annular cutters: a better way to drill big holes in thick steel

[dfkrug]

For you non-professional steel fabricators out there, here is the latest
method I use for drilling holes between 1/2" and 1 1/16" in steel plate,
up to 5/8" thick.

A lot has been written on TBN over the years about holes, but this is a
surprisingly economical way to go. I expected to see more on annular
cutters on MachineBuildersNet, but there is very little there. So here
I post.

First, a little history. I rarely drilled any big holes in thick steel until I
made my CADDigger back in the mid 90s. Back then, I had an O/A cutting
torch, but I was not very effective at cutting holes accurately enough
for my purposes. Some of the holes required were as big as 2" in 1/2"
A36 steel plate. I tried bi-metal holes saws, but it was very slow and
my Delta 16" drill press really complained. And, at 240RPM, it was WAY too
fast. I also had some of those cheapo Silver & Deming reduced-shank
twist drills for the 1" and smaller holes. I got a set from HF tools for about
$25, but they chipped easily, even in mild steel.

I also paid folks I know with milling machines to use end-cutters. I have also
paid a guy with a punch press $1/hole to do some 1-inchers in 1/2 plate.
They were OK, but inconvenient, and there was some distortion of the plate.

I upgraded my drill press to the biggest and slowest one I could find that
was not a geared-head unit. This is the 20-inch DP from HF, which is about
325#, and much sturdier than my old Delta. At 180RPM, it was still too
fast for some of these bits, however. I also moved up to Morse Taper 3
bits, which the new press supported. The bits in the photo are very nice
US-made units with MT-3 shanks that go right into the DP's quill. Much
nicer.....for at least the holes up to 1". Better US-made twist drills all worked
better than the Chinese S&D units, too. The larger bi-metal hole saws were
still not a very good solution.

I now use my plasma cutter and templates or a circle guide for holes
bigger than 1 1/16" diameter, and use weld-in DOM tubing to make up for
sloppy holes. I still need to drill anything smaller than that.

Enter annular cutters. Those familiar with magnetic drill presses have
probably seen these, and these DPs can be purchased for as little as
$500 now, less the cutters. I used a mag drill back in the mid 70s when I
was a technician in a lab, but it was many thousands of dollars. I now have
a way to use annular cutters in my drill press.

 

[dfkrug]

Here are the components of an annular cutter setup for a drill press. The
Arbor, I bought from a tool vendor in England for $55, It has an MT-3
shank to be compatible with my drill press. The cutter bit has a so-called
"Weldon" shank, which is .750" diameter, with 2 flats for securing it into
the tool holder. The pilot pin goes inside the bit, and spring pressure will
keep it in a center-punched dimple in the work to be drilled. Most
annular cutters have standardized on this Weldon shank, and they now
come from many vendors: Hougen, Milwaukee, Alfra, Champion, DeWalt,
etc.

This bit is a Champion RotoBrute XL100. You can see some mag drills in
action on the Champion site:
Champion Cutting Tool Corp.

 

[greasemonkeyok]

Does the annular cutter setup replace the chuck in a regular drill press?

Edit: Oops, you posted the answer simultaneously with my questions.

 

[dfkrug]

Inside the arbor, you can see the spring-loaded ball, which acts on the
pilot pin. The cutter and pin are mounted into the tool holder in the 2nd
photo. Coolant can be injected into the tool holder thru an optional collar,
which adds a bit to the cost. Since I am not doing production work, I
will manually apply lubricant/coolant. I bought my first bit (.750 diam,
1" long) for $18 new (eBay).

 

[dfkrug]

All set up in my DP. The 3/4" Jacobs chuck is replaced by the arbor
with my annular cutter bit. The DP has a wet table and coolant
delivery system....I first tried some fluid from Grizzly.

 

[dfkrug]

Now I am ready to drill. This is a piece of 1/2" A36 steel for a backhoe
subframe I am making. I ground off the mill scale so my mark is easier to
see and the cutter does not have to go thru the abrasive scale. You
can see the dimple that the pilot pin will hit. The nearby 1/2" holes were
drilled with a cobalt 1/2" twist bit....good enough, but the annular cutter
hole is much cleaner, and requires NO DEBURRING.

In the 2nd photo, I am drilling. The cuttings interfered with my coolant
nozzle, so I reverted to an oil can for coolant.

In the third photo, I backed off and removed the cuttings. You can see
the plug that will result when I am thru. There is less down force needed, vs
twist drills, and the 180RPM speed works much better, too.

That hole is CLEAN (last photo).

Since I drilled the hole, I bought a set of 5 RotoBrute cutters for $109,
sold on eBay, but picked up at a local tool store.

 

[mbohuntr]

I've never the term "Annular cutter", We called them "Slugger bits"..

 

[MikeD74T]

I've never the term "Annular cutter", We called them "Slugger bits"..

Jancy Slugger is a brand name of magdrill designed specifically to use annular cutters thus bits for a Slugger become "slugger bits". Other brands are Hougen & Fein. Annular cutters and adapters are readily available on EBAY. If you wait long enough you can also find cheap magdrills, the best thing ever invented for making holes in metal, 'cept plazma of course. I got a nice B&D with a 3/4 chuck for $125. MikeD74T

 

[Cami]

Annular cutters are wonderful and so are mag-drills. I used them in structural steel fabrication.

An aside regarding mag drills: You need relatively thick steel for the electromagnet to grip well. I found that for anything under about 1/2" I needed to either be gentle on the feed or put a backer plate on the other side of the work for the magnet to attract. Also, since it's an electromagnet, if you're drilling on vertical surfaces then make sure to tie the drill to something in case you loose power.

 

[TDVT]

Thanks for posting this. I have never heard of annular cutters but once I saw the picture it made sense that there IS such a thing. I have had OK success with hole saws but will start a cutter collection as needs dictate. Looks like a great way to go.