Need help with axis movement parameters

I'm a newbie to 3D printing, but i've been doing CNC milling and laser cutting for a while, using some proprietary interfaces to drive the steppers.

Now I'm setting up an Arduino Mega with Marlin, using a RAMPS 1.4 board to drive the steppers on my CNC machine, and have installed a MK8 hot end.

Doing the calculations for 200 steps/rev, 20 TPI lead screw, gives me 157.45 steps/mm (or 314.96 half-steps). I set up configuration.h accordingly, and sending a 100mm move to the X axis gave me a rather slow 8mm move. I tried the value of 314.96 and the stepper sounded like a coffee grinder and didn't move at all. Then I started experimenting with M92 commands, and found that a value of 280 results in a smooth movement of 10mm at about the 10 inch per minute speed I'm used to with the CNC. It seems like the DEFAULT_STEPS_PER_UNIT value is really a rate per unit time, rather than per unit distance. That and the fact that the axis is moving only 1/10 of the distance it's supposed to has me baffled.

There must be some setup parameter I'm missing, but I can't find it! Would someone help me please?

Walt

Under the stepper drivers on the ramps board are 3 pairs of jumper pins for setting the micro stepping. Some ramps board have these jumpers pins shorted so it is permanently in 1/16 micro stepping.

If so, you will need to do a lil surgery on the said tracks.

Quote
obewan
Under the stepper drivers on the ramps board are 3 pairs of jumper pins for setting the micro stepping. Some ramps board have these jumpers pins shorted so it is permanently in 1/16 micro stepping.

If so, you will need to do a lil surgery on the said tracks.

Thanks! I just blindly followed the instructions and installed all 3 jumpers. I'll get into it tomorrow.

Walt