Saturday, 10 November 2012

Luck + Failure

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I started a print for an order that Steve at Operation Lasertag has put in for some gun kits. I started a print off as usual, went into the kitchen to get a brew whilst listening to 'Today' on Radio 4. Radio 4 went off. Briefly I remembered something about Radio 4 being used to test whether London had been nuked. Coming to my senses I put 2 and 2 together and went to check the 3D printer. My 3D printer has a mains powered heated bed. I found this:

During the Z calibration the hot end had touched one of the bulldog clips used to fasten the print surface in place. Something had obviously shorted out the mains supply.
On dismantling the heated bed, I found that one of the 15W resistors used as a heater had gone OC, but had shorted internally to the case, raising the heated bed to 240V ac!!

I replaced the failed resistor and thankfully the hot end controller electronics that I use had survived intact, although the mains 5A fuse had blow. Lucky!
The first print I tried after repairs failed, but the extruder was playing up this time:

The fill had gaps. After checking the usual suspects, I focussed on the hot end. There had obviously been a leak as the grub screw used to fasten the nozzle in place had signs of something escaping:

Removing the brass hot end showed that the sealant I used on the threads between the brass and the peek had de-natured:

I managed to 'refurbish' the hot end. Cleaning the nozzle and re-installing with fresh sealant. There did not appear to be any internal damage to the peek/PTFE barrier. I'm waiting for the high temp sealant to set and will try again tomorrow.


nop head said...

What happened to the earth connection to the bed? That should have stopped it becoming live.

Tony said...

Ah, that would be to one that I took off and forgot to put back. Dangerous mistake!