What's the better endmill for dynamic/HSM, square or corner rad?

I've done a little bit of HSM, by no means an expert. When it comes to choosing an endmill style, what is preferred, a square tipped or corner radius tip? I've always been the guy that only cuts steel with a square tip if it's absolutely necessary. Thinking the corner rad will always hold up better and keep it's tips much longer than the square.

One of the shops I sometime sub for mainly uses square tips when they HSM. I asked them about tip wear and they looked at me funny and said they never have an issue. Is it because more of the cutter is engaged and cutting with the entire flute, not just the tips like if you were helixing down a hole or pocket?

I have gotten into the scenario where I am loaded up with square tips and if they hold up as well as the corner rads do I'll start chewing through them too.

Thanks.

If you're cutting all the way through a plate, with the tip in air, it won't matter, and the square will be cheaper. Unless you're helix boring an entry hole, in which case the corner may fail first. I get corner radius unless I absolutely need a square inside corner. Doing random short run prototype stuff, the corner always breaks down first. Common materials include 17-4 H900 and Ti6Al4V.

The square corner will always lose a life battle to a radius corner if you are cutting with it. It isn't just an old wives tale. It is a tale of heat. That sharp corner cannot get rid of heat. The heat in a corner R end mill gets spread out over the corner R and can dissipate. not so with the sharpie. You also have pretty much zero edge support at the corner.

I dunno what materials youre gonna be cutting but I try to avoid square corner end mills altogether for roughing. Get the biggest radius you can....1/2" EM with a .125 radius is a beast. In practice I really only use 1/16 radius on that tool. If I was cutting alot of hard materials then the big radius would win out for me.

I exclusively almost always rough with HSM paths and have found much better cutter life with a radius. Finish with a square on the floor and walls if needed.

Everyone's thoughts are about what I have always gone by. Stick with a rad tip as long as you can UNTIL you actually need a square tip. I HSM mostly tool steels, P20, H13, A2, S7 and D2. Some 400 series stainless also. Injection mold bases mainly so a lot of large pockets for hardened inserts. On the insert side it's mostly external HSM to get the excess stock off. No TSC or TSA, just a Vortex cold air gun running wide open.

I'll typically drill a starting hole, either blind or through depending on the pocket. Then helix the cutter in and start HSM.

Most of my cutters have a .030 rad on them. That works best for leaving a little rad in the corners where the sides meet the floor and not interfering with the inserts since they all get chamfered pretty heavy.

I'll save the square cutters for when I can stick through the material and not engage the actual tips and for when someone calls out a sharp pocket transition between the wall and floor.

I'll tack on to this question and add on which is better corner radius or corner chamfer? I know radius is much more common though mills with a corner chamfer aren't uncommon either. What would the benefits of a corner chamfer be over a radius?

CAMasochism said:

I'll tack on to this question and add on which is better corner radius or corner chamfer? I know radius is much more common though mills with a corner chamfer aren't uncommon either. What would the benefits of a corner chamfer be over a radius?

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It may be a few cents cheaper?

Radius is better. A chamfer has two 45° corners, which are better than 90° corners, but are still corners.

Tonytn36 said:

The square corner will always lose a life battle to a radius corner if you are cutting with it. It isn't just an old wives tale. It is a tale of heat. That sharp corner cannot get rid of heat. The heat in a corner R end mill gets spread out over the corner R and can dissipate. not so with the sharpie. You also have pretty much zero edge support at the corner.

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Much confused here.
In full depth HSM I would expect the opposite with the rad tipped tool getting hotter due the floor chip thickness and rubbing.
HSM is about using the side of the tool. The tip has lots of room to dissipate heat to the core.
I must be missing something major about chip formation in HSM operations.
Bob

I'll put my 2c in with the majority: The only time I use a sharp-corner end mill is if I'm doing a finish pass on something that has to have a sharp inside corner. I never rough with them at all.

PM

CarbideBob said:

Much confused here.
In full depth HSM I would expect the opposite with the rad tipped tool getting hotter due the floor chip thickness and rubbing.
HSM is about using the side of the tool. The tip has lots of room to dissipate heat to the core.
I must be missing something major about chip formation in HSM operations.
Bob

Click to expand...

I dunno Bob, that is a good thought to consider. Do you run HSM toolpaths frequently or not so much? I haven't got much hard data to support my supposition about using corner radius tools, just the experience of running them a lot. I think the heat buildup, if it is a thing, is a trade-off for longer cutter life. In theory the cutter may run hotter but youre not chipping corners, thus your tool life is longer.

Then again, heat is not much of an issue with HSM toolpaths. By nature the heat is transferred to the chip and evacuated very fast. I can run HSM tool paths for 30 minutes and my tool and workpiece is cool to the touch, even running dry. Radial chip thinning...it obviously plays a role as well. I confess I am no expert about chip thinning. So I dunno if your thoughts on heat in the cutter carries weight or not. I am sure some really smart people have done studies and have actual data on this and could explain it better than me.

CarbideBob said:

Much confused here.
In full depth HSM I would expect the opposite with the rad tipped tool getting hotter due the floor chip thickness and rubbing.
HSM is about using the side of the tool. The tip has lots of room to dissipate heat to the core.
I must be missing something major about chip formation in HSM operations.
Bob

Click to expand...

A sharp corner end mill is much more likely to chip the point off. Using a corner rad end mill it will last a LOT longer.