Drill Bits won't drill

[motoman]

A drill press usually has speed adjustable pulleys at the top. Lift up the safety cover and review an owners manual. If no manul down load one or use judgement to put the belt on the slow drive combination. I leave my little utility drill press set on low because 95% of the drilling is on mild steel (steel that will not harden in heat treat). All good advice above. Always use lubricant. The chips that come out of the hole should be the same length. If not the drill has been ground wrong. Earlier I did not mention some fundamentals of drill points...The cutting lips (2) must be the same width from the center of the drill or will not cut a round hole and will produce unequal chips. The drill point should be symmetrical (like a sharpened pencil). The cutting edges (lips ) MUST BE GROUND WITH CLEARANCE or they will not cut, just spin and overheat. This is where hand grinding is difficult for novices. Either no clearance is ground or too much is ground. Too much will work for a while in wood , but will only cut well on metal for several seconds and burn up. Jig drilling like Drill Doctor and the "swing fixtures" one bolts to a grinder may help. They set the point angle , the cutting clearance (lip angle) and lip width for you. Drill Doctor is good for small drills. The grinder jigs are criticised. I have never used either. Drills are happiest with additional "clearance" behind the cutting lip clearance. This is done with a cam grind on purchased drills ( increasing drop off from the cutting edge). But a chisel lip at the edge and then a second deeper angle behind it can also be used. By now most have simpy tuned out and I understand.

Edit: Look closely at self tapping screws and you will see a small drill tip on the end, including a cutting lip and clearance. The diameter is set as minor diameter of the screw thread which is cut in. But your properly ground drills should be better.

Drilling holes well is a joy for life and will save your bacon. If you practice and use correct speed, lubricant and align and lock down the workpiece you can do amazing things with even a lowly H frt bench drill press, like drill a hole all the way through a 1/4" bolt. Clearance is something that must be worked on. Hold up a new (good) drill and look at the cutting edge and how it immediatel drops away on the far side. Take a new drill in your fingers and twist it into wood and feel it bite. Put a metal punch depression in mild steel or drill a small hole and twist in a bigger drill-and feel it bite. A drill without clearance will not bite. Look at the drill bit that will not cut , and see if it has drag marks behind the cutting lip , a sure sign of inadequate clearance

 

[motoman]

Rave on and on...motoman. After re reading your frustration something is wrong with your drilling. One properly ground (good) drill bit properly used should last many, many drillings. Do not expect to drill metal as fast a wood. The center of a drill will not cut because the cutting lip cannot reach to center because the center (web) is the backbone of the drill. Therefore as others have mentioned pilot holes are used. Why?

If you want to drill a 3/4" dia hole , prick punch the center, and start "drilling" with a 3/4" drill you are not drilling . You are having to use great force to discplace enough metal to finally reach the cutting lips of the drill. The drill and work piece are very hot by then and you are frustrated. That is why pilot holes work. The smaller drills have smaller webs and start drilling sooner and produce a hole the 3/4" drill will drop into at its cutting edges (lips). Some of the drill brands you mentioned should work well and long, even if produced for wood and metal.

Does any this of thread help?

 

[Mad Mackie]

I agree with you on the titanium bits. I have never seen where they are any better. I do find the cobalt bits are a better bit for drilling steel that is a harder type steel. I also find they will chip or break faster then HSS but they do have a use. Now carbide drill bits are very expensive and I have found impossible to sharped. Used for drilling out a broken drill bit or tap. Now when I am saying expensive 50+ dollars per bit.

Hi reynoldston and group,
I have found the same circumstance with cobalt drill bits. I have three cobalt drill indexes and each one has a warning sticker on them about how toxic the dust is from sharpening cobalt bits and I don't sharpen them on my Drill Doctor. Carbide bits are sometimes difficult to deal with and for sure expensive. Over the years I have dropped a few carbide bits on the floor and some broke. Strange how such a hard substance can break so easily!!! Harder means more brittle.
As I have a vertical mill, metal lathe and a large floor model drill press, I have been using quality end mills more often for drilling regular fractional holes in materials including wood, aluminum and plastics.
When drilling out a broken bolt, the first and most important thing is finding the center of the broken bolt and drilling the first hole. If the bolt was broken at an angle, then the fun begins trying to find the center and maintaining the center with the first drilling.
Some years ago I broke a tap while threading a hole in a very important part. A carbide bit didn't work as the tap broke at a steep angle which is how they usually break!!! A friend of mine worked at a shop that had a laser machine, he took the piece into his shop and with the laser was able to burn out the broken tap with minimum damage to the existing threads, I was a happy camper!!! Several things contributed to the broken tap, not all number drills of the same number are the same actual size, speed of my drill press was too slow leaving a three sided hole and not a round hole, the tap had been used too many times and was fairly dull.
Lessons learned!!!
Mad Mackie in CT:laughing::biggrin::smile:

 

[gfp55]

Very good write ups motoman & Mad Mackie, You did it a way that one can picture it in ones head as one reads it. Very concise and to the point, good useful information for the layman. Just dripping with wisdom. Great job guys.

 

[bertsmobile1]

And just so we all know, the yellow carbide coating is not there for improving the cutting.
It is there because almost no metal will adhere to it so it facilitates the chip formation and clean evacuation of chips from the hole by preventing chips from welding onto the drill.
All carbides are brittle which is why they need to be backed by some softer steel

 

[shiftsuper175607]

Thanks for all the great info.

I printed out the drill bit geometry article.

Happy drilling to all!

Shift

 

[SeniorCitizen]

Buy HSS bits at a machine shop supplier. Buy cutting oil most anywhere. HD even has it. Apply a drop occasionally with a eye dropper or artists brush a pint will last most people a life time.

http://www.homedepot.com/p/Oatey-16-oz-Thread-Cutting-Oil-30200/100191834

 

[motoman]

Like an old clock wound up and finally unwinding...a word on carbide. There are grades and such cutting tools can be very expensive. The low end brazed- in tips on concrete drills can be sharpened (somewhat) with a wheel known as a "green wheel," silicon carbide. It is slow going and does not work well (for me) on metal cutting drills. Final cutting edges must be ground with diamond wheels and are very expensive. On sale a small wheel (4") starts at about $80. The H Frt "diamond" stuff has proved worthless to me. Solid carbide drills are very expensive and not necessay IMO for most people.

Back to that old favorite , the cutting lips on drill tips. I get away with a cheap 60 grit , 8" , grey wheel. A big problem for novice drill grinders is burning the tip to a softened (useless) state. What does this is 1. holding the drill too long on the wheel. 2 excessive wheel speed (like my 8" wheel) 3. fine grit 4. dirty wheel surface 5. too hard wheel. To avoid this (1) only grind briefly or dip in water (2) use a smaller wheel (3) go coarse grit, perhaps 80 (4) keep the wheel clean . Use a hand held dresser or better, buy a diamond pointed lock -on dressing tool ($30-$50) (5) Consider a "white" wheel from abrasive supply houses (like Norton). Expensive and will not last long. These may not fit a typical grinder arbor without adapter , but sweet.

There, I'm almost done.:laughing:

Ooops, Just remembered to tell you about "peck drilling." A technique that will prolong the life of your drill bits. With lube drill a couple seconds , withdraw the drill and refresh the lube in the hole. Repeat until break through. Like a chicken pecking grain. The withdrawal will also break off those two equal length chips so they do not swing around and cut you. Special machinist drills have oil passages where lube is pumped through continuously.