Mill Drill Real World CNC Feed Rate

[wmgeorge]

I've got my CNC set up (used XZYPro III stepper ) on my Roug Fu RF-31, and it does run. I'm getting max 15 IPM rapid movement, 10 IPM Feed to X - Y with NEMA 34 stepper motors, before it starts to lose steps. Z is 12/6 rates. This is running on a old, old DOS computer. This entire system is 1993 vintage serial board setup.

I'm thinking about using TurboCNC (or Mach2), new computer, and a new state of the art parallel controller and Gecko drives, and of course a new 20 amp DC power supply. The steppers are 2.2 V, 7.1 A 1.8 deg NEMA 34 stepper running about a 2:1 belt drive.

IF I go to the new setup, what am I going to gain in Real world feed rates?

I'd like to see 30 - 60 rapids and 10 - 20 feed rates, is this doable? Thanks in advance.

[KDN Tool]

A concept to think about:
My personal experience with steppers is that you are better off going direct drive to the leadscrew as a stepper makes peak torque at 0 RPM and the curve drops from there. Typically the higher the RPM of the step motor, the lower the torque so by using a 2:1 ratio, depending on the motors exact torque curve, you may have less torque generation than a direct drive set-up. Referencing Automation Direct's SureStep line: given the NEMA 34 motor with 1/10 microstepping, at 150 RPM the motor develops @240 oz/in and at 300 rpm it drops to @65 oz/in. Even doubling the 65 oz/in with a 2:1 ration (and halving the 300 RPM) only yields 130 oz/in at 150 RPM compared to the direct drive's 240 oz/in @ 150 RPM. This is a concept that does not seem to be mentioned much in the hobby CNC forums.

With the Gecko's and a minimum 48 VDC power supply you should have no problem reaching your speed goals. I have an old Jet-15 round column mill cnc'd with lousy NEMA34's, Nyden 1/8 microstepping drives, and a 48 VDC power supply and get 30-40 IPM rapids even with slighly bent lead screws. There are some nice affordable modern imported NEMA 34 steppers around now as well. The aforementioned A.D. motors are 400+ oz/in and have 2.8 Amp coils. They would lower the power supply size needs and heat generation in the Gecko's.

My two cents! (if it is worth that)

Ken
KDN Tool