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

[carpenter383]

What about using a dimmer switch to slow down a DP motor? I know it's generally not a good idea to cut power to a motor, and there would be less available torque. Anyone tried this for occasional use? I have a craftsman benchtop DP and it's slowest speed is 480

 

[Brad_Blazer]

Universal motors with brushes like on an angle grinder can be controlled that way. HF sells an inexpensive "router" speed controller that works well. Drill presses typically have synchronous AC motors that cannot be speed controlled. If it runs quietly that's what it has.

3-phase AC motors can be controlled with a variable frequency drive. Small drives with single phase input can be had for about $100-300 at The best way to buy industrial controls--low prices, fast shipping and superior service.

The problem with just slowing the motor down is that you don't get more torque like you would if you "geared" it lower. Of course on a small drill press adding a bunch of torque would just twist the spindle spline drive and ruin the press.

Back to the annular cutter thing. I have a few that I grabbed out of a dumpster. They are still in pretty good shape and there was an adapter with them. It's kind of long but it has threads on the back the same as a hole saw. The sizes I have 1", 1.25", and a smaller one I can't remember what size. I haven't really used them because the adapter doesn't fit my drill presses.

I am experimenting with using my HF pipe notcher guide bolted to a short piece of 6x8x1/2" angle iron that can be clamped to a surface to act as a poor man's "mag" drill. It works good with a hole saw but this thread makes me want to try it with the annular cutters. I'm powering it with a big hand-held drill. I also acquired a chuck like comes with the big HF drill press that goes to 3/4" and I might be able to just chuck up a bare annular cutter.

 

[dfkrug]

The problem with just slowing the motor down is that you don't get more torque like you would if you "geared" it lower.

You are correct that you can not use a speed controller on these DP
motors. What you CAN do is get a washing machine motor (free!) that
has 2 speeds and adapt that. When operating a DP at lowest speed, your
torque multiplication is such that you don't need a strong motor at all. At
high speeds, you could run into the power limits of the motor, however.

There is another type of annular cutter out there, which is designed for
thin metal. I have not seen one up close, so I do not know the differences.
Anyway, you need a pilot pin or a pilot hole and guide to make these
work. Otherwise the bit just dances all over the work.

 

[Brad_Blazer]

Travers has their cutters on sale this month.
Travers Catalog - Metalworking May 2010 - page 4

Travers Catalog - Metalworking May 2010 - page 6

They also have the drill press adapter $$
10814 #2MT X 1" HOLE" W/O COOL'T INDCR HOUGEN :: "12,000 Series" Conversion Arbors For Machine Tools | Travers Tool

 

[dfkrug]

They also have the drill press adapter $$

Those look to be very good prices. I have not hear of Travers, but
I will save the link. Thx for posting.

Your 3rd link, BRAD, shows the coolant collar that goes over the arbor.
This is the option I did not buy. If someone goes out and gets this
option, I hope they report here.

 

[Brad_Blazer]

I haven't ordered from Travers but the toolroom at work uses them. Their prices and selection seem similar to Enco.

The picture shows the collar but that's the price without it. It's double that price with the coolant collar. Is there more to it than a tee with o-rings?

Also note the 2MT is only rated for 1" holes. The 3MT for the same price is rated for 2-3/8" holes.

 

[allenr]

Can these annular cutters be sharpened when neccessary?

Or don't they get blunt if you keep the cutting fluid up to them.

 

[1962]

Can these annular cutters be sharpened when neccessary?

Or don't they get blunt if you keep the cutting fluid up to them.

Yes they can be resharpened. I send my dull annular cutters to ohio tool for sharpening. Feed speeds and coolants make a big difference in how long cutters stay sharp.

 

[killdozerd11]

Great post

I have used these for years mostly on mills or mill drills and mag drills
since building safes need properly placed holes for the locking pin frames and doors

 

[dfkrug]

The picture shows the collar but that's the price without it. It's double that price with the coolant collar. Is there more to it than a tee with o-rings?

My MT-3 Arbor came from a tool vendor in the UK, for only $55. I found
much higher prices from the few places I could find this arbor at US
vendors. The coolant collar was certainly more, and seems to remain
stationary while the bit rotates.

I have heard of these being resharpened, but I have not needed it yet.
At least one web site says if you turn these too slow, that can
increase the wear. My machinist pals are skeptical of that claim. I run
slow and cool.