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Help! => Machines, Tools and Fixtures => Topic started by: Brian Rupnow on January 09, 2022, 08:22:46 PM

Title: School me on annular cutters for milling machine
Post by: Brian Rupnow on January 09, 2022, 08:22:46 PM
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
Title: Re: School me on annular cutters for milling machine
Post by: Jasonb on January 09, 2022, 08:53:38 PM
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
Title: Re: School me on annular cutters for milling machine
Post by: BillTodd on January 09, 2022, 09:13:13 PM
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.

Title: Re: School me on annular cutters for milling machine
Post by: Jo on January 09, 2022, 09:22:49 PM
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
Title: Re: School me on annular cutters for milling machine
Post by: crueby on January 09, 2022, 09:51:08 PM
When is an annular cutter better to use than a boring head? Is it mainly a time saver?
Title: Re: School me on annular cutters for milling machine
Post by: Brian Rupnow on January 09, 2022, 10:31:00 PM
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.
Title: Re: School me on annular cutters for milling machine
Post by: Jasonb on January 10, 2022, 07:08:08 AM
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.
Title: Re: School me on annular cutters for milling machine
Post by: Jo on January 10, 2022, 07:31:32 AM
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
Title: Re: School me on annular cutters for milling machine
Post by: Roger B on January 10, 2022, 10:00:06 AM
Good quality hole saws work on aluminium and cast iron. I haven't needed to try then on steel yet.
Title: Re: School me on annular cutters for milling machine
Post by: Vixen on January 10, 2022, 10:20:17 AM
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
Title: Re: School me on annular cutters for milling machine
Post by: simplyloco on January 10, 2022, 10:47:41 AM
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...
Title: Re: School me on annular cutters for milling machine
Post by: Brian Rupnow on January 10, 2022, 01:33:43 PM
Jason--they are not for my lathe. They are for my milling machine.
Title: Re: School me on annular cutters for milling machine
Post by: bobh on January 10, 2022, 03:03:32 PM
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.
Title: Re: School me on annular cutters for milling machine
Post by: Jasonb on January 10, 2022, 03:07:20 PM
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
Title: Re: School me on annular cutters for milling machine
Post by: Brian Rupnow on January 13, 2022, 09:05:26 PM
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.

(https://imagizer.imageshack.com/img924/3878/0fqnub.jpg)
Title: Re: School me on annular cutters for milling machine
Post by: Jasonb on January 14, 2022, 07:07:40 AM
For those not looking at other forums it may be worth pointing out that the usual R8 and MT sidelock holders have the grub screw a lot further from the end so it does not easily sit on the cutters shank, Also the proper holder has two grub screws at 90deg as many cutters have two flats unlike the single flat on a milling cutter.

You also get the ctr pin hole if you want o use that.
Title: Re: School me on annular cutters for milling machine
Post by: Brian Rupnow on January 14, 2022, 09:08:37 PM
I couldn't figure out why the correct R8 holder for these annular cutters cost $75, while a standard R8 holder for a 3/4" drill was only $31. Now that I have the parts here, I see that there is a spring and a snap ring inside the correct R8 holder that lets a centering-pin retract into the body of the holder as the annular cutter passes thru the plate you are cutting. The centering pin then becomes spring loaded and pushes the "slug" out of the annular cutter after your cut so you don't have to fish for it with a pair of pliers. You can see the end of the centering pin sticking out past the face of the cutter. You can also see a centering pin setting beside the cutter---I made that one .001" undersize, which normally wouldn't matter, but in this case the pointy end is cantilevered out so far from where it is held that with 0.001" undersize it wobbled all over the place---Not what you want for centering.
(https://imagizer.imageshack.com/img923/6897/iw5M4y.jpg)