X3 mill with rails, ATC, new motor

[Jonathan]

Lately I've been working on converting an X3 mill, for myself. The eventual plan is to put linear guides on all axes, add ATC to the spindle (using similar method to the Tormach system) with a moving tool rack and replace the spindle motor with something better. To start with I'm working on the Z-axis and ATC - X and Y can wait.

Starting with the motor - this is the one I chose:



It's rated by the retailer for 6.5kW, but that's not a realistic rating - it's more like 4-5kW. That power rating is excessive, but the correspondingly high torque rating does mean I can get away without needing to change the belt. I've started rewinding it to control it with my servo motor driver using vector control - so things requiring position control of the spindle will be possible, in addition to getting a large speed range (using field weakening). That'll also allow me to test the idea of linking feed-rate to torque feedback, since the driver will know the torque at all times.

The motor clearly doesn't fit through the cutout in the side of the mill head, so I milled a hole in the top, then cut the annoying protrusion inside off with a slitting saw:



I'll machine an aluminium plate the size of the head to both support the motor and heatsink it. I've calculated that a 5M, 25mm wide HTD belt will be adequate (just about) to couple the motor to the spindle so I've ordered that and some pulleys.

I decided to put linear guides on the column to remove the various (potential) problems with the dovetail slides. To do that I've milled a small amount off the dovetail on one side of the column, then drilled and tapped lots of holes to fit some ground strip upon which the rails the rails will be mounted.

As I found a long time ago when converting the other mill, cast iron cuts well on my CNC router, so I used that to do the necessary milling and drilling:



Drilled array of holes in the back of the column so that I can mount a piece of 20mm thick aluminium to the back of it to improve the torsional stiffness. The ballscrew will be on the front between the rails, so no need to have the column open. I can also conveniently mount the motor drivers inside the column and use the aluminium plate as the heatsink.



Now to drill the rail strips - align the vice then drill, pretty simple:



For some reason people seem to like taking pictures of sawing things...so why not:



Ready to mount rails - just need to check the join on surface plate, but it seems OK.



Simple aluminium plate machined to connect bearings to head:



I've also made a start with the ATC system, but the pictures I took have gone walkies so I'll just describe it. It's basically just a copy of the Tormach system, using an MT3 3/4" collet in the spindle, linked to a drawbar with a stack of disc springs. The springs are pushed with an air cylinder to release the tool. It seem to work fine, but not tested thoroughly yet. The mildly interesting bit will be making the tool rack. I've bought another air cylinder to move the rack into position automatically and the rack can be spun into position with a stepper motor.

Edit, found one picture - here's one of the tool holders clamped in the spindle. It's pulled against a ground plate (which I'll hardened) to get the height repeatable and increase the stiffness:



That's about it for now, as I've only spent about 2 weekends on it. I've ordered the ballscrew, which apparently will take about 15-20 days to arrive (trying a different supplier, more on that later), so in the meantime I'll work on the servo driver design, finish rewinding the motor and machine the remaining trivial parts for the head and Z.