I am tring to drill holes in the handle of a knife, but when I hit the steel, I may as well just grind the bit down to a nub. What type of bit should I use?
"By the powers vested in me, I now pronounce you man and knife."
- Lee Christmas
Never underestimate the ingenuity of an idiot
There is a store on ebey that sells solid carbide drillbits, but I'm unsure of the taps. Sorry I can't remember the name of the place.
Thanks to both of you for the answers. I gotta place near home that I can pick them up for a reasonable price, so off I go!
"By the powers vested in me, I now pronounce you man and knife."
- Lee Christmas
What steel ? A carbide tip bit should do it and once it starts to cut keep the oil flowing to it and steady pressure . I've also had good success with cobalt drill bits . If its a stainless steel buy a half dozen . Then after you get it about half way drilled stop and ask yourself, now why did I want this hole in here ? DM
Good luck. I hope you have a rigid tight machine. You can get straight flute carbide drills designed for shallow hole drilling in very hard material. And I'd suggest as short a length of drill as you can get away with. It'll be more rigid and won't flex near as much. But for drilling through a shallow blade I might consider an endmill. I've used drills on things like that and the break through is terrible if you aren't careful.
I know I'm new here, but calcutta250 has it right. If your workpiece, or the drill chuck moves laterally at all, you'll snap the carbide bit.
You need a carbide drill for hardened steel. Anything less will simply heat up the blade and the drill and be a waste of time. Sometimes spring hardened pieces can be drilled using a cobalt but the cobalts don't last long doing it in my experience. Blades are not spring hard though and doing anything with a cobalt will likely be fruitless.
Two flute are my favorite types. Spade drills will work as a second choice. I'd avoid twist drills in carbides personally. They sell them and they cut fast but they are much easier to shatter and the two flute and spade drills are easy enough to do that to so you don't need to make it easier to ruin it by buying a twist type. MSC Industrial supply is where I get mine. Knife suppliers sell them and you can also buy them on the bay as I recall but no matter where you get it know that they are so hard they are brittle. They run at high speeds and you should lighten up on the press pressure just before exit. In fact its best to have another piece of hard steel scrap under the piece you are drilling to help the drill bit out so it doesn't shatter apart on exit. Exit is where most break so if you don't have a backing under the blade when drilling be particularly careful just as the drill is about to pop through the other side. Also, be advised that you should not try to force the drill faster than it can cut and remove debris so bump it down some to get the hole going, bump it back up to allow the debris to be removed, then bump it down, bump it back up and so on taking the hole through in steps not letting the blade or the carbide heat up unnecessarily. You can use cutting oil to help make the drill bit last longer also. Best to clamp the blade down and wear safety goggles using these also just in case one pops apart on you or the blade gets away from you during the job. Nothing fun about a spinning blade on a drill bit in a high speed drill press.
It might be easier and cheaper to have a shop with an edm sinker do it for you if you have the handles off. If you aren't experienced in drilling very hard material you can rack up a heck of a bill in a matter of minutes with carbide tooling.
If there is a vocational school or college nearby with a edm sinker it would be good practice for them and it would be free, probably.
The backing plate idea is a very very good one. I'd definitely do that if you are gonna try to do it. Burrs will be almost eliminated also.
Let us know how it goes.
I've never done it, but I've heard of old-time gunsmiths spot annealing rifle receivers by heating a thin steel rod to red hot then holding to the spot to be drilled. Anyone try this?
I've had a hell of time in the past few months having to drill hundreds of holes in hardened tangs. I've tried likely every trick and tip I could to make this easier on myself and then my friend Delbert Ealy told me about straight flute carbide drill bits and that was the ticket.
I actually went with carbide tipped versus full carbide because my drill press has just enough play when extended to snap the solid carbide bits.
Use lots of lube!
Do not use oil or any type of coolant for drilling with carbide unless you are prepared to flood the heck out of the tool and workpiece. If carbide gets hot and you quench it you get instant microfracturing. This causes the cutting edge to crumble and will quickly kill your tool. Real machine tools get away with running cutting fluids because they have massive coolant pumps that can pump at high volume and pressure to keep everything cool. Go with the carbide spade bit; they are cheap and they are the most indestructible carbide drill there is.
If you have an old broken endmill or solid carbide drill you can grind your own using a diamond grit grinding wheel, though these are not cheap. The bits I am talking about look like this:
Also - it is a good idea to make sure you get micrograin carbide, these are the best in terms
of wear resistance. P.S. The spot annealing trick does work, although it is really more of a spot tempering trick. However, it may as well be the same thing as it accomplishes the same result - to soften the steel.
Last edited by eKretz; 12-10-2010 at 07:12 PM.
Thanks for the tip on the lube and also the spade drill bit.
No need for a diamond wheel. The green silicon carbide wheels do a perfect job grinding carbide tooling. A lot cheaper than diamond coated wheels.
I love those little spade drills. They make a heck of a spotting drill too.
You're very welcome Dave. Green wheels (silicon carbide grit) will work to rough grind carbide but the edges will not last nearly as long as if they are diamond ground. (Think drilling a few holes between sharpenings compared to a hundred or more per grind with the diamond wheel). If you look at the edge of your carbide tool under a loupe after you grind with a green wheel and then again after you use a diamond wheel you will see why; the green wheel isn't much harder than the carbide so it doesn't grind as nice of an edge, which in turn wears out much faster. I had to use green wheels almost exclusively to grind my tooling as a machinist for about 6 years, I only use them for roughing now whenever there is a diamond wheel available. It is possible to use the green wheel then use a diamond hone or hand lap to finish the edges also; anything is better than just using the green wheel, although it will definitely still work if it's all that you have or can get. A roughly analogous comparison would be sharpening your knife on a concrete block; it will work, but by no means is it optimal. Honing/micro-bevelling with a better/finer stone afterwards or stropping is pretty much a necessity if you want a longer lasting, sharper edge.
Also, if you do hand grind, most carbide tooling should have a slight negative edge or rounded edge to help it last longer, this puts the cutting pressure behind the very edge. Only a couple thousandths to maybe a max of ten thousandths of an inch wide though, so best to just very lightly round it off with a hand lap. Now, however, we're getting more into machinist territory.
But to really need the use of diamond wheels he'd need precise geometry and all that stuff. Fixtures that cost thousands and who knows what else. What kind of a machinist are you? Tool and die maker? With a spade drill which would be...ok...for that. But I would recommend like I did before a straight flute stub length carbide drill designed for very very hard materials. If he has the machinery. If he don't have that then he is almost wasting his time which is why I recommended the edm sinker from a college or vo tech. I appreciate the knowledge though.
I am a job-shop machinist Calcutta. And forgive me, but I must disagree about needing custom fixtures to grind a drill bit. That is precisely why I did not recommend the straight flute carbide drill, since those have much weaker edges than a spade. If you notice, the actual cutting edge on the spade is negative, while on the straight flute, (or, ironically, due to your inquiry as to whether I was a Tool and Die Maker, Die Drills) the norm is a neutral edge, which is weaker.
I am able to freehand grind my carbide drills with a diamond wheel quite readily, although I probably have a great deal more practice and experience than most here. The only thing I use that could remotely be considered a fixture is a small machinist's protractor to make sure that my cutting edge angles are symmetrical (such can be had new for less than $30 and probably even less on EBay or a similar site. I must admit it may be beyond the ability of some here, but if the exact hole size is unimportant (most freehand ground drills will cut slightly large depending on how close to symmetrical one can get the cutting edges), most should be able to do passably well with a little practice. If a carbide drill can be ground on a green wheel in your estimation, I must admit to being curious why you think a fixture would be necessary to grind one with a much freer cutting diamond wheel?
I had several years ago the same problem, finally I find a tool that works on electricity. Basically you have an electrode that makes intermittent contact with the metal blade ( which is the second electrode ). At eacht contact, a bit of material is removed from electrods, it works well. The major advantage is that doesn't matter how hard is the blade and if you have a square electrod you'll have a square hole, for instance .
That machine is called a tap eroder, if it's what I think it is. They were originally made to eat away taps that were broken off in a hole while tapping. Those would work pretty good, but they are hard to find and not cheap. They work along the same lines as an EDM but use steel electrodes instead of carbon.
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