Best bit for boring steel?

paperfist

Diamond Member
Nov 30, 2000
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i have about 20 1/2” holes to bore through 1/4” steel.

What do you guys recommend and do I need to oil?

Amazon feedback leans toward those step bits, but they don’t look that great to me. Though I never used one.

Thanks!
 

PottedMeat

Lifer
Apr 17, 2002
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start out with a center punch
use a 1/8" bit as a pilot at fairly high speed with oil
you can go straight to the 1/2" as the chisel point should be smaller than 1/8", slow with oil

any oil will do. dribble some leftover 5w20 or whatever your car takes or any off the shelf cutting oil

a drill press will make this much much easier to do in a controllable manner
 

SKORPI0

Lifer
Jan 18, 2000
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Maybe something like this?
41MLC1NGGbL._AC_US218_.jpg

https://www.amazon.com/Step-Drill-Bits/b?ie=UTF8&node=256287011
 
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boomerang

Lifer
Jun 19, 2000
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I'm probably too late for this party but here goes.

You're not telling us if this is going to be done by hand or with a drill press. If with a drill press, center punch and go to town with the 1/2" drill bit. If you start with a smaller bit and work up, you'll just tear the hell out of the leading edges on the 1/2" bit. If you're good at sharpening drill bits you can approach it that way but it's unnecessary.

If you're doing it by hand, then you will want to center punch and then start with a smaller bit and work up. I think that 1/8" is too small to start but you can experiment. Try 1/8" then maybe 3/16" and see what's working best for you. 1/4" is probably too big to start with. Too much work. You're going to damage the leading edges on the 1/2" bit. More sharpening or more drill bits.

You can use oil if you wish. It does help cool the drill bit. People think drilling is a cutting action but it's actually an extruding action (when drilling metal). If you're starting small and working up, the first hole drilled is an extruding process and the subsequent increases in hole size are cutting operations which is why the leading edges will dull and/or chip.

If the holes require a great deal of accuracy in their locations and you are drilling on a drill press, use a smaller drill (1/4" would be good) and just "spot" the hole. Create a dimple to make it easier to get the right location with the 1/2" bit.

I drilled a shit-ton of holes in my working days. Mostly with the kind of drill press pictured below.

https://goo.gl/images/OalDLq
 
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paperfist

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Thanks for all the feed back.

The step bits, I dunno if they have enough 'shaft' to go through 1/4" before the next step would engage.

I can't use a drill press (at least mine is too small) because these are brackets I had made and they are 3 sided so won't fit under the press.

Accuracy doesn't matter here and I'll just be using a big ass corded drill.
 

stargazr

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paperfist

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paperfist

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Damn dunno what I did wrong but that step bit lasted all of 5 holes!

Off to order sdifox & shorty's bit suggestions.

BTW, why are steel drilling bits so long? I can't imagine attempting to go more than 1" deep...
 

herm0016

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Feb 26, 2005
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step bits are used at a pretty low rpm. how fast were you spinning it? any cutting oil?
 

PottedMeat

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Damn dunno what I did wrong but that step bit lasted all of 5 holes!
were you going way too fast ( heating up the bit ) or going too slow ( gigantic cuts ) or both?

why are steel drilling bits so long?
most of the bits you see are 'jobber' length, they're some multiple of the diameter

you can buy 'screw machine' bits that are short but anything that isn't jobber is more expensive
 

paperfist

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step bits are used at a pretty low rpm. how fast were you spinning it? any cutting oil?

I used motor oil. It didn't click to use cutting oil. Well to be honest I went as slow as the drill allowed, but it definitely revved up on me a bunch of times.

The crappy thing I didn't consider about step bits is once you fry the first few steps the rest are useless.

were you going way too fast ( heating up the bit ) or going too slow ( gigantic cuts ) or both?


most of the bits you see are 'jobber' length, they're some multiple of the diameter

you can buy 'screw machine' bits that are short but anything that isn't jobber is more expensive

Yeah mostly slow, but like I said it revved up on me.

Ah, thanks for the tip. I guess too for this application a shorter bit would get even hotter.
 

herm0016

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Feb 26, 2005
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shorter bits are better in a mill or press because they are more rigid. longer bits are less rigid and more prone to breaking due to torque or off center drilling. motor oil should be ok. the oil lubricates and helps to transfer heat from the bit to the work piece keeping everything at the same temperature.
 

sdifox

No Lifer
Sep 30, 2005
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You could have taken the whole thing to a shop and they'll drill it for you for a fee.
 

paperfist

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You could have taken the whole thing to a shop and they'll drill it for you for a fee.

I actually had these brackets made up by a fabrication shop and they were supposed to drill 6 holes for me. They only did 4 and I didn’t think this was going to be such a process or I would have taken them back.
 
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JCH13

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Sep 14, 2010
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Drilling steel without a drill press is a real bummer. You (as in human beings) can't push the bit hard enough to develop the proper thrust force on the drill bit in steel at those sizes. You're going to wear out the bits prematurely unless you take obscenely small steps. Invest in something like a drill doctor for twist drills if you have to use them in steel! I love mine.

A hole saw would be a better tool to use with a hand drill. Thrust loads for proper cutting are lower, less material is chipped (so you use less energy to make the hole), and good hole cutters will take a lot more abuse than a generic twist bit. See: https://www.mcmaster.com/4093a41

For cutting oil, just use whatever you have that isn't toxic. In my shop we use Boeshield and WD40 as cutting fluids. Occasionally motor oil. Often we'll use a water-based coolant on our mill.
 
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paperfist

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Drilling steel without a drill press is a real bummer. You (as in human beings) can't push the bit hard enough to develop the proper thrust force on the drill bit in steel at those sizes. You're going to wear out the bits prematurely unless you take obscenely small steps. Invest in something like a drill doctor for twist drills if you have to use them in steel! I love mine.

A hole saw would be a better tool to use with a hand drill. Thrust loads for proper cutting are lower, less material is chipped (so you use less energy to make the hole), and good hole cutters will take a lot more abuse than a generic twist bit. See: https://www.mcmaster.com/4093a41

For cutting oil, just use whatever you have that isn't toxic. In my shop we use Boeshield and WD40 as cutting fluids. Occasionally motor oil. Often we'll use a water-based coolant on our mill.

I was wondering about a hole saw for metal, but didn't have a chance to look into it. Also wondered why there wasn't a bit made out of grinder material. Seems like that would cut like butter though it would wear out fast.
 

JCH13

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I was wondering about a hole saw for metal, but didn't have a chance to look into it. Also wondered why there wasn't a bit made out of grinder material. Seems like that would cut like butter though it would wear out fast.

There are abrasive-tipped hole saws, like the one below, but they are generally intended for stone/ceramics/hard materials that do not chip like metal.

Hole_Saw_carbide_grit1.jpg


But abrasive drill bits are not common at all. One reason might be that it is wildly impractical to spin a drill bit fast enough grind at a high enough speed. I bet they would mostly just clog up with metal. Another reason might be that extracting the ground material would be extremely difficult.