Drilling Large Holes

R

raferguson

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I had a need to drill a 2" diameter hole in a piece of 1/8 inch thick steel. I tried a fly cutter that I rarely use. It worked OK in my drill press, but better in my mill-drill. I had to sharpen the bit, and straighten it, afterwards, but I got the hole done. The fly cutter had a 3/8" shank, was not really heavy duty.

My question is about drilling large holes in general. Is the fly cutter, crude though it is, the simplest way? I can see that it is limited in the depth that it can go, probably less than one inch. Large drill bits are expensive, especially when you only need to drill one hole one time. How about using a boring head? I do not own a boring head, yet. The boring head would permit a more exact dimension, but much of the time the exact size is not critical. Or is a boring head more to get a rough drilled hole exact?

Richard
 
Most drill presses go too fast for hoke saws.

Normally back gear slow.

In slowest speed just touch and go with lots of oil.

Sent from my SM-G781V using Tapatalk
 
A hole saw in the mill works well. Annular cutters are great, but can get expensive. Boring heads are great, and very accurate, but slow. You can only remove so much material at a time with one. You are also much more likely to get a nice straight, very circular/concentric hole.

Another option is trepanning, which is like the fly cutter mentioned, but needs a different grind on the tool to work well. If the tool is set up well, you could probably mount it in something like a boring head for very adjustable cuts.

And just to mix it up, for 1/8" thick, a plasma or torch cut would likely work well. Even if only to rough it out before finishing up with something else.

Rotary table would work as well....
 
Time consuming, but one can drill a series of small holes inside the circle, knock the piece out, then finish with one of the methods outlined above
-M
 
I have cut hundreds of holes in 3/16" steel plate using a hole saw on the drill press. Go slow, lots of lube. I replace the pilot drill with a dowel pin for more rigidity and better centering. They will also work with a hand drill

1669927905057.png

An adjustable circle cutter will also work on a drill press. I have cut 8" diameter holes with one. Solid clamping is recommended.
1669927834167.png

Trepanning on the mill with a boring head is another way.

I don't have the muscle to drill holes over 1" in diameter with a drill bit.
 
I really like the annular cutters but they are expensive. I only have 2 sizes. End up making my projects fit the sizes I have available. I am using a PM 728 and they don’t seem to require as much torque as a hole saw. Could be my hole saws are past their useful life or is that the operator.
 
Another possibility is the Clark hole cutters that can be seen on E Bay, they use 3 tool bits and are easily adjustable for most any diameter holes they come in s sizes for a range of hole sixes that is quite broad range and fairly easily sharpened by ordinary means. I might add that annular cutters are a ***** to sharpen, taking several setups on a T&C grinder to sharpen.
 
RJSakowski said:
I have cut hundreds of holes in 3/16" steel plate using a hole saw on the drill press. Go slow, lots of lube. I replace the pilot drill with a dowel pin for more rigidity and better centering. They will also work with a hand drill

View attachment 428381

An adjustable circle cutter will also work on a drill press. I have cut 8" diameter holes with one. Solid clamping is recommended.
View attachment 428380

Trepanning on the mill with a boring head is another way.

I don't have the muscle to drill holes over 1" in diameter with a drill bit.
Click to expand...
I've found that hole saws tend to load(clog) up with chips when cutting metal. Nowadays I strongly prefer annular cutters, which have good chip evacuation. They're somewhat spendier,, but I find the cost worthwhile.
 
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