Speeds & Feeds

• posted on January 15, 2010, 5:30 pm
Ok, I do not get it. How the heck do you calculate how fast to cut, turn feed, etc. I've been trying tables and formulas and basically just destroying stuff before tackling each project.
I've read a dozen pages on-line and read some of the responses here in the archives and I think there is a fundamental concept or group of constants that every person who knows how to do it assumes everybody else already knows when they explain it.
How do you calculate how fast to feed for a particular end mill?
Example, (CNC MILL) Material = aluminum Mill = .0625 (2 teeth carbide / could use tin coated or hss if it would work better) Radial depth of cut = ???? Axial Depth of cut = ???? Spindle Speed = ???? Feed Rate = ????
Limitations of the mill. Max RPM = 10,000 (Five speeds. More if I do not mind hanging the pulleys part way off the shaft) Max Plunge Rate = 10 (Z) ((Axis hangs if you try to go any faster) Max Feed Rate = 20 (X,Y) (Could probably go 30 as long as load was minimal) Holding Force of Stepper Motors = 280 ozs.
The idea is to find the fastest way to cut a pocket or du carving without breaking end mills, dulling them before the job is done, or having the machine bog down against axial forces. How can I plug in data like that to figure out what is going to work best. I'm tired of ruining work pieces and breaking mills to find out.
Then how do I plug in that data to calculate the same for a smaller or larger end mill?
With coolant?
Without coolant?
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• posted on January 16, 2010, 2:02 am

I *think* bottlebob mentioned something like 3% max of diameter per edge iirc.
Down in the link, search on 3% you will see bob indicate 1-3% of diameter as infeed per flute. I'd go with that. Bob removed metal for a living. He knows his stuff backwards and forwards.
Wes
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• posted on January 16, 2010, 5:38 am
wrote:

Basically it is called experience :-)
But seriously, perhaps you should redesign the parts or consider a different method of making the item.
It sounds as though you are carving something out of a giant block of stuff - sort of cutting the boulder down until you have removed all the parts that aren't a horse, as the sculptor said when asked how to carve a horse... Perhaps that is not the best method.
For example: If one were milling a recess in an aluminum block one might drill out much of the area with a twist drill before putting the part in the machine; then the milling would consist of simply machining to the final dimension.
Probably the major problems in shop work are concerned with either "how am I going to hold this" or "how can I do this within the capacity of my machine", rather then how to drive the machine.
Regards,
J.B.
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• posted on January 16, 2010, 4:30 pm
Have you checked the feeds & speeds section of Machinery's Handbook?
If that is hard for you to understand, you might want something like ME Consultant Pro:
http://www.cncci.com/products/mepro.htm
It calculate the speed and feed for various types of cutting tools and materials plus a bunch of other useful info.
Mike

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• posted on January 16, 2010, 6:43 pm

With an end mill that small you absolutely have to have some liquid to wash away the chips! Any coolant will keep the chips from welding to the cutting edge ofthe end mill. I am sure this is your problem! Your end mills are probably not getting dull, just welded over with aluminum.
Paul
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• posted on January 17, 2010, 10:29 pm
On Sat, 16 Jan 2010 10:43:26 -0800 (PST), " snipped-for-privacy@coinet.com"

http://www.custompartnet.com/calculator/milling-speed-and-feed
http://www.niagaracutter.com/techinfo/common_mat/6061.html