School me on annular cutters for milling machine

[Brian Rupnow]

I have just purchased three sizes of annular cutters for my manual milling machine. They have 3/4" Weldon shanks.  I bought 1" diameter, 15/16" diameter, and 7/8" diameter. I also bought three R8 collets with 3/4" capacity to make dedicated holders for the three annular cutters. Here is what I know---they require much less torque to drive them than a drill of the same diameter. they should be ran at a fairly low rpm. They require lots of lubrication (squirt on cutting oil) while working. What I don't know is this---Do they require a center "pin" to extend out past the cutting edge to pick up a center punch mark in the piece being cut. Do I have to buy appropriate center pins from a manufacturer, or can I make my own. If I have to make my own, there is a great YouTube video on how to make your own with a compression spring to automatically eject the center plug that is left inside the annular cutter. I have never used annular cutters before, so any help is appreciated.---Brian

[Jasonb]

You could have done the same thing buy just working up through your drill sizes 1/8" at a time rather than going straight in with a 1" drill and stripping your gears.

I assume these are "Rotabroach" type cutters. Not used them myself but they don't need a guide pin or pilot

[BillTodd]

I use a number of sizes upto 40mm in my small Bridgeport clone knee mill.  I hold them in  a 3/4" or19mm collet (I have a number of drills, taps and end mills fitted into 3/4" holders so I can swap tools without swapping collets.)

For most flat stock I engage backgear and feed by hand . I don't usually need a centre pin, I just go slow until it has found its centre.

If sharp they cut quick, cleanly and with little strain on the machine.

[Jo]

For Jason: An annular cutter is like a woodworker's hole saw but its for cutting metal and has a wider set of teeth round the rim, which cut on the inside, outside and the face.

As Bill says a nice sharp one goes in cleanly, one with a tooth broken off or a blunt one is likely to wobble and that's when a centre pin might be needed.

Jo

[crueby]

When is an annular cutter better to use than a boring head? Is it mainly a time saver?

[Brian Rupnow]

Jason--that is the way I drilled holes previously---start with 1/4, then 1/2, then 5/8 and worked my way up incrementally to 1". Chris--an annular cutter is much faster than a boring head because with a boring head you do have to work up incrementally until you reach the finished size. An annular cutter doesn't have to cut all of the material inside the cutting teeth--it just comes out as a round slug after the fact.--But--You can't use an annular cutter in a blind hole. It has to go all the way thru the material.

[Jasonb]

Thanks Jo I do know what they are but they don't tend to go by that name over here, More usual to call them Rotabroach cutters as they are what are used in Mag Drills.

Brian you are actually going to put more load on the lathe than by drilling in 1/8" increments as the cutters have about an 1/8" kerf so it won't save your gears but may save a bit of time. Also our variable speed machines don't have a low down back gear like Todds machine just the high/low ratio and vari speed.

[Jo]

Personally in all the years of owning a workshop the number of times I have needed to cut that sort of hole I couldn't justify the price to buy those. I have made a number of smaller hollow cutters out of silver steel for various purposes which are so quick to make 

Jo

[Roger B]

Good quality hole saws work on aluminium and cast iron. I haven't needed to try then on steel yet.

[Vixen]

Some say these hollow cutter, hole saws, can be useful for coring out a bar of cast iron when making piston rings or large cylinders. The central core can then be used to make something smaller.
Never done it that way yet
Mike

[simplyloco]

I bought some to drill big holes when I was fitting out my old 42' Dutch steel boat, the hull was 6mm thick. I borrowed a magnetic base drill to do the job, which was made remarkably easy with the right tools!
I still have them but they are now like the vacuum cleaner: gathering dust...

[Brian Rupnow]

Jason--they are not for my lathe. They are for my milling machine.

[bobh]

The pin is handy for picking up a center mark but it's real purpose is to eject the center slug after cutting the hole. A proper holder has a spring in it to kick out the slug when retracted. I know you can't order from McMaster Carr up north but this is the easiest way to show you the available commercial adaptors. https://www.mcmaster.com/arbors/for-holding~annular-cutters/ . BTW you'll love using them. Bob.

[Jasonb]

Jason--they are not for my lathe. They are for my milling machine.

Typo, it's your mill plastic gears I was talking about, you don't have plastic ones in your lathe

[Brian Rupnow]

So, after a bit of confusion (on my part), the wrong R8 collets have been returned and the correct R8 collet to hold these 3/4" Weldon shank annular cutters has been received, mounted in my mill, and a hole cut thru 1" aluminum plate. The "core" that is cut from the plate is setting on top of the plate. The hole was cut in "Low range" at 300 rpm. with lots of squirt on cutting oil. I did get the "birds-nest" of aluminum swarf which has been cleared away to take this picture. They make a beautiful smooth cut, and the milling machine doesn't sound like it is working very hard to make the hole. I am very satisfied.  The annular cutters cost about $30 each. I may buy a couple more different sizes---don't know yet.