leadscrew whip ?

[tomcat47]

Hello,
Looking for info on leadscrew whip, I'm using 1/2 8 double start
acmes, They will be 60" or 67" long I prefer 67" easier for me to build
motor & bearing mounts to acheive my table length I"m using 2 screws
on the gantry.
Could someone tell me what the critical speed is for given diameter & length or point me in the right direction ? I"m sure there has to be a
formula for calculating this.
Thanks Tom......

[vger]

The "critical" speed will change depending on the position of the gantry. It will be higher with the gantry centered compared with it being near the ends of travel. There will be a natural resonance in the screw that will be dependant on it's unsuported length, tension, and material. That natural resonance frequency will be the critical speed. You could determin the natural frequency by supporting the piece as it would be supported in the machine, and bumping it while monitoring the vibration frequency. A calibrated strobe light, vibration analyzer, or spectrum analyzer could be used to determin the frequency.

[ger21]

http://www.nookind.com/acme/AcmeCharts.cfm

The type of end mounts have a large effect on the critical speed.