Best surface finish parameters for ballnose bits

[jeffescott]

I need a long reach bit.  35 mm from holder to bit tip.   The hole is 5.5 mm id. 

I would prefer a ballnose bit to provide best finish. On the counter sink and chamfers.  

Should i use a 1/8 bit or a 3/16 bit

I generally i think both can provide a similar finish.  But the 3/16 would need a smaller step over. Step down with a stiffer shaft

Recomended parameters would be of great help as well

[brad_francola]

You may want to look at this:
https://www.harveyperformance.com/machining-advisor-pro

[CNC_Lee]

@jeffescott 

I would go with the 3/16 ball endmill as a larger radii tool will always yield a better finish with a larger stepover. As far as speed and feed starting parameters, I have had great luck with the HSMAdvisor and FSWizard products for finding a good starting point and getting off in the right direction. You can also utilize a cusp height calculator like this:  http://cncprogramming.martinchick.com/ball_mill_finish.html to determine the estimated required stepover to achieve the desired surface finish.

[seth.madore]

Here's another vote for the 3/16" tool, I always try to go with the biggest tool that is practical. That said, it would also be helpful to understand the application, so if you could share a screenshot or the actual file, you may find that our answer changes 🙂