Jump to content
HybridZ

Sharpening drill bits


Recommended Posts

I've dulled my 2nd 5/8" drill bit trying to drill out my steer knuckles, and they're kind of pricey. I have a grinding wheel, but like an idiot I've used it for shaping various plate pieces that are already on the car, so the grinding wheel isn't anything like straight on the front surface. I'm thinking I might be able to use the side of the stone to get a reasonably flat surface.

 

Just looking for tips before I give this a shot. I googled and I saw various site saying "piece of cake" or "buy the $200 machine because you'll never do it right" so I'm hoping someone might be able to give some advice.

Link to comment
Share on other sites

I would go get a grinding wheel dresser or a new wheel. The problem with using the side of the wheel is that it weakens it. It will work once or twice, but is not a long term solution...

 

Sharpening drill bits by hand can be a challenge. The larger they are, the easier it is. But if you try it out and it doesn't seem to cut well, re-sharpen and try again...

 

Sam

Link to comment
Share on other sites

I don't think what I'm doing is helping it much either. Basically it's only the outer 1/8" of the drill bit that is actually cutting, since I'm following the existing tie rod end hole. Plus my HF drill press (2nd cheapest one they have) has some crappy bushings in it so it allows the drill bit to bounce around a bit before it takes a set and starts cutting. The bit seemed to do fine when I was drilling through plate starting with a much smaller pilot hole.

 

Not much I can do about the circumstances though...

 

Thanks for the advice guys. I think what I'm going to do right now is swap the stone around so that the surface I'm grinding on is the least used surface on the stone. Then maybe I'll replace it if that doesn't work.

Link to comment
Share on other sites

For accuracy, dependability, and ease of use try a dedicated drill sharpening unit. At 39.00 dollars a pop, and up, for larger bits it wont take long to pay for it's self.

 

Check this one out. $179.00

 

http://www.grainger.com/Grainger/wwg/productIndex.shtml

 

And you can get a stone dresser if you dont want to get the dedicated unit.

A stone dresser will true up the stone face.

Link to comment
Share on other sites

I'm going to chime in for the "manual" method. I'm not especially good at it, but I've worked with machinists that sharpened them well on a regular basic, quickly and (seemingly) easily, so I know it can be done well.

 

I would start by studying a new bit. In particular, study the two-angled cutting surface; one angle (most of the "face" of the cutting surface) has a particular angle, in three dimensions, relative to the cutting surface (a plane perpendicular to the axis of the drill shaft). That is the most important angle to understand. When you sharpen it, that is the first cut you must make, taking the entire surface down a couple of mil.

 

The second cut, at the cutting surface itself, is relatively easy to cut once the "base" has been prepared, describing a surface a couple of degrees "flatter" than the base. If you're familiar with sharpening a knife, you'll understand that it's the same process, though wrapped around a shaft.

 

If you have a really ruined drill, start from scratch by grinding off the end of the bit entirely, perpendicular to the axis. Keep some water nearby, and do not overheat the steel. Though it seems like a waste of a lot of material, it's easier to see what you're going to do when you start.

 

Like sharpening a knife, it's one of those things that takes quite a bit of practice.

Link to comment
Share on other sites

If the bit is jumping around, it sounds like you are turning the bit too fast. Try slowing it down. Make sure to use a cutting fluid. Lard or beef tallow works well on steel with the added benefit of smelling like a BBQ...

 

EDIT - I just realized you were drilling out your steering knuckles. Those are hard as hammered cat turds. You need to turn the drill slow. A solid carbide bit would work best. Prodigious use of cutting fluid is called for. I don't think you have dulled it as much as burnt it up. If you overheat the drill, it looses its temper at the end. It won't cut worth a damn after that.

Link to comment
Share on other sites

Hammered cat turds, eh? They're pretty hard, I can say that much. I've got the drill press on its slowest setting. I did not use any cutting fluid, and I'm sure I overheated the bit.

 

I do have a gargantuan 1/2" hand drill which I think has a stronger motor than the press and it turns SLOW. Maybe I should go buy some cutting fluid and a new bit and give that a shot.

Link to comment
Share on other sites

I don't think it needs to be that close tolerance. I went out and tried to sharpen the bit, and I don't know what to think. It seems to be holding an edge, but it just won't cut through that stupid knuckle. I've spent literally about 3 hours trying with the hand drill and the drill press and I'm about 75% of the way through. I don't know if it's just because I did a bad job on the bit or what. I think I'm going to try another bit tomorrow and see if it cuts faster. If not I might just have to take this whole project to a machine shop, something I didn't want to do...

Link to comment
Share on other sites

Manual sharpening of bits is somewhat of an art. My dad who was a machinist/engineer for 40+ years could do any size bit with his eyes closed (with or without his reading glasses) in about 15 seconds. He taught me, but since I don't do it often, it takes me a few tries.

 

Get a good bit and try to match the angles to what you know is good. Twist the bit and and tilt it as you twist. Grind into the cutting edges. The two cutting edges need to meet near the center of the bit. The two cutting edges need to end up being very slightly higher than the back ramp. Basically you are removing material behind the cutting edges to create a sharp leading edge.

 

Good luck. It's a fun thing to do.

Link to comment
Share on other sites

Guest Jasonv8z

The machinists where I used to work weren't happy with the drill doctor because it wouldn't grind the cutting edge at a sharp enough angle. I agree with Sam. You need to keep the bit cool, otherwise it'll untemper. Believe it or not, I've started using vegetable oil. Smells like Chinese food.

Link to comment
Share on other sites

I was using some rendered fat, and it seems to work well, and the garage smells like bacon... mmmmmmm... bacon. I've only ever burnt the bit up faster using WD-40, so I'm going to stay away from that suggestion. Had a busy weekend so I didn't get out to the garage but I'm going to try and find a place that will sharpen that 5/8" bit today. Like I said, it does seem to be holding an edge, but it sure isn't cutting for crap. I'm worried that since I've spent so much time trying to get this thing to drill through that the hole is more wallowed out than it would otherwise be. Haven't figured out what to do about that yet, thinking I could weld the hole up and drill it again if all else fails. Or take a spare to a machinist and have them do it right. Again, extra expense that I don't want to deal with...

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...