Ramp speeds

[dowty]

having a little trouble in cutting a file. the z on a second pass steps a little further down then the first pass. Might this be due to ramp speeds or z travel speeds. I am running a ramp of .4ips and a z travel of .5 on a pr model with an upgraded prt z. Can someone tell me the speeds that might be accurate on their older model? or even a decent suggestion as to what the ramp speeds or how the ramp speeds should be calculated?
Thanks in advance

[beacon14]

Make sure that you are using a center-cutting bit; if the center of the end of the bit does not cut the material out of its own way as the bit plunges that can cause a loss of steps on the Z axis on pre-Alpha machines.
You can use such a bit as long as you ramp into the material at a low angle instead of using a straight down Z-plunge.