Hi,

Thanks for the suggestions and calculations (very helpful).

I should clarify that I am certainly not looking to achieve 1g accelerations now. This was simply where I happened to start when looking at online calculators - I had been looking at relatively low horsepower commercial machines, as this seemed closer to what I am trying to achieve, which led me to machines like the brother Speedio line (which I now know are some of the most dynamic machines) - I saw that they advertised 2.2g accelerations and aimed lower. I have since seen that even very high quality machines utilize much lower accelerations e.g. 0.5g. I am not necessarily targeting this, but it illustrates that 1g was a far higher target than would have been sensible for my application. I welcome your insights into a suitable target for accelerations, as this sort of information is rarely published, and I don't have experience with it myself.

I was under the impression that I could rely on the maximum/temporary torque figures as opposed to rated torque, for acceleration - I note that you have calculated on the basis of rated torque. Was this just for illustration or is this how the motor needs to be spec'd? I wonder whether the acceleration figures published by the manufacturers I mentioned are based on continuous ability, as I know the Hermle c400 is advertised as having a 20kw spindle, but this is only at a 20% duty cycle (the 100% duty cycle is only 10kw).

I had considered something like the 1.8kw DMM with the following spec which has lots of torque (I note the rotor inertia is much higher than the 750w model):

Servo Motor Model 120-DST-A6 _ _ 1

Rated Output 1.8kW

Rated Voltage 200V

Applicable Servo Drive DYN4-T01

Rated Torque 11.5Nm

Instantaneous Max. Torque 28.7Nm

Rated Current 16.7A

Max. Current 36.3A

Rated Speed 1500rpm

Max. Speed 3000rpm

Rotor Inertia 23.8kg-cm^2

Torque Coefficient 0.74N?m/A

Encoder 16-bit Absolute [ ABS-16-01 ]

I haven't been able to download any specs for the delta servo's or see prices on their website.

It looks like a rotating ball-nut design could be useful for maximizing accelerations from a given motor, but I only seem to see this design on gantries with long travel to avoid whip. I imagine this could be more difficult to incorporate.

I will have to do some investigating to see what diameter and pitch ballscrews to use, and will certainly value any suggestions. I have seen some excellent builds with max travel speed of about 15m/min but the travel lengths were much lower than mine. I certainly take your point about acceleration and toolpath following.

Thanks for the help guys.

Mike