# Thread: Question, is there a formula for this?

1. ## Question, is there a formula for this?

I have been using my newest router often, and find it difficult to predict finish quality in metals. Cutting wood is not as big a problem! The finish is consistent, as there is no end play or backlash, so it needs to be controlled with software!

Is there a formula for calculating the "Step-Over Rate" when using a ball end mill, to get a specific surface finish? (eg: 128, 64 or 32 etc.)
Or must I continue to guess?

With a lifetime of experience on manual machines, I have never had to worry about this! All I did was stone a fine radius on the cutting edge, and I could get exactly what I want!

WidgitMaster

2. I'll look around. In the meantime, try finding something on "sturtz milling".

BTW, wouldn't the feed per rev. of a given lathe tool nose radius help???????

I think Sandvik's tech section has those formulas.

Dick Z

3. I tried to download the Sandvik milling tech stuff. It wouldn't download to my computer for some reason. I seem to remember the info you're looking for being there in the past.

This getting old s*** sucks.LOL

Dick Z

4. Originally Posted by RICHARD ZASTROW
I tried to download the Sandvik milling tech stuff. It wouldn't download to my computer for some reason. I seem to remember the info you're looking for being there in the past.

This getting old s*** sucks.LOL

Dick Z
Thanks !
Widgit

5. Widgit, long time no talk!

I was just thinking of you in conjunction with Turner's Cubes of all things.

Meanwhile, there is a formula as you knew there would be. My G-Wizard Calculator has it built in:

Enter your cutter's parameters, the cut parameters, and a desired scallop height and you get back the RA, RMS Surface finish and the stepover required to achieve that finish.

One of the sneaky aspects of a ballnose is the effective cutter diameter is a function of your depth of cut if you are less than half the ball diameter deep, which is typically where you'll be. Complicates your speeds and feeds a bit, but G-Wiz has all that built in.

The Beta Test is still free to sign up for, and Beta Testers will get a special price when I start charging for G-Wizard later this year:

http://www.cnccookbook.com/CCGWizard.html

RE "Sturtz" milling is discussed a bit on my milling surface finish page here:

http://www.cnccookbook.com/MTMillSurfaceFinish.htm

You find more hits on Google if you spell it "Sturz", though I see it both ways. Clever trick and explains why 4 and 5 axis machines can achieve a better finish while profiling.

Cheers,

BW

6. emc linuxcnc has lots of g-code generators for milling
plain g-code output on python files this is opensource and you can get it within seconds to your need

if you dont use emc axis right it out to a file
for line in self.gcode:
file_out.write(line)

http://wiki.linuxcnc.org/cgi-bin/emc...ode_Generators