Ball End mill speeds

R

rmw

Cast Iron

Joined

May 3, 2007

Location

Northeast Atlanta, GA

• Dec 29, 2009

• #1

How fast should one run a 1/2" ball endmill? Since the whole edge is doing the cutting from it's center to the outer diameter, it seems you're either too fast or too slow. The material is 1/2" thick CRS, and I need to dish out the edge full depth (1/4").
Thanks, Greg

 

5

5 axis Fidia guy

Stainless

Joined

Aug 17, 2006

Location

Wisconsin

• Dec 29, 2009

• #2

Ideally you should figure out the sfpm at the WORKING dia, in your case it is going to be a comprimise. I would personally shoot for the higher end in mild steel. In any case, as you said you will be either too fast or too slow.

 

R

rmw

Cast Iron

Joined

May 3, 2007

Location

Northeast Atlanta, GA

• Dec 29, 2009

• #3

That's what I thought. I guess if the higher speed is used and the feed is kept slow, the center will still be removing chips at an acceptable if compromised rate.
Thanks, Greg

 

W

willbird

Banned

Joined

Jul 19, 2005

Location

North(very) West(very) Ohio...near exit 13 on OH t

• Dec 29, 2009

• #4

For the sake of simplicity I always used the outer dia for rpm calculations, if you end up sitting there watching the machine cut then you have time to measure and calculate the actual cutting dia :-). At the very center it is running 0 rpm anyway, and we cannot ever get over that hurdle ;-)

Bill

 

6

6jaw

Aluminum

Joined

Feb 13, 2006

Location

Fitzwilliam, NH

• Dec 29, 2009

• #5

rmw said:

How fast should one run a 1/2" ball endmill? Since the whole edge is doing the cutting from it's center to the outer diameter, it seems you're either too fast or too slow. The material is 1/2" thick CRS, and I need to dish out the edge full depth (1/4").
Thanks, Greg

Click to expand...

I took a series of machining classes at a community college in CA years ago. The simple guidance given for cutting steel with HSS was 100sfm at the largest diameter. Approximating pi allows the simple formula of 4 x cutting speed (sfm) / diameter (inches).

For form cutters like your ball endmill, the recommendation was to cut that rpm in half. I think part of that guidance was to skew towards longer cutter life for a more expensive cutter.

John

 

R

rmw

Cast Iron

Joined

May 3, 2007

Location

Northeast Atlanta, GA

• Dec 29, 2009

• #6

Thanks guys. Sounds like everybody thinks about the same thing. Outer diameter is the reference.
Greg

 

kapps

Cast Iron

Joined

Sep 17, 2007

Location

Orlando, FL

• Dec 29, 2009

• #7

I've found a lot of good info on both radial and axial chip thinning here... http://pdf.directindustry.com/pdf/ingersoll-cutting-tools/milling-catalog/Show/17869-11079-_368.html . They give a nice list for ball endmills based on cutter diameter and doc.

 

M

Mike C.

Diamond

Joined

Nov 25, 2004

Location

Birmingham, AL

• Dec 29, 2009

• #8

Important consideration for a ball end mill is feed rate. Along with that decreased surface speed toward the center goes increased chip load. Start your feed at half what you would use for a similar straight cutter in the same material, at the same rpm.

 

lane

Cast Iron

Joined

Oct 2, 2005

Location

Shreveport La.

• Dec 29, 2009

• #9

I like to rough out under size first . Say a 3/8 ball end mill then go with the 1/2 get better finish.

 

R

Rstewart

Stainless

Joined

Jun 14, 2006

Location

Huntsville Alabama

• Dec 29, 2009

• #10

There's alotta ways you can approach that situation. Since most likely your doin this on a manual machine, run the RPMs up till the chips start to discolor and back it off some.

I've also had trouble figuring out an "optimal" SPM on ballnose E.M.s

Luckily with CAD/CAM and on a CNC I can rough out evrything with a flat E.M. then go back and "surface" the rest with a ballnose.

Just remember there's basically Zero surface speed at the tip, and the full/Dia. calculated SPM when at full depth. So.... at half the depth/diameter cut you can ALMOST double the RPM's.

Just Play with it a little and you'll be fine