Grounding a frame made of aluminium extrusions?
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Hello all!
In the process of rewiring my printer (getting rid of the pasta in the back) I did some sanity checks with a multimeter and I was shocked (not literally lol) to see that the ground connection to the printbed does not ground the entire frame (most likely due to the anodising of the extrusions).
If the anodising is non-conductive is there even a need to ground the entire frame? Or does a stray current penetrate the anodising and trigger the main fuse anyway?
If not: How can I ground the entire frame without dissassembling the whole printer and sanding away the anodisation at every contact point between two extrusions? -
I can't comment on need to ground without more info....
I can say: The reliable way to connect extrusions despite anodizing, and/or the aluminium oxide layer that is a natural part of un-anodized alu, is a short jumper wire with ring terminals, drilled holes for a screw in each extrusion, "star" lock washer that will bite into alu surface.
Delta / Kossel printer fanatic
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Grounding through extrusion is tricky. If you have a mains voltage heaterbed don't rely on it. Run a ground wire that is safe for full short current (fuse on heatbed supply) to metal work closest to the heatbed and take the other end back to the main ground point. As Danal suggest starlock washers are a good way to bite into Aluminium. Anodised makes it worse, but plain aluminium is also tricky to ground.
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@danal The reason for grounding is the heated bed which runs on 230V via a SSR (should have mentioned that in the first post).
Grounding the print bed directly (i.e. the aluminium plate that the heater is attached to) is relatively easy since I can just screw the ground wire to the plate. But I also want to ground the rest of the frame for the (unlikely) event that a wire comes loose on the SSR itself and connects with the frame or when the cable to the heatbed breaks (which is also unlikely since its a multi-strand wire in a cable chain).But it's always better to be safe than roasted
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Fair enough! I think it maybe part of the regs that non-conductor (ie parts that weren't intended as conductors) metal parts are earth bonded when mains is involved.
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In New Zealand and also Australia, as we share a lot of the same regs, you are not allowed anymore than 1 ohm of resistance between the exposed metal of a class 1 appliance (which our printers are) and the earth pin on the plug. It’s called earth continuity here. I have a seperate earth wire off the AC bed and also one to the frame. I am sitting at 0.1 ohms with mine.
Regards
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@Eumldeuml, I would follow @danal's advice to ground the frame using a method that cuts through the anodising. It is possible in slotted ALU to ground into a T-Nut with star washer.
As has already been mentioned check the continuity.
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I used the plain normal metallic T nuts and corner brackets from the extrusion supplier instead of plastic when assembling and used quite a bit of force. This provided me with connections everywhere basically by accident. The T nuts are rough on the sides and bite into the material when tightened. Another way that I found is to use longer than appropriate screws with T nuts or T-slot nuts so that the screw bites into the back of the slot. Just don't use plastic as it will fatigue and break the connection.
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@edgars-batna said in Grounding a frame made of aluminium extrusions?:
I used the plain normal metallic T nuts and corner brackets from the extrusion supplier instead of plastic when assembling and used quite a bit of force. This provided me with connections everywhere basically by accident. The T nuts are rough on the sides and bite into the material when tightened. Another way that I found is to use longer than appropriate screws with T nuts or T-slot nuts so that the screw bites into the back of the slot. Just don't use plastic as it will fatigue and break the connection.
I found the same with the hammer head nuts. For the connections between extrusion pieces I used a small piece of wire to join them. This maybe isn't the best practice since you can't guarantee that the connection will remain over time, but it gave me steady continuity from any two points on the frame I could find, so I called it good.
