I dont like it when servos are talked about in KW or HP, I prefer to see the continuous torque rating. To me that seems a much better way of sizing a motor, granted the torque will be related to the KW but I have seen quite a variance between similar KW rated motors and the actual continuous rated torque.
I you have the machine already built the easiest way to get an idea of the torque you will need is to get a 2m length of flat bar, bore a hole in the centre and mount that to where your motor will connect. Get a spring balance or some weights and find out the Kg it takes to start it moving, multiply by 9.806 and you know the Nm that you need to move an axis. Obviously you will need a bit more than that but in reality it wont be much more. I did this with my Lathe and found I needed about 0.75Kg (if I remember correctly, it was a good while ago) I ended up with 10Nm AC servos and things work great 1:1. Did try a 6 Nm motor on and although it moved the axis its acceleration was poor.
Obviously you USA guys with your old fashioned measurements can use a 2ft long bar and measure in Lbs
Hood