I am converting a cnc knee mill from 3 phase to single phase.
The spindle is 3hp (2.2kw) and I am fitting a VFD in place of the HD relays that just turned the power on in FWD or REV. Speed will not be controlled directly by the VFD, only direction. The mill (Hurco KM3P) uses the common Bridgeport style variable drive pulley system and has a motor to adjust the pulleys while reading a tach for verification. After speed is set it is not monitored. This is how the current control (Hurco Max32) was designed, and for now I am retaining this control and NOT doing an LCNC conversion. Others have done this with the KM3 model which does not have the programmable speed function and it has worked great for them. I only have 1 burning question. This machine can do near rigid tapping. I have floating holders that only have about .09" total movement. The machine now taps by a G84 type action and the control reads the tach and spots the zero crossing point of the spindle reverse and ramps feed by the tach. Not perfect - but close and great for its age. The regular KM3 does not have the tach function and needs a float holder with more travel. My problem is this - with site 3phase power you can throw a motor running forward into reverse and it just does it. I'm sure the control has a ever so slight delay between relay actions to allow for mechanical times to prevent switching "shoot through" but I have no idea what this delay is. I don't think I can just switch direction on the VFD without first going through a breaking action. For any other action the machine would just open the relay, let the motor coast down for 6 seconds then apply a spindle air break to lock the spindle. E-stop drops the relay and applies the break instantly. I am using a Teco FM50-203-C and I also have the optional breaking resister. I would prefer to let the motor coast and just reverse it for tapping but I don't know if a VFD can take that kind of repeated abuse - lots of tapping. So - do I need to hook up the breaking resistor and have it set to break the motor in under a second? How would the VFD be setup under LCNC to do tapping? - I watched Ander's rigid tapping videos and it looks like it is reversing at full programmed speed. I'm trying to be as gentile and least excessive waste heat generation in the components as I can while getting the usable function. BTW - I've been dying for a chance to make it over to MPM for a visit, I am committed to a trip to the left coast in early May but I sure hope I can escape again in June. I'm just next door in Colorado. ------------------------------------------------------------------------------ Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_sfd2d_oct _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
