Use cobalt or HSS to drill in plain steel?

[sixdogs]

I have to drill about 20 1/2" holes in the side rail of a 1967 Ford truck. The frame is just mild steel but the holes are in an awkward position. I don't have to worry about the drill wandering because the plate I am bolting to the frame already has the holes punched in it so I just have to go through one thickness of steel and the first hole guides for the second. I figured to start a little with the 1/2" drill and then use the pilot hole made to get a smaller drill started and work my way up in sizes.

The question is, should I use a cobalt drill bit or stick with HSS? I'm using a Makita industrial hammer drill. On one hand, I know cobalt is for things like stainless steel but would that drill last longer for my purposes or should I just stick with HSS?

 

[tcreeley]

Both work- just have replacement bits and start with 1/8 after you mark the center with a full size bit. Go up from there - 3/8, 7/16, 1/2. Dip your bits in oil frequently, last longer.
(I'm thinking a reg drill- never used an impact drill- that might snap your small bits.)
Good luck.

 

[sd455dan]

I never used my hammer drill for anything but drilling concrete and chipping rock or concrete... then again it is an sds HSS should be fine when i need to drill a lot of holes i have bought the cobalt
keep us informed i would like to know how well the hammer function works, may want to get some sds standard bits

 

[sixdogs]

No, it's not an impact drill but an electric hammer drill that can drill regular or put a slight pounding pressure on the bit to drill better. it's the industrial hammer thing you guys are thinking of.

 

[/pine]

A small pump type oil can will be an advantage and keep your bits from dulling...a second person applying the oil as you drill will make it easier...

turn the hammer off and just use it as a regular drill...

 

[k0ua]

As said by others.. be sure to lube, and the cobalt bit will likely last longer without needing sharpening. As you are drilling a lot of holes that may be of benefit. What ever you do, keep the bit cool, and use enough pressure to keep a nice chip going.

James K0UA

 

[xrsrfn]

I use Mystic metal mover for large drilling projects. The stuff is amazing how much it helps even with a dull bit.

 

[KennyG]

Never waste an opportunity to buy a new tool! This looks like an ideal project to justify buying a Drill Doctor. Based on my experience, just go straight through with the 1/2" drill. As others have said, use lots of lube. Sharpen the drill after every couple of holes.

 

[sdfarmin]

I've used both to drill through the frame of my old Chevy truck, and both worked fine. I also kept dipping the bit in oil to keep it from overheating. I just had some oil in a bottle cap for dipping and that seemed to work fine. I first drilled a small hole with 1/8 in bit, and then with the large bit - 5/16 or whatever it was. The thing is that it takes a while, and it seems like it takes forever when you're under there. I could feel my neck muscles the next day.

 

[oosik]

Just as KennyG says. A Drill Doctor, a freshly sharpened 1/2 inch bit, lots of oil and go for it. I've never drilled that many holes at one time. And since one thickness already has the holes, to line things up, I might consider using my cutting torch.