X3 mill with rails, ATC, new motor

[Jonathan]

EDIT: Just a quick question, how come you went with ali for the column back plate rather than steel?

1) I can mount the motor drivers in the column - the aluminum plate can be used as a heatsink, so saves buying that.
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.

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?

I'm considering it - it seems worthwhile, but I might be better off just making a new base.

[Lee Roberts]

1) I can mount the motor drivers in the column - the aluminum plate can be used as a heatsink, so saves buying that.
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. I'm considering it - it seems worthwhile, but I might be better off just making a new base.

Ahh fair enough then.

I looked at a build on the zone the other day re making a base, on that build, they used a lump of granite for the base, what are your thoughts on doing that?

.Me

[embraced]

What sort of motor are you using for the spindle?
And how on earth does it achieve such a high power density?

[Jonathan]

What sort of motor are you using for the spindle?
And how on earth does it achieve such a high power density?

It's the same type of motor as I used 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.

[dazza]

a cracking thread again jon.
im looking forward to seeing how this performs,thanks for posting ;)

[Jonathan]

im looking forward to seeing how this performs,thanks for posting ;)

You're not the only one!


I finished rewinding the motor the day before yesterday, so here it is ready to varnish:




Checked the back-emf constant was correct by spinning it in the lathe and measuring the peak voltage with oscilloscope. Then powered a small light bulb with it for general amusement...




I tested the motor with my driver last night, just open loop control - will post a video if anyone's interested.


I started a job at university yesterday, so progress will be slower for now. I'll instead concentrate on finishing off the motor driver design and making them.

[Jonathan]

loved the bolt spacing theory so thanks for sharing that, cant wait to see the rest, keep up the good work !

Since you seem to like bolts, here's my justification for putting four setscrews in the motor pulley...

A setscrew works by applying a force which results in a contact force between the opposite side of the shaft and bore. Based on the tightening torque of the setscrew, we can calculate this force and if the co-efficient of friction between the shaft and bore is known, the holding torque can be determined - approximately of course.

For one screw it's very simple - the axial force on the screw is equal to the contact force (C) between the shaft and bore, so:

.
.
.
.

.
.
.

The motor shaft diameter is 12mm, we can fit M5 grubscrews, they're black and according to this list the tightening torque is about 4.7Nm, so substitute that lot in:

.

With multiple screws, we have to resolve the forces to find the effective contact force. Define the angle as the angle between the two screws, then resolve the force on one screw in the radial direction and double it to get the radial force for both screws:

.

I put the screws spaced at 90° because it makes milling the flats on the shaft easier, but this formula shows that the smaller the angle between the screws, the greater the holding torque, so 60° would have been better. For 90° that reduces to ., so now we have .. That torque is a little greater than the motor rating, but shock loads could impose much higher torques so I added another two screws further along the shaft to double the load capacity.

Some pictures I forgot to post of testing the motor: