The previously mentioned controller that I purchased is to support a smallish (1200x600x300) CNC router with 4th axis that I'm in the planning stages of building. One of the key design points, is what spindle to use (and hence support) ?

Comments/Feedback on the following would be appreciated.

A relatively simple option seems to be to select a spindle at around 2.2kw with a single phase VFD. These spindles weigh in at around 8kgs.
From what I'm told, a spindle of this size would support tool with cutting diameters of around 1/2" in wood and 3/8-1/4 in aluminium.
Can anyone offer advice from their experience ? Do 4 pole (high torque) motors make a real difference ? (I'd also be interested in information from 3.7 and 4.5kw motors) ?

A more complex option (oversize VFD, etc) would be to get a higher powered motor - if so what would the advantages of a larger motor be ?
Greater cut depth is one that springs to mind - Does this increase "linearly" with motor size ?
Let's say for a tool that would cut 2.2mm with 2.2kw motor -> would it be reasonable to expect it to cut 3.8mm deep with a 3.8kw motor ?
Tool diameter i'd expect not to increase linearly with motor power - rather the square root of power.
If this is correct, the increase from 12.7mm to 16.7mm hardly seems worth it.
Would it be reasonable to expect a linear increase in cutting speed (assuming the frame / drive motors can achieve it) ?

Are the following calculations "reasonably correct" for motor selection with a 240V single phase supply, on a circuit wired for 32A ?

This link, suggests a maximum motor current of 18.5A.

Using the figures from Ugracnc - their GMT 3.7kw and 4.5kw motors would be viable as they require 15.7A and 16.4A, the 5.5kw motor wouldn't be viable as it requires 21.1A.

So the question now moves onto the VFD - My understanding is that you need to double the 3 phase capacity of the VFD for a single phase supply, so the 3.7kw motor would require a 7.5kw VFD (closest to 7.4kw) and the 4.5kw motor a 11kw vfd (closest to 9kw). How strict is this requirement ? Another motor manufacturer makes a 3.8kw motor - I'd hope a 7.5kw VFD is "close enough" to drive this. Also, as per single phase VFDs - Does active get wired to the (R) phase, and neutral to the (T) phase ?

Also - Is "Sensorless vector control" which seems to cost around $50 - $100 more worth it ?

Lastly (well in my list), which brand of VFD to buy - The Hitachi WJ200 series seems quite popular (even if there is some grumbling about the quality of the manual); as do the Delta (E or M series support sensorless vector control) VFDs.

Any suggestions for other considerations would also be appreciated.

Cheers,
Brad.