Gene, I CNC'd one of the red Harbor Freight 7x10's by puttting a gearmotor with encoder (servo) on the lead screw and another on the x axis by mounting it on the BACK of the saddle with a sliding coupling made by drilling a cross hole in the end of the cross slide lead screw and another in the motor shaft into which I inserted a 3/32 pin which was exposed on one end only. The two shafts are connected by a hollow tube with a (tight) 3/32 slot running its length. I was warned that the slop in a gearmotor would be detrimental to a CNC setup but those of us who have been anywhere near these little toy lathes know that the backlash in the gearmotor is the least of our worries.
The gearmotors are spur gear reduction and are about 150 rpm at full throttle. The spur gearing and low ratio allows the crossfeed to be turned by hand in manual operation. By the way, I run my spindle as the A axis (fully encoded with a 256 line hp encoder) the motor is a 36 volt servo that Surplus Center used to sell for $30 with no encoder. Fortunately it had a tiny 1/8 inch or so rear spindle that was there for mounting an encoder. I can run up to about 1000 rpm using step generation from EMC2 with no problem. The servo is mounted behind the machine and uses the original belt to the countershaft. I have two configs depending on whether the spindle is in Hi or Lo but I rarely use the Hi configuration for threading. I think you could drill a hole through the rear of the existing motor into the end of the armature shaft and press in a pin which would then give you a place to mount a HP style encoder on the motor. I have done that on other DC motors to turn them into servos. Yeah I know all about skewed rotors and anti cogging and all the reasons you can't just take any old 24 volt DC motor and make a servo but I mostly go for what works.....I just don't talk as much about the stuff I tried that didn't work. I am using Gecko servo drives. I only use the spindle in servo mode when threading. I have a switch on my Power supply/driver box that I can switch to "free run" on the spindle by just disconnecting the drive and connecting DC to the motor and using it as a free running DC motor when doing simple turning not requiring spindle coordination. The up side to my spindle setup is that the spindle is not just "synchronized" to the x and z by index but is a fully functional axis with better than .5 degree resolution. I can cut any thread you can imagine in straight or taper form inside or out. The down side is that I have to write all my own threading routines because the "canned routines" don't work with an A axis spindle. I personally like writing my own routines because I am involved in this CNC world for my own self improvement and not for production. Cecil ------------------------------------------------------------------------------ Try before you buy = See our experts in action! The most comprehensive online learning library for Microsoft developers is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, Metro Style Apps, more. Free future releases when you subscribe now! http://p.sf.net/sfu/learndevnow-dev2 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
