Wednesday, 8 June 2011

Quest To Use ABS

It's been a busy couple of weeks to say the least.
The design for my modular rotary hydroponic unit is now pretty much complete and ready for testing.
1 Ring with boards to support a PE sheet sump to hold mineral solution. Can be extended to more rings, and it has been suggested to use a stock drip-tray from garden stores underneath instead of hacking that sump together from scraps.
However, to start printing and testing parts for this, I really should be using ABS, not only for its superior strength to PLA, but because when being repeatedly dipped in a nutrient solution and stressed in a warm humid atmosphere, PLA could come under attack from microbes that would otherwise turn up to biodegrade it in a compost heap.

Not to mention that if I hope to make back some of the printer cost and pay rent, then I'll have to make ABS parts for new reprappers.

If printing with ABS, then I need some kind of air filtration or extraction to cut out the fumes that would come off, and since my printer was far from a window and I didn't want to release butadiene fumes into the environment anyway, I designed and built an air filter that would use replaceable activated carbon granules.

Using an easy-to-find 80mm PC case fan.

Once I got hold of some ABS filament, I needed another spool to run it on, and the cardboard one I made was trying to come loose where it met the bushings I added, while I didn't have enough large bits of cardboard left to make another one anyway. So I designed my own printable one that would be easy to take apart and re-load with filament:
Adjustable to many sizes.

But then I had a hectic time just over a day ago when as I'd nearly printed all the parts to make the spool, my extruder had a nasty malfunction that caused it to grind into the filament instead of feeding it through. Eventually I found that this was down to a mistake on my part when I tried to fix something else that had been turning up.
I had occasionally seen filings of plastic appearing on the printbed by the end of a print, and thought maybe the bolts pushing the filament against the toothed wheel that drags it through weren't putting enough force on, and so I tightened them against the springs a bit hoping that this would make it grip better. As it turns out, this was the exact opposite of what I should have done, and they needed to be loosened so that the teeth wouldn't bite into the filament too much.

Chipped filament visible next to bolt in middle, and the part I had to remove even to get to that is at the top.

Very annoyingly, as I removed the extruder to clean out some filings, the filament snapped at the point where it had been grinding away, so I had to dismantle the extruder block to get that out. When I tried to pull the filament out there with pliers, bits just snapped off again.
 A further accident then caused one of the wires connected to the nozzle-temp measuring thermistor to snap away. Losing the length of copper wire that was actually part of the thermistor meant I could no longer re-attach that with a bootlace ferrule, and I had to replace it. Luckily the kit I got contained one spare, and I actually ended up breaking the old thermistor whilst removing it from the aluminium heating block anyway. :/

The glue that Mendel-Parts used in the hot end didn't hold up so well after this short time.

Once that was sorted I had to clear out the length of PLA that was stubbornly stuck in the PTFE heat insulation. This was finally made possible now that I had the heating block working again, and I managed to push the PLA through the nozzle (pulling it back out just wasn't happening for some reason).

Back on track after re-assembling everything, I got the last few pieces of my new spool printed, and I am quite chuffed with the results, as many of the parts seemed to push-fit quite easily.
Everything fits on there snugly at the same time, yet still has room to move! :)

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