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Drilling harden steel?


runaway parents

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I have never tried a masonry bit [usually carbide tipped] but have had good success with cobalt bits and some success with good, sharp tool-steel bits. Lots of pressure , slow speed and generous oil seem to work for me.          Charlie

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I use regular HSS drill bits, as Charlie mentioned cobalt are good.      For small holes 3/8 and under I just use a hand drill, bigger holes a mag drill when I can.     I had to drill a couple of 5/8 holes where I couldn't get my mag drill, it was a PITA but they were step drilled 3/8-1/2-5/8.     A 1/2" drill motor can break your arm if you are not aware of the situation,  never get your arms in a position where the drill can swing into an arm.

 

Steve 

2005 Peterbilt 387-112 Baby Cat 9 speed U-shift

1996/2016 remod Teton Royal Atlanta

1996 Kentucky 48 single drop stacker garage project

 catdiesellogo.jpg.e96e571c41096ef39b447f78b9c2027c.jpg Pulls like a train, sounds like a plane....faster than a Cheetah sniffin cocaine.   

 

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Fiction.  Get good quality set of cobalt steel drills and step up in size.  I drilled my frame for my Fenders with a 20v DeWalt drill using this technique.  This isn't rocket surgery.

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I drilled my rails on the Mack for mud flap mounts with good cobalt bits in a cordless drill.  Easy, no worse than mild steel.  But, it was just 3/8 holes, and the bits were sharp (Drill Doctor).

As mentioned above, beware of the bit catching and causing personal injury.

I'm no machinist, but I was taught that you want to have a pilot hole no larger than the web of the final bit.  Is that wrong?  I've broken the corners of bits by step drilling, but haven't since using the smallest pilot practical.

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3 hours ago, Darryl&Rita said:

Annular bit. Masonry bits melt when they hit re-bar, so what's it going to do with frame steel?

Hilti  has a masonry bit called a rebar cutter it is designed to cut threw rebar. Yes masonry bits are dull when you buy them I guess if you sharpen them they work fine. haven't done this myself just wondering if any body has.  In about a couple of months I am going to start prepping the truck to set the new used bed on it. Have to lengthen the frame I managed to pic up a mag drill this summer might chuck one up and give it a try

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I would use a core drill & driver intended for steel, and follow the manufacturers instructions. 

This one makes 17mm holes in 120,000 psi heat treated Kenworth frame rail nicely says a local equipment install shop. 

https://fein.com/en_ca/metal/drilling-and-core-drilling-metal/kbh-25-s-0302461/

If my truck had a concrete frame I would use percussion tools designed for masonry & concrete. 😁

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6 minutes ago, runaway parents said:

Hilti  has a masonry bit called a rebar cutter it is designed to cut threw rebar. Yes masonry bits are dull when you buy them I guess if you sharpen them they work fine. haven't done this myself just wondering if any body has.  In about a couple of months I am going to start prepping the truck to set the new used bed on it. Have to lengthen the frame I managed to pic up a mag drill this summer might chuck one up and give it a try

I would forget the masonry bit, unless you have a diamond wheel carbide is hard to grind.     I know "green wheels" work but, they are really for roughing not finish grinding.       Besides, a good sharp HSS drill is all that is needed.     I mentioned step drilling a couple holes, I did these that way only because I could not put a great deal of pressure on the drill.     With a mag drill just spot the hole and drill at size.

 

Annular bits work, they are pretty touchy on anything less than a nice flat surface.

 

Steve 

2005 Peterbilt 387-112 Baby Cat 9 speed U-shift

1996/2016 remod Teton Royal Atlanta

1996 Kentucky 48 single drop stacker garage project

 catdiesellogo.jpg.e96e571c41096ef39b447f78b9c2027c.jpg Pulls like a train, sounds like a plane....faster than a Cheetah sniffin cocaine.   

 

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Now come on now concrete frame rail? that explains the rebar I hit  HA HA .Just trying to think out of the box. Some body has got to try this who knows it might work. Who knows might be a cheaper way of doing things Always looking for ways of doing things  faster, cheaper, better. I guess you have to start with a  pilot hole and the concrete bit will finish the hole.

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You are making this far more difficult than it is.    The frame is made of high carbon steel 100-120KSI, the alloy is likely 1027 or there abouts.      A common HSS drill bit easily drills the frame, the only difficult part is constant pressure going through the thickness.      I have hand drilled 1/2 holes in AR400 with a HSS bit, that is far more difficult material to deal with.       Carbide drills work by extreme pressure, without being able to keep the carbide in cold steel it will work harden the hole.     That principal applies to all drill methods, carbide just does it faster.     

I had heard the old adage about using carbide cement drills and tried it, I even sharpened the point.    It was a poor excuse for a real carbide drill bit for metals.     The grade of carbide is lower and micro-fractures by design not want in high carbon steel.

 

Steve

2005 Peterbilt 387-112 Baby Cat 9 speed U-shift

1996/2016 remod Teton Royal Atlanta

1996 Kentucky 48 single drop stacker garage project

 catdiesellogo.jpg.e96e571c41096ef39b447f78b9c2027c.jpg Pulls like a train, sounds like a plane....faster than a Cheetah sniffin cocaine.   

 

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HSS drills with lot of fluid to make a start hole then complete a hole with one of these. They work like butter.

fUM22NYl.jpg

Mag drill with annular cutter works but lots of fluid. Pull the drill out immediately if you sense that the material is "tightening on the bit", (work hardening). Let it cool a bit and resume.

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17 minutes ago, runaway parents said:

Any way  once I get done with mag drill it will probably get stuffed over in a corner and never get used again will become available this spring so if any body is interested let me know I only have a 100 bucks into it. Would like to get it back.

Not going to ask how you got it that cheap.

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Construction company that I worked for closed there doors and sold all of there equipment . I new they had this thing and put in a request to purchase it. And sure enough they sold it to me along with a couple of grinders. They gave me a bill of sale and that was that. Guess I was at the right place at the right time. Its a older one but works fine.

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3 hours ago, runaway parents said:

Any way  once I get done with mag drill it will probably get stuffed over in a corner and never get used again will become available this spring so if any body is interested let me know I only have a 100 bucks into it. Would like to get it back.

I will take it if you can ship it to me. I will pay the shipping as well. I have wanted one for years.  

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