Ball End Mills - What's the secret?

Red96

Red96

H-M Supporter - Gold Member
H-M Supporter Gold Member
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So, I understand how the surface speed of a ball mill approaches zero near the centerline, and how that hinders proper cutting action - much like facing. CNC units seem to use ball end mills all the time - I assume that is part of the reason for the insane spindle speeds. But for the rest of us mere mortals, how in the heck does one get any kind of decent surface finish with a ball mill? I have an application coming up, in A36 steel where I need to 'route' out a semi-circular channel in 5 places. 8mm carbide ball mill, 4mm total depth, roughly 0.200" in length.

So, what's the process to get a decent surface finish in this cut? (And no, I don't have sufficient material to drill & ream, then mill off half of the hole, unfortunately)

Screenshot 2024-11-05 131335.png
 
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I suspect a lot of the CNC use involves "kellering" to create complex geometries, and they probably are careful to use the outer portions of the ball more than the tip. I think what @mmcmdl is suggesting is that you turn your part on its side, and plunge or push in to cut the slot with the side of a regular endmill. That's what I'd do.

GsT
 
Trying to learn something about ball end mills and how to use them.

There are 5 of these shoulders that need to be cut in-line, spaced about 1/2" apart on a single part, so I'd need a very long end mill, which would likely deflect some, which does matter in this case.

Though I appreciate suggestions for alternate ways to accomplish the operation, it's not the intent of this thread. looking to understand how to use a ball mill without galling the heck out of the bottom of the cut.
 
I've never had a problem with galling... I run ball end mills just like I would run square end mills.

I've never given it any thought...

-Bear
 
Red96 said:
Trying to learn something about ball end mills and how to use them.

There are 5 of these shoulders that need to be cut in-line, spaced about 1/2" apart on a single part, so I'd need a very long end mill, which would likely deflect some, which does matter in this case.

Though I appreciate suggestions for alternate ways to accomplish the operation, it's not the intent of this thread. looking to understand how to use a ball mill without galling the heck out of the bottom of the cut.
Click to expand...

I've milled miles of slot)s with ball mills in different materials.

Plenty of cutting fluid, proper speed (you may have to mill a test piece to see the differences in speeds), cleanup passes and lowered expectations.

If you need it to look "nice" All of the above plus sandpaper.
 
Exactly ! :encourage:
 
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