Feed rate question

[studysession]

I am cnc milling for the first time. How do I determine the feed rate to use? I am making a motor plate for a radio control car out of aluminum. I have no idea of the grade of ali it is.

At work they were throwing away some scrap so I asked for it and they gave it to me. It is used for shelves in computer rack cabinets. Some is 2mm thick and some is 3mm thick. I have the CNC software to do 0.15 deep cuts and keep going around cutting 0.15 with each pass until it cuts through the entire plate.

Just want to make it go faster but not sure if that is a good idea. Right now I have the feed rate set at 7.

Thanks - Keith H

[HuFlungDung]

Keith,
What size and type of cutter? What kind of machine? How many horsepower is the spindle? What is the spindle's top speed? How much torque in your steppers/servos? How good is the clamping? Do you have coolant of any sort?

[studysession]

WOW!! Loads of questions but only know the answer to just a few.

Coolant - I brush on cutting oil with a paint brush
Size of cutter is 3mm - 4 fluke (Hope that is correct term)
RPM's/Spindle top speed is 2,000rpm's.
Clamping is most excelent and strong
Brand of mill: X1 Sieg I bought from simplycnc.com
Picture of mill: http://studysession.com/h7/WorkBench.JPG

How do I tell about the stepper motors? All I know it says the brand is: Astrosyn and the model is: L705

Thanks!

[Al_The_Man]

This freebee has worked for me. http://mrainey.freeservers.com/custom.html
Al

[caitolly]

A simple rule of thumb for the shop floor.
RPM x #of flutes x chip per tooth = IPM (inch per minute)
ex: 2000 x 2 x .0015 = 6ipm
It's not all science, it's art
caitolly

P.S. get yourself a copy of the Machinists Handbook, theres more info in there than you'll ever use!

[studysession]

Cool thanks! Now what is chip per tooth?

[caitolly]

Chip per tooth is the amount of material removed per flute (cutting edge) during one revolution of the tool.
another rule is to remove as much per tooth as possible, of course there are many variables to this, size of the tool, material, depth of cut, etc.
The smaller the tool, the lighter the cut.
In some materials, like stainless, especially the 300 series, if you take too light of a cut you actually work harden the surface and eventually dull your tool in short order. You have to take a deep enough bite to break thru and under this work hardened surface to be succesfull.
If your limited by your machine's rpm and the flutes on your tool, the only variable is your feedrate. A 4 flute tool may be stronger, but has less clearance for the chips to eject, and will tend to clog up quickly, you may want to try a 2 flute.
Also, chances are the material you are using is probably pretty gummy?
If thats the case a heavy cut, (.002/.003), a good coolant flow should do the trick. also keep in mind that a "heavy" cut will result in some tool deflection, so a light finish pass will usually be needed if tolerence and appearance are critical.
And of course, you can crank up your feed untill your tool snaps, back off your feed some and try again.
"The more mistakes I make, the smarter I get"......... argument for another day.
hope this helps