Metal Objects and Hot End


I’m one of those who learned the hard way not to clean the hot end with a wire brush. I had to replace the Rambo board as a result.

What I would like to know is, does contact with any portion of the hot end, including the nozzle, with metal cause damage? For example, if I use the tweezers to remove extruded material from the nozzle, can that short out the Rambo? Or is it only a problem to touch the hexagonal portion of the hot end with a metal object?

Thanks very much,

If you short the electrical components, specifically the heater core, the thermistor, or the hotend nozzle which acts as the Z leveling probe, with a piece of metal, it fries things. Specifically it’s the act of bridging the circuits improperly. Usually its the heater core voltage being fed back into the Z min endstop wire on the nozzle. You can use metal tweezers carefully, but especially wiht the mini nozzle setup i wouldn’t reccommend it. It’s less of an issue on a taz 5 where the nozzle isn’t being activly used as a conductor.

Short what? I don’t understand (yet).

The nozzle has a ring lug with a star washer, presumably that’s the contact for the touch to level.
There are two fine wires under the little squirrel cage fan, probably for the thermistor.
And there are a couple wires shrouded in some red silicone wrap, I think that’s for the heater.
All the wires are insulated as far as I can tell.

I guess if you got aggressive with wire brush you could wreck something.

I heat up my hot end and clean it with a dry paper towel and a glove.

I’ve never worried about grabbing a string off the hot end with the metal tweezers. I had a “poor bed adhesion” the other day that left my print head covered in PLA. I wiped most of it off while hot without a problem. Yeah, there’s still some in certain areas I couldn’t reach, and it will be there until I can get to it.

If you short the nozzle to the chassis, it’s just the same as if had hit a limit switch. The four washers are connected to chassis. When the unit is on, there is 5V through a pull-up resistor on the print head.

The risk is shorting the 24 volt hotend to the 5 volt limit switch input tied to the nozzle or the thermistor input . it happens to someone about once every 2 months.

The 24v hot end is the cartridge heater, right? Is it getting shorted because the insulation is pierced? Or does the heater short to the case internally?

Thanks for the answer, by the way.

I suspect the insulation gets pierced, but I’m not sure. I’ve never wanted to find out the hard way. The heater itself should be insulated from the block, but the high temp silicon jacket on the wires is somewhat easy to puncture.

What confused me was the Lulzbot Mini quick start guide (10C) says to remove extruded filament with the included metal tweezers. They don’t say anything about not making contact with the nozzle with the tweezers. That’s why I was wondering if the short was caused by touching the hexagon shaped part, instead of the nozzle, but apparently that isn’t right.

Maybe someone from Lulzbot can clarify this?

Just a reminder that the way the auto-level works through the conduc

Remove the filament with tweezers from the top… no metal on metal since the extruder body is plastic. Tweezers usually only necessary when printing to the end of the filament spool. Otherwise just loosen the idler and pull the filament by hand.

The tweezers are precise enough to remove ooze from the nozzle. Grab the filament / plastic… forego the coffee. :slight_smile:

To really be safe, just take the time to power down the machine after heating the hotend to extrusion temp. Clean, then power up the machine. No current will be circulating through the nozzle.

Thanks! That’s very helpful.

If you look ‘closely’ at the side of the heat cartridge you will see a very small gap in the wire insulation between the cartridge body and the heater wires coming out of it. So if you press the metal bristles of the brush into that small gap you would have the 24 volts (which is on both sides of the heater cartridge wires) now connected to the metal of the nozzle/heat break. Then would be applying 24 volts directly to a 5 volt maximum input on the control board.