Use cobalt or HSS to drill in plain steel?

[k0ua]

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.

I have seen some pretty nice holes cut with a plasma I know, I don't have one either. If I had to drill the holes, I would use my 1/2 inch holesaw, Heck of a lot easier than a 1/2 inch drill bit. Just use the low speed setting on a battery operated drill, and do them quick. The cup of oil would work for the holesaw too. I have a nice Bosch set of holesaws, given to me by the wife as a Christmas gift, and that was just about the best gift I can remember getting.

James K0UA

 

[tcreeley]

I never thought a hole say would work for anything, but recently I've used them to cut 7/8 1/4 steel holes- works well taking your time- clean hole. I used them on my corded drill. Always choose the slowest speed that cuts well- your bit lasts longer, and doesn't overheat and lose its temper. Dip in oil.

 

[/pine]

Just curious...I see so many recommending "dipping" bits in oil...personally I find this cumbersome...especially working in confined spaces...whenever I can I use a drill press and a pump oiler...letting off the pressure and pumping a a little oil into the bore/bit as needed...when drilling on things that I can't get on the press I do the same with a catch rag underneath...

maybe it's just me (with R.A.) but it's much easier on my shoulders than maneuvering the drill so much to keep the bit lubed...

 

[sdfarmin]

Just curious...I see so many recommending "dipping" bits in oil...personally I find this cumbersome...especially working in confined spaces...whenever I can I use a drill press and a pump oiler...letting off the pressure and pumping a a little oil into the bore/bit as needed...when drilling on things that I can't get on the press I do the same with a catch rag underneath...

maybe it's just me (with R.A.) but it's much easier on my shoulders than maneuvering the drill so much to keep the bit lubed...

I've found that dipping into a puddle or bottle cap etc cools down the drill bit faster and the fluids can help with extracting the cuttings. Messy, but it works for me. In this case, with a cordless impact drill (heavy) in a tight space, a rest now and again might be in order.

 

[jmc]

I've found that cobalt drills last longer in a press or mill but their harder, more brittle edge chips in handheld drilling since the setup is not as stable.

Otherwise, try a 135 degree split-point over the standard 118 degree point because the 135 is sharp all the way to center. Standard points have a non-cutting zone near center that has to wallow its way thru. You won't have to push as hard with the 135 split point.

 

[mikehaugen]

If you want to use a pilot hole, I would recommend a transfer punch, or get a pilot-point bit to make the dimple, versus a regular 1/2" drill bit.

I second the opinion of the cobalt being brittle for hand-held applications. I would use a good hss, they are better than a cheap cobalt. I have also read advice about not wasting money on titanium coating for hand-held drilling, as the coating nearly instantly wears off.

 

[jimcolt]

There are differences in so called "cobalt" drills. The ones that are sold in the box stores like Home Depot often are either cobalt coated, or of a different grade of cobalt as compared to the ones that I purchase from the major online machine shop tool suppliers. If cobalt coated.....forget resharpening. The cheap cobalt drills at Home Depot and Lowes only last slightly longer than regular HSS drills. The good (read more expensive) cobalt are called solid, M42 grade cobalt, and I find the edge lasts at least 10x longer than HSS and has the ability to drill quite hard materials with no issues. They are a bit more brittle as compared to HSS drills.

A good test for drills is when you have air plasma holes that have taper and need to be drilled for better cylindricity. Often if I need 3/8" holes in a steel plate I cut the part on my cnc plasma with the holes about .010 undersized, then drill them to the proper size. Air plasma systems put a nitride edge hardening on the cut edge (about .006" thick case hardening), and about 2 or 3 holes with a HSS drill will destroy the cutting edge. I typically get over 200 holes with an M42 solide cobalt bit in this case. To me they are worth the extra money, and are easily resharpenable to boot.

Jim Colt Hypertherm

 

[Ken Pike]

I've had good luck with HSS & lots of lube. I drill a 1/8" pilot hole then straight to the 1/2" drill bit. Bit seems to catch less this way rather than stepping up in increments.

 

[LD1]

HSS is fine for what you want.

And I'd forget about stepping up the sizes unless you are dealing with something greater than 1/4 or 5/16" thick. Stuff thinner than that, and stepping up drill sizes only leaves you cutting with the very edges of that bit. And they like to bite and grab like no tomorrow. With a powerful drill and an akward position, this would concern me the most.

Just punch straight through with the 1/2" bit. if its a 2 speed drill, keep it on the low speed, and keep the bit cool. There is no reason why a good HSS bit shouldnt last all 20 holes through a frame.

 

[Charlie Packwood]

Just start drilling, as was said before mark the centre with a punch and drill a pilot hole that is the size of the web on the tip of the 1/2 drill. It should be less than 1/4 inch, I usually use 3/16 and then go straight to the 1/2 inch. The drill will not wander and the force needed will be lower than without the pilot hole but the 1/2 inch drill will not grab as much and it will be a lot easier on your wrists. Always use some sort of cutting oil, tapping fluid works really well and is usually fairly thick and stays put as you start the hole. The Drill doctor is a great tool but if you buy a good quality bit either cobalt or plain you won't need it, until you finish and put the bit away for the next time. Like was said before there is always a good reason to buy new tools.