When adding a new machine in CAM Assist, setting the Spindle torque max value is required.
The expected value in this field is the continuous rating from the spindle manufacturer. CloudNC advises customers to refer to the relevant manufacturer torque and spindle power charts to determine an appropriate spindle torque maximum value.
For example, in this chart from Mazak, the continuous torque rating of 32.2 ft lb (47.7 Nm) would be the value used in CAM Assist:
It is common for several torque curves to be published for each spindle, which reflect different duty cycles. In the first chart you can see “10% ED”, “30-min rating” and “Cont rating” curves. These reflect the fact that you can intermittently increase torque above the continuous rating without the machine shutting down. So the 10% ED curve gives you the torque you can use if you cut for 6 minutes and then shut off for the remaining 54 minutes of the hour; the 30-min rating gives you the torque you can use if you run for 50% of the time in every hour, etc. The continuous rating is the one to pick because this guarantees that you can run non-stop at that torque without overheating or derating the machine.
In this chart from DMG MORI, the continuous torque rating of 95.9 ft lb (130 Nm) would be the value used in CAM Assist:
In the example below from Okuma, the range of 198-135 Nm (146-99.5 ft lb) is clear. For conservative operation, the lower value would be entered into CAM Assist.
For some spindle manufacturers, the information needs to be interpreted slightly differently. For example, in Haas charts, torque values are often quoted at 200% spindle load, which is much higher than the continuous (i.e 100% spindle load) values needed in CAM Assist. Shops may and do exceed spindle load parameters, but only for short periods of time. In cases like this, you can scale from 200% to 100% by simply halving the quoted torque, so in the example below, if the 200% torque value is 125 Nm (92 ft lb), half of that would be 62.5 Nm (46 ft lb).
Spindles broadly have two principal operating regions: a constant torque region (up to a certain “corner” rpm) and above that, a constant power region. This can be seen in the figures above. A spindle will deliver peak torque at lower rpm, and then above the “corner” rpm, torque will begin to drop.
The trade-off between power, torque and maximum spindle speed will principally depend on the motor design, and whether there is a gearbox. A higher max spindle speed will often mean sacrificing torque and vice versa.