Hi Rye,

good to hear you are having success with the 6040. Not sure what our screech is, maybe post a video of it and we may be able to identify it.

When you start cutting metals you will need some form of cooling, even if it is just an air blast. I would also suggest you use carbide tooling due to the speed that the spindle of the machine is able to run.

Surface finish of a milled part will depend on the rigidity of the machine, the nature and hardness of the material and your feed/speed settings. For plastics you will need to get specific endmills/cutting bits in order to get the surface finish you are looking for, google this. I think I came across some straight flute endmills a while ago for this particular application.

ER11 are the type of collet that your spindle can accept. You can purchase the ER11 collets on ebay for pretty cheap but you will be limited to a 7mm diameter shank tool. This is not an issue on the 6040 as most suitable small endmills have 3.2mm(1/8"), 4,5,6mm shanks anyway. Worth getting a collet set by the way, if your machine didnt come with it.

A good place to start for feeds and speeds is the feeds and speeds wizards

Another slightly overlooked parameter is what the gcode your CAM program outputs. Some programs will prefer to output straight lines for arcs which makes ugly curved edges.

Regards