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Speed Feed and Depth per pass question
« on: June 10, 2008, 10:17:54 AM »
Hello,

 I have a Bostomatic 312 Milling Center I Converted to Mach and Rutex. Pretty stout machine.  I'm having a problem calculating the proper speed feed and depth of cut.  I've been staring at formula after formula but I think I am missing something along the way.  Here's my question:

I want to pocket mill some 304 stainless .1875 thick with a 3 flute .375 carbide end mill, coolant on.

Textbook calculations look like this:
(numbers are tool manufacturer recommendation)

RPM: 150 x 3.82 / .375 =1528 (SFM x 3.82 / tool diameter)
Feed: 1528 x .001 x 3 = 4.584 (RPM x chip load per tooth x number of flutes)

My question:
 Is the .001 x 3 or .003 chip load the same as the depth of cut per pass? 

This seems to light of a cut and to slow of a speed to me.

Confused...
Robert


Offline Graham Waterworth

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Re: Speed Feed and Depth per pass question
« Reply #1 on: June 10, 2008, 12:05:31 PM »
Hi Robert,

most tooling producers (not all) base there feeds and speeds on a cut depth equal to half the diameter.

If you read the data sheet again you may find it says something like if depth equals diameter half speed and feed, .25 depth increase by 25%

If you look through the forum there are lots of threads on this subject.

Graham.

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Offline Chaoticone

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Re: Speed Feed and Depth per pass question
« Reply #2 on: June 10, 2008, 01:27:20 PM »
Robert, Graham is the leading Feed/speed/G-code Guru. Won't find a better one here or elsewhere. He is goooooood.

Might want to look at a program named machinest mate. It has a feed speed calculator that will help get you in the zone. Best I gather, all the formulas in the world for this are only suggested starting points and all situations are different. Perfecting it comes with time and experience I think.

Brett 
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Re: Speed Feed and Depth per pass question
« Reply #3 on: June 10, 2008, 06:34:41 PM »
Robert,

Feed rate for an end mill or slot drill is not a science but a compromise, dependant on machine rigidity, main drive horsepower and axis drive power. The best guide is to set the machine up and manually feed the axis, you will feel and hear when you are going too fast or too slow. Chip load per tooth, as quoted by the cutter manufactures, is only an initial starting guide. In most cases if you can achieve it on a hobby type machine, you are doing well. Experience and confidence in your machine lets you get closer to what your particular machine can do.

Graham has pointed you in the right direction and I have attached here a .jpg of a chart I made years ago which I have pinned on the wall. This gives me a guide to get me in the right ballpark.

Ian
Re: Speed Feed and Depth per pass question
« Reply #4 on: June 10, 2008, 07:27:35 PM »
Thanks for the insight. I will experiment with what I have gathered here.

 ;)
Re: Speed Feed and Depth per pass question
« Reply #5 on: June 23, 2008, 03:54:09 PM »
Tool is making very nice chips now. 

Thanks for the kick in the butt! ;D

Robert