poster,Scrapiron I think it was, about the old ways going away. I've been in the trades for about 25 years and I've seen it go from the old flat-belt drive lathes to the new CNC machines. There is something to be said about grinding a tool, whether its a drill or a lathe knife, and getting it right. Instead of just grabbing another preformed carbide or another new drill out of the drawer..... I guess thats just progress and who are we to stand in its way. I can recall my first shop teacher telling us how they used to teach an apprentice about how to get a block of steel square, with a FILE! I guess you really can get an appreciation of a machine tool after that! Well I'm rambling, but I think you get my drift.
 
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