A different way to sharpen a drill bit

Stan in Oly, WA

Well-known Member
The other day a student showed me how he sharpens his tungstens for TIG, and I wondered whether a similar method might be used for sharpening drill bits. He put an angle grinder in a vise and turned it on. Then he put his tungsten in a drill and spun it while holding it at the correct angle against the abrasive wheel. It seems to me that it would have worked just about as well against a stationary abrasive, but that was how he did it. Would a similar procedure work for sharpening drill bits? It seems like it would be a good way to ensure that the angle was identical on both sides of the point of the bit and that it was properly centered.

Stan
 
You can't get the proper relief on a drill bit that way.

Somehow I don't think grinder in a vise, and proper shop practices are related...
 
No, nothing good could possibly come from that!

Look at the end of a known good drill bit. Where the trailing side of the flute angles slightly away from the cutting edge, that is what you want to keep right. That's called the relief.

Also the chisel angle of the cutting edge in relation to the side of the drill, about 130* for mild steel.
 
As far as it not being proper shop practice, I'm not sure I agree. We have a dedicated grinding room which has two pedestal grinders, a chop saw, and six grinding stations. The grinding stations are along two opposite walls, three stations on each side. Each three individual stations are on a continuous steel counter, separated from each other by 36" high steel side walls. Each station has a vise mounted at the center of the front edge of the steel counter. I can see the potential for accidents with every single thing that's done in that room, but not necessarily more so with an angle grinder in a vise than anything else. Unorthodox but careful is probably less risky than normal but careless. I stop people from misusing equipment, or from abusing equipment, or from outright stupidity when I see it. Beyond that, I can only warn people to wear adequate safety gear, and think about what they're doing.

Stan
 
Okay, Steve, good answer. I don't know unless I ask, and now that I've asked and gotten some answers, I know more about how a drill bit works than I did when I woke up this morning.

Stan
 
(quoted from post at 13:10:34 11/04/14) Would a similar procedure work for sharpening drill bits? It seems like it would be a good way to ensure that the angle was identical on both sides of the point of the bit and that it was properly centered.
Stan
Obviously you have never sharped a drill bit by hand.
 
Actually, that's not the proper way to grind the tungsten either. They should be ground on a dedicated wheel so the tungsten will not be contaminated and the grinding marks should be with the length of the electrode.
 
What Steve@Advance said.
The "real" machine shop type sharpeners have the rotating wheel and rotate the drill bit, and the additional magic is that the bit moves in and out every 180 degrees to properly form the relief. You have to pay attention when putting the bit in the machine so it is indexed correctly. (been a while, but that's what I remember)
 
People might disagree with me here but that is a good way to get a drill bit back into shape if it is really messed up. But you will never get the relieve right.
 
Actually the thoriated tungsten is supposed to be ground in a little grinder that captures the hazardous dust. One in ever twnety thousand wledors uses this little fixture to grind. I just hold my breath.
 
You'll have to explain that one to me. I can understand that it's not possible to get the correct relief if it's rotating while being ground, but getting the cutting edges equal and centering them is exactly what the rotation would do. Similarly, you could put the wrong point angle on the bit, but you couldn't put different point angles on the two cutting edges as you could holding a stationary bit against a grinding wheel.

Stan
 
It may be obvious, but it's not true. I've sharpened (or sharped) many bits by hand. The problem is that the results usually leave a lot to be desired.

Stan
 

I use a bench grinder to sharpen my bits. One day I was looking at my circular saw blade sharpener with a diamond wheel. It did a very nice job on the bits.
 
One way I could see this working is to run the bit in a drill, against the grinding wheel to get the proper angle and shape, then remove from the bit from the drill and grind the relief by hand.
 
When you say "by hand", I take it that you mean held in your hand rather than in the drill, but still ground on the grinding wheel. That sounds like it would be a good compromise for me. One of the problems I have when I am trying to sharpen a bit freehand is that I grind one side past the center point. What I need to do, I think, is keep a pair of magnifying glasses handy and put them on when I'm trying to do something like this. I don't need glasses for reading, so I tend to forget that they really help for fine work.

Stan
 
I have one of these :-
a173405.jpg
 

When I see one of those I wonder if the wheel is rated to be used to grind on the side.
Too many years ago in H.S. we were taught to never use the side of a grinding wheel unless we knew it was rated to be used that way.

Dusty
 
Really didn't notice it loading up the diamond more than saw blades. I like to buy the old school circular blades with no carbide teeth. They are a thinner blade, rips throught wood easier, and easier for me to sharpen.
 
(quoted from post at 14:17:23 11/05/14) You'll have to explain that one to me. I can understand that it's not possible to get the correct relief if it's rotating while being ground, but getting the cutting edges equal and centering them is exactly what the rotation would do. Similarly, you could put the wrong point angle on the bit, but you couldn't put different point angles on the two cutting edges as you could holding a stationary bit against a grinding wheel.

Stan


Holding a drill motor in hand and trying to sharpen the bit by holding it against the grinder won't get you equal length edges and therefore not a centered edge unless you can hold the drill absolutely rigid as it revolves against the wheel. If you shake or move a bit or the bit is already off a little the tendency will be for the bit to follow the angles already in place. IOW- if you have a short side and long side, the short side won't get as much pressure and the long side will get more and it introduces a wobble to the process that you would be very hard pressed to fight.
 
I use the side of my grind stone all the time. never had any problems.

For drill bits I bought a drill doctor. it does a good job. Only goes up to 1/2 inch.
 
I know you should not do it, but in a pinch I have used an angle grinder to touch up lathe and mill cutting tools that are carbides.
Thinking about it to get the relief I think you would have to rotate the drill in reverse to get the cutting angle. I am not steady enough to hold it at the right cutting angle or to get it centered with a drill.
 
so THAT'S what that thing's for!

My dad had one of those, and I see it sitting on a shelf every time I use his old shop. I never knew what it was, and I was never quite curious enough to bother trying to find out.

thanks for posting!
 
A normal but dull drill bit is rotating at say 600 rpm, yet when you touch it to a moving grinding wheel one side of it is ground off more than the other. That's ridiculous.

What that tells me is that you're one of those people who, having stated something in error, feels compelled to defend it at any length. The answer you were looking for was, "my mistake". Your persuasive explanation is going to fall apart the first time someone holds a rotating bit to a grinding wheel. In fact, I'll do it right now. I'll hold a bit by hand and grind it until the center is 1/3 of the way from one edge. To make it more interesting, I'll also grind a steep angle on the short side and a shallow angle on the long side. Then I'll chuck it into a drill and grind it against the grinder again. I know what's going to happen, but I'll do it anyway.

10 minutes later.

I took a 7/16 bit---I chose a reasonably large one so that you wouldn't think I'd purposely selected a small one so that I could control the "bucking" by brute force---and ground it so that one side was long and shallow in relation to the axis of the bit, and the other side was short and steep. Then I chucked it into a drill and held it against the grinding wheel of my bench grinder until it evened up, which took maybe ten seconds (it would have been faster but I kept taking it away from the grinder to check the progress). Then I took it out of the drill and held it by hand to provide relief behind each cutting edge---the thing that can't be done to a rotating bit.

One thing I noticed, though, was that when I tested it by drilling a hole in a scrap piece of oak, the hole it drilled was semi-circular, like a half moon. So maybe you're on to something after all. (That's BS, by the way, in case it's not obvious. I'm thinking of getting into the tall tale business.)

Stan
 
(quoted from post at 14:39:32 11/06/14) A normal but dull drill bit is rotating at say 600 rpm, yet when you touch it to a moving grinding wheel one side of it is ground off more than the other. That's ridiculous.

What that tells me is that you're one of those people who, having stated something in error, feels compelled to defend it at any length. The answer you were looking for was, "my mistake". Your persuasive explanation is going to fall apart the first time someone holds a rotating bit to a grinding wheel. In fact, I'll do it right now. I'll hold a bit by hand and grind it until the center is 1/3 of the way from one edge. To make it more interesting, I'll also grind a steep angle on the short side and a shallow angle on the long side. Then I'll chuck it into a drill and grind it against the grinder again. I know what's going to happen, but I'll do it anyway.

10 minutes later.

I took a 7/16 bit---I chose a reasonably large one so that you wouldn't think I'd purposely selected a small one so that I could control the "bucking" by brute force---and ground it so that one side was long and shallow in relation to the axis of the bit, and the other side was short and steep. Then I chucked it into a drill and held it against the grinding wheel of my bench grinder until it evened up, which took maybe ten seconds (it would have been faster but I kept taking it away from the grinder to check the progress). Then I took it out of the drill and held it by hand to provide relief behind each cutting edge---the thing that can't be done to a rotating bit.

One thing I noticed, though, was that when I tested it by drilling a hole in a scrap piece of oak, the hole it drilled was semi-circular, like a half moon. So maybe you're on to something after all. (That's BS, by the way, in case it's not obvious. I'm thinking of getting into the tall tale business.)

Stan


Stan, I don't know if you're just having a bad day or you're meds are off or maybe you just had a fight with the wife or what. What I do know is that you can't take a drill bit in a hand held drill motor and somehow hold it against a 4 1/2" angle grinder held in a vise, which is what you were talking about in your O,P and expect to get an accurately ground dill bit. Not gonna happen. Every time you touch that unbalanced wheel in that angle grinder it's going to push back. That's why we spend all that money getting tool post grinders that are rock solid to use in our lathes. Any idiot can duct tape an angle grinder to a tool post and remove metal. It doesn't mean it's going to do a good job. The Darex co and all the other grinder companies out there that have spent decades designing and producing drill grinders must have been stupid and lacked your Mod 1 Precision Elbow or they'd have been selling angle grinders and vises all this time.

Best of luck to you. When you want to know why you're drilling over sized holes give me a ring.
 
I have been sharpening bits by hand for over 50 years. When my kids started doing things in the shop, they got a drill doctor. I had to re sharpen my bits to make them cut right again. They soon quit using it.
 

My Drill Dr worked good for a few years, then it got buggered up somehow. Now I use it to rough grind and finish on the grinder with a drill gauge for reference....and a decent set of 3X reading glasses! :lol:
 

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