Tuesday, 21 August 2012

Maintenace weekend...

This weekend Huxley #710 needed some maintenance.

The most important issue to arise was failure of the heated bed soldered joint power connection. Huxley #710 was printing my latest masterpiece which is one of the largest prints I have ever designed. It's 91 mm in diameter and 38 mm tall. Of course that details none of the complexity in the part which is one of three mating parts that are required to fit together quite precisely. The interconnection between the mating parts is a three feature bayonet fixing at a 120° spacing on the diameter. If time permits I will mock up an example at some point.

Huxley heated bed PCB 3 way terminal block
The issue was that the heated bed started sparking and smoking during this rather complex and long 4 hour print. It transpired that the terminal block pin had fatigued and a dry joint occurred between the PCB pin on the power terminal and the PCB track. With the considerable current running through the table, this sparked quite nicely! Smoked, as the solder resist was cooked black and melted the solder due to the energy involved. The solder was boiling! All in the space of less than 20 seconds, it took me that long to decide not to shut down the print but only switch off the heated bed and allow the print to continue. By chance, I had safety glasses on.

Huxley #710 heated bed terminal block solder pad repair
The repair / replacement of the PCB track; as there was no copper pad left due to the heat. Was to remove some solder resist from good PCB track further down the PCB towards the heated bed and use some solder wick braid to create a bridge between the pin and PCB. To secure the Terminal block in place I super glued the 3 way terminal block to the PCB prior to soldering the joints. I have previously found super glue to be OK provided that the temperature does not get in the region above 95C. Taking super glue above these temperatures is not a good idea as I believe it gives of cyanide gas. Whatever it gives off I can tell you it's not good and should be avoided.

The root cause is straight forward to understand, as you have no doubt guessed from the picture of the power connection to the table. The PCB 3 way screw terminal is essentially exposed to a side force. In fact, thousands of times as the table moves back and forth. It's likely that the PCB 3 way screw terminal was not seated correctly and so after around 300 meters of printing, the soldered joint was the weak point and turned into a dry joint. The rest as they say is history.

To improve the situation the connection to the heated bed might have to be made in line with the direction of travel and additionally perhaps the cable clamped to the PCB to offer a strain relief.

So Huxley #710 sprang into life again and then maintenance incident number two occurred

Z coupling detachment
Both Z couplings had become loose and were no longer attached to - well anything. So I reconnected the Z couplings and re-aligned the system, which I have developed some proficiency in now.

I am starting to think I may be a heavy user of my RepRap Huxley.

Another project spin off - Nokia LCD CAD STEP model
Spakrfun Nokia 5110 LCD Display
One of the things I have been working on for the project is a display housing for a Nokia 5110 84 x 48 pixel LCD display from Sparkfun. The unit was actually acquired from Proto-Pic as we don't have a Sparkfun in the UK.

So if you would like a CAD model of the Sparkfun Nokia 5110 LCD display

Sparkfun Nokia 5110 LCD Display CAD model

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