The new spindle for our cnc mill has now been installed. The aluminium plates holding the bearings are now supported by steel plates on all four sides. A bracket for holding the motor has been made, with elongated mounting holes for tensioning the belt. We're now using the Z-axis with linear rails and a ballscew, the conversion for the X- and Y-axes is still work in progress..
The spindle from below. We see the aluminium plate holding the lower bearing. We still need to fit a guard plate which protects the bearing from chips, coolant etc.
A major improvement over the old spindle is that the new spindle is belt driven instead of the gears we had on the old one. This reduces noise a lot, which makes running the machine for longer periods of time much more pleasant. The belt is a 1:1 ratio AT5 standard belt. The 750 W ABB induction motor we are using now does about 3000rpm, so for small tools (6mm or so) we are still lacking a bit in spindle rpm. The plan is to replace this motor with a 1 kW servo which will do 4500 rpm maximum, and could also be geared 1:2 since it will be driven by a closed-loop system and we can monitor the load on the motor.
The spindle has an MT3 taper, and we're now using ER25 collet toolholders which hopefully will mean that we can input the tool length into EMC and not have to re-set the Z coordinate zero on every toolchange.
Preliminary tests show that the finish on milled surfaces has improved a lot with the new spindle. Face-milling now produces an almost 'mirror' finish, and milling with the side of an end-mill now produces acceptable surface quality when previously the finish was quite horrible... The real acid-test for our machine will come when we get the linear rails and ballscres installed for X and Y, and also convert the whole control to AC servos - then we should have a machine that can produce good quality parts at a reasonable rate.