Drill bits for steel, 3/8" and smaller

[iclark]

Consider learning how to sharpen a twist drill.  Even if its made of the best gee-whiz steel, a dull bit isn't your friend. Sharpening isn't all that hard.  There are some people that will discard a dull pencil rather than figure out how to sharpen it.

I never heard anyone disagree with that when drilling iron or steel.

Back in my student days, the senior machinists kept a selection of drill bits around (that were not what they considered sharp) for drilling brass or bronze. I can't remember for sure which way they went for aluminum (thick stock, not thin sheet metal), but I think that they leaned towards a bit dull.

In all cases, with appropriate cutting fluids.

I have a vague recollection that it was largely about getting chips rather than long, whipping strands of material being removed. There might also have been something about sharp drill bits ground at the usual angle for drilling steel tending to cut in too quickly and jam in soft metals.

[Timberwolf]

I never heard anyone disagree with that when drilling iron or steel.

Back in my student days, the senior machinists kept a selection of drill bits around (that were not what they considered sharp) for drilling brass or bronze. I can't remember for sure which way they went for aluminum (thick stock, not thin sheet metal), but I think that they leaned towards a bit dull.

In all cases, with appropriate cutting fluids.

I have a vague recollection that it was largely about getting chips rather than long, whipping strands of material being removed. There might also have been something about sharp drill bits ground at the usual angle for drilling steel tending to cut in too quickly and jam in soft metals.

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HSS drills can be easily "modified" on a bench grinder or small whetstone to facilitate drilling in hard materials..by what we call "lipping"...that's just knocking the cutting edge back [slightly reducing the rake angle}.Makes the edge stronger...Easily done with a diamond file as well. A slightly more negative rake angle is beneficial for cutting, drilling brass and will prevent it from "grabbing" as it exits the material.

[KyleD]

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HSS drills can be easily "modified" on a bench grinder or small whetstone to facilitate drilling in hard materials..by what we call "lipping"

I didn't know there was a name for this but it deserves one. I do this for drilling in plexiglass and Lexan. a normal bit self feeds and can break the plastic. I just put the bit in a vice to hold it upright and take a couple of strokes with a little business card sized diamond plate level across the top of the cutting edge until I can see the "lip" as a little more than a shiny edge. I have a small collection of bits I have done this with but the small lip would sharpen out of the edge easily if I needed a special size and didn't have a spare bit in that size.

[Roly]

I didn't know there was a name for this but it deserves one. I do this for drilling in plexiglass and Lexan. a normal bit self feeds and can break the plastic. I just put the bit in a vice to hold it upright and take a couple of strokes with a little business card sized diamond plate level across the top of the cutting edge until I can see the "lip" as a little more than a shiny edge. I have a small collection of bits I have done this with but the small lip would sharpen out of the edge easily if I needed a special size and didn't have a spare bit in that size.

I didn't know the name either but we did that for drilling copper bus bars.  I painted those bits orange and separated them.   Roly

[Timberwolf]

I didn't know the name either but we did that for drilling copper bus bars.  I painted those bits orange and separated them.   Roly

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Lipping also works for drilling thin sheet metals..It's not as prone to climbing the drill flutes.

[brianwelch]

Good stuff...
Thanks

[Bob10]

Learn something new everyday.  I had to drill a 5/8" hole in some 1/4" diamond plate Monday started using a step drill as it was what I had with me.  
Well seems that was a bad idea had to wait until I got back to the shop and use an old set of bits I picked up out of a machine shop closure.  It's now in the box that travels with me when I need to carry tools someplace

[tablesawtom]

There is, if I remember right ( 76 years old now)  27 different grades of  high speed steel that carry a T number. Then there is M2 and M4. Usually M2 is a great trade off. There are cheap drill bits made in china that may get you though a job and then there are industrial quality bits. The best place to get them is an industrial supplier or an on line company like MSC or MC something. again memory thing. 

Most jobber drills are 121 degree pointed. Have worked in a machine shop since 1962 and still work in one 15 hours a week and have never used a 135 point yet. I am sure that there is a reason for that point angle, probably a productions application. 

I do not normally use any coolant when drilling. steel. if it is deep then a water based coolant is best but hard on the drill. It is also the easiest to clean it up but you don't have a mess if you don't use any.  A good rule of thumb is if using coolant whether oil or water it needs to be flood cooled. Intermittent cooling shocks the tool steel.

The cutting speed of 1018 steel is 100 but 50 works better on light machines like home drill presses. The formula is  Cutting speed times 4 divided by the diameter equals RPM and if you are going to error error to the slow side.

Copper likes a single cutting edge so a drill sharpened slightly off center will cut a slightly larger hole. Copper heads up rapidly and expands and the hole get smaller and the drill will grab. and freeze up and more than likely brake. A good coolant for copper helps but not found in local hardware stores. Iron, which is mostly fount cast, doesn't need any coolant least of all oil. The loose carbon that care of that. Bronze takes a flat grind on the face of the drill as does the tap used to tap bronze. I would have to post a picture of that.

A sheet metal drill bit is more like a brad point with out the spurs. 

The biggest problem with drilling metal is when the drill bit exits out the bottom of the piece. It can get real grabby. Here I think a 135 point angle drill bit would be a better choice but I have never used one so I can't say for sure.

And the last thing is probable hole size. A 1/4 inch drill bit can not drill a .250 hole it will drill a hole bigger. No two matters can occupy the same space at the same time.

My advise it go to an industrial supply store, bit the bullet, buy a quality set of fractional drill bit up to 1/2 inch. then buy a Drill Doctor drill sharpener to keep them sharp and forget all the stuff you read and then get on with your life.

[thewalnutguy]

Thanks in advance

In my experience I've found I break more drill bits trying to enlarge a hole than I do by drilling the entire diameter in one pass. The back side of the drill bit serves like the bevel of a lathe chisel, limiting how deeply the cutting edge can enter into the material. When you're enlarging an existing hole, there is very little bevel behind the cutting edge and you're exerting all the pressure on a very short length of the cutting edge causing the cutting edge to dig more deeply into the material. The same thing occurs when completing the drill-through the material remaining near the outer surface becomes thin enough that it bends outwards and the bevel is no longer able to control the depth of cut and the outer tip of the cutting edge is then able to cut deeper into the material  which is why the bit grabs the material and tries to spin it. That's my theory, maybe I'm wrong. But I figure if it hurts when you do something then don't do that.