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.
Last edited by Jonathan; 24-06-2014 at 01:14 AM.
I cut out the back plate for column, will leave the tapping for a rainy day:
The spacing of the bolts is loosely based on the theory here - namely make the stress cones under the bolts intersect to get maximum stiffness. This diagram illustrates that:
Made a ballnut mount for Z:
Remembered the cutout for the ballnut mount in the Z-plate. Clamped directly to mill bed to ensure parallelism.
Here's a picture of the drawbar I made earlier for the ATC:
That may not be the final number of disc springs - but there will be quite a lot to ensure they're not operated outside the recommended region to get long life.
Last edited by Jonathan; 24-06-2014 at 11:59 PM.
Excellent Jonathan - this is something I will also be attempting soon, so will be following with interest.
BTW if you are going to use linear rails/bearings on all X and Y and using the "fill in" the dovetail method you used on the Z, are you going to lose ~60mm in the Z due to the height of those units?
We defo needed some cnc "mill conversion" logs on here, loved the bolt spacing theory so thanks for sharing that, cant wait to see the rest, keep up the good work !
EDIT: Just a quick question, how come you went with ali for the column back plate rather than steel?
EDIT 2: I dont know if it will apply to you, but i recently watched a build log where the guy filled in any voids in the base and so on with a mix of stone and epoxy, will you be doing that as well or?
Last edited by Lee Roberts; 25-06-2014 at 11:48 AM..Me
2) Aluminium is easier for me to machine.
3) I had a 1.50x0.74x0.02m sheet of aluminium 'lying around' and I'm not sure where to buy steel plate for a reasonable price.
Last edited by Jonathan; 26-06-2014 at 12:22 PM.
What sort of motor are you using for the spindle?
And how on earth does it achieve such a high power density?
here - permanent magnet synchronous motor (PMSM), with an outer rotor. The high power density partly stems from the magnets, which replace the rotor magnetising current in, for example, an induction motor, resulting in lower losses. There is more to it than that though - e.g. differences in cooling.
This is how far I've got with rewinding the motor - two phases done, but I do have a low resistance from one phase to the stator, so I'll probably have to re-do that one and be more careful.
Cut out the motor mount for Z from 20mm thick aluminium yesterday:
This morning I cut the motor mounting plate for the spindle motor:
This is where it fits:
The large pulley (60T) isn't all the way on the spindle shaft, but this shows the general idea. The spindle pulley is keyed and the motor pulley fixed using four grubscrews, which should be sufficient...more on that later.
The spindle pulley is much bigger than the original gear, so I had to mill a bit off the top cover to clear the pulley and belt:
Z-ballnut mount (again):
I just need to make the Z-ballscrew bearing mounts, finish rewinding the motor and make the driver, decide if I need an encoder on the spindle and then I can continue with the ATC.
Last edited by Jonathan; 29-06-2014 at 10:20 AM.
a cracking thread again jon.
im looking forward to seeing how this performs,thanks for posting ;)
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