Originally Posted by
bobeson
I have encountered a lot of grief when working with steel on my pcnc1100, and found a few key factors besides feeds and speeds that affected the amount of chatter I was experiencing.
Most of the considerations relate to machine rigidity.
The machine needs to be in a top-notch state of tune, particularly including properly adjusted: gibs, ball screw bearings, motor couplings, way lube, and column tram.
Minimize tool runout to equalize chip loads per tooth.
The spring-loaded power draw bar introduces lots of flexibility, and swapping the draw bar belleville springs out for an equivalent-length solid bushing improves performance substantially.
I find high-speed steel tools more effective for steel on the pcnc - they cut more easily at low speeds. I stick with 3/8" max end mills, with 5/16" and 1/4" doing a lot of the heavy lifting. Yes, this slows things down quite a bit.
How deep of a skin cut are you taking off this hot-rolled stock? A lot of folks recommend 0.060-0.100" removal to get out of problems from the skin. I try to use 1018 for most of my steel work. A36 is tricky stuff.