Which Drill Bit for Steel

[Ken45101]

Soundguy gave good advice, as usual. For quater inch holes in mild steel, the drill bit brand shouldn't matter.

 

[flusher]

Some of the best bits I've used are Milwaukee's. After they dull, the Drill Doctor does only a fair to middlin job for me getting them back in shape.

Ditto on the bits and the DD.
I run these twist drills at slow speeds (100-150 rpm) and generally run them dry. Drill fluids are mostly for cooling the bit, not lubricating. Running them slow minimizes heating.

 

[eastexan]

1/4" holes would be better done with a higher speed drill than a 1/2". The smaller the drill bit, the faster they need to turn. Any decent sharp drill bit should make childs play out of 12 1/4" holes in mild steel. Did you use a centre punch before drilling? This makes a big difference too as the bit can wander around when trying to start the hole which could be a factor in the bit breaking. The combination of too slow a speed and too much force on the bit will make matters worse. Cutting fluid helps but even dry, a properly sharpened bit should drill pretty easy. Should have 2 flutes when cutting properly. I've drilled a bunch of holes dry and if the bit is cutting properly, it doesn't overheat.

Sorry, but that's terrible advice.
Cutting fluid not only helps but is essential when drilling thicker material. No matter how sharp a bit is, it will start out cutting good and then soon get hot and ruin without some type of coolant. Been there, done that, in my younger days. If you're drilling something thin, then you might get away with it.

And as far as a faster speed being better.
You will see machine shops drilling, cutting threads, with the machines turning fast. But you will also see a torrent of cutting fluid pouring over the area to keep them cool. Faster speeds without coolant will ruin the bit faster because of more friction.

I will agree about using a center(centre) punch, though. Especially on round stock. :thumbsup:

 

[jmc]

If a drill bit is labeled "Titanium", don't buy it- it's mislabeled and if they don't know the difference, they shouldn't be in the drill business. Some drills have that gold titanium nitride coating (a ceramic) and those can be good ones but the company should know the drill is not actually made out of titanium.

A relatively new drill point that works well in hand held drilling is a 135 degree split point. Since the split point has sharp edges that goes all the way to the point, you don't need to push as hard. The garden variety 118 degree point has sharp edges almost to the point but the very point is not sharp and so it wallows out instead of cuts, the hole center. These needs more pressure.

Cobalt drills are harder and consequently, more brittle than HSS so they chip and break easier in a hand held setup. They're usually better than HSS though, in a production setup.

There must be RPM charts for the drill material, drill diameter, work piece material, and coolant situation online. SFM or 'surface feet per minute' might be part of your search terms.

 

[Depmandog]

I have been known to work up a gob of spit to lube/cool that random hole that I am drilling. Works well when you forgot to bring the oil along.

And as others have said, sharp bit, slow speed (I increase rpm / decrease pressure at point of breakthrough) and something to cool the bit / spit if that's all ya got!

 

[Beltzington]

Thanks All, got it - pilot holes, slow speed and keep both yourself and the bit cool . I like the water hose idea, much less mess than oil for outside projects.
Found Home Depot carries Milwaukee Black Oxide bits for a reasonable cost if bought in a set, I will leave the $6 bits on the shelf. I have been needing new bits for years but always managed to get the hole drilled and than forgot about it. 30+ years ago I had a Craftsman bit sharpener but it was a pain to use so I got rid of it in a garage sale, I will keep an eye out for a sale on the Drill Doctor.

 

[Shield Arc]

If you can find someone who knows how to sharpen a drill bit by hand, it will only take you a few minutes to learn. I taught member Furu in about 5-minutes.

 

[JIGBUILDER]

As my user name implies I was a aircraft tool maker/jigbuilder (hard and soft). We drill/ream/tap the majority of holes on large assy jigs by hand in steel or aluminum sometimes 2"-4" thick. On larger diameter drilled holes a 3 or 4 flute core drill works best as it doesn't hang like a 2 flute bit. If its a reamed hole a drill block makes it much easier and a better job.

For just small 1/4" drilled holes in 3/8" steel I prefer a #10 HSS split point drill as a pilot holes and then a #10 piloted X 1/4" drill to finish. Or if a piloted drill isn't available a 1/4" non piloted cobalt lasts for several dozen holes. I run the #10 bits at 1000 -1200 rpm with a few drops of cutting oils along the way. Its not necessary to flood the bit/material. One bit should do dozens of holes by hand. Stick with a good brand like a Morse or equivalent.
I find cobalt drill bits require lot of pressure and better suited for drill press work. I also find the cobalt small relief angle allows for a longer lasting bit when stepping out a hole size.

If your drilling hot rolled steel (HRS) it has a crust and can dull any drill bit in a hurry. Sometimes the crust needs to be hit with a grinding wheel/sanding disc to get rid of it.

Hold the drill motor steady and give'r h........

 

[Arc weld]

"Or if a piloted drill isn't available a 1/4" non piloted cobalt lasts for several dozen holes. I run the #10 bits at 1000 -1200 rpm with a few drops of cutting oils along the way. Its not necessary to flood the bit/material. One bit should do dozens of holes by hand. Stick with a good brand like a Morse or equivalent."

Thank you JIGBUILDER, that is what I was getting at. A few drops of oil/cutting fluid is good but you need around 1000 RPM for a 1/4" bit and a decent properly sharpened bit . Most 1/2" drills turn less than 500 RPM. I think the companies that make electric drills know what speed they should be. The flutes are pretty thin and if they come out shiny, the bit isn't too hot. If they come out blue and purple, then the bit is overheating. Sometimes just giving a spray of cutting fluid on the bit before drilling is all you need.

 

[Furu]

If you can find someone who knows how to sharpen a drill bit by hand, it will only take you a few minutes to learn. I taught member Furu in about 5-minutes.

With a good example of how to do it hand sharpening is not hard to do at all; Shield Arc showed me how as he stated.

I found that a lot of drill bits new are not sharpened properly. I ended up buying a 7/8" bit for a project and it did not cut for hill of beans. Very frustrating. After I learned how to hand sharpen I sharpened the 7/8" bit and WOW does it cut nice now. Learn how and do not hesitate to sharpen even your new ones if they do not cut properly. You can even go back and sharpen the broken bits if they still have any flute left and use them.