What did I do wrong drilling these holes?

[Raul-02]

The first three holes went OK, but halfway through the fourth one, the drill started overheating and smoking, and stopped progressing. It was now blunted. So I stepped down to 21/64" and tried again in the same hole, but that one overheated and blunted, too. It

the options are few and very simple
1) too much speed
When drilling or machining steel you need to go slow. There are exceptions but they involve carbide high coolant flow and super rigid machinery.
2) no lube or improper lube.
For steel, you need one of the following: a good water soluble based synthetic coolant OR a high sulfur cutting oil like what OATY sells at the BORG. Motor oil, WD40, 3-in One, etc., are all as worthless as sand as cutting oils. I use this https://www.amazon.com/gp/product/B00065UD56/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 in my mister on my milling machine and lathes.
For aluminum Kero is great. So WD40 ( which is just expensive kero with a touch of hydrotreated light pump oil) works great.
3) Cheap **** Chinesium drills.
Buy your drills from a good mill supply and be willing to pay extra, or go here and buy their KFD or Cobalt

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[SmallChange]

Revisiting this old thread. I needed a couple 15/32 holes in half inch steel today. It was a mounting plate on a 2" hitch, so I suppose inexpensive mild steel. I drilled them with a new DeWalt cobalt pilot point bit from a set I got on Amazon, with Tap Magic EP-Extra fluid, at 140 RPM, on my drill press. No pilot hole. I got neat springy chips that were only warm to the touch, clean smooth shiny bores, and no chatter at all.

I think I did several things right instead of several things wrong.

This will mount a cheap 6.5" vise on a SSQA adapter, so I can grab and hold and lift heavy things in the vise in whatever position.

Thanks all!

 

[etpm]

For a hardware store drill bit those DeWalt cobalt pilot point are surprisingly high quality. The pilot point is not only quite useful for starting the hole it also helps to get round holes in thin metal. Regular 118 degree point drill bits tend to make triangular shaped holes in thin metal. I'm happy to see you are using proper cutting fluid. Thanks for posting on your progress.
Eric, retired machinist

 

[SmallChange]

Regular 118 degree point drill bits tend to make triangular shaped holes in thin metal.

Yes. Actually this seems pretty interesting to me. There are special drill bits you can get for drilling square holes and hexagonal holes. The square hole bit has 3 edges, and the hex hole drill bet has 5. The flutes are straight, no twist. They mount in a special adapter that leaves the bit free to wander sideways a little, so the bit chatters or walks around the hole. I've never used one but have seen pictures and sales lit.
So, it makes sense that a bit with 2 edges will cut a triangular hole, if it's free to walk around the hole. And, even with flutes that twist, thin metal does nothing to brace the flutes higher up where they are at a different angle.

 

[SmallChange]

Drilling Square and Hexagonal Holes

Turns out it’s also possible to drill hexagonal hole using a very similar tool based on the Reuleaux pentagon. The video immediately above, again from jacquesmaurel, shows a tool he describes as a “Vika attachment,” mounted in a lathe, boring an hexagonal hole in a piece of stock. The video...

makezine.com

 

[PhysAssist]

I have had similar problems. The only solution I found to work consistently is to use good quality cobalt bits……

All of the above, using slow bits speeds, hardened/sharpened drill bits, and some [almost any] kind of lubrication are helpful.

There is one other thing that no one, except the OP mentioned [in passing] at least as far as I have read so far, was that drilling a pilot hole really eases the whole drilling process.

Even a 1/8" pilot hole will make the larger bit bite and chew through the stock more readily and with less heat and friction.

Also, unless you have annular cutters [mostly for larger holes], stepped drill bits can really make the process easier, except in really thick metal.

 

[SmallChange]

There is one other thing that no one, except the OP mentioned [in passing] at least as far as I have read so far, was that drilling a pilot hole really eases the whole drilling process.

Wait, wait. Drilling a pilot hole was part of the problem, and I suspect the biggest part. When there's a pilot hole, only outer parts of the two edges will cut metal, and they can take turns advancing, which makes chatter.

I used pilot point bits when it worked right, and they're different, because chatter would force the pilot point to jump around, which is difficult for it to do.

Somebody along the way here said they wouldn't use pilot holes on anything smaller than, what, half an inch? Something like that.

 

[5030]

When there's a pilot hole, only outer parts of the two edges will cut metal, and they can take turns advancing, which makes chatter.

Only if the cutting edges aren't balanced.

 

[SmallChange]

Only if the cutting edges aren't balanced.

Actually, I think it's the other way around. If the edges aren't balanced, only the one that sticks out further does the cutting, and it won't chatter. An extreme example of this would be the large diameter stepped cone drill bits for drilling large holes in sheet metal. They have only one cutting edge, so as unbalanced as possible. I've used these lots of times and never had one chatter -- and that's for large holes in sheet metal, which would be about as prone to chattering as it could be.
Having unbalanced cutting edges leads to other problems. I think there's more friction and heat, and I bet it's harder to drill an accurate size. So, I'm not proposing our drill bits should have uneven edges.
But balanced cutting edges would chatter if given the chance by a pilot hole. The earlier mentions of special drills for drilling square or hex holes are, you might say, extreme examples of this.

 

[5030]

I only drill holes in sheet metal with Blu-Mol bits.