Who Makes the Best Corner Rounders?

boosted · Nov 28, 2020

Dumb question. Who makes the best corner rounders?

We do mostly low quantity parts, and only break out the corner rounders once or twice a year. I'm going to setup a few permanently and add them to the digital tool database, so it's less painfull when we do put them in action.

Who's tools should I be purchasing?

Job Shopper TN · Nov 28, 2020

Hard to beat Maritool for their price vs quality. Harvey makes some great corner round mills bit they’re about twice the price. I’d definitely go for Mari if you just want some general tools to bust out for odd jobs.

kazlx · Nov 28, 2020

I use Mari all the time for corner rounders and they work great.

mmurray70 · Nov 28, 2020

Anybody else surprised by the cost of HSS radius cutters? Why are these so expensive? I dont use them often but needed a variety on hand for the occasional job that needs a rad. Hate to say this, but I bought a bunch from aliexpress and they seem to work just fine.

Only compliaint is that they dont seem to go perfectly tangent on top, leave a tiny bit of an angle. Not sure if this is a quality issue or by design to be more forgiving with gouging on top. Prices are crazy. Like $6 for a 3mm rad vs $65 for a 1/8" rad cutter from mcmaster. Nice to have a few of these on hand for job shop work anyway. Still probably better off buying quality tooling for longer runs, or if you need absolutely perfect rad.

Finegrain · Nov 28, 2020

mmurray70 said:
Only compliaint is that they dont seem to go perfectly tangent on top, leave a tiny bit of an angle. Not sure if this is a quality issue or by design to be more forgiving with gouging on top.

I use Harvey "flared" corner rounders that are purposely done that way. It gives you a few thousandths wiggle room in Z before the corner digs in and you get a prominent line. Without the flare you have zero room between just right and ugly line.

Regards.

Mike

kazlx · Nov 28, 2020

And although I love McMaster, they are probably the worst place to buy tooling unless you have to have it ASAP.

DavidScott · Nov 28, 2020

Another vote for the flared ones, 5 degrees per edge of flare. Otherwise I use MariTools too. I can't say there is any difference in the quality of cut whether Mari or Harvey, just that Harvey has them in a flared version.

13engines · Nov 28, 2020

Finegrain said:
I use Harvey "flared" corner rounders that are purposely done that way. It gives you a few thousandths wiggle room in Z before the corner digs in and you get a prominent line. Without the flare you have zero room between just right and ugly line.

Regards.

Mike

Here's a 2nd on the Harvey 5 degree flares for the very same reason. Programming is easy as they're always radius plus 5 thou on the DOC. And the radius and tip size combinations are endless.

BugRobotics · Nov 28, 2020

Another vote for Harvey

Rick Finsta · Nov 28, 2020

I have used Maritool but prefer a Harvey or Sandvik with the 5deg angle.

Delw · Nov 29, 2020

I been using solid carbide internal tool company for years they have a small angle/flare on them as well. Mc mastercarr sells there stuff also.

I had some 321 stainless that need a rad edge with a 32 finish. tried there coated ones bought 4 only use one side on a few hundred parts.

implmex · Nov 29, 2020

Hi Boosted:
I suppose just surface milling them with a bullnose cutter is not an option?
I HATE corner rounding cutters except in small sizes and for jobs I must make time on.
Surface milling them makes them so much nicer and is not nearly as hard on the machine, but it does take a fair bit longer.
I haven't run a corner rounding cutter in years, except on the manual mill when I didn't want the job up on a CNC.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

boosted · Nov 29, 2020

implmex said:
Hi Boosted:
I suppose just surface milling them with a bullnose cutter is not an option?
I HATE corner rounding cutters except in small sizes and for jobs I must make time on.

I very much agree about corner rounders being a big PITA. We are leaving way too much time on the table by surfacing everything though. It's totally fine for one-offs, but has turned into a bad habit that I see lingering for a lot of 20 or 30 part runs. I feel like designating a couple of tools and making it as painless as possible will encourage the guys to start using them more frequently.

Garwood · Nov 29, 2020

implmex said:
Hi Boosted:
I suppose just surface milling them with a bullnose cutter is not an option?
I HATE corner rounding cutters except in small sizes and for jobs I must make time on.
Surface milling them makes them so much nicer and is not nearly as hard on the machine, but it does take a fair bit longer.
I haven't run a corner rounding cutter in years, except on the manual mill when I didn't want the job up on a CNC.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Why does it take so long?

I do several families of parts with 3/8" and 1/2" radius outside corners in 6061 and buzz right through most toolpaths in one pass and done. Some inside corners will grab a bit so I'll take a finish pass. This is with carbide in a 50 taper machine.

I've had good luck buying new solid carbide relieved outside corner mills on Ebay for 50% or less of new. I don't like HSS. Never holds up, deflects, etc.

implmex · Nov 29, 2020

Hi Garwood:
Somewhere we must have crossed our wires in the conversation:
When I say "surface milling" I'm talking about using a ball cutter or a bullnose cutter and following the radiused surface in small increments taking many passes.
It's slow because of the many passes.

The time gain, of course, is that with a corner rounding cutter, the feature is cut in one pass.
Since it's a form cutter, the loads are high and the cutter must be positioned almost perfectly relative to the workpiece, otherwise, as you are aware of I'm sure, the job looks like a pig's breakfast; often with lines at both extreme ends of the radii, and a lumpy, torn out surface especially with HSS cutters in steel.
As I'm sure you're also well aware, a form cutter also cannot go up or down in Z worth a shit (especially in internal corners), so it's useful for 2D corner rounding but not for 3D corner rounding.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Mud · Nov 29, 2020

There is also Superbee for inserted corner rounders. I use them and like them.

Rick Finsta · Nov 30, 2020

implmex pretty much every part I make has a 0.125" outside corner radius on it. I would spend hours a week 3D contouring those. For one offs or where I've got a compound radius intersection I always contour. I think each has its place.

implmex · Dec 1, 2020

Hi Rick:
I don't disagree with you at all.
When you need to make time on a 2D contour there's no substitute for a formcutter to put the feature on the part, regardless whether it's a chamfer or a radius or some other shape.

But I still hate them for the screwing around that's often needed to get them just right and the racket the bigger cutters often make and the crappy finish they often leave, and since I don't do production, I avoid them when I can.
In my world, an extra ten minutes to surface mill all the rads is nothing when there's already a gazillion hours in the part.
Obviously, it isn't like that in many other people's worlds, so whatever works is as right as it needs to be.

So horses for courses, and yes, I fully agree that each has its place.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Mtndew · Dec 1, 2020

boosted said:
Who makes the best corner rounders?

There is no "best".

mutiny · Dec 1, 2020

Frank Mari has been extremely receptive to changes/additions to his tooling line in the past. I wouldn't be surprised if we see some corner rounders with a 5deg flare show up on MariTool soon...

Who Makes the Best Corner Rounders?

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