Quality Control...

posted 5 Oct 2014, 11:51 by Colin Bell   [ updated 11 Oct 2014, 08:45 ]

...is a wonderful thing. On my 3 day old PrintrBot Simple Metal, I had a component failure - not unusual on 3D printers for sure, but this is just ridiculous.

The offending component is shown on the right of the picture above - this is the inductive sensor probe used for automatic bed levelling on the PrintrBot. It's a fantastic solution and cuts out a lot of crap calibrating. The issue here is that PrintrBot are using (I assume) very cheap versions of these probes (a quick seach on eBay shows I can buy 10 of them for $25 - they are farming them out at $25 each!).

Now, as an enthusiast electronics engineer, I'm the first to admit that sometimes components just fail - that's just life, move on...but in this case I'm a bit pissed off about it - the device worked out of the box, and then just randomly started to intermittently stop working, resulting in some bed crashes and spoiled prints. A quick look on the forums shows that this has been escalated several times, and is a known design flaw. I have of course opened a support ticket, so we'll see what happens with that.

What actually happens is that the cable that runs from the metal probe directly into the printers mainboard has three wires within the sleeving - for some reason, the signal wire breaks very easily (most likely due to the movement of the Z/Y axis'. What you will observe is that the status light will come on when its near to the bed (or any other metal object) as normal, but the signal never makes it to the mainboard. 

Running an M119 command to check end-stop status showed that the end-stop was 'Triggered' all the time regardless of the real status. 

This means that the printer cannot home Z, or more importantly cannot perform it's auto levelling procedure prior to a print.

Rather than put the printer on ice for a couple of months until I can get to the UK and pick up spares, I decided to hack the cheap-o cable off and make up a new one. Fortunately, in my case this worked well (so far!) however I'm still annoyed that I had to do this on what is effectively a three day old machine. If it was bleeding edge I could understand it, but these things have been available for several months now - there's no excuse for this at all in my opinion.

Update: PrintrBot agreed to send me a replacement inductive sensor, even though their policy is 30 days from receipt - which in my case is over by several months since I actually bought the machine. My repair is still holding up well, and I likely won't change it now unless it fails, however it's always good to have spares!