Use cobalt or HSS to drill in plain steel?

[PHPaul]

Typically, it's NOT a good idea to use the multi-step increasing hole size approach. That puts all the load on the outer web of the bit and will lead to chipping and breaking.

For a half-inch hole, the most I would do is drill a 1/8th pilot hole to keep the bigger bit from wandering until it gets started.

A properly sharpened (preferably new) bit should do it in one pass.

My results with a Drill Doctor have been...sketchy.

 

[mikehaugen]

My results with a Drill Doctor have been...sketchy.

Mine too... years ago I worked in a trailer manufacturing plant where we drilled a lot of holes. They had a drill bit sharpener that worked awesome, but I'm sure was expensive. Anything 1/2" or bigger I learned to sharpen by hand, and got pretty good at it- it was actually faster and just as good as the machine was with the smaller bits.

 

[flusher]

Typically, it's NOT a good idea to use the multi-step increasing hole size approach. That puts all the load on the outer web of the bit and will lead to chipping and breaking.

For a half-inch hole, the most I would do is drill a 1/8th pilot hole to keep the bigger bit from wandering until it gets started.

A properly sharpened (preferably new) bit should do it in one pass.

My results with a Drill Doctor have been...sketchy.

Right on. The DD works OK for me with larger size drills (1/4" up) but I find it difficult to get a good sharpening on smaller sizes.

 

[flusher]

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...

Drill oil is primarily for cooling the bit, not for lubricating. In aerospace manufacture where jillions of holes are drilled for a plane using conventional twist drills, the fluid is more like soapy water. Rivet holes are drilled in aluminum sheet and structure on the assembly line without any cooling, just with sharpened bits. Aircraft assembly line areas are generally squeaky clean--you don't see the assemblers splashing through puddles of cutting fluid that's accumulated on the floor.

 

[clairjohns]

make sure the hammer feature of that hammer drill is turned off or locked out. you want a smooth aplication of toqure on the drill bit. HSS is fine. use a small drill to drill a pilotl hole first. ( a little larger than the web of the drill is all you want). Your drill motor ( the drill ) should rotate the drill at a speed of about 500 rpm. Your hammer drill, may have a speed of over 1,500 rpm, this is fine for the pilot drill. but, will " burn up " the 1/2 inch bit.

 

[/pine]

Drill oil is primarily for cooling the bit, not for lubricating. In aerospace manufacture where jillions of holes are drilled for a plane using conventional twist drills, the fluid is more like soapy water. Rivet holes are drilled in aluminum sheet and structure on the assembly line without any cooling, just with sharpened bits. Aircraft assembly line areas are generally squeaky clean--you don't see the assemblers splashing through puddles of cutting fluid that's accumulated on the floor.

Actually my point was more about applying the oil etc...The premise is to reduce friction thus reducing heat (i.e., cooling)...again, IMO it is more effective to "squirt" a drop or two of oil/cutting fluid without removing the bit to dip the bit...as stated it's easy to catch any excess with a rag or drip pan...

 

[sixdogs]

Great advice and thanks to everyone--I really learned a lot. The plan was to drill these over the weekend but a storm blew in and I got behind on some other chores. Thanks again.