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

[dudz]

I have made a mount. But those speeds are for when the spindle is mounted. When I mount the extruder, I will take the spindle off the Z plate.

[Trispectiv]

True, you will be able to reach slightly faster feedrates after taking the spindle off. Well, drop a couple of photos after you have run your first couple of test prints.

[dudz]

will do. Still waiting for other parts to arrive

[vargai]

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[dudz]

How thick can I go with the aluminium bed ? (using a silicone heater of 900W 230V). The full size of the Aluminium is 470mm by 300mm. I have a 3mm piece but the span seems to large for 3mm. Can I go 5 or 6mm ? It will only be supported in the corners

[Trispectiv]

There are few (or none) printers that use a 470mm long bed supported at the corners only. The reason is the aspect you mentioned yourself, you have a 470mm long sheet of aluminium supported at the ends only. There will definitely be some deflection at the middle of that length. If your deflection is 0.1mm and you are printing 0.1mm layers, you have a deflection of one full layer thickness at that spot. It can be suppressed by using a raft or setting a thicker first layer in your slicer, but you will soon find these methods inconvenient.

I would assume a 5mm aluminium thickness would be required, but it also depends on the aluminium alloy in terms of stiffness. You will probably have an extra sheet of glass/mirror/borosilicate on top of it, which will be your actual printing surface. The extra glass layer will tend to remove the deflection. However, even so, if in theory the glass manages to keep its straightness while the aluminium is slightly bent at the middle, the missing contact surface will mean less heat conductivity.

All printing surfaces over 300mm I have built were not supported by the 4 corners method. 3 parallel beams were laid under the bed - one on each side and one at the middle. No springs were used and during calibration the beams were shimmed under after checking the surface with a dial indicator.

Silicone heaters are effective but more dangerous then the usual 12V/24V stuff. I would add a thermal fuse or two under that bed.

[dudz]

Thanks. Very helpful. I did think about supporting it more or less the way you suggested, but I am paranoid about supporting underneath the silicone heater (I dont know how much stress the silicone heaters will stand). Because It is a CNC machine, the bed will be put on and taken off when I need to mill, so I need to make it as easy as poss