Please pay attention to the Spindle Working Speed ! 
Engraving machine spindle motor may be clearly different than Milling machine spindle.

For engraving machine, the higher spindle speed, the greater cutting force. the lower speed, the smaller cutting force, if spindle speed is too low may be caused spindle stalled or VFD burned.

So, depending on the different materials, set spindle speed to 12,000 ~ 24,000 is most appropriate. 
1) ABS/PVC/POM/Nylon and other plastic materials use about 16,000rpm. 
2) 6061 aluminum and H59 brass use about 16000~20000rpm.
3) Acrylic use about 17,000~22,000rpm. 
Different materials should be more testing............

For a water-cooled spindle, we need to use correct ways to maintain it.
1. The cooling water, you can choose either tap water or deionized water. Please add a little common antirust into water ( the kind used in water tank of cars is OK).

2. You need to ensure that the spindle runs normally, so that you must avoid the water-cooled spindle lacks water. During operation, please check the surface temperature of the spindle regularly to prevent from a hot spindle.

3. Please measure the temperature of the cooling water periodically, you’d better keep the cooling water within 30 degree centigrade. When the environment temperature is high ( in summer), please use a big-size water tank. When the temperature of the cooling water is rising, you can lower the temperature by adding more water.

4. If you use tap water, please change the water periodically ( change one time in a week)

5. When the temperature in winter is below 5 degree centigrade, please add some anti-freezing solution into the cooling water.

6. If you don’t use the machine for a long time, you must use compressed air to blow out the water in the spindle until there is no water in it............