[georgebarr]

I need to machine some mild steel. I know that in order to machine mild steel, the spindle rpm must be set very low. I have tried using a variable router speed control, but with this setup my routers minimum speed is about 8000 rpm. My question is, what is the speed range for machining mild steel (drilling holes, etc)? Also, what type of motor do I need? I have considered using an order hand drill with a variable speed control device. This setup does slow the rpm's down, but the torque at low speeds seems little. Any advice?

[HuFlungDung]

George,

If you are using High speed steel tools (such as drills), you need to limit the largest circumferential speed of the tool to 100 (or less) feet traveled per minute. For a 1/4" diameter tool, this would be about 1500 rpm. The forumula is:
1200/(Pi * tool diameter).

For carbide tools you can run 3 or 4 times faster.

A variable speed drill would put you in a much better speed range. You might want to use a 3/8 or 1/2 rated drill, in order to get sufficient gearing to do something. Mind you, none of those tools have spindles or chucks that are made for the side loads of milling, but you can certainly drill with them.

[avsfan733]

I have been taught that you never put a mill in a drill chuck

[steele]

I have been taught that you never put a mill in a drill chuck

I didn't think you where supposed to put an electric drill on a router either. I think a milling cutter in a drill chuck is going to be the least of George's problems. George, I know next to nothing about routers but make sure you have a ridgid setup and can feed slowly and accurately at the same time.
Good luck,
Jim
www.picopascal.com

[gibbsman]

Try out-sourcing your job to a professional shop, no offence but if you guys are talking about cutting mild steel with a drill press or such then you guys are just asking to loose a finger or two.

[Kmed]

8000 rpm can work. Are you using a cnc or manual mill, what are your maximum cutting speeds etc. FWIW I just milled a 6x8x2" block of 4130, takeing 3/4 of the material weight out. I used 7000 RPM 36 ipm, .04 stepover, and .05 depth of cut with a ball end mill. The finish pass was in the high speed spindle, 25k rpm, 1/4" ball end mill .01 step over, .01 depth of cut, 82ipm.. Both were cut dry with air blast, with OSG exo carb endmills.

More info is really needed on you setup to get you some better advise.