Hard Milling By The Numbers

I thought this article might interest some. It's from the latest issue of Modern Machine Shop.
Has some formulas and tips on where to start with feeds and
speeds for hard milling:
http://www.mmsonline.com/articles/040802.html
Best, Steve
--


Regards,
Steve Saling
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Steve:
You took the words/site right out of my mouth, so to speak. <g>

Coincidentally, I was drilling, tapping, counterboring a turned 13" dia. disk yesterday that was supposedly in the middle 40's RC. Tending to push the envelope on what I can get away with, I tried doing some .375 X .250 deep counterbores with a new 3/16" 3 flute Whispercut end mill. At first I tried 2000 RPM & 10 IPM (98 SFPM & .0016 Chip load), not allowing for any chip thinning. The end mill didn't last two counterbores before wearing the flute tips off. So I backed the feed and speed off to 1000 RPM & 5 IPM on a four flute end mill (49 SFPM & .0012 Chip load). At those numbers the end mill lasted the 10 holes without visible wear. Too bad I didn't read the article first, or I could have tried 10,000 RPM (The site's Recommended RPM for a 3/16" dia. tool for cutting 45 RC material is 12,000 to 20,000 RPM).
The Hard milling MMS site also had an comment toward the end that has some bearing on the concept that you can get a better finish by feeding faster (that seems to be held by at least one person in here).
=======================================================================Feed rate affects surface finish as well. The pass of each cutting edge as the tool advances creates a "cusp" of its own. Therefore, if a smooth surface is the goal, then the same value calculated as the limit of the radial depth should also be applied as the upper limit on the inch-per-tooth feed rate of the tool. ======================================================================-- BottleBob http://home.earthlink.net/~bottlbob
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