[VTBromley]

Hey all,

I'm working on cutting some mold surfaces and the way I'm doing it currently is I rough it out leaving 0.03" on all surfaces with a square end mill. My depth of cut is also 0.03" so it creates a stepped surface. Then I come back with a ball end mill and run it with whatever stepover creates 0.0001" scallop height as calculated by mastercam. In short this is an extremely small stepover, but it produces the surface roughness that is required. However, visually there are little marred spots on the surface from what looks to be chip rubbing. I'm concerned with chip thinning at such a small radial engagement. Is there any good way to overcome this? Could it be a feeds/speeds problem?

I have a 4 flute 1/4" ball carbide running at 80 ipm and 6100 RPM
I also have a 2 flue 1/2" ball carbide running at 60 ipm and 3000 RPM

Thanks!

[Charlie Gary]

Are you machining aluminum, steel, silly putty? Do you have chips piling up in places? What kind of condition is your coolant in? What kind of coolant are you using? Does your toolpath go back and forth, or is it always a climb cut?

[VTBromley]

I'm machining 6061-T6.

Chips should not be piling up. I'm machining in a Haas VF-3 with flood coolant, three nozzles all pointed at the cutting surface.

Condition is relatively new, less than a month old. Not sure of the brand though...

It is always a climb cut.

[mc_n_g]

Others may disagree here but:
I would check the end of that carbide ballmill with a 10x-30x lens and see what the flutes look like that are doing the cutting.
I am guessing here that you may have some smear because the cutting edge is built up or slightly rounded from rubbing.
You might want to try a HSS ballmill to see if the problem still appears. If the HSS flutes get rubbed down you are moving too slow.
If it does you are probably smearing the extremely small step over rather than cutting it.
Your 6061 could be 'gooey' and giving you bad results also.
I am guessing your chipload it not high enough for the ballmill.
Dapra has a reference for depth of cut vs speed factor.
Just a quick look listed your effective depth of cut for 0.25 = about 0.16 and they listed a feed increase of at around 1.7x (this is for insert cutter but it gives you an idea something is off in your run model)