How to drill larger holes?

R

raferguson

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I have just gone through some suffering trying to drill some holes between 3/4 inch and 1.5 inch diameter in 1/4 inch steel plate. In hindsight, I should have used thinner stock, as I did not need much strength. My drill press is not happy drilling holes around 1 inch diameter, so I had to gradually increase the hole size with my 1/2 inch shank drill bits. Even a 1 inch hole took a lot of time. Not sure what my lowest RPM is on my drill press, maybe 200 rpm. My mill-drill will go down to about 100 rpm. Since I did not have any bits over one inch, I grabbed my cheap hole drill set, but it took forever just to get halfway through the plate, so it turned into a fiasco. The accuracy of the hole diameter was not critical in this case. I don't drill big holes very often, but I need a realistic way to drill holes over 1 inch diameter.

What should I have done? Not sure that I want to drop $150 for a decent set of hole saws, but maybe that is the right answer. One review said that a $60 set would not go through 1/4 inch steel more than once. Are hole saws even a good idea in steel? I notice that they use "annular cutters" with magnetic drill presses. Could I use annular cutters in my mill-drill? Annular cutters are fairly expensive, I note. I don't have a boring head, but my understanding is that they don't make holes, they make them bigger, so that would not have helped much, I would still have had to drill the large hole before I could use the boring head. Is there an alternative that I am missing?

Glad that you have a beginner forum so that I can ask beginner questions. ;-)
 
Annular cutters do work well for this. https://www.bing.com/images/search?...5380bc1d49&cbn=EntityAnswer&cbi=0&FORM=IARRTH
I have also chucked pieces up in my 4 jaw by centre punching and clamping the tailstock center against the punch marks. Tighten the chuck maintaining the centre on the punch mark. Drilling a hole with a smaller bit in the tailstock and the finish boring with a boring bar.
If you have multiple pieces and accuracy isn't critical, I have also tack welded the pieces together and performed the same operation in the lathe.
Cheers
Martin
 
Annular cutter with enough force to drive it. You can get by with a decent hole saw (Lennox bimetal) and plenty of cutting oil. Again you need adequate torque at low speed. I have certainly drilled 1/4" steel with these. The hole will not be dimensionally accurate as you noted. Sometimes drilling from each side makes it a little easier. If your drill press is not up to the power requirement nothing will work well.
Robert
 
There are a range of tools and options available, but much depends on the variables: material type, material thickness, accuracy required, equipment available and how much more money you want to throw at it.

rpm has a huge influence
at 200rpm (and assuming HSS cutter and mild steel work-piece, where I typically run at 80 sfpm) gives a max tool diameter of around 1.5"
Any bigger than that and the sfpm gets too high.

regular drill bits
I use up to about 3/4" comfortably on my drill press at its' slowest speed. Always clamp the work!
Any bigger I use morse-taper shank drill bits.
Bigger ones I only really use on the lathe so I can use slower speed, as @Martin W mentions above.

step drills
For "sheet metal" step drills work very well. The next step can deburr the hole, however the material cannot be thicker than the steps or you end up with stepped holes too. Honestly, yes, I have flipped the work and opened up the other side.....
1611497968973.png


hole saws
be certain to get "bi-metal" hole saws that have HSS teeth on a regular steel "cup" (ie. NOT the carbon steel ones!)
1/4" plate would be about my limit for typical bi-metal hole saws.....and that is slow and screechy in the big 3-4" ones even with low speed and cutting oil
the removed slug can be used for other projects; I make custom washers this way
1611498017725.png


annular cutters
I'd like to have a full set, but I don't have thousands of dollars to spend on tools I'd use so infrequently.
I have a couple smaller annular cutters that I bought when I found good prices, but I haven't used them yet since I need to make a special arbour for them.
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trepanning on the lathe is also an option, but you need to be careful when the centre comes loose that nothing gets jammed. You are better of to stop a little short and knock it out. it is difficult to go very deep.

"circle cutters"

I have always found them more useful in wood than metals, they are just not rigid enough and chatter/squeal...even though the link below says:
Adjustable for making 1-3/4" to 7-1/2" holes in steel, brass, aluminum, plastics, wood, hardboards, and other materials.
Click to expand...
1611497883139.png
https://www.kbctools.ca/itemdetail/1-805-55


-brino
 
If you watch Ebay you might find some large drill bits for reasonable prices with taper shanks you could use in your mill-drill
Sometimes people sell them when they have been sharpened so many times they are pretty short, but for you that may be fine
-Mark
 
Most drill presses don't turn slow enough for big bits like that. I find that 50 -75rpms is best for those big bits. Your pilot hole only needs to be as large as the web of your larger finish hole size drill bit. Stepping up closely in size destroys the cutting face and sides of your bits with excessive pressure and heat.
 
I had a friend with just this problem, larger holes in 1/4” plate, 1.5” D. I had a center cutting end mill that size, but drilled out a small hole first, which I think speeds things up a bit. The mill peeled chips out like mad, made the whole process effortless and left him amazed. And jealous.
 
The beauty of the annular cutter, is the quality of the cut hole....
 
Cadillac STS said:

Looks like these punches are for thinner metal but are there some for 1/4 inch steel?

Maybe a punch that could be driven with a press like the harbor freight 20 ton?

For me I would use my CNC mill for a hole like that.
Click to expand...

The force required to punch a hole is proportional to the perimeter of the hole times the thickness of the stock times the shear strength of the material. A 1.5" diameter hole in 1/4" mild steel plate would require something like 72,000 lbs of force.
 
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