Adding 3D printer ability to my CNC / advice needed please

[dudz]

The heater is controlled via PID temp controller using a Thermocouple. Your supporting suggestions sound good. I will plan around this idea.

[Trispectiv]

It doesn't matter which method you use for temperature control and temperature reading. A thermal fuse should still be used with a wall plugged heater. You never know when your thermocouple slips of the heater and starts indicating room air temperature instead of heater temperature. This fools your PID controller that it still has not reached the target temperature and supplies current continuously to the heater. 120-150 degrees thermal fuses are cheap, you can even scrap them from certain household appliances (some baby bottle sterilizers have 130-140 degrees thermal fuses, for example).

[dudz]

Ok I hear you. I am bolting the thermocouple to the bed, but I get what you are saying. Good idea
What tolerance are we talking about regarding the flatness of the plate ?

0.005mm ??

[Trispectiv]

It pretty much depends on the layer height you are printing at.

If you are printing 0.1mm layers and your surface has a 0.1mm deflection in the middle, you are one full layer off. Meaning that a) if your surface is 0.1mm lower, there will be almost no first layer adhesion in that spot, or b) if your surface is 0.1mm higher, there will be no room to extrude the plastic as the surface will act like a plug against the tip of the hotend, creating backpreasure or even jamming the extruder.

If you are printing 0.3mm layers and your surface has a 0.1mm deflection, you still have some error margin, the first layer will still be printed but if you flip the piece over and look at that first layer, you will notice the imperfections.

Once you lay your first layer, if it sticks, after the first couple of layers (depending on how bad the deflection was) the print settles and layers will be fine.

Simple methods to get around this:
-Z probing, a probe tests the surface in various spots and automatically compensates for the found variations by adding/subtracting Z height according to the surface deviation.
-raft, a discardable raft is printed first and then the actual object
-thicker first layer, the thicker the layer the easier it will swallow any slops in the surface
-probably many other

I would expect the surface to be within +/-0.005mm compared to the center.

[Boyan Silyavski]

Dont forget to share the results . It will be very interesting to see how it worked. After all it was not a small investment. Mini review with some pictures will be nice.