Large Diameter Drilling

[PolyPill]

I'm wonding what other people do for drilling large diameter holes in 4 in stainless steel. I'm looking at 2.5 in and ~ 6.575 in. I really only need to drill about 10 holes then I wont need it again, so I didn't want to spend hundreds of dollars on having a special bit made. Is there anything I can rig up myself? Even if it took me all day to drill 1 hole that would be fine for what I need.

Has anyone done this before? Is this possible to do myself or am I going to have to pay a machine shop to do it?

[DareBee]

We can't help you much if you don't tell us what you are drilling.
We need stainless grade and material size (3 dimensions) and in which direction you are "drilling" through it.

[PolyPill]

We can't help you much if you don't tell us what you are drilling.
We need stainless grade and material size (3 dimensions) and in which direction you are "drilling" through it.

Sorry, I didn't think that was really needed.

I haven't started anything yet, so I'm really free to use what ever steel I want, but I was thinking Stainless 409. The dimensions don't have to be exact, but in the neighborhood of a 4 in cube, 4x4x4, for the 2.5 in hole. Since it's a cube the direction doesn't matter either, but I'd like to use a drill press....so vertically.

Lets just go with the 2.5 in right now, the larger 6.575 one isn't very important.

[HuFlungDung]

Use a lathe. Or hire it done on a lathe. This permits you to open the hole with a smaller drill, rather than requiring super torque, and a super tool to go along with it. Plus it allows you to do a nice accurate finish bore without a lot of fooling around.

If I had to do it in a larger part, I might open the hole with a drill, and then use circular interpolation to enlarge it on the cnc mill. This method works okay, but does tend to use up a few more inserts than the lathe would.

[PolyPill]

So if I rig up a DIY lathe, start with a smaller cutting tool and slowly work out to my 2.5in I should be able to do it? or should I bring this to shop?

[Mcgyver]

bring it to a shop. you say rig up a diy lathe as if its a few hour's work? If you can in fact rig up a lathe a a few hours, have at it. you need a lathe or mill with a boring head, or a boring mill for this job

[HuFlungDung]

~snip~ If you can in fact rig up a lathe a a few hours, have at it. ~snip~

LoL, amen brother

There is a bar tool called a "Multi-tool" which uses ordinary HSS cutters in kind of a piloted shank. This might work if you have the patience to fool with it. It will still require a bit of torque to take much of a cut with it. Each pass with the multi-tool would require a new pilot to guide the tool for the next pass.

[Geof]

I looked up the machinability of 409 stainless steel and found this:

"Machining this alloy produces tough, draggy chips with heavy build-up. While this alloy can be machined in the annealed condition, it tends to perform better in the cold drawn or heat treated condition."

I think your only hope is boring on a decent size lathe, my initial approach would be to go slow (100 fpm or less) using a HSS tool with a good extreme pressure lubricant and experiment with the positive top rake on the tool.

[DareBee]

The piloted drill (spade insert cutter) would work in easy to machine material but I wouldn't hold my breath in 409 SS.
The spade drill tooling will easily cost you at least twice what paying a shop to do it would.
I suggest you take both parts to be made to have done at a shop at the same time. It will save you paying setup costs twice.
If your drill press has power feed you could clamp your part on the table and use a boring head in your drill press.
I will assume that if you don't have a mill or lathe you probably dont have a $5000 drill press either ;-)

[DareBee]

I just noticed Russia and Canada only so far in this thread.
cool

[PolyPill]

I just picked 409 SS out of a list based on price and a list of their uses. I just wanted something strong, maybe I should first ask what sort of steel I should use.

Now that I'm aware it is prone to chipping it probably wouldn't be a very good choice for any kind of tooling.

So I want a 4x4x4 inch cube of metal with a 2.5 in hole through the center that will be stressed on a daily basis, what sort of steel should I use?

I'm sorry, but I'm a total newbie when it comes to this sort of fabrication.

[Geof]

Now the questions you have to answer are; how much stress, in what direction relative to the structure, is it a stress that goes on and stays on or does it cycle, does the direction of stress reverse, is this 4" cube with the 2.5" hole through it going to be welded into a larger structure or os it bolted in some way? And probably others I cannot think of at the moment.

If you have a very high stress then you maybe need a high carbon steel for strength but if the stress is cyclic or reversing you have to start considering fatigue so you have to start considering alloy steels with good fatigue resistance. Then if you are going to weld this part you bring in a lot of other consideration such as annealing or normalizing after welding.

Maybe making the hole is a small problem compared with all the other things you have to consider.


I agree with the cool comment about just Canada and Russia represented so far.