View Full Version : "Corn-cob" end milling cutters

06-27-2007, 02:24 AM

06-27-2007, 03:30 AM
I use the solid carbide 1/2" corn cobs (mostly 3 flute) for almost all my cutting except for finish cutting when side milling. I can get them for something like $6-$8 each from a guy that pulls the time-outs from a CNC shop. They calculate a max runtime such that they know they are almost never going to fail or dull (and so scrap multi-thousand dollar parts - aerospace) before they are pulled still fully functional and stacked in a bin. The big corn cobs apparently never get resharpened, but the standards often get end sharpened till they reach some minimum, but they are all carbide and I've accumulated a pretty good selection. Anyway, I use those corn cob carbides for all my roughing and save the nice sharp HSS 2 and 4 flutes for only finish work when side milling. Works great and saves a pile on cutters...

06-27-2007, 03:39 AM

Peter S
06-27-2007, 04:44 AM
Sometimes called Roughing, Rippa or Ripping end mills, very good on light mills like a Bridgeport when you have lots of material to remove. I have only used them in sizes around say 20mm diameter, not the small diameters. Normally you can take the diameter in depth of cut on a Bridgeport, in mild steel anyway.
I guess the main reason they may not be that commonly used is a good brand is expensive, possibly several times the price of a similar sized end mill?

06-27-2007, 06:15 AM

Virgil Johnson
06-27-2007, 06:35 AM
FYI. Roughing mills have a tendency to slip (pull outward) when used in a R8 collet and a heavy cut is taken. By this I don't mean the cutter comes flying out only that it will move slightly over the course of the cut cutting deeper as you progress. I'm sure more than one part has been scrapped by this phenomenon.

06-27-2007, 06:56 AM

J Tiers
06-27-2007, 09:18 AM
They really do work.......

Not so long ago I was making a new jaw for a steady, and decided to try the new rougher. Drilled a hole in the stock, and went down the 12mm thick stock with a 10mm roughing end mill in one pass to make the adjusting slot for the jaw.

The mill has a 1/4 HP motor...... I could barely crank the thing fast enough to keep it cutting, it was done so fast I was shocked.

Nice thing is, the chips are easy to brush up. Not those nasty long spears, but chips that act more like sand. That's good, because if you are doing much stock removal you'll generate lots of chips with the rougher, in a hurry.

I tend to use the roughers first, now. If the surface is non-critical, I'll leave it as-finished, the parallel grooves look a bit like a shaper or planer cut, not ugly enough to have to finish unless required.

06-27-2007, 10:13 AM
Roughers work great, I would use them at work to rough out large keyways like a .875 or a 1" keyway. I would use a 3/4" rougher to hog out the bulk of the metal then finish up with a normal endmill.

06-27-2007, 11:26 AM
Did you guys know you can make these?

Take a two flute end mill, using a slitting wheel in a bench grinder carefully put notches down one flute. You have to be careful that the notch is wider opposite the cutting edge for relief. Repeat the notching on the opposite flute making sure the second set of notches are staggered from the first.

The same can be done with a four flute cutter, just needs a bit more care to stagger the notches.

Of course the homemade ones aren't quite as good as the factory type. Still good cutters though. The homemade are a good way to salvage a dull end mill.

Another variation of the homemade is to notch only only flute, leaving the other un-notched. Provided your holders run true this gives the best of both worlds, a rougher and finisher in one.

The corncob style pictured leave a serrated finish on the work. There are other varieties of factory made that have a more square profile of the individual teeth so they don't leave the serrations on the work.

I use 3/8" corncobs to profile parts out of 3/8" thick 316 SS plate. We can go full depth in one pass.

Another interesting application is to have the factory made rougher's re-fluted for extra chip clearance to mill 7075 aluminum. With flood coolant in that material there seems to be no limit to the depth of cut.

06-27-2007, 11:36 AM
Roughing endmills are great. The general recommendation is to increase the Feed Per Tooth by 50%-100% over a normal (smooth flute) endmill.
In some of the Speeds and Feeds tables you'll see a second column for roughers with that FPT modifier applied.

Because of the serrated flutes, I don't think they can be resharpened without special equipment.

06-27-2007, 11:51 AM
They are not somtimes called roughing end mills, they are always called roughing end mills. If you try to find them in a tool catalog and ask for corn cob end mills you will never find them.

They may be as much as twice the price of standard end mills. They are for fast removal of metal and leave a rough surface and, as stated, they do suck out of a collet and destroy your work and maybe your vise or table so be careful.

06-27-2007, 12:29 PM

Because of the serrated flutes, I don't think they can be resharpened without special equipment.

Yes, to properly sharpen them they have to be re-fluted. That does require a bit more equipment than a simple OD grind.

Most production sharpening now seems to be done on CNC grinding machines so the re-fluting is not a big deal.

However, it would be a big deal if an individual took a single roughing cutter to a grind shop and asked for a sharpening.

06-27-2007, 12:31 PM

and, as stated, they do suck out of a collet and destroy your work and maybe your vise or table so be careful.

This is a good reason to not use a collet to hold an end mill, rougher or not.

06-27-2007, 01:10 PM
Yes, if I intend to take heavy cuts I would try to use a holder rather than collet. However I have rarely had them come out with less than half the diameter cuts.

DR, the sharpening is no problem for the manual grinding shops in Lou Ky. and they are not expensive to resharpen. I have had several resharpened.

edit: I use cobalt roughing end mills. I very seldom use carbide end mills. They are not user friendly on manual mills and to expensive.

06-27-2007, 02:24 PM
I've used roughing end mills on my manual machine and they have worked well, but lots of users of CNC machines have moved from them to variable helix carbide endmills like the Hanita Varimill and the SGS Z carb.

I've started using these on my CNC knee mill and they are amazing, I don't grit my teeth when I have to cut steel any more. Cutting mild steel with a varimill is as smooth as cutting 6061 aluminum. You can also both rough and finish with the same tool and the finish isn't too bad.

On a manual machine using carbide endmills is a little touchy since feeding them too slow can ruin them, but they can work great in a powerfeed situation on a manual, just be sure to clear chips with an air blast to avoid chip recutting.

Paul T.

06-27-2007, 02:28 PM
Indeed, roughers are awesome to do the heavy lifting when you've got a light machine. Shovel the bulk out with a rougher and finish with your sharpest regular endmill.

I always use an endmill holder (actually, I keep a 1/2" 3 flute rougher in one always) to preclude the dreaded downward creep.

I picked up several roughing end mills at cabin fever last year including a 6 flute solid carbide one, new in a tube for $5. Must have cost $50 new, and it makes metal disappear.

06-27-2007, 08:43 PM
I use roughers all the time at work and have yet to have one suck out of a collet, using a good old bridgeport and some decent quality collets. I dont over tighter the draw bar either just a normal tightening with my wrench. I run them full depth of the diameter and side cut 1/2 the diameter, climb cut in X with the powerfeed and conventional in the Y where I dont have a power feed, they really dont like conventional cutting as much though. Coolant or air is necessary IMHO