Ok, I have a few questions.

I have typically only machined aluminum and I have no problems running that, but I need to be doing some steel too. I decided that tonight was a good night to start, and, I subsequently snapped off a .25" endmill.

I was trying to machine a "step" into the jaws that came with my vise. I just wanted to do a slot that .15' deep. Normally, I do that in aluminum soft jaws, but it's a new vice and I don't have any soft jaws for it yet so I figured that adding a step into the jaws that came with the vise wouldn't be a big deal.

That being said, here is what I looked up/calculated for feeds/speeds.

Cutter Diameter: .25 HSS
Surface Feet per Minute: 120
Calculated RPM: 1833

Number of Teeth: 2
Chip Load: .003
Calculated Feed Rate: 11ipm

I tried doing a Depth of Cut of .05" deep.

  • What the heck did I do wrong?
  • How do I choose the SFM and ChipLoad accurately?
  • I've been using Whitney Tool I Speed and Feed Calculator for my feed/speed calculation and their only recommendation is .002 to .005 for chip load as a starting point.
  • How do I choose how deep of a cut I can make at one time? I was always told that you should take the diameter of your endmill and divide it by 3 and that is usually a safe number. Is this just for aluminum? I didn't think so, but it appears that my thinking is flawed.


If someone can help give me a better understanding of feeds and speeds, I would be forever in your debt. Some of the values have been a guessing game with me and I'm tired of being frustrated with feeds and speeds.

Also, does it mean that I should be able to double the RPM and double the feed rate?

Thanks in advance,
Wade