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Drilling

you can drill a 1/8 hole to the depth. then go with the next pilot drill bit which should be matching the 1 1/16 bits centre. then use the 1 1/16 bit to drill the hole slowly. you must use cutting oil like rapid tap and drill slow or the bit will get hot. must drill slow , like 350-500 rpm. some bit are made so you don't need a pilot hole as this screws up the bit. I am presuming you are using a drill press.
 
Depends om how much power you have. I have a lot so I would do that in 3 steps, first one always being a center drill. 2nd step would be a pilot hole as the other poster said near the size of the the web of the big bit. Then drill the hole. A common mistake is making the pilot hole too large or taking too many small steps. The correct RPM for any HHS bit is the fasest speed that does not cause discoloration of the chip. It is also a mistake to feed it too slow as the vast percentage of heat is carried away by the chip, not the cutting oil as is often posted.
 
(quoted from post at 04:28:26 04/23/19) I need to drill a 1-1/16 in dia hole, 3" deep in some large steel bar stock what steps of drill sizes should I use?
Click to expand...
I would start with a big center drill (maybe a #5 or so), then shoot a 1/4" ish down to depth, then the finish size. Speed would need to be plenty slow with oil. You're looking for chips the color of straw.
 
I assume you have a mill, drill press, or a mag base.

Trying to drill it by hand will be near impossible.

I would drill through with a 1/2" first, then follow with the 1 1/16.

Probably about 60-80 RPM, lots of down pressure and coolant or cutting oil.
 
(quoted from post at 13:36:03 04/23/19) I assume you have a mill, drill press, or a mag base.

Trying to drill it by hand will be near impossible.

I would drill through with a 1/2" first, then follow with the 1 1/16.

Probably about 60-80 RPM, lots of down pressure and coolant or cutting oil.
Click to expand...
He said he has a lathe. And 1/2" first is WAY too big.
 
What others have said, but will add you do have a properly sharpened sharp drill bit right? And too slow is better than too fast.
 
....He said he has a lathe. And 1/2" first is WAY too big.
Click to expand...

Depends on the lathe....

When I started working in a machine shop back in the 70s, I was running a lathe that we ran a 6" diameter drill with no pilot hole. Nearly as much time spent shoveling chips as cutting!
 
You should measure the drill point of the largest drill that you intend to use. Your pilot hole should be slightly smaller than the point. Then use the biggest drill that you have that is going to be below your finished size. Finish with a boring bar. This method should reduce the chance of chatter when drilling.
 
(quoted from post at 18:07:48 04/23/19)
....He said he has a lathe. And 1/2" first is WAY too big.
Click to expand...

Depends on the lathe....

When I started working in a machine shop back in the 70s, I was running a lathe that we ran a 6" diameter drill with no pilot hole. Nearly as much time spent shoveling chips as cutting!
Click to expand...
I've been a machinist for 45 years, covering everything from prototypes to 60 cycles per minute screw machines, and I stand by my statement.
 
What is your tolerances? Do you mean round bar stock? Are you going all the way thru or drilling a pocket? If it is indicated in on the lathe I would run a center 1/2" drill in about a 1/4" and follow with 1/2" drill to the bottom depth of the point. I would then drill to depth with a 1 inch drill and finish with a boring bar for high tolerances If I didn't have a mill open. If your not worried about tolerances I would use a smaller pilot drill after the center drill and then 1 1/16 drill bit. On the lathe it is easy to see if you are running off center as the drill bit will move around.

High tolerance holes that have to match mating sides.

2vkjk3ixevZ4.jpg
 
Should have posted this picture rather than the first one. The hole for multiple inserts is done before the profile cutting.

2vDST6gxevZ4.jpg
 
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